A pixellated germanium Compton camera is currently being developed for imaging 511 keV sources in nuclear medicine. It was built by ORTEC and consists of two planar Ge detectors (the scatter and the absorption detector) housed within the same cryostat. The scatter and absorption detectors have 152 and 25 4×4 mm2 pixels respectively. The readout electronics was developed at Daresbury Laboratory UK and consists of 15 GRT4 VME cards and a PowerPC. The system is controlled by a PC running MIDAS software. This paper reports the current status of camera development. The pixel energy resolution has been measured to give an average of
Fretwurst E, Adey J, Al-Ajili A, Alfieri G, Allport PP, Artuso M, Assouak S, Avset BS, Barabashi L, Barcz A, Bates R, Biagi SF, Bilei GM, Bisello D, Blue A, Blumenau A, Boisvert V, Bolla G, Bondarenko G, Borchi E, Borrello L, Bortoletto D, Boscardin M, Bosisio L, Bowcock TJV, Brodbeck TJ, Broz J, Bruzzi M, Brzozowski A, Buda M, Buhmann P, Buttar C, Campabadal F, Campbell D, Candelori A, Casse G, Cavallini A, Charron S, Chilingarov A, Chren D, Cindro V, Collins P, Coluccia R, Contarato D, Coutinho J, Creanza D, Cunningham L, Dalla Betta GF, Dawson I, de Boer W, De Palma M, Demina R, Dervan P, Dittongo S, Dolezal Z, Dolgolenko A, Eberlein T, Eremin V, Fall C, Fasolo F, Ferbel T, Fizzotti F, Fleta C, Focardi E, Forton E, Garcia C, Garcia-Navarro JE, Gaubas E, Genest MH, Gill KA, Giolo K, Glaser M, Goessling C, Golovine V, Sevilla SG, Gorelov I, Goss J, Bates AG, Gregoire G, Gregori P, Grigoriev E, Grillo AA, Groza A, Guskov J, Haddad L, Harkonen J, Hauler F, Hoeferkamp M, Honniger F, Horazdovsky T, Horisberger R, Horn M, Houdayer A, Hourahine B, Hughes G, Ilyashenko I, Irmscher K, Ivanov A, Jarasiunas K, Johansen KMH, Jones BK, Jones R, Joram C, Jungermann L, Kalinina E, Kaminski P, Karpenko A, Karpov A, Kazlauskiene V, Kazukauskas V, Khivrich V, Khomenkov V, Kierstead J, Klaiber-Lodewigs J, Klingenberg R, Kodys P, Kohout Z, Korjenevski S, Koski M, Kozlowski R, Kozodaev M, Kramberger G, Krasel O, Kuznetsov A, Kwan S, Lagomarsino S, Lassila-Perini K, Lastovetsky V, Latino G, Lazanu I, Lazanu S, Lebedev A, Lebel C, Leinonen K, Leroy C, Li Z, Lindstrom G, Linhart V, Litovchenko P, Litovchenko A, Giudice AL, Lozano M, Luczynski Z, Luukka P, Macchiolo A, Makarenko LF, Mandic I, Manfredotti C, Manna N, Garcia SM, Marunko S, Mathieson K, Melone J, Menichelli D, Messineo A, Metcalfe J, Miglio S, Mikuz M, Miyamoto J, Moll M, Monakhov E, Moscatelli F, Naoumov D, Nossarzewska-Orlowska E, Nysten J, Olivero P, Oshea V, Palviainen T, Paolini C, Parkes C, Pesseri D, Pein U, Pellegrini G, Perera L, Petasecca M, Plemonte C, Pignatel GU, Pinho N, Pintilie I, Pintilie L, Polivtsev L, Polozov P, Popa A, Popule J, Pospisil S, Pozza A, Radicci V, Rafi JM, Rando R, Roeder R, Rohe T, Ronchin S, Rott C, Roy A, Ruzin A, Sadrozinski HFW, Sakalauskas S, Scaringella M, Schiavulli L, Schnetzer S, Schumm B, Sciortino S, Scorzoni A, Segneri G, Seidel S, Seiden A, Sellberg G, Sellin P, Sentenac D, Shipsey I, Sicho P, Sloan T, Solar M, Son S, Sopko B, Sopko V, Spencer N, Stahl J, Stolze D, Stone R, Storasta J, Strokan N, Sudzius M, Surma B, Suvorov A, Svensson BG, Tipton P, Tomasek M, Tsvetkov A, Tuominen E, Tuovinen E, Tuuva T, Tylchin M, Uebersee H, Uher J, Ullan M, Vaitkus JV, Velthuis J, Verbitskaya E, Vrba V, Wagner G, Wilhelm I, Worm S, Wright V, Wunstorf R, Yiuri Y, Zabierowski P, Zaluzhny A, Zavrtanik M, Zen M, Zhukov V, Zorzi N (2005) Recent advancements in the development of radiation hard semiconductor detectors for S-LHC, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 552 (1-2) pp. 7-19 ELSEVIER SCIENCE BV
Moll M, Adey J, Al-Ajili A, Alfieri G, Allport PP, Artuso M, Assouak S, Avset BS, Barabash L, Barcz A, Bates R, Biagi SF, Bilei GM, Bisello D, Blue A, Blumenau A, Boisvert V, Bolla G, Bondarenko G, Borchi E, Borrello L, Bortoletto D, Boscardin M, Bosisio L, Bowcock TJV, Brodbeck TJ, Broz J, Bruzzi M, Brzozowski A, Buda M, Buhmann P, Buttar C, Campabadal F, Campbell D, Candelori A, Casse G, Cavallini A, Charron S, Chilingarov A, Chren D, Cindro V, Collins P, Coluccia R, Contarato D, Coutinho J, Creanza D, Cunningham W, Dalla Betta GF, Dawson I, de Boer W, De Palma M, Demina R, Dervan P, Dittongo S, Dolezal Z, Dolgolenko A, Eberlein T, Eremin V, Fall C, Fasolo F, Fizzotti F, Fleta C, Focardi E, Forton E, Fretwurst E, Garcia C, Garcia-Navarro JE, Gaubas E, Genest MH, Gill KA, Giolo K, Glaser M, Goessling C, Golovine V, Sevilla SG, Gorelov I, Goss J, Bates AG, Gregoire G, Gregori P, Grigoriev E, Grillo AA, Groza A, Guskov J, Haddad L, Harkonen J, Hauler F, Hoeferkamp M, Honniger F, Horazdovsky T, Horisberger R, Horn M, Houdayer A, Hourahine B, Hughes G, Ilyashenko I, Irmscher K, Ivanov A, Jarasiunas K, Johansen KMH, Jones BK, Jones R, Joram C, Jungermann L, Kalinina E, Kaminski P, Karpenko A, Karpov A, Kazlauskiene V, Kazukauskas V, Khivrich V, Khomenkov V, Kierstead J, Klaiber-Lodewigs J, Klingenberga R, Kodys P, Kohout Z, Korjenevski S, Koski M, Kozlowski R, Kozodaev M, Kramberger G, Krasel O, Kuznetsov A, Kwan S, Lagomarsino S, Lassila-Perini K, Lastovetsky V, Latino G, Lazanu S, Lazanu I, Lebedev A, Lebel C, Leinonen K, Leroy C, Li Z, Lindstrom G, Linhart V, Litovchenko A, Litovchenko P, Lo Giudice A, Lozano M, Luczynski Z, Luukka P, Macchiolo A, Makarenko LF, Mandic I, Manfredotti C, Manna N, Marti i Garcia S, Marunko S, Mathieson K, Melone J, Menichelli D, Messineo A, Metcalfe J, Miglio S, Mikuz M, Miyamoto J, Monakhov E, Moscatelli F, Naoumov D, Nossarzewska-Orlowska E, Nysten J, Olivera P, OShea V, Palvialnen T, Paolini C, Parkes C, Passeri D, Pein U, Pellegrini G, Perera L, Petasecca K, Piemonte C, Pignatel GU, Pinho N, Pintilie I, Pintilie L, Polivtsev L, Polozov P, Popa A, Popule J, Pospisil S, Pozza A, Radicci V, Rafi JM, Rando R, Roeder R, Rohe T, Ronchin S, Rott C, Roy A, Ruzin A, Sadrozinski HFW, Sakalauskas S, Scaringella M, Schiavulli L, Schnetzer S, Schumm B, Sciortino S, Scorzoni A, Segneri G, Seidel S, Seiden A, Sellberg G, Sellin P, Sentenac D, Shipsey I, Sicho P, Sloan T, Solar M, Son S, Sopko B, Sopko V, Spencer N, Stahl J, Stolze D, Stone R, Storasta J, Strokan N, Sudzius M, Surma B, Suvorov A, Svensson BG, Tipton P, Tomasek M, Tsvetkov A, Tuominen E, Tuovinen E, Tuuva T, Tylchin M, Uebersee H, Uher J, Ullan M, Vaitkus JV, Velthuis J, Verbitskaya E, Vrba V, Wagner G, Wilhelm I, Worm S, Wright V, Wunstorf R, Yiuri Y, Zabierowski P, Zaluzhny A, Zavrtanik M, Zen M, Zhukov V, Zorzi N (2005) Development of radiation tolerant semiconductor detectors for the Super-LHC, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 546 (1-2) pp. 99-107 ELSEVIER SCIENCE BV
Flexible radiation dosimeters have been produced incorporating thick films (>1 ¼m) of the semiconducting polymer
poly([9,9-dioctylfluorenyl-2,7-diyl]-co-bithiophene). Diode structures produced on aluminium-metallised poly(imide)
substrates, and with gold top contacts, have been examined with respect to their electrical properties. The results suggest
that a Schottky conduction mechanism occurs in the reverse biased diode, with a barrier to charge injection at the
aluminium electrode. Optical absorption/emission spectra reveal a band gap of 2.48 eV for the polymer. The diodes have
been used for direct charge detection of 17 keV X-rays, generated by a molybdenum source. Using operating voltages of
-10 and -50 V respectively, sensitivities of 54 and 158 nC/mGy/cm3 have been achieved. Increasing the operating
voltage shows that the diodes are stable up to approximately -200 V without significant increase in the dark current of
the device (
Sellin PJ, Davies AW, Boroumand F, Lohstroh A, Ozsan ME, Parkin J, Veale M (2007) IBIC characterization of charge transport in CdTe : Cl, SEMICONDUCTORS 41 (4) pp. 395-401 MAIK NAUKA/INTERPERIODICA/SPRINGER
Simon A, Sellin PJ, Lohstroh A (2004) IBIC imaging of intra-crystallite charge transport in CVD diamond at reduced temperature, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 219 pp. 1022-1026 ELSEVIER SCIENCE BV
Prekas G, Sellin PJ, Veeramani P, Davies AW, Lohstroh A, Ozsan ME, Veale MC (2010) Investigation of the internal electric field distribution under in situ x-ray irradiation and under low temperature conditions by the means of the Pockels effect, JOURNAL OF PHYSICS D-APPLIED PHYSICS 43 (8) ARTN 085102 IOP PUBLISHING LTD
Duarte DD, Bell SJ, Lipp J, Schneider A, Seller P, Veale MC, Wilson MD, Baker MA, Sellin PJ, Kachkanov V, Sawhney KJS (2013) Edge effects in a small pixel CdTe for X-ray imaging,Journal of Instrumentation 8 (10)
Large area detectors capable of operating with high detection efficiency at energies above 30 keV are required in many contemporary X-ray imaging applications. The properties of high Z compound semiconductors, such as CdTe, make them ideally suitable to these applications. The STFC Rutherford Appleton Laboratory has developed a small pixel CdTe detector with 80 × 80 pixels on a 250 ¼m pitch. Historically, these detectors have included a 200 ¼m wide guard band around the pixelated anode to reduce the effect of defects in the crystal edge. The latest version of the detector ASIC is capable of four-side butting that allows the tiling of N × N flat panel arrays. To limit the dead space between modules to the width of one pixel, edgeless detector geometries have been developed where the active volume of the detector extends to the physical edge of the crystal. The spectroscopic performance of an edgeless CdTe detector bump bonded to the HEXITEC ASIC was tested with sealed radiation sources and compared with a monochromatic X-ray micro-beam mapping measurements made at the Diamond Light Source, U.K. The average energy resolution at 59.54 keV of bulk and edge pixels was 1.23 keV and 1.58 keV, respectively. 87% of the edge pixels present fully spectroscopic performance demonstrating that edgeless CdTe detectors are a promising technology for the production of large panel radiation detectors for X-ray imaging.© 2013 IOP Publishing Ltd and Sissa Medialab srl.
Tsvetkova T, Sellin P, Dimova-Malinovska D, Angelov O, Krastev V, Stefanov P, Avramova I (2010) X-ray photoelectron study of high-energy He+ implanted a-SiC:H thin films, Journal of Physics: Conference Series 253 (1)
Wilson MD, Barnes P, Cernik RC, Hansson CCT, Jacques S, Jones LL, Seller P, Sellin PJ, Sochi T, Veale MC, Veeramani P, Withers PJ, Youd CP (2010) Comparison of the X-ray performance of small pixel CdTe and CZT detectors, IEEE Nuclear Science Symposium Conference Record pp. 3942-3946
The Rutherford Appleton Laboratory has built a small pixel detector for spectroscopic measurements of high energy X-rays using CdTe and CdZnTe. The detector has an array of 20×20 pixels on a 250¼m pitch with each pixel bonded to a separate channel on an application specific integrated circuit (ASIC). Each channel in the ASIC contains a charge preamplifier, leakage current compensation circuit, shaping amplifier and peak hold circuit. In recent years there has been an increase in the availability of high quality CdTe and CdZnTe material and the contacting technology required for low leakage current small pixel devices. The energy resolution and stability of the X-ray performance of 1mm thick CdTe with Aluminum Schottky contact pixels and 2mm thick CdZnTe grown by travelling heater method (THM) are measured. The CdTe detectors had an energy resolution of 1 to 1.1keV at 75keV. The THM CdZnTe had an energy resolution of 1.3keV at 75keV. The stability of the performance was measured over a 12 hour exposure with the detectors biased to -500V and held at 25°C. The CdZnTe exhibited stable performance whereas the CdTe suffered from bias induced polarization, the onset of which was delayed by cooling the detectors to 12°C.
Sellin PJ, Jaffar G, Jastaniah SD (2004) Performance of digital algorithms for n/gamma pulse shape discrimination using a liquid scintillation detector, 2003 IEEE NUCLEAR SCIENCE SYMPOSIUM, CONFERENCE RECORD, VOLS 1-5 pp. 1057-1060 IEEE
Bourgoin JC, Sun GC, Sellin PJ, Yin S (2004) Charge collection in epitaxial GaAs p/i/n radiation detectors, Proceedings of SPIE - The International Society for Optical Engineering 5198 pp. 150-153
We describe the mode of operation of a detector for direct photon-electron conversion at room temperature, made of epitaxially grown GaAs. Contrary to bulk grown materials, epitaxial layers are free of defects, i.e. exhibit long lifetimes and high carrier mobilities, and have uniform electronic properties. However, the depleted zone is of limited extension, consequence of the level of the residual doping impurities, which are not compensated by defects. These detectors are adapted to X-ray imaging, in particular for low energy medical applications such as mammography, because of the availability of large areas (up to 4 inches in diameter), standard technological processes for making pixellated detectors and cost. However, charges in the neutral region can be collected by diffusion and we shall present data allowing to illustrate and evaluate this effect. Finally photocurrent measurements obtained under medical conditions demonstrate that, for the detector used, only a small fraction of the photocurrent originates from diffusing charges. They also show how a 120 ¼m thick GaAs epitaxial detector competes with a 0.5 mm thick CdZnTe detector.
We report a study of pulse shapes of a radiation detector with a sandwich structure fabricated from chemical vapor deposited (CVD) polycrystalline diamond. The pulse shapes were recorded at room temperature using 5.486 MeV alpha particles from 241Am source. Only "fast" component was observed in the electron predominated pulses, whereas both "fast" and "slow" components were obtained in the hole predominated pulses, suggesting that electron charge drift is prompt and no detrapping occurred. In contrast, hole charge drift is slower than expected and trapping-detrapping took place during hole travel process. © 2005 Materials Research Society.
Boardman DA, Sellin PJ (2001) Design and characterisation of high electron mobility transistors for use in a monolithic GaAs X-ray imaging sensor, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 466 (1) pp. 226-231 ELSEVIER SCIENCE BV
Xu Y, Jie W, Sellin P, Wang T, Liu W, Zha G, Veeramani P, Mills C (2009) Study on temperature dependent resistivity of indium-doped cadmium zinc telluride, JOURNAL OF PHYSICS D-APPLIED PHYSICS 42 (3) ARTN 035105 IOP PUBLISHING LTD
CdTe and CdZnTe material is an excellent candidate for the fabrication of high energy X-ray spectroscopic detectors due to their good quantum efficiency and room temperature operation. The main material limitation is associated with the poor charge transport properties of holes. The motivation of this work is to investigate the performance characteristics of a detector fabricated with a drift ring geometry that is insensitive to the transport of holes. The performance of a prototype Ohmic CdTe drift ring detector fabricated by Acrorad with 3 drift rings is reported; measurements include room temperature current voltage characteristics (IV) and spectroscopic performance. The data shows that the energy resolution of the detector is limited by leakage current which is a combination of bulk and surface leakage currents. The energy resolution was studied as a function of incident X-ray position with an X-ray microbeam at the Diamond Light Source. Different ring biasing schemes were investigated and the results show that by increasing the lateral field (i.e. the bias gradient across the rings) the active area, evaluated by the detected count rate, increased significantly. © 2014 IOP Publishing Ltd and Sissa Medialab srl.
Alruhaili A, Sellin PJ, Lohstroh A, Boothman V, Veeramani P, Veale MC, Sawhney KJS, Kachkanov V (2015) Development of a CZT drift ring detector for X and gamma ray spectroscopy, JOURNAL OF INSTRUMENTATION 10 ARTN P04005 IOP PUBLISHING LTD
Gkoumas S, Lohstroh A, Sellin PJ (2009) Low temperature time of flight mobility measurements on synthetic single crystal diamond, DIAMOND AND RELATED MATERIALS 18 (11) pp. 1338-1342 ELSEVIER SCIENCE SA
Sellin PJ (2003) Recent advances in compound semiconductor radiation detectors, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 513 (1-2) pp. 332-339 ELSEVIER SCIENCE BV
Burger A, Derenzo S, Moses B, Luke P, Archer D, Bolotnikov A, Boston A, Fabris L, Franks L, Friedrich S, Iwanczyk JS, Kernan W, Payne S, Rockett P, Royle G, Rozenfeld A, Sellin P, Sjoden G, Sturm B (2009) Editorial conference comments by the editors, IEEE Transactions on Nuclear Science 56 (3) pp. 1034-1034 IEEE
Xu Y, Jie W, Zha G, Gao J, Wang T, Fu L, Sellin P (2009) A study on the low energy X/³-ray spectral response of CdZnTe planar detectors, Guangxue Xuebao/Acta Optica Sinica 29 (11) pp. 3072-3077
Lohstroh A, Sellin PJ, Gkoumas S, Al-Barakaty H, Veeramani P, Ozsan ME, Prekas G, Veale MC, Parkin JM, Davies AW (2010) The effect of fast neutron irradiation on the performance of synthetic single crystal diamond particle detectors,DIAMOND AND RELATED MATERIALS 19 (7-9) pp. 841-845
ELSEVIER SCIENCE SA
Nouh SA, Naby AA, Sellin PJ (2007) Modification induced by proton irradiation in Makrofol-DE polycarbonate, RADIATION MEASUREMENTS 42 (10) pp. 1655-1660 PERGAMON-ELSEVIER SCIENCE LTD
Tsvetkova T, Takahashi S, Sellin P, Gomez-Morilla I, Angelov O, Dimova-Malinovska D, Zuk J (2011) Optical Pattern Fabrication in Amorphous Silicon Carbide with High-Energy Focused Ion Beams, ACTA PHYSICA POLONICA A 120 (1) pp. 56-59 POLISH ACAD SCIENCES INST PHYSICS
Baier N, Brambilla A, Feuillet G, Lohstroh A, Renet S, Sellin P (2007) EBIC and IBIC imaging on polyerystalline CdTe, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 576 (1) pp. 5-9 ELSEVIER SCIENCE BV
Veale MC, Bell SJ, Jones LL, Seller P, Wilson MD, Allwork C, Kitou D, Sellin PJ, Veeramani P, Cernik RC (2010) Investigating the small pixel effect in CdZnTe Hard X-ray detectors the PIXIE ASIC, IEEE Nuclear Science Symposium Conference Record (NSS/MIC) pp. 3789-3792
Samic H, Sun GC, Donchev V, Nghia NX, Gandouzi M, Zazoui M, Bourgoin JC, El-Abbassi H, Rath S, Sellin PJ (2002) Characterization of thick epitaxial GaAs layers for X-ray detection, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 487 (1-2) pp. 107-112 ELSEVIER SCIENCE BV
Dedic V, Franc J, Sellin PJ, Grill R, Perumal V (2012) Study on electric field in Au/CdZnTe/In detectors under high fluxes of X-ray and laser irradiation, JOURNAL OF INSTRUMENTATION 7 ARTN P02011 IOP PUBLISHING LTD
Breese MBH, Sellin PJ, Alves LC, Knights AP, Sussmann RS, Whitehead AJ (2001) Imaging of charge transport properties in polycrystalline CVD diamond using IBIC and IBIL microscopy, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 181 pp. 219-224 ELSEVIER SCIENCE BV
Davis NJ, Ward RP, Rusek K, Clarke NM, Tungate G, Griffith JAR, Hall SJ, Karban O, Martel-Bravo I, Nelson JM, Gómez-Camacho J, Davinson T, Ireland DG, Livingston K, Macdonald EW, Page RD, Sellin PJ, Shepherd-Themistocleous CH, Shorter AC, Woods PJ (2004) Tensor analyzing powers for 7Li induced transfer breakup reactions, Physical Review C - Nuclear Physics 69 (6) pp. 064605-064601
The T20 analyzing powers have been measured for the 120Sn(7Li, 8Be 2±) 119In and 120Sn(7Li, 6Li* ± + d) 121Sn transfer breakup reactions, using a 70 MeV beam. The data exhibit excellent agreement with the results of coupled reaction channels calculations, providing an important test of these calculations when applied to the transfer breakup reaction mechanism.
Taggart MP, Payne C, Sellin PJ (2016) Neutron-gamma discrimination via PSD plastic scintillator and SiPMs, Journal of Physics: Conference Series 763 (1) 012007 Institute of Physics
The reduction in availability and inevitable increase in cost of traditional neutron detectors based on the 3He neutron capture reaction has resulted in a concerted effort to seek out new techniques and detection media to meet the needs of national nuclear security. Traditionally, the alternative has been provided through pulse shape discrimination (PSD) using liquid scintillators. However, these are not without their own inherent issues, primarily concerning user safety and ongoing maintenance. A potential system devised to separate neutron and gamma ray pulses utilising the PSD technique takes advantage of recent improvements in silicon photomultiplier (SiPM) technology and the development of plastic scintillators exhibiting the PSD phenomena. In this paper we present the current iteration of this ongoing work having achieved a Figure of Merit (FoM) of 1.39 at 1.5 MeVee.
Darambara DG, Sellin PJ, Maehlum G (2004) A low-angle X-ray scatter breast-imaging system based on a novel multi-element Si-pad array operated in spectroscopic mode, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 525 (1-2) pp. 253-257 ELSEVIER SCIENCE BV
Silicon Photomultipliers (SiPM) are solid-state pixelated photodetectors. Lately these sensors have been investigated for Time
of Flight Positron Emission Tomography (ToF-PET) applications, where very good coincidence time resolution of the order of
hundreds of picoseconds imply spatial resolution of the order of cm in the image reconstruction. The very fast rise time typical
of the avalanche discharge improves the time resolution, but can be limited by the readout electronics and the technology used to
construct the device. In this work the parameters of the equivalent circuit of the device that directly affect the pulse shape, namely
the quenching resistance and capacitance and the diode and parasitic capacitances, were calculated. The mean rise time obtained
with different preamplifiers was also measured.
Sellin PJ, Rossi G, Renzi MJ, Knights AP, Eikenberry EF, Tate MW, Barna SL, Wixted RL, Gruner SM (2001) Performance of semi-insulating gallium arsenide X-ray pixel detectors with current-integrating readout, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 460 (1) pp. 207-212 ELSEVIER SCIENCE BV
Sellin PJ, Davies AW, Gkoumas S, Lohstroh A, Ozsan ME, Parkin J, Perumal V, Prekas G, Veale M (2008) Ion beam induced charge imaging of charge transport in CdTe and CdZnTe, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 266 (8) pp. 1300-1306 ELSEVIER SCIENCE BV
© 2015 IOP Publishing Ltd.Fully spectroscopic x/³-ray imaging is now possible thanks to advances in the growth of wide-bandgap semiconductors. One of the most promising materials is cadmium zinc telluride (CdZnTe or CZT), which has been demonstrated in homeland security, medical imaging, astrophysics and industrial analysis applications. These applications have demanding energy and spatial resolution requirements that are not always met by the metal contacts deposited on the CdZnTe. To improve the contacts, the interface formed between metal and semiconductor during contact deposition must be better understood. Gold has a work function closely matching that of high resistivity CdZnTe and is a popular choice of contact metal. Gold contacts are often formed by electroless deposition however this forms a complex interface. The prior CdZnTe surface preparation, such as mechanical or chemo-mechanical polishing, and electroless deposition parameters, such as gold chloride solution temperature, play important roles in the formation of the interface and are the subject of the presented work. Techniques such as focused ion beam (FIB) cross section imaging, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS) and current - voltage (I-V) analysis have been used to characterize the interface. It has been found that the electroless reaction depends on the surface preparation and for chemo-mechanically polished (1 1 1) CdZnTe, it also depends on the A/B face identity. Where the deposition occurred at elevated temperature, the deposited contacts were found to produce a greater leakage current and suffered from increased subsurface voiding due to the formation of cadmium chloride.
Ruddy FH, Seidel JG, Sellin P (2009) High-resolution alpha spectrometry with a thin-window silicon carbide semiconductor detector, IEEE Nuclear Science Symposium Conference Record (NSS/MIC) pp. 2201-2206 IEEE
The potential for high-resolution alpha-particle energy spectrometry in high-temperature, high-radiation environments using thin-window 4H-SiC radiation detectors has been demonstrated. 238Pu alpha-particle peaks separated by only 42.7 keV have been completely resolved using a SiC Schottky detector with a 400 AÃÂ¿ titanium Schottky contact (entrance window). The observed FWHM for the 238Pu 5499.2-keV alpha particle peak is 20.6 keV or 0.37%. Factors affecting the observed alpha-particle energy resolution in SiC detectors will be discussed.
Bruzzi M, Adey J, Al-Ajili A, Alexandrov P, Alfieri G, Allport PP, Andreazza A, Artuso M, Assouak S, Avset BS, Barabash L, Baranova E, Barcz A, Basile A, Bates R, Belova N, Biagi SF, Bilei GM, Bisello D, Blue A, Blumenau B, Boisvert V, Bolla G, Bondarenko G, Borchi E, Borrello L, Bortoletto D, Boscardin M, Bosisio L, Bowcock TJV, Brodbeck TJ, Broz J, Brukhanov A, Brzozowski A, Buda M, Buhmann P, Buttar C, Campabadal F, Campbell D, Candelori A, Casse G, Cavallini A, Chilingarov A, Chren D, Cindro V, Citterio M, Collins P, Coluccia R, Contarato D, Coutinho J, Creanza D, Cunningham W, Cvetkov V, Dalla Betta GF, Davies G, Dawson I, de Boer W, De Palma M, Demina R, Dervan P, Dierlamm A, Dittongo S, Dobrzanski L, Dolezal Z, Dolgolenko A, Eberlein T, Eremin V, Fall C, Fasolo F, Ferbel T, Fizzotti F, Fleta C, Focardi E, Forton E, Franchenko S, Fretwurst E, Gamaz F, Garcia C, Garcia-Navarro JE, Gaubas E, Genest MH, Gill KA, Giolo K, Glaser M, Goessling C, Golovine V, Sevilla SG, Gorelov I, Goss J, Gouldwell A, Gregoire G, Gregori P, Grigoriev E, Grigson C, Grillo A, Groza A, Guskov J, Haddad L, Harkonen J, Harding R, Hauler F, Hayama S, Hoeferkamp M, Honniger F, Horazdovsky T, Horisberger R, Horn M, Houdayer A, Hourahine B, Hruban A, Hughes G, Ilyashenko I, Irmscher K, Ivanov A, Jarasiunas K, Jin T, Jones BK, Jones R, Joram C, Jungermann L, Kalinina E, Kaminski P, Karpenko A, Karpov A, Kazlauskiene V, Kazukauskas V, Khivrich V, Khomenkov V, Kierstead J, Klaiber-Lodewigs J, Kleverman M, Klingenberg R, Kodys P, Kohout Z, Korjenevski S, Kowalik A, Kozlowski R, Kozodaev M, Kramberger G, Krasel O, Kuznetsov A, Kwan S, Lagomarsino S, Lari T, Lassila-Perini K, Lastovetsky V, Latino G, Latushkin S, Lazanu S, Lazanu I, Lebel C, Leinonen K, Leroy C, Li Z, Lindstrom G, Lindstrom L, Linhart V, Litovchenko A, Litovchenko P, Litvinov V, Lo Giudice A, Lozano M, Luczynski Z, Luukka P, Macchiolo A, Mainwood A, Makarenko LF, Mandic I, Manfredotti C, Garcia SM, Marunko S, Mathieson K, Mozzanti A, Melone J, Menichelli D, Meroni C, Messineo A, Miglio S, Mikuz M, Miyamoto J, Moll M, Monakhov E, Moscatelli F, Murin L, Nava F, Naoumov D, Nossarzewska-Orlowska E, Nummela S, Nysten J, Olivero P, Oshea V, Palviainen T, Paolini C, Parkes C, Passeri D, Pein U, Pellegrini G, Perera L, Petasecca M, Piatkowski B, Piemonte C, Pignatel GU, Pinho N, Pintilie I, Pintilie L, Polivtsev L, Polozov P, Popa AI, Popule J, Pospisil S, Pucker G, Radicci V, Rafi JM, Ragusa F, Rahman M, Rando R, Roeder R, Rohe T, Ronchin S, Rott C, Roy P, Roy A, Ruzin A, Ryazanov A, Sadrozinski HFW, Sakalauskas S, Scaringella M, Schiavulli L, Schnetzer S, Schumm B, Sciortino S, Scorzoni A, Segneri G, Seidel S, Seiden A, Sellberg G, Sellin P, Sentenac D, Shipsey I, Sicho P, Sloan T, Solar M, Son S, Sopko B, Spencer N, Stahl J, Stavitski I, Stolze D, Stone R, Storasta J, Strokan N, Strupinski W, Sudzius M, Surma B, Suuronen J, Suvorov A, Svensson BG, Tipton P, Tomasek M, Troncon C, Tsvetkov A, Tuominen E, Tuovinen E, Tuuva T, Tylchin M, Uebersee H, Uher J, Ullan M, Vaitkus JV, Vanni P, Velthuis J, Verzellesi G, Verbitskaya E, Vrba V, Wagner G, Wilhelm I, Worm S, Wright V, Wunstorf R, Zablerowski P, Zaluzhny A, Zavrtanik M, Zen M, Zhukov V, Zorzi N (2005) Radiation-hard semiconductor detectors for SuperLHC, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 541 (1-2) pp. 189-201 ELSEVIER SCIENCE BV
Simon A, Sellin P, Lohstroh A, Jeynes C (2003) Ion beam indneed charge microscopy imaging of CVD diamond, MICROSCOPY OF SEMICONDUCTING MATERIALS 2003 (180) pp. 449-452 IOP PUBLISHING LTD
Wang SG, Sellin PJ, Zhang Q, Lohstroh A, Ozsan ME, Tian JZ (2005) The effects of plasma post-treatment on the photoresponsivity of CVD diamond UV photodetectors, DIAMOND AND RELATED MATERIALS 14 (3-7) pp. 541-545 ELSEVIER SCIENCE SA
Sellin PJ, Galbiati A (2005) Performance of a diamond x-ray sensor fabricated with metal-less graphitic contacts, APPLIED PHYSICS LETTERS 87 (9) ARTN 093502 AMER INST PHYSICS
Jurewicz I, Worajittiphon P, King AA, Sellin PJ, Keddie JL, Dalton AB (2011) Locking carbon nanotubes in confined lattice geometries--a route to low percolation in conducting composites., J Phys Chem B 115 (20) pp. 6395-6400
A significant reduction in the electrical percolation threshold is achieved by locking carbon nanotubes (CNTs) in a predominantly hexagonally close-packed (HCP) colloidal crystal lattice of partially plasticized latex particles. Contrary to other widely used latex processing where CNTs are randomly distributed within the latex matrix, for the first time, we show that excluding CNTs from occupying the interior volume of the latex particles promotes the formation of a nonrandom segregated network. The electrical percolation threshold is four times lower in an ordered segregated network made with colloidal particles near their glass transition temperature (T(g)) in comparison to in a random network made with particles at a temperature well above the T(g). This method allows for a highly reproducible way to fabricate robust, stretchable, and electrically conducting thin films with significantly improved transparency and lattice percolation at a very low CNT inclusion which may find applications in flexible and stretchable electronics as well as other stretchable technologies. For instance, our technology is particularly apt for touch screen applications, where one needs homogeneous distribution of the conductive filler throughout the matrix.
Wang S, Sellin PJ, Lian J, Ozsan E, Chang S (2009) Improvement of Electron Field Emission in Patterned Carbon Nanotubes by High Temperature Hydrogen Plasma Treatment, CURRENT NANOSCIENCE 5 (1) pp. 54-57
Scuffham JW, Pani S, Seller P, Sellin PJ, Veale MC, Wilson MD, Cernik RJ (2015) Imaging of Ra-223 with a small-pixel CdTe detector, JOURNAL OF INSTRUMENTATION 10 ARTN C01029 IOP PUBLISHING LTD
Xu Y, Jie W, Sellin PJ, Wang T, Fu L, Zha G, Veeramani P (2009) Characterization of CdZnTe Crystals Grown Using a Seeded Modified Vertical Bridgman Method, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 56 (5) pp. 2808-2813 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Jiang Q, Brinkman AW, Cantwell BJ, Mullins JT, Dierre F, Basu A, Veeramani P, Sellin P (2009) Growth of Thick Epitaxial CdTe Films by Close Space Sublimation, JOURNAL OF ELECTRONIC MATERIALS 38 (8) pp. 1548-1553 SPRINGER
Boothman V, Alruhaili A, Perumal V, Sellin P, Lohstroh A, Sawhney K, Kachanov S (2015) Charge transport optimization in CZT ring-drift detectors, JOURNAL OF PHYSICS D-APPLIED PHYSICS 48 (48) ARTN 485101 IOP PUBLISHING LTD
The use of organic materials as radiation detectors has grown, due to the easy processability in liquid
phase at room temperature and the possibility to cover large areas by means of low cost deposition
techniques. Direct charged-particle detectors based on solution-grown Organic Semiconducting Single
Crystals (OSSCs) are shown to be capable to detect charged particles in pulse mode, with very good
peak discrimination. The direct charged-particle detection in OSSCs has been assessed both in the planar
and in the vertical axes, and a digital pulse processing algorithm has been used to perform pulse
height spectroscopy and to study the charge collection efficiency as a function of the applied bias voltage.
Taking advantage of the charge spectroscopy and the good peak discrimination of pulse height
spectra, an Hecht-like behavior of OSSCs radiation detectors is demonstrated. It has been possible to
estimate the mobility-lifetime value in organic materials, a fundamental parameter for the characterization
of radiation detectors, whose results are equal to lscoplanar¼ (5 .5 6 0.6 ) 106 cm2
lssandwich¼ (1 .9 6 0.2 ) 106 cm2
/V, values comparable to those of polycrystalline inorganic detectors.
Moreover, alpha particles Time-of-Flight experiments have been carried out to estimate the drift
mobility value. The results reported here indicate how charged-particle detectors based on OSSCs possess
a great potential as low-cost, large area, solid-state direct detectors operating at room temperature.
More interestingly, the good detection efficiency and peak discrimination observed for chargedparticle
detection in organic materials (hydrogen-rich molecules) are encouraging for their further exploitation
in the detection of thermal and high-energy neutrons. VC 2016 AIP Publishing LLC.
Chaudhuri SK, Lohstroh A, Nakhostin M, Sellin PJ (2012) Digital pulse height correction in HgI 2 ³-ray detectors, Journal of Instrumentation 7 (4) T04002 Elsevier
We report on the application of digital pulse processing algorithms to improve the
spectroscopic performance of a 1.2 mm thick planar HgI2 g-ray detector. We have used offline
processing of pulses which were recorded using a high resolution waveform digitizer. The recovery
processes include long duration shaping to avoid ballistic deficit in the case of slow pulses, and
the application of biparametric correction techniques to compensate for charge loss. Pulses of
duration as long as 100 ms were recorded to facilitate long duration shaping. Two different pulse
processing algorithms, viz. semi-Gaussian and moving window deconvolution, were applied and
their performance was compared. The application of long duration shaping and digital chargeloss
correction improved the energy resolution at 662 keV by more than 20% and the peak to
background ratio by a factor of two. The resolution and the peak to background ratio were further
seen to improve drastically upon rejection of counts with very slow rise-time. A 2.6% energy
resolution at 662 keV with 14:1 peak to background ratio was obtained.
Scuffham JW, Wilson MD, Pani S, Duarte DD, Veale MC, Bell S, Seller P, Sellin PJ, Cernik RJ (2012) Evaluation of a new small-pixel CdTe spectroscopic detector in dual-tracer SPECT brain imaging, IEEE Nuclear Science Symposium Conference Record pp. 3115-3118
Simultaneous dual-tracer brain imaging has the potential to shorten patient pathways in the diagnosis of neurodegenerative diseases, but the poor spectral resolution of conventional gamma cameras limits the utility of this technique. Solid state detectors offer improved capability to distinguish between two radioisotopes, but the technology has yet to be fully evaluated in the field of scintigraphic neuroimaging. We present imaging results for a new small-pixel CdTe detector in simultaneous dual-radioisotope scintigraphy of a brain phantom containing Tc-99m and I-123. Quantitative comparison is made with images of the same phantom obtained using a conventional gamma camera. We show that the CdTe detector offers improved scatter rejection and greatly reduced cross-talk between the energy windows. In addition, the new detector is able to resolve low-energy fluorescence x-rays from the source, which could be incorporated into SPECT reconstruction algorithms. Details of the planned development of the detector into a clinical demonstrator are discussed. © 2012 IEEE.
Quinn T, Bates R, Bruzzi M, Cunningham W, Mathieson K, Moll M, Nelson T, Nilsson HE, Pintillie I, Reynolds L, Sciortino S, Sellin P, Strachan H, Svensson BG, Vaitkus J, Rahman M (2003) Comparison of bulk and epitaxial 4H-SiC detectors for radiation hard particle tracking, IEEE Nuclear Science Symposium Conference Record 2 pp. 1028-1033
Measurements and simulations have been carried out using bulk and epitaxial SiC detectors. Samples were irradiated to fluences of around 1014 hardrons/cm2. Material of thickness 40um gave a charge collection efficiency of 100% dropping to around 60% at 100¼m thickness. Detailed MEDICI simulations incorporated the main defect levels in SiC, the vanadium center, Z-center and a mid-gap level as measured by deep level transient spectroscopy and other techniques. Calculated recombination currents and charge collection efficiencies at varying fluences were comparable to experimental data. The study suggests that SiC detectors will operate up to fluences around 10 16/cm2 as required by future particle physics experiments.
Lohstroh A, Sellin PJ, Gkoumas S, Parkin J, Veeramani P, Prekas G, Veale MC, Morse J (2008) Ion beam induced charge (IBIC) irradiation damage study in synthetic single crystal diamond using 2.6 MeV protons, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 (9) pp. 2211-2215 WILEY-V C H VERLAG GMBH
Sellin PJ, Prekas G, Lohstroh A, Ozsan M, Perumal V, Veale M, Seller P (2009) Real-time imaging of the electric field distribution in CdZnTe at low temperature, Materials Research Society Symposium Proceedings 1164 pp. 15-24
Real time imaging of the electric field distribution in CZT at low temperature has been carried out using the Pockels electro-optical effect. CZT detectors have been observed to show degraded spectroscopic resolution at low temperature due to so-called ?polarization? phenomena. By mounting a CZT device in a custom optical cryostat, we have used Pockels imaging to observe the distortion of the electric field distribution in the temperature range 240K - 300K. At 240K the electric field has a severely non-uniform depth distribution, with a high field region occupying
Al-Qaradawi IY, Sellin PA, Coleman PG (2002) Tests of a diamond field-assisted positron moderator, Applied Surface Science 194 (1-4) pp. 29-31
Diagnostic studies have been performed on a 70 ¼m thick diamond film with a view to its development as a possible field-assisted moderator (FAM) for slow positron emission. The film was coated on one side with a 200 nm gold electrode and on the other with a similar thickness of gold in the form of a fine mesh (10 ¼m lines, 40 ¼m spaces) in the central part of the diamond surface and a solid edge for electrical contact. A potential difference of up to 300 V could be held across the film with a leakage current of
Yang DJ, Wang SG, Zhang Q, Sellin PJ, Chen G (2004) Thermal and electrical transport in multi-walled carbon nanotubes, PHYSICS LETTERS A 329 (3) pp. 207-213 ELSEVIER SCIENCE BV
Davies AW, Lohstroh A, Ozsan ME, Sellin PJ (2005) Spatial uniformity of electron charge transport in high resistivity CdTe, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 546 (1-2) pp. 192-199 ELSEVIER SCIENCE BV
Darambara DG, Sellin PJ, Maehlum G (2004) A novel detection system consisting of a large-area sensor and a multicell Si-pad array operated in spectroscopic mode for X-ray breast imaging, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 51 (4) pp. 1641-1647 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Darambara DG, Sellin PJ, Maehlum G (2004) A novel detection system consisting of a large area sensor and a multi-cell Si-pad array operated in spectroscopic mode for X-ray breast imaging, 2003 IEEE NUCLEAR SCIENCE SYMPOSIUM, CONFERENCE RECORD, VOLS 1-5 pp. 1011-1015 IEEE
Jastaniah SD, Sellin PJ (2004) Digital techniques for n/gamma pulse shape discrimination and capture-gated neutron spectroscopy using liquid scintillators, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 517 (1-3) pp. 202-210 ELSEVIER SCIENCE BV
The performance of single crystal CdZnTe radiation detectors is dependent on both the bulk and the surface properties of the material. After single crystal fabrication and mechanical polishing, modification of the surface to remove damage and reduce the surface leakage current is generally achieved through chemical etching followed by a passivation treatment. In this work, CdZnTe single crystals have been chemically etched using a bromine in methanol (BM) treatment. The BM concentrations employed were 0.2 and 2.0 (v/v) % and exposure times varied between 5 and 120 s. Angle resolved XPS and sputter depth profiling has been employed to characterize the surfaces for the different exposure conditions. A Te rich surface layer was formed for all exposures and the layer thickness was found to be independent of exposure time. The enriched Te layer thickness was accurately determined by calibrating the sputter rate against a CdTe layer of known thickness. For BM concentrations of 0.2 (v/v) % and 2 (v/v) %, the Te layer thickness was determined to be 1.3 ± 0.2 and 1.8 ± 0.2 nm, respectively. The BM etched surfaces have subsequently been passivated in a 30 wt.% H2O2 solution employing exposure time of 15 s. The oxide layer thickness has been calculated using two standard XPS methodologies, based on the Beer-Lambert expression. The TeO2 thickness calculated from ARXPS data are slightly higher than the thickness obtained by the simplified Beer-Lambert expression. For BM exposures of 30-120 s followed by a passivation treatment of 30 wt. % H2O2 solution employing an exposure time 15 s, the ARXPS method gave an average TeO2 thickness value of 1.20 nm and the simplified Beer-Lambert expression gave an average thickness value of 0.99 nm. © 2012 Elsevier B.V. All rights reserved.
Sellin PJ, Breese MBH, Galbiati A (2000) Spectroscopic response of coplanar diamond alpha particle detectors, IEEE Nuclear Science Symposium and Medical Imaging Conference 1
The performance of a CVD diamond radiation detector with an inter-digitated coplanar electrode geometry is reported. The coplanar structure produces a shallow lateral electric field distribution and consequently charge transport occurs in a region close to the growth surface of the CVD diamond film, where the drift lengths are maximised. The spectroscopic performance of the coplanar diamond detector was investigated using alpha particles from a 241Am source, and also using a scanning 2 MeV proton microprobe. A broad full energy peak was observed using 5.49 MeV alpha particles, with an overall charge collection efficiency of approximately 16% at a bias voltage of 300V. Images obtained from the proton microprobe demonstrate the inhomogeneous pulse height response across the active surface of the detectors, caused by a combination of the polycrystalline diamond material and also non-uniform electric field profile.
Wang S, Wang R, Sellin PJ, Chang S (2009) Carbon Nanotube Based DNA Biosensor for Rapid Detection of Anti-Cancer Drug of Cyclophosphamide, CURRENT NANOSCIENCE 5 (3) pp. 312-317
Rath S, Sellin PJ, Breese MBH, Herman H, Alves LC, Holland AH (2003) Microscopic evaluation of spatial variations in material and charge transport properties of CdZnTe radiation detectors, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 512 (1-2) pp. 427-432 ELSEVIER SCIENCE BV
Tsvetkova T, Sellin P, Carius R, Angelov O, Dimova-Malinovska D, Zuk J (2009) Optical contrast formation in amorphous silicon carbide with high-energy focused ion beams, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 267 (8-9) pp. 1583-1587 ELSEVIER SCIENCE BV
Babar S, Sellin PJ, Watts JF, Baker MA (2012) An XPS study of bromine in methanol etching and hydrogen peroxide passivation treatments for cadmium zinc telluride radiation detectors, Applied Surface Science
The performance of single crystal CdZnTe radiation detectors is dependent on both the bulk and the surface properties of the material. After single crystal fabrication and mechanical polishing, modification of the surface to remove damage and reduce the surface leakage current is generally achieved through chemical etching followed by a passivation treatment. In this work, CdZnTe single crystals have been chemically etched using a bromine in methanol (BM) treatment. The BM concentrations employed were 0.2 and 2.0 (v/v) % and exposure times varied between 5 and 120 s. Angle resolved XPS and sputter depth profiling has been employed to characterize the surfaces for the different exposure conditions. A Te rich surface layer was formed for all exposures and the layer thickness was found to be independent of exposure time. The enriched Te layer thickness was accurately determined by calibrating the sputter rate against a CdTe layer of known thickness. For BM concentrations of 0.2 (v/v) % and 2 (v/v) %, the Te layer thickness was determined to be 1.3 ± 0.2 and 1.8 ± 0.2 nm, respectively. The BM etched surfaces have subsequently been passivated in a 30 wt.% H
solution employing exposure time of 15 s. The oxide layer thickness has been calculated using two standard XPS methodologies, based on the Beer-Lambert expression. The TeO
thickness calculated from ARXPS data are slightly higher than the thickness obtained by the simplified Beer-Lambert expression. For BM exposures of 30-120 s followed by a passivation treatment of 30 wt. % H
solution employing an exposure time 15 s, the ARXPS method gave an average TeO
thickness value of 1.20 nm and the simplified Beer-Lambert expression gave an average thickness value of 0.99 nm. © 2012 Elsevier B.V. All rights reserved.
Simon A, Jeynes C, Webb RP, Finnis R, Tabatabian Z, Sellin PJ, Breese MBH, Fellows DF, van den Broek R, Gwilliam RM (2004) The new Surrey ion beam analysis facility, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 219 pp. 405-409 ELSEVIER SCIENCE BV
Wang SG, Zhang Q, Yang DJ, Sellin PJ, Zhong GF (2004) Multi-walled carbon nanotube-based gas sensors for NH3 detection, DIAMOND AND RELATED MATERIALS 13 (4-8) pp. 1327-1332 ELSEVIER SCIENCE SA
Sellin PJ, Hoxley D, Lohstroh A, Simon A, Cunningham W, Rahman M, Vaitkus J, Gaubas E (2004) Ion beam induced charge imaging of epitaxial GaN detectors, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 531 (1-2) pp. 82-86 ELSEVIER SCIENCE BV
Galbiati A, Breese MBH, Knights AP, Sealy B, Sellin PJ (2001) Characterisation of a coplanar CVD diamond radiation detector, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 466 (1) pp. 52-57 ELSEVIER SCIENCE BV
Menezes T, Sellin PJ, Jenneson PM (2004) Characterisation of a multiple-line fluorescence X-ray tube for security imaging applications, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 525 (1-2) pp. 342-345 ELSEVIER SCIENCE BV
Sellin PJ, Breese MBH (2001) Spectroscopic response of coplanar diamond alpha particle detectors, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 48 (6) PII S0018-9499(01)10693-3 pp. 2307-2312 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Scuffham JW, Scuffham JW, Sellin PJ, Wilson MD, Seller P, Veale MC, Jacquesd SDM, Cernik RJ (2012) A CdTe detector for hyperspectral SPECT imaging, Journal of Instrumentation 7 (8)
A Cadmium Telluride (CdTe) detector has been developed for multiple-radioisotope SPECT imaging. The 22 cm detector has 8080 pixels on a 250 mm pitch and a three-side buttable design so that it can be tiled into larger arrays. The detector is termed hyperspectral as it measures the energy of every photon that interacts in the CdTe to give fully spectroscopic information from 5-200 keV in each pixel. The detector has been tested for applications in multipleradioisotope SPECT imaging using a 1mm diameter pinhole configuration and standard phantom test objects containing Tc-99m, I-123 and Ga-67. The detector has an average pixel energy resolution (FWHM) of 0.75% at the I-123 photopeak of 159 keV. We demonstrate the system's capability of resolving spatial features of 2 mm, although the spatial resolution of the detector is limited only by the pixel size and pinhole magnification factor. These characteristics are superior to alternative detectors currently in use in clinical SPECT systems. When imaging multiple radioisotopes simultaneously, we show that there is very little cross-talk between adjacent photopeaks, leading to superior image contrast. The detector is also capable of resolving fluorescence x-rays from the radioactive source, which could be used to improve image count statistics or derive information about the attenuation properties of the source. The performance presented here, and the ability to tile the detector modules to create a clinically useful field of view, makes this technology a strong candidate to be used in future solid-state SPECT cameras. © 2012 IOP Publishing Ltd and Sissa Medialab srl.
Burger A, Derenzo S, Moses B, Luke P, Archer D, Bolotnikov A, Boston A, Fabris L, Franks L, Friedrich S, Iwanczyk JS, Kernan W, Payne S, Rockett P, Royle G, Rozenfeld A, Sellin P, Sjoden G, Sturm B (2009) Conference Comments by the Editors, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 56 (3) pp. 724-724 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Veale MC, Bell SJ, Jones LL, Seller P, Wilson MD, Allwork C, Kitou D, Sellin PJ, Veeramani P, Cernik RC (2011) An ASIC for the Study of Charge Sharing Effects in Small Pixel CdZnTe X-Ray Detectors, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 58 (5) pp. 2357-2362 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Pearson CJ, Dobon JJV, Regan PH, Sellin PJ, Morton E, Nolan PJ, Boston A, Descovich M, Thornhill J, Cresswell J, Lazarus I, Simpson J (2002) Digital gamma-ray tracking algorithms in segmented germanium detectors, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 49 (3) pp. 1209-1215 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
The electrical characteristics and fast neutron response of a High Temperature Chemical Vapour Deposition (HTCVD) grown semi-insulating bulk SiC wafer has been measured. Current - Voltage measurements demonstrated a low leakage current in the region of 10-10 to 10-12 A with a bulk resistivity of at least 1012 - 1013 ©.cm. Alpha particle spectroscopy measurements demonstrated an electron charge collection efficiency of up to 90% with reasonable reproducibility of the acquired spectra. Evidence of (incident particle) rate dependent polarisation was seen following a constant applied bias combined with alpha irradiation over a period of time (order of tens of minutes). The ability of the wafer to detect fast neutrons was demonstrated and a comparison drawn with the MCNPX simulated response of a bulk SiC device. Comparing the MCNPX simulated response of a bulk SiC device to that of a silicon device suggests a superior ability to detect fast neutrons with an intrinsic efficiency 1.7 times that of silicon. © 1963-2012 IEEE.
Xu Y-D, Jie W-Q, Bai X-X, Wang T, Fu L, Zha G-Q, Sellin P (2009) Non-destructive characterization and selection of X/³-ray detector-grade CdZnTe crystals, Proceedings of SPIE - The International Society for Optical Engineering 7385 SPIE
Infrared (IR) transmission spectra and IR microscopy images were measured to evaluate the sliced CdZnTe crystals grown under different starting charges using modified vertical Bridgman method. Upon comparing the corresponding electric properties and charge transport performance, IR absorption within the wave-number range from 500 to 2500 cm-1 was potentially attributed to the free carrier absorption caused by the ionized impurities. The size and density of Te particles were not sensitive to IR transmission spectra over the same wave-number range. However, the electric field was modified around isolated Te particles, in such a way that the impurities gettering in the Te inclusions. With respect to the high resistive CdZnTe crystals, IR transmission measurements demonstrated that the mean transmittance is higher than 60% in the wave-number region from 500 to 4000 cm-1. IR microscopy shown the typical diameters of Te particles present in the material were in the range of 6-9 ¼m, and the density of the particles was 1-4×105 cm-3. The obtained electron mobility lifetime product (¼Ä)e value was in the range of 1-3×10-3 cm2V-1 by using well-known alpha particle spectra at room temperature. The fabricated CdZnTe thin planar detector showed the typical energy resolution was approximately 5.7% for the 59.5 keV peak at room temperature, without any additional signal processing.
Darambara DG, Speller RD, Sellin P (2002) Development of a dual-detector system based on a-Si : H Arrays and multi-element silicon detectors for diffraction-enhanced breast imaging, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 49 (3) pp. 1012-1016 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Jiang Q, Brinkman AW, Veeramani P, Sellin PJ (2010) Epitaxial Growth of High-Resistivity CdTe Thick Films Grown Using a Modified Close Space Sublimation Method, JAPANESE JOURNAL OF APPLIED PHYSICS 49 (2) UNSP 025504 JAPAN SOC APPLIED PHYSICS
Bell SJ, Baker MA, Chen H, Marthandam P, Perumal V, Schneider A, Seller P, Sellin PJ, Veale MC, Wilson MD (2013) A multi-technique characterization of electroless gold contacts on single crystal CdZnTe radiation detectors,Journal of Physics D: Applied Physics 46 (45)
Cadmium zinc telluride (CdZnTe) is now established as a popular choice of sensor for the detection of ³-rays and hard x-rays, leading to its adoption in security, medical and scientific applications. There are still many technical challenges involving the deposition of high-quality, uniform metal contacts on CdZnTe. A detailed understanding of the interface between the bulk CdZnTe and the metal contacts is required for improvements to be made. To understand these complex interfaces, a range of complementary materials characterization techniques have been employed, including x-ray photoelectron spectroscopy depth profiling, focused ion beam cross section imaging and energy dispersive x-ray spectroscopy. In this paper a number of Redlen CdZnTe detectors with asymmetric anode/cathode contacts have been investigated. The structures of the contacts were imaged and their compositions identified. It was found that the two stage electroless indium/electroless gold deposition process on 'polished only' surfaces formed a complex heterojunction on the cathode, incorporating compounds of gold, gold-tellurium, tellurium oxide (of varying stoichiometry) and cadmium chloride up to depths of several 100 nm. Trace amounts of indium were found, in the form of an indium-gold compound, or possibly indium oxide. At the surface of the CdZnTe bulk, a thin Cd depleted layer was observed. The anode heterojunction, formed by a single stage electroless gold deposition, was thinner and exhibited a simpler structure of gold and tellurium oxide. The differing (asymmetric) nature of the anode/cathode contacts gave rise to asymmetric current-voltage (I-V) behaviour and spectroscopy. © 2013 IOP Publishing Ltd.
Choubey A, Veeramani P, Pym ATG, Mullins JT, Sellin PJ, Brinkman AW, Radley I, Basu A, Tanner BK (2012) Growth by the Multi-tube Physical Vapour Transport method and characterisation of bulk (Cd,Zn)Te, Journal of Crystal Growth 352 (1) pp. 120-123
Growth by the Multi-tube Physical Vapour Transport technique and characterisation of bulk (Cd,Zn)Te is described. The crystalline perfection and uniformity of zinc content have been mapped by infra-red transmission and microscopy, X-ray diffraction and photoluminescence. X-ray double crystal rocking curve full widths at half maximum as low as 43 in have been obtained and a mean zinc mole fraction of 0.03 has been found to vary by less than ±0.003 over the diameter of a 50 mm boule. The material exhibits a resistivity in the 2×10 9 ©cm range and planar devices fabricated from this material have shown electron mobility lifetime products of 4.07×10 -3 cm 2 V -1. © 2012 Elsevier B.V.
Valiente-Dobon JJ, Pearson CJ, Regan PH, Sellin PJ, Gelletly W, Morton E, Boston A, Descovich M, Nolan PJ, Simpson J, Lazarus I, Warner D (2003) Performance of a 6x6 segmented germanium detector for gamma-ray tracking, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 505 (1-2) pp. 174-177 ELSEVIER SCIENCE BV
Pani S, Saifuddin SC, Ferreira FIM, Scuffham JW, Stratmann P, Wilson MD, Veale MC, Bell S, Seller P, Sellin PJ, Cernik RJ (2012) Optimization of K-edge subtraction imaging using a pixellated spectroscopic detector,IEEE Nuclear Science Symposium Conference Record pp. 3063-3066
Conventional K-edge subtraction imaging is based around the acquisition of two separate images at energies respectively below and above the K-edge of a contrast agent. This implies increased patient dose with respect to a conventional procedure and potentially incorrect image registration due to patient motion. © 2012 IEEE.
Semiconducting polymers have previously been used as the transduction material in x-ray dosimeters, but these devices have a rather low detection sensitivity because of the low x-ray attenuation efficiency of the organic active layer. Here, we demonstrate a way to overcome this limitation through the introduction of high density nanoparticles having a high atomic number (Z) to increase the x-ray attenuation. Specifically, bismuth oxide (Bi
) nanoparticles (Z=83 for Bi) are added to a poly(triarylamine) (PTAA) semiconducting polymer in the active layer of an x-ray detector. Scanning electron microscopy (SEM) reveals that the Bi
nanoparticles are reasonably distributed in the PTAA active layer. The reverse bias dc currentvoltage characteristics for PTAABi
diodes (with indium tin oxide (ITO) and Al contacts) have similar leakage currents to ITO/PTAA/Al diodes. Upon irradiation with 17.5keV x-ray beams, a PTAA device containing 60wt% Bi
nanoparticles demonstrates a sensitivity increase of approximately 2.5 times compared to the plain PTAA sensor. These results indicate that the addition of high-Z nanoparticles improves the performance of the dosimeters by increasing the x-ray stopping power of the active volume of the diode. Because the Bi
has a high density, it can be used very efficiently, achieving a high weight fraction with a low volume fraction of nanoparticles. The mechanical flexibility of the polymer is not sacrificed when the inorganic nanoparticles are incorporated. © 2012 IOP Publishing Ltd.
Choubey A, Veeramani P, Pym ATG, Mullins JT, Sellin PJ, Brinkman AW, Radley I, Basu A, Tanner BK (2012) Growth by the Multi-tube Physical Vapour Transport method and characterisation of bulk (Cd,Zn)Te, Journal of Crystal Growth 352 (1) pp. 120-123 Elsevier
Wang SG, Sellin PJ, Zhang Q, Yang DJJ (2005) Nonvolatile memory from single-walled carbon nanotube-based field effect transistors, CURRENT NANOSCIENCE 1 (1) pp. 43-46 BENTHAM SCIENCE PUBL LTD
Franc J, D?di
V, Zázvorka J, Hakl M, Grill R, Sellin PJ (2013) Flux-dependent electric field changes in semi-insulating CdZnTe, Journal of Physics D: Applied Physics 46 (23)
We studied polarization in semi-insulating detector-grade cadmium zinc telluride without and with high optical flux. We employed the Pockels electro-optic effect combined with two perpendicular sources of light. A beam of red light or an infrared laser was applied parallel to the direction of the electric field acting as a source of electron-hole pairs. Infrared radiation from the monochromator illuminated the sample perpendicular to the direction of the electric field and changed the occupation of deep levels and therefore the depth profile of the bulk electric field. Spectral measurements of the Pockels effect were used to determine energy levels responsible for polarization and to find the optimal wavelength for optical depolarization of the detectors. © 2013 IOP Publishing Ltd.
El-Abbassi H, Rath S, Sellin PJ (2001) Characterisation of vertical gradient freeze semi-insulating InP for use as a nuclear radiation detector, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 466 (1) pp. 47-51 ELSEVIER SCIENCE BV
Veale MC, Sellin PJ, Lohstroh A, Davies AW, Parkin J, Seller P (2007) X-ray spectroscopy and charge transport properties of CdZnTe grown by the vertical Bridgman method, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 576 (1) pp. 90-94 ELSEVIER SCIENCE BV
V, Zázvorka J, Rejhon M, Franc J, Grill R, Sellin PJ (2014) Temporal and temperature evolution of electric field in CdTe:In radiation detectors, Journal of Applied Physics 116 (5)
We employed measurement of the Pockels electro-optic effect to study the electric field and space charge dynamics in semi-insulating CdTe doped with indium. We performed measurements of time and temperature dependence of the electric field. The polarization due to space charge build-up decreases with increasing temperature. Increase of temperature, therefore, leads to de-polarization in CdTe:In detectors which are opposite to the CdTe:Cl samples studied to date. We have shown that the thermally activated depolarization cannot be explained by the conventional model used for the description of space charge formation so far and an alternative model involving a recombination level was suggested and successfully used. © 2014 AIP Publishing LLC.
A new class of X-ray sensor ? in which there is a blend of poly(triarylamine) (PTAA) and 6,13-bis(triisopropylsilylethynyl) (TIPS)-pentacene in the active layer of a diode structure ? has been developed. The crystalline pentacene provides a fast route for charge carriers and leads to enhanced performance of the sensor. The first time-of-flight charge-carrier mobility measurement of this blend is reported. The mobility of PTAA and TIPS-pentacene in a 1:25 molar ratio was found to be 2.2 × 10?5 cm2 V?1 s?1 (averaged for field strengths between 3 × 104 and 4 × 105 V cm?1), which is about 17 times higher than that obtained in PTAA over the same range of field strengths. This higher mobility is correlated with a fourfold increase in the X-ray detection sensitivity in the PTAA:TIPS-pentacene devices.
Breese MBH, Vittone E, Vizkelethy G, Sellin PJ (2007) A review of ion beam induced charge microscopy, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 264 (2) pp. 345-360 ELSEVIER SCIENCE BV
Owens A, Barnes A, Farley RA, Germain M, Sellin PJ (2011) GaN detector development for particle and X-ray detection, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Sellin PJ, Breese MBH, Knights AP, Alves LC, Sussmann RS, Whitehead AJ (2000) Imaging of charge transport in polycrystalline diamond using ion-beam-induced charge microscopy, APPLIED PHYSICS LETTERS 77 (6) pp. 913-915 AMER INST PHYSICS
Scuffham J, Wilson M, Pani S, Duarte D, Veale M, Bell S, Jacques S, Seller P, Sellin P, Cernik R (2012) High resolution dual-tracer brain SPECT with a new high-performance CdTe detector, EUROPEAN JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING 39 pp. S230-S230 SPRINGER
Sun GC, Lenoir M, Breelle E, Samic H, Bourgoin JC, El-Abbassi H, Sellin PJ, Montagne JP (2003) X-ray detector with thick epitaxial GaAs grown by chemical reaction, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 50 (4) pp. 1036-1038 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Semiconducting polymer X-radiation detectors are a completely new family of low-cost radiation detectors with potential application as beam monitors or dosimeters. These detectors are easy to process, mechanically flexible, relatively inexpensive, and able to cover large areas. However, their x-ray photocurrents are typically low as, being composed of elements of low atomic number (Z), they attenuate x-rays weakly. Here, the addition of high-Z nanoparticles is used to increase the x-ray attenuation without sacrificing the attractive properties of the host polymer. Two types of nanoparticles (NPs) are compared: metallic tantalum and electrically insulating bismuth oxide. The detection sensitivity of 5 µm thick semiconducting poly([9,9-dioctylfluorenyl-2,7-diyl]-co-bithiophene) diodes containing tantalum NPs is four times greater than that for the analogous NP-free devices; it is approximately double that of diodes containing an equal volume of bismuth oxide NPs. The x-ray induced photocurrent output of the diodes increases with an increased concentration of NPs. However, contrary to the results of theoretical x-ray attenuation calculations, the experimental current output is higher for the lower-Z tantalum diodes than the bismuth oxide diodes, at the same concentration of NP loading. This result is likely due to the higher tantalum NP electrical conductivity, which increases charge transport through the semiconducting polymer, leading to increased diode conductivity.
Nakhostin M, Podolyak Z, Sellin PJ (2013) Application of pulse-shape discrimination to coplanar CdZnTe detectors, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 729 pp. 541-545
A digital pulse-shape discrimination algorithm for the identification of multi-site ³-ray interactions in coplanar CdZnTe detectors has been developed. The algorithm is used to suppress the Compton continuum in ³-ray spectroscopy measurements by rejecting the single-site events. The results of our study with a 15×15×7.5 mm3 detector demonstrate the effectiveness of this approach for revealing low intensity ³-ray peaks in the examined energy range (511-1274 keV), which is of importance for environmental and security applications. The method is also very useful for background reduction in the neutrinoless double beta-decay experiments for which coplanar CdZnTe detectors are of interest. © 2013 Elsevier B.V.
Schirru F, Lohstroh A, Sellin J, Nara Singh S, Scruton L, Bentley A, Fox P, Banu A, McCleskey M, Roeder T, Simmons E, Alharbi A, Trache L, Freer M, Parker D, Banu A (2012) Development of large area polycrystalline diamond detectors for fast timing application of high-energy heavy-ion beams,Journal of Instrumentation 7 (5) P05005
Institute of Physics
We have studied the effects of electrode fabrication and detector capacitance on the time resolution of large area electronic grade polycrystalline chemical vapour deposited diamond sensors that are suitable for time of flight measurements of heavy ions at relativistic velocities. Sensors were prepared both in house, with Al or Au metal contacts, and commercially fabricated with Au/diamond-like carbon contacts.
Ar and a mixture of
O beams at 16.3, 33.5 and 21-23 MeV/u, respectively were used on these devices whilst arranged in transmission geometry. Signal processing only began over one meter away from the sensors. The present approach, where we have large-area/large capacitance multi-strip detectors with processing electronics at some distance from the target, is compatible with anticipated space limitations in particle- identification and tracking setups at existing and planned nuclear fragmentation facilities. In a systematic study under these conditions, we demonstrate that the time resolution is limited by detector capacitance and energy deposition in the sensors. An intrinsic time resolution Ã
= (44±5) ps was achieved for a diamond detector of
Avella P, De Santo A, Lohstroh A, Sajjad MT, Sellin PJ (2012) A study of timing properties of Silicon Photomultipliers, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 695 pp. 257-260
Silicon Photomultipliers (SiPMs) are solid-state pixelated photodetectors. Lately these sensors have been investigated for Time of Flight Positron Emission Tomography (ToF-PET) applications, where very good coincidence time resolution of the order of hundreds of picoseconds imply spatial resolution of the order of cm in the image reconstruction. The very fast rise time typical of the avalanche discharge improves the time resolution, but can be limited by the readout electronics and the technology used to construct the device. In this work the parameters of the equivalent circuit of the device that directly affect the pulse shape, namely the quenching resistance and capacitance and the diode and parasitic capacitances, were calculated. The mean rise time obtained with different preamplifiers was also measured. © 2011 Elsevier B.V.
Lohstroh A, Sellin PJ, Boroumand F, Morse J (2007) High gain observed in X-ray induced currents in synthetic single crystal diamonds, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 204 (9) pp. 3011-3016 WILEY-V C H VERLAG GMBH
Diamond is considered as tissue equivalent, due to its low atomic number, which makes it a particular attractive material for medical radiation dosimetry applications. X-ray dosimeters made of natural single crystal diamonds are commercially available and routinely used, with typical gain values of about 0.5. The selection of suitable natural diamonds for this purpose is time and cost intensive. We report an X-ray induced current study in synthetic single crystal diamonds. Similar to natural diamond dosimeters, the devices had to be pre-irradiated before use to achieve a reproducible performance. We compare two chemical vapour deposited (CVD) samples grown by Element Six Ltd (UK). D1 was a high purity sample contacted in a sandwich structure with an asymmetric contact pair. Sample D2 was cut vertically and contained some nitrogen rich layers. It was contacted with two Ohmic contacts, which partly covered the high temperature/high pressure substrate material. Particle spectroscopy suggests better charge transport in D1 compared to D2, most likely caused by the lower purity. In contrast to this, large gain values up to 6 x 104 and a sensitivity of similar to 30 mC/Gy were measured at field strengths of 2 kV/cm in D2, and only 7 mu C/Gy in D1, despite their comparable volumes. We deduce that the gain observed in these devices is affected by the electrical properties of the metal-diamond contacts. The response time of the high gain device was in the order of minutes, which is longer than expected by a purely photoconductive process. Long persistent currents have been reported before in diamond under UV irradiation and modifications of gain and response time by surface treatment of UV detectors are known in the literature, highlighting the influence of the surface and contact interface on the device operation. Our results indicate that synthetic single crystal diamond provides a promising material for high sensitivity tissue-equivalent X-ray dosimeters. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Sellin PJ, Lohstroh A, Davies AW, Galbiati A, Parkin J, Wang SG, Simon A (2007) Charge transport in polycrystalline and single crystal synthetic diamond using ion beam induced charge imaging, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 260 (1) pp. 293-298 ELSEVIER SCIENCE BV
Parkin J, Sellin PJ, Davies AW, Lohstroh A, Ozsan ME, Seller P (2007) alpha Particle response of undoped CdMnTe, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 573 (1-2) pp. 220-223 ELSEVIER SCIENCE BV
Wang SG, Sellin P (2005) Pronounced hysteresis and high charge storage stability of single-walled carbon nanotube-based field-effect transistors, APPLIED PHYSICS LETTERS 87 (13) ARTN 133117 AMER INST PHYSICS
Tumer TO, Yin S, Cajipe V, Flores H, Mainprize J, Mawdsley G, Rowlands JA, Yaffe MJ, Gordon EE, Hamilton WJ, Rhiger D, Kasap SO, Sellin P, Shah KS (2003) High-resolution pixel detectors for second generation digital mammography, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 497 (1) pp. 21-29 ELSEVIER SCIENCE BV
Tsvetkova T, Sellin P, Carius R, Angelov O, Dimova-Malinovska D (2007) High-energy He+ ion beam induced modification in a-SiC : H, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS 9 (2) pp. 375-378 NATL INST OPTOELECTRONICS
Allwork C, Kitou D, Chaudhuri S, Sellin PJ, Seller P, Veale MC, Tartoni N, Veeramani P (2012) X-Ray Beam Studies of Charge Sharing in Small Pixel, Spectroscopic, CdZnTe Detectors,IEEE TRANSACTIONS ON NUCLEAR SCIENCE 59 (4) pp. 1563-1568
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Recent advances in the growth of CdZnTe material have allowed the development of small pixel, spectroscopic, X-ray imaging detectors. These detectors have applications in a diverse range of fields such as medical, security and industrial sectors. As the size of the pixels decreases relative to the detector thickness, the probability that charge is shared between multiple pixels increases due to the non zero width of the charge clouds drifting through the detector. These charge sharing events will result in a degradation of the spectroscopic performance of detectors and must be considered when analyzing the detector response. In this paper charge sharing and charge loss in a 250 ¼m m pitch CdZnTe pixel detector has been investigated using a mono-chromatic X-ray beam at the Diamond Light Source, U.K. Using a 20 ¼m m beam diameter the detector response has been mapped for X-ray energies both above (40 keV) and below (26 keV) the material $K$-shell absorption energies to study charge sharing and the role of fluorescence X-rays in these events. © 2012 IEEE.
Abdel-Rahman MAE, Lohstroh A, Sellin PJ (2011) The effect of annealing on the X-ray induced photocurrent characteristics of CVD diamond radiation detectors with different electrical contacts, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 208 (9) pp. 2079-2086
Descovich M, Nolan PJ, Boston AJ, Dobson J, Gros S, Cresswell JR, Simpson J, Lazarus I, Regan PH, Valiente-Dobon JJ, Sellin P, Pearson CJ (2005) The position response of a large-volume segmented germanium detector, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 553 (3) pp. 512-521 ELSEVIER SCIENCE BV
Owens A, Barnes A, Farley RA, Germain M, Sellin PJ (2012) GaN detector development for particle and X-ray detection, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 695 pp. 303-305
We report on preliminary alpha particle and X-ray measurements on a number of prototype GaN PIN diodes. The aim of the study was to investigate the potential use of GAN based radiation detectors for radiation hard, high temperature, solar blind space applications. The devices have a planar structure consisting of a 2 ¼m epitaxial GaN layer grown on a highly doped n-type Al xGa 1-xN nucleation layer, which in turn is deposited on a p-type 4H-SiC substrate. Au ohmic contacts were applied to the top of the GaN layer and the bottom of the substrate. A number of different sized devices were tested with contact diameters ranging from 0.4 mm to 0.7 mm. All devices showed good diode behaviour with reverse leakage currents in the tens to hundreds of micro-amp range. C-V measurements showed that the GaN layers were fully depleted for biases >20 V. When exposed to a 5.5 MeV alpha particle source, the devices showed a spectroscopic response with energy resolutions of
Pani Silvia, Saifuddin SC, Ferreira Filipa, Henthorn N, Sellers P, Sellin Paul, Stratmann P, Veale MC, Wilson MD, Cernik RJ (2017) High energy resolution hyperspectral X-ray imaging for low-dose contrast-enhanced digital mammography,IEEE Transactions on Medical Imaging 36 (9) pp. 1784-1795
Contrast-enhanced digital mammography (CEDM) is an alternative to conventional X-ray mammography for imaging dense breasts. However, conventional approaches to CEDM require a double exposure of the patient, implying higher dose and risk of incorrect image registration due to motion artifacts.
A novel approach is presented, based on hyperspectral imaging, where a detector combining positional and high-resolution spectral information (in this case based on Cadmium Telluride) is used. This allows simultaneous acquisition of the two images required for CEDM. The approach was tested on a custom breast-equivalent phantom containing iodinated contrast agent (Niopam 150®).
Two algorithms were used to obtain images of the contrast agent distribution: K-edge subtraction (KES), providing images of the distribution of the contrast agent with the background structures removed, and a dual-energy (DE) algorithm, providing an iodine-equivalent image and a water-equivalent image. The high energy resolution of the detector allowed the selection of two close-by energies, maximising the signal in KES images and enhancing the visibility of details with low surface concentration of contrast agent. DE performed consistently better than KES in terms of contrast-to-noise ratio of the details; moreover, it allowed a correct reconstruction of the surface concentration of the contrast agent in the iodine image.
Comparison with CEDM with a conventional detector proved the superior performance of hyperspectral CEDM in terms of the image quality/dose trade-off.
The presence of carbon atoms in silicon carbide and diamond makes the materials
ideal candidates for direct fast neutron detectors. Furthermore the low atomic number,
strong covalent bonds, high displacement energies, wide band gap and low intrinsic
carrier concentrations make these semiconductor detectors potentially suitable for
applications where rugged, high temperature, low gamma sensitivity detectors are
required, such as Active Interrogation, Electronic Personal Neutron Dosimetry and
Harsh Environment Detectors.
A thorough direct performance comparison of the detection capabilities of semiinsulating
silicon carbide (SiC-SI), single crystal diamond (D-SC), polycrystalline
diamond (D-PC) and a self-biased epitaxial silicon carbide (SiC-EP) detector has been
conducted and benchmarked against a commercial silicon PIN (Si-PIN) diode, in a
wide range of alpha (Am-241), beta (Sr/Y-90), ionising photon (65keV to 1332keV)
and neutron radiation fields (including 1.2MeV to 16.5MeV mono-energetic neutrons,
as well as neutrons from AmBe and Cf-252 sources).
All detectors were shown to be able to directly detect and distinguish both the
different radiation types and energies by using a simple energy threshold discrimination
method. The SiC devices demonstrated the best neutron energy discrimination ratio
(Emax[n=5MeV] / Emax[n=1MeV] ~5), whereas a superior neutron/photon cross
sensitivity ratio was observed in the D-PC detector (Emax[AmBe] / Emax[Co-60] ~16).
Further work also demonstrated that the cross sensitivity ratios can be improved
through use of a simple proton-recoil conversion layer.
Stability issues were also observed in the D-SC, D-PC and SiC-SI detectors while
under irradiation, that being a change of energy peak position and/or count rate with
time (often referred to as polarisation effect). This phenomenon within the detectors
was non-debilitating over the time period tested (>5h) and as such, stable operation
Furthermore, the D-SC, self-biased SiC-EP and a semi-insulating SiC detector were
shown to operate over the temperature range -60C to +100C.
Although the use of semi-insulating silicon carbide material for radiation detection purposes has been previously demonstrated, its use in practical applications has been inhibited by space charge stability issues caused by defect concentrations within the material, the so called polarisation effect, by which the count rate and resultant spectrum changes with irradiation time. This is a result of the charge carriers generated during irradiation filling deep level defects within the material, causing space charge buildup and de-activating that trap level until the trapped charge is re-emitted. Consequently, the time dependence of the polarisation effect has been determined by a combination of parameters that can be influenced during operation, namely the incident radiation intensity, ambient light, temperature and bias. The material properties have also been considered through the use of materials with different defect capture cross sections, concentrations and energy level. A thorough characterisation of the alpha irradiation induced polarisation phenomenon in semi-insulating silicon carbide has been conducted to demonstrate that stable operation detectors are in fact possible with this material. The effects were compared to single crystal diamond and polycrystalline diamond, which are known to exhibit similar polarisation issues. The polarisation rate as an effect of incident flux, bias and temperature was determined, with the depolarisation rate as a function of ambient light and bias also demonstrated. Consequently it has been shown that stable operation can be maintained for detectors made from semi-insulating SiC material of active thickness 350 ¼m at incident alpha radiation fluxes of ±400 V). Furthermore, polarisation can be suitably managed or reduced through the use of light illumination and elevated temperatures (373 K).
A digital timing method aiming to minimize the time walk caused by the depth-dependent pulse shape variations in CdTe detectors has been developed. Detector pulses are digitized at the preamplifier stage and a full digital process is carried out to deduce and correct the time walk according to the interaction depth. A time resolution of 6.52 ns FWHM at an energy threshold of 150 keV with a CdTe detector (10×10×1 mm3) is achieved, which is close to the intrinsic resolution of the detector. The method improves the time resolution with no loss of detection efficiency and it is easy to implement. It is confirmed that the slow mobility and the short lifetime of the holes are major obstacles for further improvement in the timing performance of the CdTe detectors. The method is applicable to any semiconductor detector.
Cadmium zinc telluride (CdZnTe) is a leading sensor material for spectroscopic X/g-ray
imaging in the fields of homeland security, medical imaging, industrial analysis and
astrophysics. The metal-semiconductor interface formed during contact deposition is of
fundamental importance to the spectroscopic performance of the detector and is primarily
determined by the deposition method. A multi-technique analysis of the metalsemiconductor
interface formed by sputter and electroless deposition of gold onto (111)
aligned CdZnTe is presented. Focused ion beam (FIB) cross section imaging, X-ray
photoelectron spectroscopy (XPS) depth profiling and current-voltage (IV) analysis have
been applied to determine the structural, chemical and electronic properties of the gold
contacts. In a novel approach, principal component analysis has been employed on the XPS
depth profiles to extract detailed chemical state information from different depths within
the profile. It was found that electroless deposition forms a complicated, graded interface
comprised of tellurium oxide, gold/gold telluride particulates, and cadmium chloride. This
compared with a sharp transition from surface gold to bulk CdZnTe observed for the
interface formed by sputter deposition. The electronic (IV) response for the detector with
electroless deposited contacts was symmetric, but was asymmetric for the detector with
sputtered gold contacts. This is due to the electroless deposition degrading the difference
between the Cd- and Te-faces of the CdZnTe (111) crystal, whilst these differences are
maintained for the sputter deposited gold contacts. This work represents an important step
in the optimisation of the metal-semiconductor interface which currently is a limiting factor
in the development of high resolution CdZnTe detectors.
Recent improvements in the growth of wide-bandgap semiconductors, such as cadmium zinc telluride (CdZnTe or CZT), has enabled spectroscopic X/³-ray imaging detectors to be developed. These detectors have applications covering homeland security, industrial analysis, space science and medical imaging. At the Rutherford Appleton Laboratory (RAL) a promising range of spectroscopic, position sensitive, small-pixel Cd(Zn)Te detectors have been developed. The challenge now is to improve the quality of metal contacts on CdZnTe in order to meet the demanding energy and spatial resolution requirements of these applications. The choice of metal deposition method and fabrication process are of fundamental importance. Presented is a comparison of two CdZnTe detectors with contacts formed by sputter and electroless deposition. The detectors were fabricated with a 74 × 74 array of 200 ¼m pixels on a 250 ¼m pitch and bump-bonded to the HEXITEC ASIC. The X/³-ray emissions from an 241Am source were measured to form energy spectra for comparison. It was found that the detector with contacts formed by electroless deposition produced the best uniformity and energy resolution; the best pixel produced a FWHM of 560 eV at 59.54 keV and 50% of pixels produced a FWHM better than 1.7 keV . This compared with a FWHM of 1.5 keV for the best pixel and 50% of pixels better than 4.4 keV for the detector with sputtered contacts.
Spectroscopic X-ray imaging is an emerging technology with applications in the fields of medical imaging, security, science and industrial analysis. The wide bandgap semiconductor cadmium zinc telluride (CdZnTe) is the leading sensor material for this technology. Refinements in the growth process have delivered consistent improvements in both yield and quality of single crystal CdZnTe. The fabrication of metal contacts required for electronic readout is now considered to be the limiting factor for small pixel CdZnTe detector performance. This includes preparation of the CdZnTe surface, deposition of the metal contacts and pixellation. The current work is concerned with understanding and improving the detector fabrication process. A range of complementary characterisation techniques have been used to analyse the metal-semiconductor interface formed by electroless and sputter deposition of gold contacts onto CdZnTe. The characterisation included focused ion beam (FIB) cross section imaging, chemical analysis with X-ray photoelectron spectroscopy (XPS) and electronic analysis with current-voltage (IV) measurements. The electroless deposition was found to produce a complicated interface consisting of a surface gold layer on top of a mixed interface of gold, tellurium oxide and cadmium chloride. The effective barrier height of this contact was measured to be 0.78 ± 0.04 eV under positive bias and 0.83 ± 0.02 eV under negative bias. The interface of sputter deposited gold contacts was simple in comparison, with a sharp interface between the gold and CdZnTe and a barrier height of 0.64 ± 0.02 eV under positive bias and 0.78 ± 0.02 eV under negative bias. An optimised detector fabrication process has been developed. This process involves forming gold contacts on mechanically polished-only CdZnTe by electroless deposition. Pixellation is achieved with a positive photoresist prior to gold deposition. A small pixel (250 ¼m pitch) CdZnTe detector fabricated in this manner and bonded to the HEXITEC ASIC has produced a single pixel FWHM energy resolution at 59.54 keV of 560 eV, with a modal FWHM resolution of 1.5 keV across the full 74 × 74 pixel array.
An important factor for the high performance of light-harvesting devices is the presence of surface trappings. Therefore, understanding and controlling the carrier recombination of the organic?inorganic hybrid perovskite surface is critical for the device design and optimization. Here, we report the use of aluminum zinc oxide (AZO) as the anode to construct a p?n junction structure MAPbBr3 nuclear radiation detector. The AZO/MAPbBr3/Au detector can tolerate an electrical field of 500 V·cm?1 and exhibit a very low leakage current of 3 contact was reduced from 2.17 × 1010 to 8.7 × 108 cm?2 by annealing at 100 °C under an Ar atmosphere. Consequently, a photocurrent to dark current ratio of 190 was realized when exposed to a green light-emitting diode with a wavelength of 520 nm (air?1 cm?2 was achieved under 80 kVp X-ray at an electric field of 50 V·cm?1. These results demonstrate the use of surface engineering to further optimize the performance of MAPbBr3 detectors, which have many potential applications in medical and security detection with low radiation dose brought to the human body.
We report on the pulse shape discrimination (PSD) performance of plastic scintillators manufactured by Eljen Corporation and Amcrys. In this study we investigate the fast neutron and gamma performance of the plastic scintillators when coupled to the SensL J-series silicon photomultiplier (SiPM) and read out with fast waveform digitisers with an ADC resolution of 14-bits and a sample rate of 500 MS/s. The investigation observes a significant PSD performance increase for the SensL J-series SiPM in comparison to the previous C-series, and also for the latest variants of plastic scintillator from both suppliers.
Analysis was performed using a Synchronous Charge Integration Pulse Shape Discrimination (PSD) algorithm which was applied to data acquired from a mixed fast neutron/gamma radiation field from an AmBe neutron source. The collected pulses were processed offline with the energy and PSD parameters calculated. The quality of the PSD performance was characterised by a common figure of merit (FoM). The best n- separation was found by the newer Eljen EJ-276 scintillator with a FoM value of 3.03 ± 0.03 at an energy of 1.5 MeV gamma equivalent. The Amcrys UPS-113NG material achieved a FoM value of 2.60 ± 0.04.
The use of EJ-299 for security applications, with a focus on active interrogation environments,
has been investigated; in this application a plastic scintillator capable of n/gamma
discrimination is extremely attractive. Development of a system incorporating EJ-299
for this application requires consideration of the effect of a high flux, dynamic, mixed
neutron/gamma field on performance. Using EJ-299 plastic scintillator, the effects of
geometry on the observed quality of pulse shape discrimination (PSD) is demonstrated,
through the use of a digital data acquisition system and a digital version of the charge
integration PSD algorithm. Figure of merit data (FOM) shows that as the geometry
moves away from a cube like structure towards flat panel shapes, PSD deteriorates. The
effect of the incident flux on the observed quality of PSD for EJ-299 has been investigated
using an X-Ray generator. Separate neutron and gamma energy calibrations for
an EJ-299 detector have been obtained through the use of well defined end point energy
neutrons and sealed gamma sources. Throughout the thesis, discussion is had on how
to best optimize a digital data acquisition system (DAQ) for PSD.
The pulse pile-up effect can significantly degrade the spectroscopic performance of scintillation radiation detectors at high counting rates. This paper reports on a digital pulse processing method for shortening the duration of scintillation pulses, thereby alleviating the pulse pile-up effect. The method operates based on replacing the decay-time constant of the scintillation pulses with a shorter decay-time constant. The details of the digital algorithm are presented and the performance of the method at a high counting rate of 795 kHz is experimentally examined with a NaI(Tl) detector. The effects of the pulse shortening on the spectroscopic performance of the system are also discussed.
In this work we investigate the potential use as a thermal neutron detector of cerium-doped gadolinium aluminium gallium garnet (GAGG:Ce) coupled to a silicon photomultiplier (SiPM). The response to thermal neutrons has been measured, with two strong low energy neutron-indicative peaks clearly identifiable below 100 keV and additional ³ peaks at higher energies. The neutron-related peaks are produced by a combination of contributions from excited states of the two isotopes 156Gd and 158Gd which can be clearly resolved in our GAGG scintillation detector. In particular, two peaks due to neutron-induced ³-ray emission are observed at approximately 82 keV and 260 keV, with best achieved energy resolutions of 24.1 ± 0.2% and 22.7 ± 0.7% respectively. Three different scintillator volumes (0.1 cm3, 0.4 cm3, and 1 cm3) were investigated and the respective results for each configuration will be presented.
Our findings show that a GAGG-SiPM based detector can be used as a compact, efficient thermal neutron detector in a low ³-ray contamination environment.
We investigate the performance of Fourier-based neutron/gamma Pulse Shape Discrimination (PSD) algorithms applied to plastic scintillators that are coupled to silicon photomultipliers (SiPM). The detector acquired data from a mixed fast neutron and gamma field which was emitted from an AmBe source. Pulses produced from the detector were fully digitised for off-line analysis with the algorithms. We describe the performance of two Fourier-based PSD algorithms, Fourier Gradient Analysis (FGA) and Fourier Area Analysis (FAA), and compare their performance to the Charge Comparison Method (CCM). To compare the algorithms? PSD performance the figure of merit (FoM) was calculated at various energies for each of the algorithms. The CCM analysed the pulses in the time domain whereas the other two algorithms processed the pulses within the frequency domain. Moreover, the detector was tested with different acquisition record lengths, in order to determine any impact on algorithm performance. It was determined that the FAA algorithm provided the best overall performance achieving a FoM of 1.57(1) at 1 MeVee with a 1.6 µs record length. Furthermore, the detector was tested using different load resistors which allowed the decay time of the pulses to be optimised. The influence of SiPM pulse decay time on the performance of the PSD algorithms is also presented.
In response to the Fukushima Daiichi Nuclear Power Plant accident, there has occurred the
unabated growth in the number of airborne platforms developed to perform radiation mapping?each
utilising various designs of a low-altitude uncrewed aerial vehicle. Alongside the associated
advancements in the airborne system transporting the radiation detection payload, from the
earliest radiological analyses performed using gas-filled Geiger-Muller tube detectors, modern
radiation detection and mapping platforms are now based near-exclusively on solid-state scintillator
detectors. With numerous varieties of such light-emitting crystalline materials now in existence,
this combined desk and computational modelling study sought to evaluate the best-available
detector material compatible with the requirements for low-altitude autonomous radiation detection,
localisation and subsequent high spatial-resolution mapping of both naturally occurring and
anthropogenically-derived radionuclides. The ideal geometry of such detector materials is also
evaluated. While NaI and CsI (both elementally doped) are (and will likely remain) the mainstays
of radiation detection, LaBr3 scintillation detectors were determined to possess not only a greater
sensitivity to incident gamma-ray radiation, but also a far superior spectral (energy) resolution over
existing and other potentially deployable detector materials. Combined with their current competitive
cost, an array of three such composition cylindrical detectors were determined to provide the best
means of detecting and discriminating the various incident gamma-rays.
Zhao Dou, Xu Meng, Xiao Bao, Zhang Binbin, Yan Lei, Zeng Guoqiang, Dubois Alain, Sellin Paul, Jie Wanqi, Xu Yadong (2020) Purely organic 4HCB single crystals exhibiting high hole mobility for direct detection of ultralow-dose X-radiation,Journal of Materials Chemistry A 8 (10) pp. 5217-5226
Royal Society of Chemistry
Precise detection of low-dose X-radiation using purely organic direct detectors is vital for tissue-equivalent dosimeters and safety control in medical radiation treatment, but it still remains a challenge. Here, we report a promising organic radiation detector based on 4-hydroxycyanobenzene (4HCB, C7H5NO) single crystals. Plate-like 4HCB single crystals up to 18 × 15 × 1.2 mm3 in size are obtained by an optimized solvent evaporation method, thanks to the clarification of the two-dimensional nucleation growth mechanism. After post surface treatment, the leakage current of the 4HCB detector is no larger than 0.1 pA under an electric field of 600 V cm?1. The fabricated detectors show a capability of detecting 241Am 5.49 MeV ± particles with a well resolved full energy peak. The calculated hole mobility (¼h) and hole mobility lifetime product (¼Ä)h are 3.40 cm2 V?1 s?1 and 8.50 × 10?5 cm2 V?1, respectively. Simultaneously, under a 50 kVp X-ray beam, a detection limit as low as 0.29 ¼Gyair s?1 with a high sensitivity of 10 ¼C Gyair?1 cm?2 is achieved in the bias range of 40?100 V, contributing to a superior X-ray imaging capability with a spatial resolution of 0.9 lp mm?1 at a low-dose rate (below 150 ¼Gyair s?1) of exposure.
Posar Jessie A., Davis Jeremy, Brace Owen, Sellin Paul, Griffith Matthew J., Dhez Olivier, Wilkinson Dean, Lerch Michael L.F, Rosenfield Anatoly, Petasecca Marco (2020) Characterization of a plastic dosimeter based on organic semiconductorphotodiodes and scintillator,Physics & Imaging in Radiation Oncology 14 pp. 48-52
Background and purpose:
Measurement of dose delivery is essential to guarantee the safety of patients under-going medical radiation imaging or treatment procedures. This study aimed to evaluate the ability of organic semi conductors, coupled with a plastic scintillator, to measure photon dose in clinically relevant conditions, and establish its radiation hardness. Thereby, proving organic devices are capable of being a water-equivalent, mechanically flexible, real-time dosimeter.
Materials and methods:
The shelf-life of an organic photodiode was analyzed to 40 kGy by comparison of the charge-collection-efficiency of a 520 nm light emitting diode. A non-irradiated and pre-irradiated photodiode was coupled to a plastic scintillator and their response to 6 MV photons was investigated. The dose linearity,dose-per-pulse dependence and energy dependence was characterized. Finally, the percentage depth dose (PDD)between 0.5 and 20 cm was compared with ionization chamber measurements.Results:Sensitivity to 6 MV photons was (190 ± 0.28) pC/cGy and (170 ± 0.11) pC/cGy for the non-irra-diated and pre-irradiated photodiode biased at ?2 V. The response was independent of the dose-per-pulsebetween 0.031 and 0.34 mGy/pulse. An energy dependence was found for low keV energies, explained by theenergy dependence of the scintillator which plateaued between 70 keV and 1.2 MeV. The PDD was within ± 3%of the ionization chamber.
Coupling an organic photodiode with a plastic scintillator provided reliable measurement of a rangeof photon energies. Dose-per-pulse and energy independence advocate their use as a dosimeter, specifically image-guided treatment without beam-quality correction factors. Degradation effects of organic semi conducting materials deteriorate sensor response but can be stabilized.
Plastic scintillators are used in scenarios where gamma-ray identification is necessary and can be scaled to large sizes for use in applications such as particle physics and nuclear security. In particular, modern plastic materials with the ability to detect neutrons via Pulse Shape Discrimination (PSD) are providing exciting new avenues of research for the field. The pulse shapes for these materials have characteristic decay time constants based on the radiation interaction causing scintillation emission. The materials exhibit this capability with volumes of a few cubic centimetres, but when scaled to larger volumes, the PSD performance diminishes. By identifying the cause of this deterioration, methods can be determined and implemented to increase PSD performance.
Through the course of the work reported on, methods for increasing the performance are identified. In one instance, the detector configuration should be chosen based upon the application. The accompanying PSD algorithm should be selected based on the configuration and application environment to achieve maximum performance. When designing the detector configuration, simulations should be used as a tool to help maximise performance. The simulations presented in this thesis have identified that pulse shapes change based on many aspects of the scintillation system. By modelling the light transport, it has been found that the emission direction of scintillation light alters the pulse shape decay times. The light arrives in different distributions based on the directionality. Moreover, these distributions change based on reflector type, the percentage reflectivity and location of the scintillation emission. PSD relies on differences in the decay time constants of pulse shapes. These factors outlined lead to additional time constants being convolved with the pulse shape. This creates variation in the PSD parameter calculated in the algorithms. This variation increases with the scintillator volume and is the cause of reduced performance with large-sized plastic scintillators.
Numerous techniques and equipment have been developed to provide a capability for the detection of special nuclear materials (SNM), but due to the necessary
security measures surrounding these materials alternate, or proxy, neutron sources are
often utilised in their stead. In this paper we report the neutron and gamma pulse
shape discrimination (PSD) response of plastic scintillator to mixed neutron/gamma
beams produced from two radionuclide neutron sources, and also from an SNM source
of weapons-grade plutonium. We discuss the suitability of using radionuclide sources,
with appropriate shielding configurations as proxy sources for SNM.
A 3ý n-discrimination level has been achieved for an SNM source at a low-level
energy threshold of ý220 keVee when a shielding conýguration of 5 cm of lead was
implemented. Varying amounts of lead and HDPE shielding were also investigated with the 3ý limit being reached by ý240 keVee. This work shows that an AmBe neutron source serves as an appropriate SNM proxy achieving a comparable value for ýgure of merit above ý1 MeVee. For energies below
1 MeVee down to ý100 keVee a closer approximation of the expected FoM for SNM can be attained when using 252Cf as a proxy source or by utilising an \enhanced" AmBe
source with the addition of a further low energy ray source.
We report on the retrofitting of a standard DP2 environmental radiation monitor replacing the photomultiplier tube with a silicon photomultiplier (SiPM). The use of a SiPM has several advantages for a hand-held radiation monitor, including convenient low voltage operation and physical robustness. The SiPM is used to replace the existing photomultiplier tube, and we report the detection efficiency and alpha/beta discrimination performance of the modified probe compared to an unmodified version.