Taggart MP (2016) Development of radiodetection systems towards miniaturised quality control of PET and SPECT radiopharmaceuticals, Lab On a Chip: microfluidic and nanotechnologies for chemistry, biology, and bioengineering Royal Society of Chemistry
The ability to detect radiation in microfluidic devices is important for the on-chip analysis of radiopharmaceuticals,
but previously reported systems have largely suffered from various limitations including
cost, complexity of fabrication, and insufficient sensitivity and/or speed. Here, we present the use of
sensitive, low cost, small-sized, commercially available silicon photomultipliers (SiPMs) for the detection
of radioactivity inside microfluidic channels fabricated from a range of conventional microfluidic chip
substrates. We demonstrate the effects of chip material and thickness on the detection of the positronemitting
isotope, [18F]fluoride, and find that, while the SiPMs are light sensors, they are able to detect
radiation even through opaque chip materials via direct positron and gamma (³) ray interaction. Finally,
we employed the SiPM platform for analysis of the PET (positron emission tomography) radiotracers
2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) and [68Ga]gallium-citrate, and highlight the ability to detect
the ³ ray emitting SPECT (single photon emission computed tomography) radiotracer, [99mTc]
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.
As a result of their thermoluminescent response, low cost commercial glass beads have been demonstrated to offer potential use as radiation dosimeters, providing capability in sensing different types of ionising radiation. With a linear response over a large range of dose and spatial resolution that allows measurements down to the order of 1 mm, their performance renders them of interest in situations in which sensitivity, dynamic range, and fine spatial resolution are called for. In the present work, the suitability of glass beads for characterisation of an AmericiumBeryllium (241AmBe) neutron source has been assessed. Direct comparison has been made using conventional 3He and boron tri-fluoride neutron detectors as well as Monte Carlo simulation. Good agreement is obtained between the glass beads and gas detectors in terms of general reduction of count rate with distance. Furthermore, the glass beads demonstrate exceptional spatial resolution, leading to the observation of fine detail in the plot of dose versus distance from source. Fine resolution peaks arising in the measured plots, also present in simulations, are interesting features which based on our best knowledge have previously not been reported. The features are reproduced in both experiment and simulation but we do not have a firm reason for their origin. Of greater clarity is that the glass beads have considerable potential for use in high spatial resolution neutron field characterisation, subject to the availability of a suitable automated TLD reader.
It is widely known that SiPM photodetectors have a strong temperature dependence. TrueInvivo is currently developing an automated TLD reader with the intention of replacing the PMT with a SiPM, taking advantage of the low power consumption, small form-factor, and low cost the SiPM has to offer. Here we discuss our initial investigations into the suitability of this switch in applied technology, present spectroscopic response as a function of SiPM temperature, and the effectiveness of some options to mitigate this concern. It was found that while the SiPM is indeed affected by variations in temperature a recovery of 50-60% in gain and resolution could be achieved with a rudimentary cooling system.
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.
Taggart M.P., Akers C., Laird A.M., Hager U., Ruiz C., Hutcheon D.A., Bentley M.A., Brown J.R., Buchmann L., Chen A.A., Chen J., Chipps K.A., Choplin A., D'Auria J.M., Davids B., Davis C., Diget C.Aa., Erikson L., Fallis J., Fox S.P., Frischknecht U., Fulton B.R., Galinski N., Greife U., Hirschi R., Howell D., Martin L., Mountford D., Murphy A.St.J., Ottewell D., Pignatari M., Reeve S., Ruprecht G., Sjue S., Veloce L., Williams M. (2019) A direct measurement of the ¹wO(±,³)²¹Ne reaction in inverse kinematics and its impact on heavy element production,Physics Letters B 798 134894 pp. 1-6
During the slow neutron capture process in massive stars, reactions on light elements can both produce and absorb neutrons thereby influencing the final heavy element abundances. At low metallicities, the high neutron capture rate of 16O can inhibit s-process nucleosynthesis unless the neutrons are recycled via the ¹wO(±,n)²pNe reaction. The efficiency of this neutron recycling is determined by competition between the ¹wO(±,n)²pNe and ¹wO(±,³)²¹Ne reactions. While some experimental data are available on the former reaction, no data exist for the radiative capture channel at the relevant astrophysical energies.
The ¹wO(±,n)²pNe reaction has been studied directly using the DRAGON recoil separator at the TRIUMF Laboratory. The reaction cross section has been determined at energies between 0.6 and 1.6 MeV , reaching into the Gamow window for core helium burning for the first time. Resonance strengths for resonances at 0.63, 0.721, 0.81 and 1.122 MeV have been extracted. The experimentally based reaction rate calculated represents a lower limit, but suggests that significant s-process nucleosynthesis occurs in low metallicity massive stars.
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.
The response of LaBr3(Ce) and LaCl3(Ce) scintillators to fast neutrons is investigated.
Neutron-induced charged-particle reactions are observed in both materials when exposed to the fast neutrons produced by an AmBe source, with pulse-shape discrimination used to separate channels. LaBr3(Ce) is found to have the best separation between reaction channels, while LaCl3(Ce)
has a significantly higher efficiency.
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.