A fast-timing experiment was performed at the Argonne National Laboratory in December 2015 and January 2016, measuring decay radiation of fission products from a 252Cf fission source. Details of the set-up, integration with Digital Gammasphere, and the data acquisition system are presented. The timing performance of the set-up, capable of measuring lifetimes from the nanosecond region down to tens of picoseconds, is discussed. First preliminary results from the fast-timing analysis of the fission fragment data are presented
Paul N, Corsi A, Obertelli A, Doornenbal P, Authelet G, Baba H, Bally B, Bender M, Calvet D, Chateau F, Chen S, Delaroche J, Delbart A, Gheller J, Giganon A, Gillibert A, Girod M, Heenen P, Lapoux V, Libert J, Motobayashi T, Niikura M, Otsuka T, Rodr1guez T, Rousse J, Sakurai H, Santamaria C, Shimizu N, Steppenbeck D, Taniuchi R, Togashi T, Tsunoda Y, Uesaka T, Ando T, Arici T, Blazhev A, Browne F, Bruce A, Carroll R, Chung L, Cortes M, Dewald M, Ding B, Flavigny F, Franchoo S, Gorska M, Gottardo A, Jungclaus A, Lee J, Lettmann M, Linh B, Liu J, Liu Z, Lizarazo C, Momiyama S, Moschner K, Nagamine S, Nakatsuka N, Nita C, Nobs C, Olivier L, Patel Z, Podolyak Z, Rudigier M, Saito T, Shand CM, Soderstrom P, Stefan I, Orlandi R, Vaquero V, Werner V, Wimmer K, Xu Z (2017) Are there signatures of harmonic oscillator shells far from stability? - First spectroscopy of 110Zr, Physical Review Letters 118 (3) 032501
American Physical Society
The first measurement of the low-lying states of the neutron-rich
was performed via in-beam
-ray spectroscopy after one proton removal on hydrogen at
excitation energies were found at 185(11) keV in
, and 235(7) keV in
, while the
) ratios are 3.1(2), close to the rigid rotor value, and 2.7(1), respectively. These results are compared to modern energy density functional based configuration mixing models using Gogny and Skyrme effective interactions. We conclude that first levels of
exhibit a rotational behavior, in agreement with previous observations of lighter zirconium isotopes as well as with the most advanced Monte Carlo shell model predictions. The data, therefore, do not support a harmonic oscillator shell stabilization scenario at
. The present data also invalidate predictions for a tetrahedral ground state symmetry in
Lettmann M, Werner V, Pietralla N, Doornenbal P, Obertelli A, Rodríguez T, Sieja K, Authelet G, Baba H, Calvet D, Château F, Chen S, Corsi A, Delbart A, Gheller J, Giganon A, Gillibert A, Lapoux V, Motobayashi T, Niikura M, Paul N, Roussé J, Sakurai H, Santamaria C, Steppenbeck D, Taniuchi R, Uesaka T, Ando T, Arici T, Blazhev A, Browne F, Bruce A, Caroll R, Chung L, Cortés M, Dewald M, Ding B, Flavigny F, Franchoo S, Górska M, Gottardo A, Jungclaus A, Lee J, Linh B, Liu J, Liu Z, Lizarazo C, Momiyama S, Moschner K, Nagamine S, Nakatsuka N, Nita C, Nobs C, Olivier L, Patel Z, Podolyak Z, Rudigier M, Saito T, Shand C, Söderström P, Stefan I, Vaquero V, Wimmer K, Xu Z (2017) Triaxiality of neutron-rich 84;86;88Ge from low-energy nuclear spectra, Physical Review C 96 (1) 011301(R)
American Physical Society
-ray transitions between low-spin states of the neutron-rich 84;86;88Ge were measured by means
-ray spectroscopy at 270 MeV/u. Excited 6+
1 , 4+
1;2 and 2+
1;2 states of 84;86Ge and 4+
1;2 states of 88Ge were observed. Furthermore a candidate for a 3+
1 state of 86Ge was identified.
This state plays a key role in the discussion of ground-state triaxiality of 86Ge, along with other
features of its low-energy level scheme. A new region of triaxially deformed nuclei is proposed in
the Ge isotopic chain.
Daniel T, Kisyov S, Regan PH, Marginean N, Podolyak Z, Marginean R, Nomura K, Rudigier M, Mihai R, Werner V, Carroll R, Gurgi LA, Oprea A, Berry TA, Serban A, Nita C, Sotty C, Suvaila R, Turturica A, Costache C, Stan L, Olacel A, Boromiza M, Toma S (2017) ³ -ray spectroscopy of low-lying excited states and shape competition in Os 194, Physical Review C 95 (2) 024328
American Physical Society
The properties of excited states in the neutron-rich nucleus 194Os have been investigated using the 192Os(18O,16O)194Os reaction with an 80 MeV beam provided by the IFIN-HH Laboratory, Bucharest. Discrete ³ -ray decays from excited states have been measured using the hybrid HPGe-LaBr3(Ce) array RoSPHERE. The current work identifies a number of previously unreported low-lying nonyrast states in 194Os as well as the first measurement of the half-life of the yrast 2+ state of 302(50) ps. This is equivalent to a B(E2 : 2+ 0+) = 45(16) W.u. and intrinsic quadrupole deformation of ²eff = 0.14(1). The experimental results are compared with Hartree-Fock-Bogoliubov?interacting-boson-model calculations and are consistent with a reduction in a quadrupole collectivity in Os isotopes with increasing neutron number.
Chen S, Doornenbal P, Obertelli A, Rodr1guez T, Authelet G, Baba H, Calvet D, Chateau F, Corsi A, Delbart A, Gheller J, Giganon A, Gillibert A, Lapoux V, Motobayashi T, Niikura M, Paul N, Rousse J, Sakurai H, Santamaria C, Steppenbeck D, Taniuchi R, Uesaka T, Ando T, Arici T, Blazhev A, Browne F, Bruce A, Caroll R, Chung L, Cortes M, Dewald M, Ding B, Flavigny F, Franchoo S, Gorska M, Gottardo A, Jungclaus A, Lee J, Lettmann M, Linh B, Liu J, Liu Z, Lizarazo C, Momiyama S, Moschner K, Nagamine S, Nakatsuka N, Nita C, Nobs C, Olivier L, Orlandi R, Patel Z, Podolyak Z, Rudigier M, Saito T, Shand CM, Soderstrom P, Stefan I, Vaquero V, Werner V, Wimmer K, Xu Z (2017) First Indication for Shape Transitions in Neutron-rich Selenium Isotopes, Physical Review C: Nuclear Physics
American Physical Society
Neutron-rich 88,90,92,94Se isotopes were studied via in-beam ³-ray spectroscopy after production from nucleon removal at intermediate energies at the Radioactive Isotope Beam Factory. ³-³ coincidence analysis allowed to establish level schemes for the first time in these nuclei, including the 2+ 1 0 + gs, 4+ 1 2 + 1 transitions and their energy ratio R4/2. Low-lying 2+ 2 levels and their branching to the 2+ 1 and 0+ gs states were observed. The experimental results are in good agreement with self-consistent beyond-mean-field calculations based on the Gogny D1S interaction, suggesting ground state shape transition from oblate to prolate then back to oblate between N = 52 ? 60 and indicating shape coexistence.
Shand C, Podolyak Z, Górska M, Doornenbal P, Obertelli A, Nowacki F, Otsuka T, Sieja K, Tostevin J, Tsunoda Y, Authelet G, Baba H, Calvet D, Château A, Chen S, Corsi A, Delbart A, Gheller J, Giganon A, Gillibert A, Isobe T, Lapoux V, Matsushita M, Momiyama S, Motobayashi T, Niikura M, Otsu H, Paul N, Péron C, Peyaud A, Pollacco E, Roussé J, Sakurai H, Santamaria C, Sasano M, Shiga Y, Steppenbeck D, Takeuchi S, Taniuchi R, Uesaka T, Wang H, Yoneda K, Ando T, Arici T, Blazhev A, Browne F, Bruce A, Carroll R, Chung L, Cortés M, Dewald M, Ding B, Dombrádi Z, Flavigny F, Franchoo S, Giacoppo F, Gottardo A, HadyDska-Kl?k K, Jungclaus A, Korkulu Z, Koyama S, Kubota Y, Lee J, Lettmann M, Linh B, Liu J, Liu Z, Lizarazo C, Louchart C, Lozeva R, Matsui K, Miyazaki T, Moschner K, Nagamine M, Nakatsuka N, Nishimura S, Nita C, Nobs C, Olivier L, Ota S, Orlandi R, Patel Z, Regan P, Rudigier M, ^ahin E, Saito T, Söderström P, Stefan I, Sumikama T, Suzuki D, Vajta Z, Vaquero V, Werner V, Wimmer K, Wu J, Xu Z (2017) Shell evolution beyond Z = 28 and N = 50: Spectroscopy of 81,82,83,84 Zn, Physics Letters B 773 pp. 492-497
We report on the measurement of new low-lying states in the neutron-rich 81,82,83,84Zn nuclei via in-beam ³ -ray spectroscopy. These include the View the MathML source41+21+ transition in 82Zn, the View the MathML source21+0g.s.+ and View the MathML source41+21+ transitions in 84Zn, and low-lying states in 81,83Zn were observed for the first time. The reduced View the MathML sourceE(21+) energies and increased View the MathML sourceE(41+)/E(2+1) ratios at N=52N=52, 54 compared to those in 80Zn attest that the magicity is confined to the neutron number N=50N=50 only. The deduced level schemes are compared to three state-of-the-art shell model calculations and a good agreement is observed with all three calculations. The newly observed 2+2+ and 4+4+ levels in 84Zn suggest the onset of deformation towards heavier Zn isotopes, which has been incorporated by taking into account the upper sdg orbitals in the Ni78-II and the PFSDG-U models.
Jentschel M, Blanc A, de France G, Köster U, Leoni S, Mutti P, Simpson G, Soldner T, Ur C, Urban W, Ahmed S, Astier A, Augey L, Back T, Ba'czyk P, Bajoga A, Balabanski D, Belgya T, Benzoni G, Bernards C, Biswas D, Bocchi G, Bottoni S, Britton R, Bruyneel B, Burnett J, Cakirli R, Carroll R, Catford W, Cederwall B, Celikovic I, Cieplicka-OryDczak N, Clement E, Cooper N, Crespi F, Csatlos M, Curien D, CzerwiDski M, Danu L, Davies A, Didierjean F, Drouet F, Duchêne G, Ducoin C, Eberhardt K, Erturk S, Fraile L, Gottardo A, Grente L, Grocutt L, Guerrero C, Guinet D, Hartig A, Henrich C, Ignatov A, Ilieva S, Ivanova D, John B, John R, Jolie J, Kisyov S, Krticka M, Konstantinopoulos T, Korgul A, Krasznahorkay A, Kröll T, Kurpeta J, Kuti I, Lalkovski S, Larijani C, Leguillon R, Lica R, Litaize O, Lozeva R, Magron C, Mancuso C, Martinez E, Massarczyk R, Mazzocchi C, Melon B, Mengoni D, Michelagnoli C, Million B, Mokry C, Mukhopadhyay S, Mulholland K, Nannini A, Napoli D, Olaizola B, Orlandi R, Patel Z, Paziy V, Petrache C, Pfeiffer M, Pietralla N, Podolyak Z, Ramdhane M, Redon N, Regan P, Regis J, Regnier D, Oliver R, Rudigier M, Runke J, Rza'ca-Urban T, Saed-Samii N, Salsac M, Scheck M, Schwengner R, Sengele L, Singh P, Smith J, Stezowski O, Szpak B, Thomas T, Thürauf M, Timar J, Tom A, Tomandl I, Tornyi T, Townsley C, Tuerler A, Valenta S, Vancraeyenest A, Vandone V, Vanhoy J, Vedia V, Warr N, Werner V, Wilmsen D, Wilson E, Zerrouki T, Zielinska M (2017) EXILL?a high-efficiency, high-resolution setup for ³-spectroscopy at an intense cold neutron beam facility, Journal of Instrumentation 12 (11) pp. P11003-P11003
In the EXILL campaign a highly efficient array of high purity germanium (HPGe) detectors was operated at the cold neutron beam facility PF1B of the Institut Laue-Langevin (ILL) to carry out nuclear structure studies, via measurements of ³-rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent flux of about 108 n s?1cm?2 at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM Clover detectors, four to six anti-Compton shielded large coaxial GASP detectors and two standard Clover detectors. For a part of the campaign the array was combined with 16 LaBr3:(Ce) detectors from the FATIMA collaboration. The detectors were arranged in an array of rhombicuboctahedron geometry, providing the possibility to carry out very precise angular correlation and directional-polarization correlation measurements. The triggerless acquisition system allowed a signal collection rate of up to 6 × 105 Hz. The data allowed to set multi-fold coincidences to obtain decay schemes and in combination with the FATIMA array of LaBr3:(Ce) detectors to analyze half-lives of excited levels in the pico- to microsecond range. Precise energy and efficiency calibrations of EXILL were performed using standard calibration sources of 133Ba, 60Co and 152Eu as well as data from the reactions 27Al(n,³)28Al and 35Cl(n,³)36Cl in the energy range from 30 keV up to 10 MeV.
Heine M., Courtin S., Fruet G., Jenkins D.G., Morris L., Montanari D., Rudigier M., Adsley P., Curien D., Della Negra S., Lesrel J., Beck C., Charles L., Dené P., Haas F., Hammache F., Heitz G., Krauth M., Meyer A., Podolyak Zs., Regan P.H., Richer M., de Séréville N., Stodel C. (2018) The STELLA apparatus for particle-Gamma coincidence fusion measurements with nanosecond timing, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 903 pp. 1-7
The STELLA (STELlar LAboratory) experimental station for the measurement of deep sub-barrier light heavy-ion fusion cross sections has been installed at the Andromède accelerator at the Institut de Physique Nucléaire, Orsay (France). The setup is designed for the direct experimental determination of heavy-ion fusion cross sections as low as tens of picobarn. The detection concept is based on the coincident measurement of emitted gamma rays with the UK FATIMA (FAst TIMing Array) and evaporated charged particles using a silicon detector array. Key developments relevant to reaching the extreme sub-barrier fusion region are a rotating target mechanism to sustain beam intensities above 10¼A, an ultra-high vacuum of 10?8 mbar to prevent carbon built-up and gamma charged-particle timing in the order of nanoseconds sufficient to separate proton and alpha particles.
Wiederhold J., Werner V., Kern R., Pietralla N., Bucurescu D., Carroll R., Cooper N, Daniel T., Filipescu D., Florea N., Gerst R-B., Ghita D., Gurgi Laila, Jolie J., Ilieva Ralitsa, Lica R., Marginean N., Marginean R., Mihai C., Mitu I. O., Naqvi F., Nita C., Rudigier Matthias, Stegemann S., Pascu S., Regan Patrick (2019) Evolution of E2 strength in the rare-earth isotopes Hf174,176,178,180, Physical Review C 99 (2)
Mean lifetimes of yrast states of the isotopes 174,176,178,180Hf have been measured using fast- electronic scintillation timing. Excited states of 74,176,178Hf were populated via ² decay, while 180Hf was populated via Coulomb excitation. The lifetimes of the 2+
1 and 4+ 1 states of all isotopes and the lifetimes of the 6+ 1 states of 174,178Hf were measured, using the slope and the centroid shift methods. The mean lifetime, Ä (4+ 1 ) = 85(13) ps, of 178Hf has been determined for the first time. In addition, the mean lifetimes of the 2?
1 and the 3? 1 states of 176Hf have been determined. Systematic uncertainties on the evolution of data as a function of neutron number were reduced by using the same setup for all the isotopes of interest. The data are in agreement with other recent lifetime measurements where available and shows a shift of the maximum of collectivity for the Hf isotopic chain from neutron midshell at N = 104 to N = 100.
Paul N, Obertelli A, Bertulani C, Corsi A, Doornebal P, Rodriguez-Sanchez J. L., Authelet G, Baba H, Calvet D, Chateau F, Chen S, Delbart A, Gheller J. M, Giganon A, Gilibert A, Isobe T, Lapoux V, Matsushita M, Momiyama S, Motobayashi T, Niikura M, Otsu H, Peron C, Peyaud A, Pollaco E. C, Rousse J. Y, Sakurai H, Santamaria C, Sasano M, Shiga Y, Steppenbeck D, Takeuchi S, Taniuchi R, Uesaka T, Wang H, Yoneda K, Ando T, Arici T, Blazhev A, Browne F, Bruce A. M., Carroll Richard, Chung L. X., Cortes M. L, Dewald M, Ding B, Dombradi Zs, Flavigny F, Franchoo S, Giacoppo F, Gorska M, Gottardo A, Hadynska-Klek Katarzyna, Korkulu Z, Koyama S, Kubota Y, Jungclaus A, Lee J, Lettmann M, Linh B.D, Liu J, Liu Z, Lizarazo C, Louchart C, Lozeva R, Matsui K, Miyazaki T, Moschner K, Nagamine S, Nakatsuka N, Nita C, Nishimura S, Nobs C.R, Olivier L, Ota S, Patel Z, Podolyak Zsolt, Rudigier Matthias, Sahin E, Saito T. Y, Shand Callum, Soderstrom P. A, Stefan I. G., Sumikama T, Suzuki D, Orlandi R, Vaquero V, Vajta Zs, Werner V, Wimmer K, Wu J, Xu Z (2019) Prominence of Pairing in Inclusive (p,2p) and (p,pn) Cross Sections from
Neutron-Rich Nuclei, Physical Review Letters
American Physical Society
Fifty-five inclusive single nucleon removal cross sections from medium mass neutron-rich nuclei
impinging on a hydrogen target at ý 250 MeV/nucleon were measured at the RIKEN Radioactive Isotope Beam Factory. Systematically higher cross sections are found for proton removal from nuclei with an even number of protons compared to odd-proton number projectiles for a given neutron separation energy. Neutron removal cross sections display no even-odd splitting contrary to nuclear
cascade model predictions. Both effects are understood through simple considerations of neutron separation energies and bound state level densities originating in pairing correlations in the daughter nuclei. These conclusions are supported by comparison with semi-microscopic model predictions,highlighting the enhanced role of low-lying level densities in nucleon removal cross sections from loosely-bound nuclei.
evi? N., Lebois M., Wilson J.N., Thisse D., Qi L., Matea I., Ibrahim F., Verney D., Babo M., Delafosse C., Adsley F., Tocabens G., Gottardo A., Popovitch Y., Nemer J., Canavan R., Rudigier M., Belvedere K., Boso A., Regan P., Podolyak Zs., Shearman R., Bunce M., Inavov P., Oberstedt S., Lopez-Martens A., Hauschild K., Ljungvall J., Chakma R., Lozeva R., Söderström P.-A., Oberstedt A., Etasse D., Ralet D., Blazhev A., Gerst R.-B., Hafner G., Cieplicka-OryDczak N., Iskra L., Fornal B., Benzoni G., Leoni S., Bottoni S., Henrich C., Koseoglou P., Wiederhold J., Homm I., Surder C., Kroll T., Knezevic D., Dragic A., Cortes L., Warr N., Miernik K., Adamska E., Piersa M., Rezynkina K., Fraile L., Benito Garcia J., Sanchez V., Algora A., Davies P., Guadilla-Gomez V., Fallot M., Kurtukian-Nieto T., Schmitt C., Heine M., Reygadas Tello D., Yavachova M., Diakaki M., Zeiser F., Paulson W., Gestvang D. (2019) Spectroscopy of neutron induced reactions with the -ball spectrometer, Acta Physica Polonica B 50 (3) pp. 297-304
The -ball is a high-efficiency hybrid spectrometer which consists of
both germanium (Ge) detectors and associated anti-Compton BGO shields,
coupled to lanthanum bromide (LaBr3) detectors. The hybrid configuration
provides a combination of both excellent energy and timing resolutions.
The -ball geometry allows the coupling with the LICORNE directional
neutron source at the ALTO facility of the IPN, Orsay. This opens the
possibility to perform precise spectroscopy of neutron induced reactions
and was used for two experiments during the recent experimental campaign.
These two experiments are described here: 1. Spectroscopy of the
neutron-rich fission fragments produced in the 238U(n; f) and 232Th(n; f)
reactions; 2. Spectroscopy above the shape isomer in 238U. The 238U(n; f)
and 232Th(n; f) reactions produce hundreds of neutron-rich nuclei on which
gamma-ray spectroscopy can be performed. The main goal of the experiment
aiming to populate the shape isomer in 238U is the measurement of
the gamma-ray and fission decay branches as well as determination of level
scheme in the super-deformed minimum. The shape isomer is populated
by 238U(n; n') reaction, which gives a very advantageous population cross
section over other reactions. More detailed descriptions of these two -ball
experiments will be presented here.
Rudigier M., Canavan R.L., Regan P.H., Söderström P.-A., Lebois M., Wilson J.N., Jovancevic N., Bottoni S., Brunet M., Cieplicka-Orynczak N., Courtin S., Doherty D.T., Hadynska-Klek K., Heine M., Iskra W., Karayonchev V., Kennington A., Koseoglou P., Lotay G., Lorusso G., Nakhostin M., Nita C.R., S. Oberstedt S., Podolyak Zs., Qi L., Régis J.-M., Shearman R., Walker P.M., Witt W. (2019) Isomer spectroscopy and sub-nanosecond half-live determination in 178w using the NuBall array, Acta Physica Polonica B 50 (3) pp. 661-667
The reaction of a pulsed 18O beam on a 164Dy target was studied in
the first experiment with the NuBall array at the IPN Orsay, France. Excited
state half-lives were measured using the fast timing method with 20
LaBr3(Ce) detectors. The timing characteristics of the fully digital acquisition
system is briefly discussed. A value for the previously unknown
half-life of the first excited 4+ state in 178W is presented.
Gamba E. R., Bruce A. M., Lalkovski S., Rudigier M., Bottoni S., Carpenter M. P., Zhu S., Anderson J. T., Ayangeakaa A. D., Berry T. A., Burrows I., Gallardo M. Carmona, Carroll R. J., Copp P., Cullen D. M., Daniel T., Martínez G. Fernández, Greene J. P., Gurgi L. A., Hartley D. J., Ilieva R., Ilieva S., Kondev F. G., Kröll T., Lane G. J., Lauritsen T., Lazarus I., Lotay G., Nic? C. R., Podolyak Zs., Pucknell V., Reed M., Regan P. H., Rohrer J., Sethi J., Seweryniak D., Shand C. M., Simpson J., SmoleD M., Stefanova E. A., Vedia V., Yordanov O. (2019) Fast-timing measurements in the ground-state band of ¹¹tPd, Physical Review C 100 (4) 044309 pp. 044309-1
American Physical Society
Using a hybrid Gammasphere array coupled to 25 LaBr3(Ce) detectors, the lifetimes of the first three levels of the yrast band in ¹¹tPd populated via ²u²Cf decay, have been measured. The measured lifetimes are Ä+=103(10)ps, Ä+=22(13)ps, and Ä+d10ps for the 2z, 4z, and 6z levels, respectively. Palladium-114 was predicted to be the most deformed isotope of its isotopic chain, and spectroscopic studies have suggested it might also be a candidate nucleus for low-spin stable triaxiality. From the lifetimes measured in this work, reduced transition probabilities B(E2;JJ?2) are calculated and compared with interacting boson model, projected shell model, and collective model calculations from the literature. The experimental ratio RB(E)=B(E2;4z2z)/B(E2;2z0z)=0.80(42) is measured for the first time in ¹¹tPd and compared with the known values RB(E) in the palladium isotopic chain: the systematics suggest that, for N=68, a transition from ³-unstable to a more rigid ³-deformed nuclear shape occurs.
Rudigier M., Walker P. M., Canavan R.L., Podolyak Zs., Regan P. H., Söderström P.-A., Lebois M., Wilson J.N., Jovancevic N., Blazhev A., Benito J., Bottoni S., Brunet M., Cieplicka-Orynczak N., Courtin S., Doherty D. T., Fraile L.M., Hadynska-Klek K., Heine M., Iskra A.W., Jolie J., Karayonchev V., Kennington A. R., Koseoglou P., Lotay G., Lorusso G., Nakhostin M., Nita C.R., Oberstedt S., Qi L., Régis J.-M., Sánchez-Tembleque V., Shearman R., Witt W., Vedia V., Zell K.O. (2020) Multi-quasiparticle sub-nanosecond isomers in 178W, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 801 135140
We report on the first measurement of the half-lives of and four-quasiparticle states in the even-even nucleus 178W. The sub-nanosecond half-lives were measured by applying the centroid shift method to data taken with LaBr3(Ce) scintillator detectors of the NuBall array at the ALTO facility in Orsay, France. The half-lives of these states only became experimentally accessible by the combination of several experimental techniques - scintillator fast timing, isomer spectroscopy with a pulsed beam, and the event-by-event calorimetry information provided by the NuBall array. The measured half-lives are and for the and states, respectively. The decay transitions include weakly hindered E1 and E2 branches directly to the ground-state band, bypassing the two-quasiparticle states. This is the first such observation for an E1 transition. The interpretation of the small hindrance hinges on mixing between the ground-state band and the t-band.
Rudigier M., Podolyak Zs., Regan P.H., Bruce A.M., Lalkovski S., Canavan R.L., Gamba E.R., Roberts O., Burrows I., Cullen D.M., Fraile L.M., Gerhard L., Gerl J., Gorska M., Grant A., Jolie J., Karayonchev V., Kurz N., Korten W., Lazarus I.H., Nita C.R., Pucknell V.F.E., Régis J.-M., Schaffner H., Simpson J., Singh P., Townsley C.M., Smith J.F., Vesic J. (2020) FATIMA ? FAst TIMing Array for DESPEC at FAIR, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 969 163967
The components, working principle and characteristics of FATIMA (FAst TIMing Array), a fast-timing detector system for DESPEC at FAIR, are described. The core system includes 36 LaBr3(Ce) scintillator detectors, a mounting frame for the DESPEC station and a VME-based fast-timing data acquisition system. The current electronic timing circuit is based on V812 constant fraction discriminators and V1290 time-to-digital converters. Gamma-ray energies are measured using V1751 digitisers. Characteristics of the core FATIMA system including efficiency, energy, and coincidence resolving time, as well as limitations, are discussed on the basis of test measurements performed in the S4 cave at GSI, Germany. The coincidence ³-³ time resolution for the prompt 60Co cascade is determined to be ~320 ps full width at half maximum. The total full energy peak efficiency at 1 MeV for the 36 detector array in the DESPEC setup is 2.9%. The energy-dependent prompt response centroid curve with the current CFD/TDC combination is shown to be smooth; the centroid shift method can be applied for the measurement of half-lives below 200 ps. An overview of applications of the FATIMA detectors as an ancilliary system in combination with other detector arrays during recent years is given. Data on the operation of the detectors in the presence of magnetic fields are presented.