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Jan 29, 2022, 9:08:54 AM
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High-DR High-Resolution Gamma-Ray Spectroscopy with 3” LaBr3 and SiPMs (#531)
D. Di Vita1, 2, L. Buonanno1, 2, F. Canclini1, 2, G. Ticchi1, 2, M. Carminati1, 2, F. Camera2, 3, C. Fiorini1, 2
1 Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria (DEIB), Milano, Italy
We present a high-dynamic-range, high-resolution, gamma-ray spectrometer based on a 3" co-doped lanthanum bromide (LaBr3(Ce+Sr)) crystal (73 ph/keV conversion efficiency, 25 ns decay time) coupled to 144 Silicon Photomultipliers (SiPMs) from Fondazione Bruno Kessler. The system reaches 2.6% energy resolution at 662 keV (137Cs emission peak) and 100 keV - 30 MeV energy dynamic range thanks to a custom ASIC with automatic gain adaptation. Experimental measurements will focus on the benefits of a gain-switching approach compared to a fixed gain, on the performance at high count-rate, and on validating an improved custom temperature compensation platform for the SiPMs.
Keywords: SiPM, LaBr3, Gamma spectroscopy, High dynamic range, HDR
Neutron Counting in Mixed Neutron-Gamma Fields with Common NaI(Tl) Detectors (#331)
G. Pausch1, A. Kreuels1, F. Scherwinski1, Y. Kong1, M. Kuester1, R. Lentering1, J. R. Stein1
1 Target Systemelektronik GmbH & Co. KG, Wuppertal, North Rhine-Westphalia, Germany
Iodine-comprising scintillators as NaI(Tl) are capable of detecting thermal neutrons with surprising efficiency, even in the presence of ambient gamma radiation. This is due to a peculiarity of the 128I level scheme. De-excitation cascades following neutron captures in 127I, a constituent of NaI with quite large neutron capture cross-section, often involve the 167.4 keV state of 128I with 175 ns half-life, which feeds another isomeric level, the 137.9 keV state with 845 ns half-life. Strong transitions involving these levels are highly converted, they mostly generate signals in the crystal. A sequence of three pulses within a few microseconds, the second and third one corresponding to energy depositions around 30 keV and 138 keV, respectively, is a distinct feature of such a de-excitation cascade and a clear signal for a neutron capture in 127I. The paper demonstrates thermal-neutron detection with a common ø2”x 2” NaI(Tl) scintillation detector by identifying such triple-pulse sequences in the digitized detector signals. Energy depositions and time delays of the (often piled-up) sub-pulses with respect to the event trigger reflecting a prompt part of the cascade are determined by consecutive stripping of the signal components. Random triple events, caused by ambient gamma radiation or statistical fluctuations exceeding the trigger threshold, are strongly suppressed by energy and time cuts defining valid delayed contributions. Another measurement using a 6Li co-doped ø2”x 2” NaI(Tl) (NAIL™) scintillator allowed estimating the neutron detection efficiency attained with this novel technique.
Keywords: Neutrons, neutron detection, gamma rays, gamma spectroscopy, scintillation detector
Thermal Ageing of Crystal Scintillators and Optical Coupling Materials (#575)
K. L. Loughney1, S. J. Bell2, A. G. Tuff3, P. J. Sellin1
1 University of Surrey, Department of Physics, Guildford, United Kingdom
The degradation in optical properties of scintillation detector components is an important consideration in the lifetime of radiation detectors. Thermal cycling has been used to accelerate the ageing process of six coupling materials and two scintillators: CsI:Tl and GAGG:Ce crystals. Samples were aged to the equivalent of one year real-time. The optical properties of each sample were characterised pre and post-ageing. Coupling materials showed percentage transmission (%T)
AcknowledgmentThank you to the University of Surrey, National Physical Laboratory and Kromek Ltd. for the funding of this project.
Keywords: GAGG:Ce, CsI:Tl, Thermal Ageing, Optical Coupling
Improvements in the crystal growth of Tl-based scintillators for gamma-ray and neutron detection using the Vertical Bridgman technique (#931)
P. Bhattacharya1, L. Pandian1, E. Van Loaf1, J. Tower1, K. Shah1
1 Radiation monitoring devices, Imaging, Watertown, Massachusetts, United States of America
Thallium based scintillators are recently getting considerable attention for gamma-ray and neutron detection. The high effective Z and density of these crystals along with their high photoelectric conversion efficiency make them attractive scintillators for radiation detection. In this work, we report on challenges in the growth of large volume crystals of Tl2ZrCl6, (TZC), Tl2LiYCl6 (TLYC) and Tl2NaYCl6 (TNYC) using the Vertical Bridgman technique. The basic properties of these crystals have been reported using small sized crystals, but larger crystals have shown some translucency. We have carried out purification of the starting compounds as well as zone refining of synthesized charge materials to reduce precipitates in the larger volume crystals. The best scintillation light yield obtained for intrinsic TZC is 33,000 Ph/MeV with an energy resolution of 3.9 % at 662 keV using purified ZrCl4. TZC crystals show clear pulse shape discrimination between gamma-rays and fast neutrons. The highest light yield for undoped TLYC crystals has been measured to be 25,000 ph/MeV with an energy resolution of 4.4% at 662 keV. The gamma equivalent energy is 1.8 MeV for thermal neutron detection. The TNYC crystal with 0.3% Ce3+ show similar light yield of 23,000 ph/MeV with an energy resolution of 5% at 662 keV. The zone refining of synthesized charges and subsequent crystal growth of these crystals are in progress, the results of which will be presented.
AcknowledgmentThis research was supported in part by the U.S. Department of Defense, DTRA, under grant award no. HDTRA1-19-1-0014, the Department of the Homeland Security, CWMD, under grant award no. 20CWDARI00036-01-00, and the Department of Energy under grant award no. DE-SC0015793. The content of this paper does not necessarily reflect the position or the policy of the federal government, and no official endorsement should be inferred
Keywords: Gamma-ray detector, neutron detection, Scintillator, Tl-based halide, Bridgman technique.
Comparison of LYSO and GAGG scintillators for a single segmented scintillator-based 4π FOV Compton camera (#770)
H. Lee1, W. Lee2, 3
1 Korea University, Health Science Research Center, Seoul, Republic of Korea
Image performances of 3-dimensional position - sensitive Compton cameras based on a single segmented scintillator - lutetium yttrium oxyorthosilicate (LYSO) and gadolinium aluminum gallium garnet (GAGG) were compared to each other. Because the Compton camera has 4π field of view, it can detect and reconstruct radiation source at any directions. However, in case of using LYSO scintillator, when the activity of the radiation source is low, the reconstructed image shows several artifacts. Natural lutetium contains 2.6% of Lu-176 which emits beta particle and gamma rays, and these radiations can be detected as a background noise, which causes artifacts in the reconstructed image. A GAGG scintillator has relatively lower density and effective atomic number than LYSO scintillator. However, it has high light yield and equivalent decay time to LYSO scintillator and has no intrinsic radioactivity. In this study, image performances of position-sensitive 4π Compton camera using single segmented LYSO and GAGG scintillators are compared based on signal to noise ratio and full width at half maximum value. This work gives guideline to choose an appropriate scintillator for position-sensitive 4π Compton camera with various energies and activities of radiation sources.
AcknowledgmentThis work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MIST) (No. 2020R1A2C1005924) and by the Nuclear Safety Research Program thjrough the Korea Foundation Of Nuclear Safety (KoFONS) using the financial resource granted by the Nuclear Safety and Security Commission (NSSC) of the Republic of Korea (No. 1903006).
Keywords: LYSO, GAGG, position-sensitive, Compton camera
Micro-columnar CsBr:Eu storage phosphor for high-efficiency high energy photon radiography panels (#984)
J. Wang1, M. S. J. Marshall1, S. Miller1, F. Moretti2, E. Bourret-Courchesne2, B. Singh1, V. Nagarkar1
1 Radiation Monitoring Devices Inc., Watertown, Massachusetts, United States of America
Eu-doped CsBr films (CsBr:Eu) exhibit excellent sensitivity for X-rays and are superior storage phosphors for high energy photon radiography imaging applications when coupled with thick copper or tungsten substrates. We report on the growth of micro-columnar CsBr:Eu films on copper and tungsten substrates for these high energy photon (MeV) radiography panels. Our films exhibit dense uniformly distributed micro columns with an average width of ~ 10 µm and a sharp needle-like top. The advantage for this micro-columnar structured film is that the light can be channeled through the narrow columns to improve both light emission and spatial resolution. We also determined the optimal Eu concentration in CsBr for the best storage phosphor performance. Thick micro-columnar structured films up to 2 mm were achieved on 2” x 2” metallic substrates, with the ability to further scale up to larger sizes. Furthermore, we studied the stability of the film and introduced a protective moisture barrier coating to improve the durability of this phosphor screen.
AcknowledgmentThis work was performed under the auspices of the U.S. Department of Energy by Lawrence Berkeley National Laboratory under Contract DE-AC02-05CH11231. The project was funded by the U.S. Department of Energy, National Nuclear Security Administration, Office of Defense Nuclear Nonproliferation Research and Development (DNN R&D).
Keywords: radiography, storage phosphor, CsBr:Eu, micro-columnar film growth, X-ray imaging
Range correction of the response of the FOOT experiment (#284)
S. Argiro'1, 2, R. A. Diaz5, N. Bartosik2, F. Cavanna2, P. Cerello2, V. Ferrero2, E. Fiorina2, G. Giraudo2, E. L. Torres5, N. Pastrone2, F. Pennazio2, M. Pullia3, L. Ramello4, 2, L. Scavarda1, 2, M. Sitta4, 2
1 University of Turin, Physics Department, Turin, Italy
The lack of information about fragmentation cross sections in beam-tissue nuclear interactions limits the precision of clinical treatment planning systems for particle therapy. FOOT is a nuclear physics experiment under construction that will fill the gap in experimental data on the differential cross sections for the production of secondary fragments in such interactions with beam energies up to 400 MeV/u. By extending the energy range up to 800 MeV/u, the measured data will also be valuable for radioprotection in space to understand fragmentation processes that take place in spacecraft shieldings . The FOOT collaboration is building a detector designed for the identification of heavy fragments in a reverse-kinematics configuration, through the measurement of their momentum, energy and time of flight with very high resolution. The energy will be measured with a calorimeter composed by 320 BGO crystals coupled to SiPM photodetectors, that must cover a dynamic range from tens of MeVs to about 10 GeV. Several test beams have been performed to choose the best configuration of SiPMs, crystal wrapping, electronic readout in order to achieve the required performance. The latest measurements performed at CNAO (Pavia, Italy) with a 3x3 crystal module show a quite linear response and an energy resolution below 2% across the whole dynamic range. Furthermore, a mathematical method for compensation of the effect of thermal fluctuations on the detector response has been implemented, which eliminates the need for a dedicated temperature-control system. Finally, the effect of the ion penetration depth on the detector response has been studied using experimental data and FLUKA and GEANT4 simulations: the signal amplitude is reduced by about 33% because of light absoprtion, diffusion and multiple reflections. A correction method to compensate for this signal loss as a function of the depth was also developed.
Keywords: hadrotherapy, calorimeter, fluka simulation, R&D, scintillation detector