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Ros, A., Lerche, C. W., Sebastia, A., Sanchez, F., & Benlloch, J. M. (2014). Retroreflector arrays for better light collection efficiency of gamma-ray imaging detectors with continuous scintillation crystals without DOI misestimation. J. Instrum., 9, P04009–14pp.
Abstract: A method to improve light collection efficiency of gamma-ray imaging detectors by using retroreflector arrays has been tested, simulations of the behaviour of the scintillation light illuminating the retroreflector surface have been made. Measurements including retroreflector arrays in the setup have also been taken. For the measurements, positron emission tomography (PET) detectors with continuous scintillation crystals have been used. Each detector module consists of a continuous LSO-scintillator of dimensions 49x49x10 mm(3) and a H8500 position-sensitive photo-multiplier (PSPMT) from Hamamatsu. By using a continuous scintillation crystal, the scintillation light distribution has not been destroyed and the energy, the centroids along the x- and y-direction and the depth of interaction (DOI) can be estimated. Simulations have also been run taking into account the use of continuous scintillation crystals. Due to the geometry of the continuous scintillation crystals in comparison with pixelated crystals, a good light collection efficiency is necessary to correctly reconstruct the impact point of the gamma-ray. The aim of this study is to investigate whether micro-machine retro-reflectors improve light yield without misestimation of the impact point. The results shows an improvement on the energy and centroid resolutions without worsening the depth of interaction resolution. Therefore it can be concluded that using retroreflector arrays at the entrance side of the scintillation crystal improves light collection efficiency without worsening the impact point estimation.
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ATLAS Collaboration(Abat, E. et al), Bernabeu Verdu, J., Castillo Gimenez, V., Costa, M. J., Escobar, C., Ferrer, A., et al. (2011). A layer correlation technique for pion energy calibration at the 2004 ATLAS Combined Beam Test. J. Instrum., 6, P06001–35pp.
Abstract: A new method for calibrating the hadron response of a segmented calorimeter is developed and successfully applied to beam test data. It is based on a principal component analysis of energy deposits in the calorimeter layers, exploiting longitudinal shower development information to improve the measured energy resolution. Corrections for invisible hadronic energy and energy lost in dead material in front of and between the calorimeters of the ATLAS experiment were calculated with simulated Geant4 Monte Carlo events and used to reconstruct the energy of pions impinging on the calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 area. For pion beams with energies between 20 GeV and 180 GeV, the particle energy is reconstructed within 3% and the energy resolution is improved by between 11% and 25% compared to the resolution at the electromagnetic scale.
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BRIKEN Collaboration(Tarifeño-Saldivia, A. et al), Tain, J. L., Domingo-Pardo, C., Agramunt, J., Algora, A., Morales, A. I., et al. (2017). Conceptual design of a hybrid neutron-gamma detector for study of beta-delayed neutrons at the RIB facility of RIKEN. J. Instrum., 12, P04006–22pp.
Abstract: BRIKEN is a complex detection system to be installed at the RIB-facility of the RIKEN Nishina Center. It is aimed at the detection of heavy-ion implants, β-particles, γ-rays and β-delayed neutrons. The whole detection setup involves the Advanced Implantation Detection Array (AIDA), two HPGe Clover detectors and a large set of 166 counters of 3He embedded in a high-density polyethylene matrix. This article reports on a novel methodology developed for the conceptual design and optimisation of the 3He-tubes array, aiming at the best possible performance in terms of neutron detection. The algorithm is based on a geometric representation of two selected parameters of merit, namely, average neutron detection efficiency and efficiency flatness, as a function of a reduced number of geometric variables. The response of the detection system itself, for each configuration, is obtained from a systematic MC-simulation implemented realistically in Geant4. This approach has been found to be particularly useful. On the one hand, due to the different types and large number of 3He-tubes involved and, on the other hand, due to the additional constraints introduced by the ancillary detectors for charged particles and gamma-rays. Empowered by the robustness of the algorithm, we have been able to design a versatile detection system, which can be easily re-arranged into a compact mode in order to maximize the neutron detection performance, at the cost of the gamma-ray sensitivity. In summary, we have designed a system which shows, for neutron energies up to 1(5) MeV, a rather flat and high average efficiency of 68.6%(64%) and 75.7%(71%) for the hybrid and compact modes, respectively. The performance of the BRIKEN system has been also quantified realistically by means of MC-simulations made with different neutron energy distributions.
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Barrio, J., Etxebeste, A., Lacasta, C., Muñoz, E., Oliver, J. F., Solaz, C., et al. (2015). Performance of VATA64HDR16 ASIC for medical physics applications based on continuous crystals and SiPMs. J. Instrum., 10, P12001–12pp.
Abstract: Detectors based on Silicon Photomultipliers (SiPMs) coupled to continuous crystals are being tested in medical physics applications due to their potential high resolution and sensitivity. To cope with the high granularity required for a very good spatial resolution, SiPM matrices with a large amount of elements are needed. To be able to read the information coming from each individual channel, dedicated ASICs are employed. The VATA64HDR16 ASIC is a 64-channel, charge-sensitive amplifier that converts the collected charge into a proportional current or voltage signal. A complete assessment of the suitability of that ASIC for medical physics applications based on continuous crystals and SiPMs has been carried out. The input charge range is linear from 20 pC up to 55 pC. The energy resolution obtained at 511 keV is 10% FWHM with a LaBr3 crystal and 16% FWHM with a LYSO crystal. A coincidence timing resolution of 24 ns FWHM is obtained with two LYSO crystals.
Keywords: Solid state detectors; Photon detectors for UV, visible and IR photons (solid-state) (PIN diodes, APDs, Si-PMTs, G-APDs, CCDs, EBCCDs, EMCCDs etc); Front-end electronics for detector readout; Gamma detectors (scintillators, CZT, HPG, HgI etc)
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Muñoz, E., Barrio, J., Bemmerer, D., Etxebeste, A., Fiedler, F., Hueso-Gonzalez, F., et al. (2018). Tests of MACACO Compton telescope with 4.44 MeV gamma rays. J. Instrum., 13, P05007–13pp.
Abstract: Hadron therapy offers the possibility of delivering a large amount of radiation dose to tumors with minimal absorption by the surrounding healthy tissue. In order to fully exploit the advantages of this technique, the use of real-time beam monitoring devices becomes mandatory. Compton imaging devices can be employed to map the distribution of prompt gamma emission during the treatment and thus assess its correct delivery. The Compton telescope prototype developed at IFIC-Valencia for this purpose is made of three layers of LaBr3 crystals coupled to silicon photomultipliers. The system has been tested in a 4.44 MeV gamma field at the 3 MV Tandetron accelerator at HZDR, Dresden. Images of the target with the system in three different positions separated by 10 mm were successfully reconstructed. This indicates the ability of MACACO for imaging the prompt gamma rays emitted at such energies.
Keywords: Compton imaging; Instrumentation for hadron therapy; Gamma detectors (scintillators, CZT, HPG, HgI etc); Photon detectors for UV, visible and IR photons (solid state) (PIN diodes, APDs, Si PMTs, G APDs, CCDs, EBCCDs, EMCCDs etc)
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