Borja-Lloret, M., Barrientos, L., Bernabeu, J., Lacasta, C., Muñoz, E., Ros, A., et al. (2023). Influence of the background in Compton camera images for proton therapy treatment monitoring. Phys. Med. Biol., 68(14), 144001–16pp.
Abstract: Objective. Background events are one of the most relevant contributions to image degradation in Compton camera imaging for hadron therapy treatment monitoring. A study of the background and its contribution to image degradation is important to define future strategies to reduce the background in the system. Approach. In this simulation study, the percentage of different kinds of events and their contribution to the reconstructed image in a two-layer Compton camera have been evaluated. To this end, GATE v8.2 simulations of a proton beam impinging on a PMMA phantom have been carried out, for different proton beam energies and at different beam intensities. Main results. For a simulated Compton camera made of Lanthanum (III) Bromide monolithic crystals, coincidences caused by neutrons arriving from the phantom are the most common type of background produced by secondary radiations in the Compton camera, causing between 13% and 33% of the detected coincidences, depending on the beam energy. Results also show that random coincidences are a significant cause of image degradation at high beam intensities, and their influence in the reconstructed images is studied for values of the time coincidence windows from 500 ps to 100 ns. Significance. Results indicate the timing capabilities required to retrieve the fall-off position with good precision. Still, the noise observed in the image when no randoms are considered make us consider further background rejection methods.
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Martin-Luna, P., Esperante, D., Prieto, A. F., Fuster-Martinez, N., Rivas, I. G., Gimeno, B., et al. (2024). Simulation of electron transport and secondary emission in a photomultiplier tube and validation. Sens. Actuator A-Phys., 365, 114859–10pp.
Abstract: The electron amplification and transport within a photomultiplier tube (PMT) has been investigated by developing an in-house Monte Carlo simulation code. The secondary electron emission in the dynodes is implemented via an effective electron model and the Modified Vaughan's model, whereas the transport is computed with the Boris leapfrog algorithm. The PMT gain, rise time and transit time have been studied as a function of supply voltage and external magnetostatic field. A good agreement with experimental measurements using a Hamamatsu R13408-100 PMT was obtained. The simulations have been conducted following different treatments of the underlying geometry: three-dimensional, two-dimensional and intermediate (2.5D). The validity of these approaches is compared. The developed framework will help in understanding the behavior of PMTs under highly intense and irregular illumination or varying external magnetic fields, as in the case of prompt gamma-ray measurements during pencil-beam proton therapy; and aid in optimizing the design of voltage dividers with behavioral circuit models.
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ATLAS Collaboration(Adragna, P. et al), Castelo, J., Castillo Gimenez, V., Cuenca, C., Ferrer, A., Fullana, E., et al. (2010). Measurement of pion and proton response and longitudinal shower profiles up to 20 nuclear interaction lengths with the ATLAS Tile calorimeter. Nucl. Instrum. Methods Phys. Res. A, 615(2), 158–181.
Abstract: The response of pions and protons in the energy range of 20-180 GeV, produced at CERN's SPS H8 test-beam line in the ATLAS iron-scintillator Tile hadron calorimeter, has been measured. The test-beam configuration allowed the measurement of the longitudinal shower development for pions and protons up to 20 nuclear interaction lengths. It was found that pions penetrate deeper in the calorimeter than protons. However, protons induce showers that are wider laterally to the direction of the impinging particle. Including the measured total energy response, the pion-to-proton energy ratio and the resolution, all observations are consistent with a higher electromagnetic energy fraction in pion-induced showers. The data are compared with GEANT4 simulations using several hadronic physics lists. The measured longitudinal shower profiles are described by an analytical shower parametrization within an accuracy of 5-10%. The amount of energy leaking out behind the calorimeter is determined and parametrized as a function of the beam energy and the calorimeter depth. This allows for a leakage correction of test-beam results in the standard projective geometry.
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Villaescusa-Navarro, F., & Dalal, N. (2011). Cores and cusps in warm dark matter halos. J. Cosmol. Astropart. Phys., 03(3), 024–16pp.
Abstract: The apparent presence of large core radii in Low Surface Brightness galaxies has been claimed as evidence in favor of warm dark matter. Here we show that WDM halos do not have cores that are large fractions of the halo size: typically, r(core)/r(200) less than or similar to 10(-3). This suggests an astrophysical origin for the large cores observed in these galaxies, as has been argued by other authors.
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ATLAS Collaboration(Abat, E. et al), Castillo Gimenez, V., Ferrer, A., Gonzalez, V., Higon-Rodriguez, E., Mitsou, V. A., et al. (2010). Study of energy response and resolution of the ATLAS barrel calorimeter to hadrons of energies from 20 to 350 GeV. Nucl. Instrum. Methods Phys. Res. A, 621(1-3), 134–150.
Abstract: A fully instrumented slice of the ATLAS detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. In this paper, the results of the measurements of the response of the barrel calorimeter to hadrons with energies in the range 20-350 GeV and beam impact points and angles corresponding to pseudo-rapidity values in the range 0.2-0.65 are reported. The results are compared to the predictions of a simulation program using the Geant 4 toolkit.
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