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Guerrero, C., Cano-Ott, D., Mendoza, E., Tain, J. L., Algora, A., Berthoumieux, E., et al. (2012). Monte Carlo simulation of the n_TOF Total Absorption Calorimeter. Nucl. Instrum. Methods Phys. Res. A, 671, 108–117.
Abstract: The n_TOF Total Absorption Calorimeter (TAC) is a 4 pi BaF2 segmented detector used at CERN for measuring neutron capture cross-sections of importance for the design of advanced nuclear reactors. This work presents the simulation code that has been developed in GEANT4 for the accurate determination of the detection efficiency of the TAC for neutron capture events. The code allows to calculate the efficiency of the TAC for every neutron capture state, as a function of energy, crystal multiplicity, and counting rate. The code includes all instrumental effects such as the single crystal detection threshold and energy resolution, finite size of the coincidence time window, and signal pile-up. The results from the simulation have been validated with experimental data for a large set of electromagnetic de-excitation patterns: beta-decay of well known calibration sources, neutron capture reactions in light nuclei with well known level schemes like Ti-nat, reference samples used in (n,gamma) measurements like Au-197 and experimental data from an actinide sample like Pu-240. The systematic uncertainty in the determination of the detection efficiency has been estimated for all the cases. As a representative example, the accuracy reached for the case of Au-197(n,gamma) ranges between 0.5% and 2%, depending on the experimental and analysis conditions. Such a value matches the high accuracy required for the nuclear cross-section data needed in advanced reactor design.
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Hornillos, M. B. G., Gorlychev, V., Caballero, R., Cortes, G., Poch, A., Pretel, C., et al. (2011). Monte Carlo Simulations for the Study of a Moderated Neutron Detector. J. Korean Phys. Soc., 59(2), 1573–1576.
Abstract: This work presents the Monte Carlo simulations performed with the MCNPX and GEANT4 codes for the design of a BEta deLayEd Neutron detector, BELEN-20. This detector will be used for the study of beta delayed neutron emission and consists of a block of polyethylene with dimensions 90 x 90 x 80 cm(3) and 20 cylindrical (3)He gas counters. The results of these simulations have been validated experimentally with a (252)Cf source in the laboratory at UPC, Barcelona. Also the first experiment with this detector has been carried out in November 2009 in JYFL, Finland. In this experiment the neutron emission probability after beta decay of the fission products (88)Br, (94,95)Rb, and (138)I has been measured; this data is still under analysis. Simulations with MCNPX and GEANT4 have been performed in order to obtain the efficiency of the BELEN-20 detector for each of the above nuclei using the neutron energy distribution corresponding to each nucleus.
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Zhang, X., Xiao, Y. T., & Gimeno, B. (2020). Multipactor Suppression by a Resonant Static Magnetic Field on a Dielectric Surface. IEEE Trans. Electron Devices, 67(12), 5723–5728.
Abstract: In this article, we study the suppression of the multipactor phenomenon on a dielectric surface by a resonant static magnetic field. A homemade Monte Carlo algorithm is developed for multipactor simulations on a dielectric surface driven by two orthogonal radio frequency (RF) electric field components. When the static magnetic field is perpendicular to the tangential and normal RF electric fields, it is shown that if the normal electric field lags the tangential electric field by pi/2, the superposition of the normal and tangential electric fields will trigger a gyro-acceleration of the electron cloud and restrain the multipactor discharge effectively. By contrast, when the normal electric field is in advance of the tangential electric field by pi/2, the difference between the normal and tangential electric fields drives gyro-motion of the electron cloud. Consequently, two enhanced discharge zones are inevitable. The suppression effects of the resonant static magnetic field that is parallel to the tangential RF electric field or to the normal RF electric field are also presented.
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Ortega, P. G., Torres-Espallardo, I., Cerutti, F., Ferrari, A., Gillam, J. E., Lacasta, C., et al. (2015). Noise evaluation of Compton camera imaging for proton therapy. Phys. Med. Biol., 60(5), 1845–1863.
Abstract: Compton Cameras emerged as an alternative for real-time dose monitoring techniques for Particle Therapy (PT), based on the detection of prompt-gammas. As a consequence of the Compton scattering process, the gamma origin point can be restricted onto the surface of a cone (Compton cone). Through image reconstruction techniques, the distribution of the gamma emitters can be estimated, using cone-surfaces backprojections of the Compton cones through the image space, along with more sophisticated statistical methods to improve the image quality. To calculate the Compton cone required for image reconstruction, either two interactions, the last being photoelectric absorption, or three scatter interactions are needed. Because of the high energy of the photons in PT the first option might not be adequate, as the photon is not absorbed in general. However, the second option is less efficient. That is the reason to resort to spectral reconstructions, where the incoming. energy is considered as a variable in the reconstruction inverse problem. Jointly with prompt gamma, secondary neutrons and scattered photons, not strongly correlated with the dose map, can also reach the imaging detector and produce false events. These events deteriorate the image quality. Also, high intensity beams can produce particle accumulation in the camera, which lead to an increase of random coincidences, meaning events which gather measurements from different incoming particles. The noise scenario is expected to be different if double or triple events are used, and consequently, the reconstructed images can be affected differently by spurious data. The aim of the present work is to study the effect of false events in the reconstructed image, evaluating their impact in the determination of the beam particle ranges. A simulation study that includes misidentified events (neutrons and random coincidences) in the final image of a Compton Telescope for PT monitoring is presented. The complete chain of detection, from the beam particle entering a phantom to the event classification, is simulated using FLUKA. The range determination is later estimated from the reconstructed image obtained from a two and three-event algorithm based on Maximum Likelihood Expectation Maximization. The neutron background and random coincidences due to a therapeutic-like time structure are analyzed for mono-energetic proton beams. The time structure of the beam is included in the simulations, which will affect the rate of particles entering the detector.
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Gimenez-Alventosa, V., Gimenez, V., & Oliver, S. (2021). PenRed: An extensible and parallel Monte-Carlo framework for radiation transport based on PENELOPE. Comput. Phys. Commun., 267, 108065–12pp.
Abstract: Monte Carlo methods provide detailed and accurate results for radiation transport simulations. Unfortunately, the high computational cost of these methods limits its usage in real-time applications. Moreover, existing computer codes do not provide a methodology for adapting these kinds of simulations to specific problems without advanced knowledge of the corresponding code system, and this restricts their applicability. To help solve these current limitations, we present PenRed, a general-purpose, standalone, extensible and modular framework code based on PENELOPE for parallel Monte Carlo simulations of electron-photon transport through matter. It has been implemented in C++ programming language and takes advantage of modern object-oriented technologies. In addition, PenRed offers the capability to read and process DICOM images as well as to construct and simulate image-based voxelized geometries, so as to facilitate its usage in medical applications. Our framework has been successfully verified against the original PENELOPE Fortran code. Furthermore, the implemented parallelism has been tested showing a significant improvement in the simulation time without any loss in precision of results. Program summary Program title: PenRed: Parallel Engine for Radiation Energy Deposition. CPC Library link to program files: https://doi .org /10 .17632/rkw6tvtngy.1 Licensing provision: GNU Affero General Public License (AGPL). Programming language: C++ standard 2011. Nature of problem: Monte Carlo simulations usually require a huge amount of computation time to achieve low statistical uncertainties. In addition, many applications necessitate particular characteristics or the extraction of specific quantities from the simulation. However, most available Monte Carlo codes do not provide an efficient parallel and truly modular structure which allows users to easily customise their code to suit their needs without an in-depth knowledge of the code system. Solution method: PenRed is a fully parallel, modular and customizable framework for Monte Carlo simulations of the passage of radiation through matter. It is based on the PENELOPE [1] code system, from which inherits its unique physics models and tracking algorithms for charged particles. PenRed has been coded in C++ following an object-oriented programming paradigm restricted to the C++11 standard. Our engine implements parallelism via a double approach: on the one hand, by using standard C++ threads for shared memory, improving the access and usage of the memory, and, on the other hand, via the MPI standard for distributed memory infrastructures. Notice that both kinds of parallelism can be combined together in the same simulation. Moreover, both threads and MPI processes, can be balanced using the builtin load balance system (RUPER-LB [30]) to maximise the performance on heterogeneous infrastructures. In addition, PenRed provides a modular structure with methods designed to easily extend its functionality. Thus, users can create their own independent modules to adapt our engine to their needs without changing the original modules. Furthermore, user extensions will take advantage of the builtin parallelism without any extra effort or knowledge of parallel programming. Additional comments including restrictions and unusual features: PenRed has been compiled in linux systems withg++ of GCC versions 4.8.5, 7.3.1, 8.3.1 and 9; clang version 3.4.2 and intel C++ compiler (icc) version 19.0.5.281. Since it is a C++11-standard compliant code, PenRed should be able to compile with any compiler with C++11 support. In addition, if the code is compiled without MPI support, it does not require any non standard library. To enable MPI capabilities, the user needs to install whatever available MPI implementation, such as openMPI [24] or mpich [25], which can be found in the repositories of any linux distribution. Finally, to provide DICOM processing support, PenRed can be optionally compiled using the dicom toolkit (dcmtk) [32] library. Thus, PenRed has only two optional dependencies, an MPI implementation and the dcmtk library.
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