Establishment and Application of Diamond Detector Analysis System

Department of Nuclear EngineeringIn this study, a diamond detector in a mixed neutron-photon field of the CROCUS research reactor at ??cole Polytechnique F??d??rale de Lausanne (EPFL) is modeled. Simulations are carried out to analyze pulses from the diamond detector in more detail, which induce a novel discovery. Through a code-to-code comparison, the Monte Carlo codes SERPENT v2.1.29 and GEANT4 v10.04.p02 are selected for the CROCUS whole core calculation and the detailed physics modeling in the diamond crystal, respectively. The neutron and prompt gamma ray contributions to the detector are modeled by a two-step procedure (SERPENT2/GEANT4), and the simulation of the delayed gamma ray contribution is carried out by a three-step procedure (SERPENT2/STREAM-SNF/GEANT4). The simulations show that the fraction of the gamma-to-neutron fluxes in the diamond detector is approximately 91.4%, and that of the delayed-to-prompt gamma fluxes is approximately 47.2%. By using the flux spectra calculated at the location of the detector, the physics of particle interactions with the diamond crystal is investigated. The contributions of the neutrons and gamma rays to the diamond detector signal amount to approximately 27% and 73%, respectively. The energies and positions of the particles contributing to the detector signal as tallied in GEANT4 are employed to reconstruct numerical pulses and create a scatter plot. In the scatter plot, pulses are arranged according to the energy for each calculation width, which is defined as the width at 0% of the maximum amplitude. The proton recoil plot shows two bands, one due to protons impacting the anode and the other by protons impacting the cathode, thus showing that protons do not have sufficient energy to penetrate the diamond crystal and have the same probability of interacting with the anode and cathode. This tendency also appears as a high-energy tail in a pulse energy spectrum consisting of the number of pulses according to the energy distribution. Meanwhile, neutron scattering collisions have a homogeneous distribution in the crystal. Hence, a structure with a higher count at the ballistic center region (BCR) is observed and is probably related to the amplitude of the BCR pulses being higher. Thus, it is possible to observe better pulses resulting from the energy depositions at the BCR. Finally, the modeling performance is assessed by comparing the calculated results with the experimental data. In the pulse energy spectrum, a curve produced by the simulations matches with that produced by the measurements. The slope of the curves between 1 MeV and 2 MeV is mainly produced by gamma interactions. The high-energy tail is produced by neutron interactions, especially, the proton recoil. The lithium converter reactions in the diamond detector account for 14.31% and 15.13% beyond 1.34 MeV for the measurement and simulation, respectively, showing consistency.clos