A geometric factor calculation method based on the isotropic flux assumption

Abstract

One of the instruments onboard the China Seismic Electromagnetic Satellite (CSES) is the Low Energy Particle Detector (LEPD). The primary objective of LEPD is to provide measurements of the fluxes, energy spectra and pitch angles of 100 keV to 10 MeV electrons and protons from 2 to 50 MeV in the Earth's magnetosphere. The geometric factor is one of the principle parameters of a detector, which converts the physical quantity—count rate to the particle quantity-flux. In this paper, we calculated the geometric factor of LEPD via computer modeling of an isotropic radiation environment. It was first demonstrated that the radiation intensity related should obey a cosine-law, then a general sampling method of generating this distribution via GPS of GEANT4 was explained. Furthermore, combined with flux normalization, a comparison of the geometric factor calculation of a set of 2-layer detectors with different shapes (cylinder, truncated cone and rectangle) was performed. Results show a generally good agreement between simulation and analytical calculations for the cylinder and truncated cone detectors, and the result of the rectangular one, for which there is no accurate analytical formula, is consistent with the previous simulated results by others. As a practical instance of the 2-layer rectangle detector, the geometric factor of LEPD is 10.336±0.036 cm2·sr for 10 MeV proton and 8.211±0.032 cm2·sr for 8 MeV electron.

Fifteenth Workshop Solar Influences on the Magnetosphere, Ionosphere and Atmosphere

“…The geometry we use is shown in Figure 2. The approach used in the modeling of the instrument is presented in [Zhao et al, 2013] and [Pak et al, 2018]. Figure 3 shows the schematic diagram of the simulation.…”

Interpreting the GeV-TeV gamma-ray spectra of local giant molecular clouds using GEANT4 simulation

“…The material distributions in the GMCs are then irradiated by the primary particles using the abovementioned energy distributions in the kinetic energy range of 10 −1 -10 7 GeV from a spherical surface surrounding the GMC geometry. The angular distribution of the particle momenta is done using the cosine-law to ensure the isotropic irradiance of the molecular clouds [53]. The data are taken from: Voyager 1 (red points) [43], PAMELA (green points) [44], AMS-02 (blue points) [27], CREAM (magenta points) [45], IceTop(cyan points) [46], KASCADE (yellow points) [47], TUNKA (Orange points) [48], DAMPE (olive points) [49].…”

A Numerical Method to Analyze Geometric Factors of a Space Particle Detector Relative to Omnidirectional Proton and Electron Fluxes

“…It is assumed in this study that the incident particle fluxes are isotropic because such conditions are often found in space (Wilson et al 1991;NCRP 2006;Durante & Cucinotta 2011). To simulate an isotropic flux, electrons and protons are produced from the surface of a hypothetical sphere which is sufficiently large to encompass the model instrument in this investigation (Wilson et al 2005;Ersmark 2006;Yando et al 2011;Martinez & Kingston 2012;Zhao et al 2013). There are three inputs needed for particle generation on the surface of the hypothetical sphere; the initial values of 1) the position vector (x pos , y pos , z pos ), 2) the momentum vector (p x , p y , p z ), and 3) the energy (E init ).…”

“…To produce isotropic fluxes within the sphere from each initial position of the particles, the half sinesquared value of the directional polar angle sin θ ′ (sin 2 θ ′ /2) is uniformly generated in the range [0, 1/2], and the directional azimuth angle ϕ ′ is uniformly drawn from the range [0, 2π] (Zhao et al 2013).…”

“…The geometric factor G, which includes the contributions of particles from outside the FOV due to particle penetration, scattering or other physical mechanisms, can be calculated via Monte Carlo simulations (Wu & Armstrong 1988;Jun et al 2002). The response of the model instrument under isotropic flux over the full 4π steradians of space is assumed to be (Yando et al 2011;Zhao et al 2013; The projected area of the hypothetical shooting sphere is drawn as a red arc (designated as filtering process 1). The shaded area in blue is defined to select momentum vector that would yield direct detection in the absence of any interaction with the instrument structures (designated as filtering process 2).…”