Abstract
Depending on the radiation field, the absorbed dose rate can depend significantly upon the size of the detectors or the phantom used in the models. In deep space (interplanetary medium) the radiation field is on avarage dominated by Galactic Cosmic Ray (GCR) nuclei. Here, the deep space dose rate that a typical small silicon slab detector measures is compared to a larger phantom corresponding to an ICRU sphere with a 15 cm radius composed of water. To separate and understand respective effects from the composition, size and shape differences in the detectors, this comparison is implemented in several steps. For each phantom, the absorbed dose rate due to GCR nuclei up toZ= 28, as a function of solar modulation conditions, is calculated.The main components of the GCR flux are protons, followed by helium nuclei and electrons, withZ> 2 nuclei accounting for approximately 1% of the total number of particles. Among the light nuclei withZ> 2, most abundant ones are C, N and O. In this study, we use the GEANT4 model to calculate the absorbed dose (energy deposited as ionization, divided by mass) due to the GCR flux provided by the Badhwar-O’Neill 2010 (BON-10) model. Furthermore, we investigate how the determined absorbed dose rate changes throughout the solar cycle by varying the GCR models from solar minimum to solar maximum conditions. The developed model is validated against the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) microdosimeter measurements. In our current approach, we do not consider the effects of shielding, which will always be present under realistic scenarios.A second goal of this study is to quantify the contribution of eachZ= 1, …, 28 GCR nuclei to absorbed dose rate, in relation to the phantom characteristics. For eachZwe determine the most relevant energy range in the GCR spectra for absorbed dose rate estimations. Furthermore, we calculate a solar modulation dependent conversion factor to convert absorbed dose rate measured in silicon to absorbed dose rate in water. This information will improve our understanding of the radiation environment due to GCR in the near-Earth deep space and also benefit further modeling efforts by limiting the number and energy range of primary particle species that have to be considered.
Highlights
The Galactic Cosmic Ray (GCR) flux is often approximated as a constant, isotropic radiation field which ionizes matter
The deep space dose rate that a typical small silicon slab detector measures is compared to a larger phantom corresponding to an International Commission on Radiation Units and Measurements (ICRU) sphere with a 15 cm radius composed of water
We investigate in this paper the validity of the described silicon-to-water conversion factor and if/how it may change under different experiment setups including the detector size, shape, material and different GCR fluxes under different solar modulation conditions
Summary
The Galactic Cosmic Ray (GCR) flux is often approximated as a constant, isotropic radiation field which ionizes matter. We investigate in this paper the validity of the described silicon-to-water conversion factor and if/how it may change under different experiment setups including the detector size, shape, material and different GCR fluxes under different solar modulation conditions. If we were to compare these two phantoms directly in our model, we could not attribute and quantify the contribution by each different effect including composition difference (water and silicon), shape difference (slab and sphere, disk) and size difference. We present here a detailed analysis of GCR-induced absorbed dose rate of different particle species under different solar modulation conditions We report such calculated modulation dependent factors for converting dose from silicon detectors to water material respectively for three different phantom geometries.
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