Radiation shield requirements for manned nuclear propulsion space vehicles

Space radiation quality factor for Galactic Cosmic Rays and typical space mission scenarios using a microdosimetric approach

“…Microdosimetric quantities are important when studying the interaction of radiation with matter at sufficient small volumes of μm down to nm, in order to account for energy-loss straggling and the finite range of the liberated secondary electrons (δ-rays) (Rossi and Zaider 2012). In the context of microdosimetry, non-stochastic quantities, such us LET and absorbed dose, are replaced with their microdosimetric analogs of lineal energy (y) and specific energy(z) , respectively.…”

“…In the context of microdosimetry, non-stochastic quantities, such us LET and absorbed dose, are replaced with their microdosimetric analogs of lineal energy (y) and specific energy(z) , respectively. Lineal energy is the energy imparted (ε) to the matter by a single energy-deposition event, which consists of statistically correlated depositions of energy as, for example, those by high energy particles and/or their secondary electrons divided by the mean chord length (l) of the volume under study (International Commission on Radiation Units andMeasurements 1983, 2011;Rossi and Zaider 2012):…”

“…Because of the inherent statistical nature of the energy deposition process, each radiation quality is described by a probability density function f (y) . As a result, one can define two mean values of y , namely the frequency-mean lineal energy (y F ) and the dose-mean lineal energy (y D ) (Rossi and Zaider 2012):…”

“…For many radiobiological effects (including cancer-related effects), the RBE (or Q ) increases with LET up to a certain value, beyond which any additional increase of LET causes a reduction of the biological effect (the so-called overkill effect Joint Task Group on Radiation Protection Quantities et al 1986;Rossi and Zaider 2012)). This is particularly relevant to the heavy-ion component of the GCR owing to their very high LET values.…”

“…On the contrary, microdosimetric approaches describe the radiation quality through the stochastic analog of LET, lineal energy ( y ) (International Commission on Radiation Units and Measurements 1986). The microdosimetric quality factor ( Q ) can be calculated via y using the ICRU Report 40 (Joint Task Group on Radiation Protection Quantities et al 1986) methodology or the Theory of Dual Radiation Action (TDRA) (Kellerer and Rossi 1978;Kellerer 1985;Rossi and Zaider 2012). Theoretical calculations of y-spectra for ions relevant to GCR, require specialized Monte-Carlo codes (e.g., GEANT-4 DNA, PHITS, PART RAC , KURBUC) (Incerti et al 2010;Alloni et al 2012;Liamsuwan et al 2014;Nikjoo et al 2016;Matsuya et al 2021Matsuya et al , 2022 or analytical microdosimetric models.…”