DOSEFIELD: A Transparent 1-D Deep-Space Radiation Dose and Shielding Model with Source-Traceable Constants

Abstract

DOSEFIELD is an open, deterministic one-dimensional model of the deep-space galactic cosmic ray (GCR) radiation environment: a parametric GCR spectrum is transported through a slab shield in the continuous-slowing-down approximation and converted to absorbed dose and ICRP-60 dose-equivalent in water. Every constant is taken from a cited primary source, and no parameter is fitted to any validation target. Against NIST PSTAR proton stopping-power tables the Bethe-Bloch engine agrees to a maximum deviation of 1.55% above 10 MeV across five low-Z materials (4.03% including the 1-10 MeV region, where shell corrections are omitted). Against the MSL/RAD cruise measurement, evaluated at a solar modulation and shield thickness chosen independently of the measurement, the model returns an absorbed dose of 0.308 mGy/day against a measured 0.458 +/- 0.032 mGy/day (ratio 0.67x), a dose-equivalent of 1.473 mSv/day against a measured 1.75 +/- 0.30 mSv/day (ratio 0.84x), and a mean quality factor <Q> of 4.78 against a measured 3.82 +/- 0.25 (ratio 1.25x). The propagated 1-sigma-style input uncertainty on the dose-equivalent is 14.6% (GCR flux, stopping-power data and this run's PSTAR deviation combined in quadrature), which does not cover the absorbed-dose shortfall: that shortfall is model-form error from un-transported secondary production, and it is reported rather than corrected. Contemporaneous in-cruise neutron measurements (6 +/- 2 microGy/day) account for only about 4% of the model's absorbed-dose deficit, so the deficit is attributed to secondary charged particles and target fragments, not neutrons. At equal areal density the model ranks five shield materials strictly by hydrogen content (H2 < CH4 < polyethylene < water < aluminium) at every thickness tested from 5 to 40 g/cm2; liquid hydrogen reduces dose-equivalent by up to 44.2% relative to aluminium. This paper reports a methods and validation study, not a new physical result: the value of the work is a fully inspectable, source-traceable implementation and an honest, quantitative account of where and why it disagrees with flight data.