DOSEFIELD: A Transparent 1-D Deep-Space Radiation Dose and Shielding Model, Compared with NIST PSTAR and the MSL/RAD Cruise Measurement

DOSEFIELD is an open, deterministic one-dimensional model of the deep-space galactic cosmic ray (GCR) radiation environment: a parametric GCR spectrum is transported in the continuous-slowing-down approximation through a uniform spherical shell of shielding, the same areal density being crossed in every direction (4π, normal thickness), and converted to absorbed dose and ICRP-60 dose-equivalent in water at the centre of the shell. Constants whose source has not been traced are identified in the Limitations section. No constant was fitted to the validation data. Against NIST PSTAR proton stopping-power tables the Bethe–Bloch engine agrees to a maximum deviation of 1.55 % between 10 and 1000 MeV across five low-Z materials (4.09 % including the 1–10 MeV region, where shell corrections are omitted), and to 0.466 % between 1000 and 10 000 MeV, the upper limit of the PSTAR tables. Against the MSL/RAD cruise measurement — evaluated at a solar modulation W = 47.50 derived from the Oulu neutron-monitor record over the averaging window of Zeitlin et al., not over the whole cruise, excluding the days of the five solar energetic particle (SEP) events, and behind 16 g/cm² of aluminium — the model returns an absorbed dose of 0.264 mGy/day against a measured 0.458 ± 0.032 mGy/day (ratio 0.58x), a dose-equivalent of 1.318 mSv/day against a measured 1.75 ± 0.30 mSv/day (ratio 0.75x), and a mean quality factor of 4.995 against a measured 3.82 ± 0.25 (ratio 1.31x). The propagated 1σ-style input uncertainty on the dose-equivalent is ±20.5 % (GCR flux, stopping-power data and this run's PSTAR deviation, combined in quadrature). The measured dose-equivalent lies outside this band, and the band does not cover the absorbed-dose shortfall: that shortfall is treated as model-form error from untransported secondary production, and it is reported rather than corrected. The cruise neutron dose rate measured by Köhler et al. (3.8 ± 1.2 µGy/day; 6 ± 2 µGy/day when extrapolated over 0.1–1000 MeV) is 0.83 % (1.31 %) of the measured absorbed dose of 458 µGy/day and 1.96 % (3.09 %) of the model's 0.194 mGy/day deficit, so the deficit is attributed, as a hypothesis, to secondary charged particles and target fragments. At equal areal density the model ranks five shield materials strictly by hydrogen content (hydrogen < methane < polyethylene < water < aluminium, hydrogen and methane with gas-phase stopping constants) at every thickness tested from 5 to 40 g/cm²; hydrogen gives a dose-equivalent up to 44.2 % below aluminium (solar minimum, W = 0, primaries only; about 43.7 % with liquid-hydrogen constants). Adding simplified Bradt–Peters projectile fragmentation softens from 4.995 to 4.598 and widens polyethylene's advantage over aluminium at 20 g/cm² from 11.6 % to 33.3 %, but does not raise absorbed dose toward the measurement (0.264 to 0.221 mGy/day) — the signature of a model that produces no neutrons or target fragments. AI disclosure: During the preparation of this work, the author used Claude (Anthropic) to draft and edit the manuscript text, to review the code repository in read-only mode, and to cross-check literature. The author reviewed and edited the content and takes full responsibility for it.