Doses from galactic cosmic ray particles under spacecraft shielding

This work presents the results of calculating the absorbed and equivalent doses from galactic cosmic ray (GCR) particles under a spacecraft shielding of up to 50 g cm-2 in space beyond the Earth's magnetic field during solar minimum and maximum. The calculations are made for normal incidence of a broad particle beam onto a semi-infinite plane shielding layer. The doses are calculated at a point under shielding in biological tissue for primary protons, for alpha particles, and for Be, N, Si, and Fe nuclei which are representative of all the charged groups of GCR particles. The particle passages through matter are calculated by solving the radiation transfer equation, making allowance for nuclear collisions and for the contribution of the main secondary radiation components to the total dose. The input data (the inelastic interaction cross-sections, the fragmentation parameters, the mean multiplicities of secondaries, etc.) are either prescribed values or values published elsewhere. The equivalent GCR particle doses are calculated making allowance for two ways of representing the dependence of the quality factor on the linear energy transfer of particles in biological tissue. The component composition of the particle doses and the contributions of secondary components to the total dose are analyzed as functions of the shielding thickness. The attenuation curves of the doses defined by different forms of the differential GCR energy spectra are compared with each other. The resultant values of the doses beyond the Earth's magnetic field are compared with the values found elsewhere and with the standard doses adopted in the U.S.S.R. for space flights up to 3 yr. (author)