Alterations in Dose and Lineal Energy Spectra Under Different Shieldings in the Los Alamos High Energy Neutron Field

摘要

Nuclear interactions of space radiation with shield materials result in alterations in dose, and lineal energy spectra, that depend on the specific elemental composition, density, and thickness of the material. The shielding characteristics of some materials have been studied using charged particle beams and radiation transport models, by examining the risk reduction using either the conventional dose equivalent approach or the neoplastic transformation probabilities. Secondary neutrons contribute a significant fraction of the total radiation exposure in space. An experiment to study the changes in dose and lineal energy spectra by shielding materials was carried out at the LANSCE (Los Alamos Nuclear Science Center) neutron facility. This neutron spectrum is shown to be similar to the spectrum expected in the International Space Station habitable modules. It is shown that with a shielding thickness of about 5 grams per square centimeter (roughly the depth taken for blood-forming-organ) the conventional radiation risk increases, in some cases by as much as a factor of 2. This shows the role of neutrons is more important for risk estimation than previously envisioned. The neutron dose decreases with thickness of about of 20 grams per square centimeter, suggesting that both charged and neutral components of space radiation should be included to determine the effectiveness of shielding material.