Radiation Shielding Properties of Lunar Regolith and Regolith Simulant

Content Provider	Semantic Scholar
Author	Miller, Jack Taylor, Lawrence A. DiGiuseppe, Michael Heilbronn, Lawrence H. Sanders, G. Zeitlin, C. J.
Copyright Year	2008
Abstract	Introduction: Exposure to space radiation will be a limiting factor in future manned missions to the moon. In contrast to the brief stays by the Apollo astronauts, in the coming decades humans will remain on the lunar surface for weeks and eventually months at a time. Chronic exposure to highly ionizing ions in the galactic cosmic radiation (GCR) and sporadic acute exposures to solar protons are serious hazards that can be mitigated in part by radiation shielding. The spacecraft, spacesuits and rovers will provide only modest shielding, and the expense of transporting material to the moon will allow for little if any artificial supplemental shielding material. An obvious alternative is the essentially unlimited supply of lunar regolith, if ways can be found to effectively use it. We have undertaken a study of the radiation transport and dose reduction properties of lunar regolith, using samples returned by the Apollo missions and several types of synthetic regolith and regolith simulant, with the objectives of evaluating regolith as potential shielding and of man-made regolith as a surrogate for use in ground-based studies. The use of synthetics and simulant is essential, owing to the extreme scarcity of Apollo soil. Fortuitously, particle accelerators originally designed for use in high energy physics and radiation therapy produce beams of protons and heavier charged particles at energies comparable to the most biologically damaging components of the GCR and solar protons. Measurements: Two sets of measurements have been made thus far at the HIMAC accelerator at the National Institute of Radiological Sciences, Chiba, Japan. A pilot study explored the projectile charge and mass dependence of radiation dose behind regolith for a single beam energy and the variation of shielding effectiveness of lunar mare and highland regolith from several sites, as well as synthetic regolith and simulant. A follow-on study measured the average energy deposition as a function of depth— essentially a depth-dose distribution—for a particular beam passing through one type of simulant. The methods are similar to those described in detail in Refs. [1] and [2]. The average energy deposited in solid state detectors by charged particles before and after passing through the samples was used to estimate radiation dose reduction as a function of regolith thickness. Sixteen different samples of regolith and simulant at areal densities between 6 and 13 gm/cm were exposed to a beam 400 MeV/u B ions. The percent dose reduction per unit areal density varied between 0.7% and 1.0%, comparable to aluminum and approximately half that of polyethylene (Fig. 1). No significant difference in dose reduction between Apollo samples, synthetic regolith and lunar simulant was observed. The similarity of regolith to aluminum when normalized to areal density is not surprising: the weighted average charge and atomic weight of typical lunar regolith is similar to that of aluminum. These results indicate that regolith simulant is an adequate substitute for lunar samples for purposes of radiation protection studies.
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Alternate Webpage(s)	http://www.lpi.usra.edu/meetings/nlsc2008/pdf/2028.pdf
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article