Measurements of radon emanation from Apollo 11, 12, and 14 fines

Abstract

Less than 0.13% of all 222Rn atoms produced in Apollo 11 fines 10084 emante from this material at temperatures ranging from about 25–35°C and a pressure of about 10 −2 torr. The value for Apollo 12 fines 12007 is < 0.73% or < 0.57%, depending on the adopted U content. For the combined Apollo 14 fines 14003 + 14259 we find a minimum value of 0.23%, and a maximum value of 0.55%. Emanation of 220Rn has been observed in the case of the Apollo 14 fines. The relatively small emanation rates could be due to the absence of interstitial air and water on the lunar surface as has been suggested by Lindstrom et al. [5]. However, it seems also possible that U and Th are principally contained in the lunar fines within minerals which are intrinsically poor radon emanators, such as zircons. The small emanation rates require 100% 222Rn escape from a regolith thickness of about 10 m (U ∼ 4 ppm) to explain the observed 210Po activity in Mare Tranquillitatis by Turkevich et al. [3]. However, this problem cannot be settled satisfactorily until emanation measurements have been made at temperatures of about 120°C.