Cosmogenic and Primordial Radionuclides in Lunar Samples by Nondestructive Gamma-Ray Spectrometry

Abstract

The ⁷Be, ²²Na, ²⁶Al, ⁴⁴Ti, ⁴⁶SC, ⁴⁸V ⁵¹Cr, ⁵⁴Mn, ⁵⁶Co, ⁵⁷Co, ⁵⁷CO, ⁴⁰K, ²³⁸U, and ²³²Th were measured in lunar fines and portions of three rocks. Major production of cosmogenic radionuclides is due to solar protons, thus their concentrations are far different than those in meteorites. Surface exposures of the rocks and fines are long compared with the 0.74 million year half-life of ²⁶Al. Lunar fines show substantially higher concentrations of low energy reaction products. The ratios of thorium to uranium are extremely constant at 3.8, which indicates very little geochemical differentiation and are in good agreement with a common nucleosynthesis for lunar and earth materials.