Radioactive Isotopes on the Moon

Abstract

There has been an active interest in observing and accounting for radioactive products produced by cosmic rays in meteorites since the early suggestion by Bauer (1947) that the helium observed in meteorites was mostly produced by cosmic rays. The first searches for tritium in iron meteorites by Fireman (1958) led to the possibility of measuring the cosmic ray exposure ages of meteorites. By the time of the first lunar landing there were a number of laboratories engaged in measuring radioactive and stable products produced by cosmic rays in meteorites and earth bound satellites. These studies led to new knowledge of the period of time a meteorite fragment was exposed to cosmicP rays. It was found that stone meteorites were exposed for periods of 2 to 30 million years, whereas some iron meteorites were exposed for many hundreds of millions of years. By studying selected radioisotope pairs it was found that the galactic cosmic ray intensity has been essentially constant for the last 500,000 years (35Ar, 36Cl), and perhaps there has been a lower cosmic ray intensity a few billion years ago (36Cl–40K). Radioactive products were also applied to studying the gradient in the galactic cosmic ray intensity within the solar system as a result of modulation by the magnetic fields associated with the solar wind. Many studies were made of the distribution of cosmic ray spallation products in meteorites and these data were interpreted in terms of nuclear cascade processes. Information on these various topics can be obtained from reviews and numerous original papers [1, 2].KeywordsSolar FlareLunar SurfaceLunar RegolithLunar SoilIron MeteoriteThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.