Record of cosmic-ray intensity in the meteorites

Extensive data now exist on the abundance of radioactive and stable nuclides produced by cosmic rays in iron meteorites. Half-lives of radioactive species range from 16 days to 1.2×109 years. In this paper these data are compared with calculated production rates based on derived energy spectra of nuclear-active particles in meteorites and experimental excitation functions. Both relative and absolute amounts of the various species are in approximate agreement if the flux of cosmic rays is assumed not to have varied. The variation, averaged over the half-life of each species, does not appear to exceed a factor of 2 in any case, except possibly K40, for which the data are still insufficient. It is concluded that the cosmic-ray intensity has been constant, in this sense, at least over millions of years.