Investigations of cosmic-ray-produced nuclides in iron meteorites. VI: The Signer-Nier model and the history of the cosmic radiation

The simple model first proposed by Martin (1953) to describe the interaction of cosmic rays with meteoritic iron and subsequently used by Signer and Nier (1960) to calculate the spatial distribution of cosmogenic noble gas nuclides in spherical meteoroids is presently subjected to a rigorous mathematical evaluation. In the framework of the model, the abundance ratio of any two of the cosmogenic nuclides He-3, He-4, Ne-21, and Ar-38, is correlated with the ratio of any other pair of these nuclides. These ratios depend only on the effective irradiation hardness in the sample. The model-derived correlations agree with the corresponding experimental correlations, except for samples from relatively great depths. The model also makes it possible to derive a P(21)-He-4/Ne-21 diagram that predicts dependences on meteoroid size and sample depth; each location in this field being associated with a distinct combination of meteoroid size and sample depth.