On the Influence of Cosmic Radiation on the Isotopic Composition of the Elements

When cosmic radiation interacts with the atomic nuclei of the atmosphere, it produces a great number of stable as well as radioactive isotopes. The radioactive isotopes are fairly easy to detect but the production of stable isotopes can only be detected by the changes in isotopic composition of the elements that might be caused by this effect. The amounts of Li⁶, Ne²¹, and A³⁶ that are produced in this way have been calculated. If the mean intensity of cosmic radiation in the past has been the same as at present it turns out that the production of these isotopes causes a change in isotopic composition which is barely detectable.

A study of this effect gives a possibility of obtaining information about the cosmic-ray intensity in the past. If no cosmic-ray effect is found, it shows that the mean cosmic-ray intensity in the past could not have been considerably higher than at present. If the cosmic-ray intensity during the earlier stages in the earth's evolution were higher than at present, one could expect easily detectable changes in the isotopic composition of some elements.