Neutron activation terrestrial

Elzie, J. L. Neutron Activation of Silver, Cadmium, Indium, Tin, Antimony, Tellurium, and Iodine Analysis of Meteoritic, Terrestrial, and Lunar Materials. Thesis. University of California, Los Angeles (1972). 135 p. 26 52906... 

When these isotopes decay they form numerous active daughter nuclides with different half-lives. Nuclear reactions of the neutrons from cosmic radiation produce tritium ( H) and C. These enter the biosphere by way of air currents and precipitation and are therefore classified as terrestrial radiation. In part, the decay of some extremely long-living isotopes ( K, Rb) that have existed since the earth was formed is also responsible for terrestrial radiation. These isotopes form inactive disintegration products. Rocks may also contain radionuclides, but to greatly differing extents the average is 0.5 mSv/a. 

---