Spatial distribution of the atmospheric radionuclide production by galactic cosmic rays and its imprint in natural archives

Abstract

We used the GEANT4 toolkit to simulate the altitude and latitude profiles of the production rate of 14C, 10Be and 36Cl radionuclides by the galactic cosmic ray (GCR) interactions in the terrestrial atmosphere at a varying geomagnetic field. We found that applying two intranuclear cascade models incorporated in GEANT4 (Binary Intranuclear Cascade, BIC, and Bertini Intranuclear Cascade, BERT) result in significantly different production rate values. We present the conclusions about the certain model relevance to the abundance of these isotopes in the surface fallout, ice-core records and lunar soil depth profile. Comparison of our simulations with the recent publication of Poluianov et al. (2016) shows a good agreement for 14C (BIC) and 10Be (BERT) and a definite by the factor 2–3 difference in the 36Cl (BIC) atmospheric yield functions. Also, the mean level and amplitude of the 10Be variations in polar ice from central regions of Antarctica and Greenland could be accounted for its tropospheric production by GCRs. The fallout rate of 36Cl there can be explained assuming its additional input from the stratosphere. Significant additional variations of radionuclide sedimentation rate in polar regions may arise due to tropopause height changes even at a constant atmospheric production rate of the certain isotope.