Production and transfer of cosmogenous tritium in the Earth atmosphere in the «PARMA» model

Abstract

The paper analyses contribution of reactions (n,X) and (p,X) on nitrogen and oxygen nuclei to the production and transfer of cosmogenic tritium in the Earth atmosphere. To calculate the fluxes of secondary protons and neutrons in the nuclear-electromagnetic cascade, the analytical model «PARMA» was used. The model is based on analytical approximations of both numerous experimental data and computer simulation data, and allows one to calculate the fluxes of various particles of secondary cosmic radiation (nucleons, muons, a- and b-particles) with the choice of a given energy range, atmospheric height, geomagnetic cutoff rigidity, solar activity. The problem of vertical turbulent diffusion of tritium in the Earth's atmosphere was solved and the dependence of its concentration on altitude was obtained. Numerical integration of the transport equations was carried out using the integro-interpolation method. An estimate of the total reserve of cosmogenic tritium in the Earth's atmosphere, balanced by turbulent diffusion, decay and cosmogenic formation, was given, which amounted to ~1.9∙10¹⁷ Bq. The calculation results show that the earth's atmosphere contains no more than 10% of all cosmogenic tritium. The results are generally consistent with earlier empirical and semi-empirical models confirming that man-made tritium currently accounts for the majority of the total tritium supply