Production and Transport of Cosmogenic Tritium in the Earth’s Atmosphere in the PARMA Model

An analysis is performed of the contribution from reactions (n, X) and (p, X) on nitrogen and oxygen nuclei to the production and transport of cosmogenic tritium in the Earth’s atmosphere. Fluxes of secondary protons and neutrons in a nuclear–electromagnetic cascade are calculated with the PARMA analytical model. PARMA is based on analytical approximations of data from numerous experiments and computer simulations that allow us to calculate the fluxes of different particles of secondary cosmic radiation (nucleons, muons, a- and b-particles) using a variety of energies, atmospheric heights, geomagnetic cutoff rigidities, and solar activities. The problem of vertical turbulent diffusion of tritium in the Earth’s atmosphere is solved, and the dependence of its concentration on altitude is obtained. Transport equations are integrated numerically by means of integro-interpolation. The estimated total amount of cosmogenic tritium in the Earth’s atmosphere, balanced by turbulent diffusion, decay, and cosmogenic formation, is found to be ~1.9 × 10 Bq. Calculations show that the atmosphere contains no more than 10% of Earth’s cosmogenic tritium. Results are generally consistent with earlier empirical and semiempirical models, confirming that anthropogenic tritium currently accounts for most of the total amount.