Radon Flux Density In Conditions Of Permafrost Thawing: Simulation Experiment

Abstract

This paper describes a five-month experiment (February – July 2021) measuring the gradual thaw diffusion of radon-222 (further in the article – radon) from a frozen environment in NW Russia (i.e. Arhangelsk region). Red clay substrate containting a high content of 226Ra filled the bottom insides of 200-liter barrel holding the source of radon and buried at 1.6 m depth (e.g., the radium source zone), then covered with native soil, filled with water and frozen under in-situ conditions. Radon measurements were carried out from soil surface above the container (disturbed soil layer) and at background location (undisturbed soil layer). Several periods of increased radon flux density were observed, which was related to radium source zone thawing. It was shown that in 1-2 days after thawing of the radium source zone and drying of the upper soil layer, the radon flux increases sharply – more than 8 times compared to background values. These results show a strong relationship between radon flux density and soil temperature profiles at different depths. The calculations of radon sourced from frozen and thawed zones show how temperature phase of substrate (e.g. clays) control the barrier influence of radon migration. It reduced them by 10-20 times (according to the results of a theoretical calculation), depending on the characteristics of frozen rocks (density, porosity). Thus, the barrier function of permafrost is related to the physical properties of ice and frozen rocks. These temperture phases controls radon emanation coefficients and significantly influences the migration of radon to the earth’s surface.