Annual Deposition of Sr-90, Cs-137 and Pu-239, 240 from the 1961-1980 Nuclear Explosions: A Simple Model

Abstract

The annual deposition of Sr-90, Cs-137, Pu-239, 240, and Pu-238 were observed from 1959 to 1984 at the Meteorological Research Institute (MRI). In order to interpret the serial trends of the annual radioactive deposition at the MRI, a semi-empirical box model of atmospheric transport was developed. The model divides the atmosphere of the Northern Hemisphere into four compartments: the atmosphere above 21km, stratosphere below 21km, active mixing and exchange (AME) layer near the tropopause, and the troposphere. The transfer between the compartments follows the firstorder kinetics. The half residence times for transfer between upper and lower stratospheric compartments, between the lower and AME layer compartments, and between the AME layer and troposphere are 0.5, 0.7 and 0.3yrs, respectively. It is revealed that as a long-term monitoring of the annual deposition of radioactive debris in the mid-latitude area, the model quantitatively permits the calculation of stratospheric inventories and trends of annual deposition of debris injected into the stratosphere which are characterized by apparent residence times of 0.5 to 1.7yrs. This simple model is useful to predict the annual deposition amount of radioactive debris from the thermonuclear explosion for practical purposes.