The Behavior of 137Cs and Other Fallout Radionuclides on a Michigan Dairy Farm

Abstract

The behavior of the fallout radionuclides ¹³⁷Cs, ⁵⁴Mn, ¹⁴⁴Ce-Pr and ⁹⁰Sr in the milk-food chain was studied at a commercial dairy farm near Tecumseh, Michigan during 1964 and 1965. The main purpose of the study was to develop mathematical models to describe the movement of radionuclides from air to milk. Three models are presented: the first predicts the total deposition on precipitation collectors given the air concentration and rainfall rate; the second predicts the concentration in forage from air concentration, rainfall rate, and the rates at which the forage grows and is consumed by the dairy herd; the third predicts the milk concentration from the concentration in each type of feed and the rate at which each feed type is consumed by the dairy herd. The first two models are applicable to all four radionuclides but the milk model is valid only for ¹³⁷Cs. Milk concentrations for the other three radionuclides are treated individually. The model for deposition on precipitation collectors was developed independently and is shown to predict weekly deposition rates to within a factor of three (95% of the time). This uncertainty is reduced as the time span for the prediction is increased. Development of the other two models was based in part on data from the Tecumseh study; both still require independent verification. The forage model fits the weekly experimental data to within a factor of 2.2. The milk model fits the weekly measurements of ¹³⁷Cs concentrations to within a factor of 1.5. The error of the latter 2 models also decreases as the time span for the prediction is increased.