The caesium‐137 content of man related to fallout in rain, 1957–76

Amounts of ¹³⁷Cs in residents of Central Southern England were smaller during 1974–76 than at any time during the previous 17 years, and 17 times lower than those recorded during 1964–65. A simple model has been developed, empirically relating ¹³⁷Cs in rainfall during 1957–76 to the ensuing burdens in man, and the results suggest that a slowly‐declining reservoir of deposited material from the weapons tests of 1955–63 currently contributes as much dietary contamination as the low levels of recent fall out. ¹³⁷Cs burdens are therefore unlikely to decline by more than a factor of 2–3 during the next decade, even in the absence of additional weapons tests. The radiation dose rate from the current (early 1977) average level of ¹³⁷Cs in these subjects is however only one percent of that delivered by the body's natural ⁴⁰K.