The assessment of late effects on a population exposed to activity released into the environment

The long term effects resulting from an accidental release of radioactive material are considered. The magnitude of the release is defined in terms of the percentage of total excess cancer mortalities relative to the number that would have been expected in the same population had the accident not occurred. The increased risk is expressed as the change in life expectancy as a function of age at the time of exposure. Loss of life-years per person is calculated for an increase of 0.1, 1, 10 and 100% in cancer deaths and are quoted for ages 1, 10, 20, 30, 40 and 50 years at time of exposure. The variation of the effect with age may be summarised using the ratio of the reduced life expectancy to the reduced life expectancy for a person aged zero at the time of the accident. For the initial external dose, this ratio exhibits a linear decrease up to about age 45 years at the rate of about 2% per year so, for example, the increased risk for a person aged 40 at exposure is 20% of the increased risk of a child just born. Similar estimates are made for a dose which is prolonged over 50 years, to represent doses from internally incorporated radionuclides.