2025
Volume 25, Number 1/2, pp. 8-45
Deaths from radiation-induced cancer amongst the Hiroshima and Nagasaki bomb survivors
P. Thomas
Faculty of Science and Engineering, University of Bristol, Queen’s Building, University Walk, Bristol BS8 1TR, UK
It is now possible, as the 80th anniversary of the atomic bombing of Hiroshima and Nagasaki approaches, to estimate, with good accuracy, the long term effect of the flash of radiation released by the two bombs in early August 1945. While, in the past, there have been fears that delayed effects would very seriously impair the lives of all those who survived, it is clear, now that most of the evidence is in, that deaths of survivors caused by radiation will make up only one or, at most, two per cent, of the total number. Industrial pollution may provide the closest analogy to the damage to human health the radiation has caused in the long term. Survivors will have faced an additional chance of death that is between 20 and 40 per cent of the probability of dying from man-made air pollution in the UK. The long delay between exposure and possible death means that even those who die prematurely will probably have lived a long life. Even survivors receiving an average dose of 2,250 mGy, far above the threshold for acute radiation sickness, can expect to live to a median age of 78 years 169 days, nine months more than the life expectancy at birth for an infant born in the UK in 2000, and a year and ten months longer than an American baby born in that year could expect to live. The average survivor can expect to lose about 1½ months of life compared with an inhabitant of one of the two cities who received a negligible dose. The survivors of the atomic bombs have shared in the general uplift in Japan’s life expectancy since the end of the Second World War. Despite the slightly elevated risk the survivors have faced as a result of their exposure to radiation in 1945, their lives will, on average, have been decades longer than those of their forebears. While the Life Span Study (LSS) carried out by the Radiation Effects Research Foundation (RERF) starts on 1 October 1950, the time of a national census, this paper uses actuarial methods to explore the period from August 1945 to 1 October 1950 as well. This is allowed by introducing the notion of an LSS Core Precursor Cohort, which is a superset of the LSS Core Cohort used in the RERF studies. Probabilistic modelling, common in reliability engineering, is then applied to assess the number of deaths from radiation-induced cancer, both solid cancer and leukaemia, there will be amongst the members of the LSS Core Precursor Cohort in the 110 year period between the dropping of the bombs and 2055, when the youngest possible survivor will be 110 years old. The results for this cohort are then extended to the whole population of survivors, including the military survivors who returned to their homes across Japan after the war.