I was looking through a popular junior science primer recently. It is generally a clearly written exposition of some basic principles of physics, chemistry and biology. Various general remarks are made in the introductory chapter, e.g. on the sources of energy used by society. Ia the few paragraphs devoted to nuclear energy, my eye was caught by a description of the health effects of the ionising radiation released when the atomic bomb: (A bomb) was exploded our Nagasaki in 1945. The description echoes a widely held exaggerated view of the effects of the radiation released in the explosion.
Specifically, the authors say the radiation released in the bombing killed 25,000 people, and, subsequently, numerous genetic defects were noted resulting from exposure to the radiation. The truth of the matter is that the effects of the radiation alone were not as severe as this, and, so far, the Japanese A bomb data provide no evidence of genetic damage.
Let me say at this stage that I have no intention of trying to minimise the consequences of the use of the first atomic weapons on Japan. I believe science betrayed itself in developing the atomic bomb and that the first use of the bombs was a turning point not only in warfare, but in history. I also accept that in both cases, i.e. development of the bomb and use of the weapon, powerful arguments applied. But that is a story for another day.
The data on the survivors of the atomic explosions in Japan are the single most important study on which estimates of the health effects of human exposure to ionising radiation are based. Scientifically, the data are very good, and results based on their analysis are used in setting standards to ensure protection of workers and the public from ill health effects arising from useful applications of the use of ionising radiation, e.g. in medicine.
Two A bombs were exploded in Japan at the end of the second World War. The first was exploded over the city of Hiroshima on August 6th, 1945, and the second over the city of Nagasaki three days later. Although small in comparison to the nuclear weapons now available, the explosive power of the first Abombs was immensely greater than that of conventional bombs. The explosive power of the Hiroshima bomb was equivalent to about 15 thousand tons of TNT, and that of the Nagasaki bomb to about 25 thousand tons of TNT.
Atomic bombs differ from conventional weapons in that their explosion releases large amounts of radioactivity and radiation in addition to the tremendous heat and blast energies.
Hiroshima had a civilian population of 250,000. Some 45,000 people died on the day of the explosion, and a further 19,000 died within the next four months. Nagasaki had a population of 174,000. Some 22,000 people died on the first day, and 17,000 more during.
The next four months. These are recorded civilian deaths. Unrecorded deaths of military personnel and foreign workers may have added significantly to these figures.
It is impossible to estimate what proportion of these 103,000 deaths were caused by radiation alone, rather than by the extremely high temperatures and blast pressure caused by the explosions. It is known that the radiation effects alone would have been sufficient to kill a majority of those exposed within a kilometre of ground zero (i.e. the point below which the bombs exploded), within days or weeks. However, most of those who died in this area would have been killed more or less instantly from the effects of blast, fire and falling buildings. In other words, they died in ways indistinguishable from the countless people who died in conventional bombing attacks on Cologne, Essen or London. Actually, the loss of life in the A bomb explosions was considerably less than from the fire raids on Tokyo a few months before, or on Dresden the previous year, when 130,000 people died.
A commission was established immediately after the end of the war to study the long term effects of exposure to the atomic radiation on the health of the survivors. This work continues to this day and is called the Life Span Study (LSS). The two major ill health effects that may result from exposure to ionising radiation are (a) cancer, and (b) transmission of a hereditary defect to the next, and/or later generations. Excess cancers have been noted amongst the survivors of the A bomb explosions. However, it is too early yet to get significant results on genetic effects (if there are any).
A total of 86,572 people who survived the atomic explosions have been followed up in the LSS study. 52,200 of these received significant doses of radiation - average dose 260 mSv (we each receive an annual dose of about 3 mSv in Ireland, mostly from natural radiation). The first type of cancer to emerge after exposure to radiation is cancer of the blood - leukaemia. Among the 52,200 significantly exposed survivors, 176 died from leukaemia between 1950 and 1990. Of these, 6 (49 per cent) are attributable to radiation exposure.
Solid cancers show up after the leukaemias. In the significantly exposed group, there were 4,687 deaths from solid cancers between 1950 and 1990. Of these, 341 are attributable to radiation, i.e. 7 per cent. Of the 4,863 total cancer deaths in this significantly exposed group, 427 (9 per cent) are attributable to radiation exposure. In other words, the other 91 per cent of cancer deaths would have occurred anyway, if no atomic bomb explosions had occurred.
Essentially, everything we know about radiation induced transmission of hereditary defects comes from laboratory experiments with animals. The largest group of humans available for such a study is the Japanese survivors of the A bomb explosions. However, in order to get statistically meaningful data in the study of transmission of hereditary defects, very large numbers of subjects are necessary, and the Japanese cohort is rather small by these standards.
Also, insufficient time has passed since exposure to the radiation. Several generations must elapse before the full extent of any effects would be expected to show up. At the present time there is no evidence of any genetic changes in the children born to the Japanese survivors.
The 20th century has produced many powerful symbols by which it will be remembered. An example of a good symbol is the image of Neil Armstrong standing on the moon. Two examples of bad symbols are the swastika and the huge mushroom cloud rising into the sky. I believe the latter is the worst of all, and that it has deeply scarred the human psyche for more than 50 years.