For weak or medium-strength doses, the effects are not as clear-cut and predictable as they can be for stronger bursts of radiation. The large role played by chance in determining the potential effects of exposure has led to such effects being termed probabilistic.
These probabilistic effects correspond to cellular transformation rather than destruction, whose effcts occur generally years after the original exposure.
Symptoms such as cancers or genetic problems appear some considerable time after the radiation which may have caused them, and are therefore very difficult to distinguish from identical symptoms with different sources. Other potential causes of cancer include chemical poisoning, tobacco smoke and exposure to UV light.
In the probabilistic domain of weak doses below 100 mSv, it is the probability of a cancer appearing - and not its seriousness - that goes up with increasing dose. On an individual level, if a cancerous tumour appears a few years after exposure to radiation, it is impossible to make any valid causal connection. There is no tags allowing to link the symptoms to radioactivity.
In the general public mind, it is common to associate a cancer or a death with even a low dose of radioactivity. Such is the case for the widespread belief that a lot of people in France have developed thyroid cancers related to the Tchernobyl accident. Clear-cut cause-effect relationships are rare, and such connections can only be assumed for either very high doses or very specific symptoms. An example is the large proportion of lung cancer sufferers among uranium miners in the 1950’s before an adequate ventilation had been installed in uranium mines . In the case of the civilian and military personnel who developed cancer after working near French nuclear bomb sites in the Sahara or in Mururoa in the 1960’s, the situation is not clear. In principle Doses were low in average, but in some cases exposures may have been higher for individuals than estimated at the time.
As a case study we can examine the death of the American actor John Wayne, which several newspapers attributed to exposure to radiation. Wayne died at 72 of stomach cancer, 25 years after having played Genghis Khan in a 1954 motion picture filmed in the Nevada desert. The filming site was within a hundred mile radius of Yucca Flats, one of the American nuclear bomb test sites.
Was the time he spent in this radioactive area responsible for John Wayne's death? Let's ignore the sensationalist melodrama proposed by the French tabloid France-Dimanche in July 2007, suggesting that 'the Duke' had been exposed to a dose 400 times over the lethal limit. Had that been the case, the actor would never have made it into 1955. His cancer may have been provoked by the unfortunate choice of filming location, but John Wayne was a heavy smoker and the radioactivity may not have been his main problem.
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