Radiation thresholds

published in:
New Scientist

30 October 04


In the light of the series of letters you have published on nuclear power, a study that calls into question the "linear no-threshold" (LNT) theory of radiation may be of interest.

In 1983 a group of 180 apartment buildings was completed in Taiwan. Somebody had made a serious mistake. They had mixed into the concrete a considerable amount of highly radioactive cobalt-60.

This meant that ultimately, for a period of between 9 and 20 years, 10,000 people lived in buildings so radioactive that when it started they were receiving an average of 74 millisieverts of radiation per year, a level that declined thereafter because cobalt-60 has a half-life of 5.27 years. Compare this with the rate of 0.5 mSv above background--the normal maximum exposure for radiation workers--or a total of 15 mSv, the maximum safe limit for land fit for habitation, according to US government standards.

With the LNT theory, which is currently in use worldwide for assessing nuclear risks, there is no lower limit for the level at which radioactivity is lethal for humans (hence the term "no threshold"). So these buildings, inhabited for a decade and a half before the radioactivity was traced and measured, should be the site of a truly massive cancer death rate.

They aren't.

A thorough and methodical tracing of all the 4000 families by a team led by W. L. Chen of Taiwan, director of medical radiation technology at Taiwan's National Yang Ming University has resulted in an unequivocal and spectacular result. Cancer rates of people who had lived in those highly radioactive buildings are down to 3.6 per cent of prevailing Taiwanese rates. The full report is available in English on www.jpands.org/vol9no1/chen.pdf .

For many years there has been an unfashionable alternative to the LNT theory called hormesis. This claims that intermediate level radioactivity actually stimulates life and improves health. There has been significant evidence for this (the deaths at Hiroshima did not appear to fit the LNT pattern, there are places in India and Iran with background radiation of 15 mSv or higher and with no observed increase in cancer, and numerous studies of radon in homes have found a reverse correlation between radon levels and cancer rates). Nonetheless, such has been our fear of all things nuclear that the LNT theory has been absolutely accepted, despite the fact that there has never been any actual evidence for it.

This study, however, is so detailed, has such well-defined boundary conditions, and has such a clear result (proving a reduction in cancers of 96.4 per cent) that there can no longer be any intellectual doubt whatsoever. Radioactivity in low doses is good for us.

The effect of this proof on our nuclear power industries can hardly be underestimated, since with the collapse of the LNT go most of the fears that have so crippled them. The implications for medicine, however, cannot even begin to be estimated, as the way is now open for serious research on how hormesis works and how it can be used to serve us.

It is interesting to note that the healing water from the world's great spas has always been mildly radioactive and that medicine has up to this point been unable to find out why. I wonder what the future holds for such places.

Neil Craig

Glasgow, UK