Professor Wade Allison of the Department of Physics at Keble College Oxford has written an article that looks at the safety of nuclear radiation on the human population.
In simple terms the effect of ionising radiation on life may be described by a plot of damage against dose. Such characteristic curves may be made for single cells examined in vitro, for individual organs and for complete creatures. In the absence of perfect data some assumptions have to be made. The mathematically simplest solution is that the characteristic is linear, a straight line through the origin with slope alpha
damage =alpha x dose
This is called the Linear No Threshold (LNT) assumption and the consequence of adopting it is made clear in this quotation from Sir Richard Doll
Whether there is a threshold dose below which no effect is produced is still open to doubt, but on present knowledge it seems unlikely that any such threshold exists. It must, therefore, be assumed that even very small doses produce some small risk.
However, mathematical simplicity is unusual in the natural world and such an assumption cannot be justified unless uniquely required by observational data.
You can read the full article here.
There is considerable evidence for the threshold & indeed for a beneficial effect for low levels of radiatio.
Those US states with high levels of background radiation generally have lower cancer rates; the negative relation between radon in homes & lung cancer has been repeatedly demonstrated, most thoroughly by Profesor Cohen http://www.world-nuclear.org/sym/1998/cohen.htm ; the hormesis effect on plants, microbes & lab animals (where unlike humans experiment is ethical) have, repeatedly, for over a century shown the hormesis effect & are not now disputed; health records of nuclear reactor workers, nuclear naval dockyard workers & UK radiologists have all shown improved health; a Taiwanese apartment complex, built with steel contaminated by Co60 & which is as close to a controlled human experiment as possible, showed a cancer reduction of 97% compared to the population at large http://www.jpands.org/vol9no1/chen.pdf ; there are parts of the world like Kerala in India where natural background radiation is anything up to 200 mSv a year, 13 times the official safe limit yet no adverse effects have been noticed over thousands of year; in the disgravceful & quite unscientific decision in 1964 to quietly euthanase a herd of cows exposed to a bomb test in 1946 having achieved extreme longevity; in the failure of Chernobyl to produce any statistical increase in long term cancers let alone the up to 250,000 predicted.
See also http://a-place-to-stand.blogsp.....l/Hormesis
Or perhaps there is some scientist somewhere in the world who will disagree with a UK government committee & say there is real evidence for LNT??
A small comment:
For example some investigations (D.J. Strom, DOE Conract, 2003) show that for acute uniform dose less than 30mSv not any early, deterministic, effects (no effects on human) are observed.
Late effects –stochastic- are approximated with linear function between dose and risk in the interval 0-150mSV.
Limit for the individual effective dose for the population is 1mSv/Year (0,15mSv/Year from gaseous and liquid discharges) during NPP normal operation or deviations and 5mSv/Year for the first year after design basis accident (in our Regulations and many others).
Occupational yearly limit is less than 50mSv and optimized much bellow this limit (many times).
The accepted regulatory limits are low enough to decrease to minimum the health effects on the population, environment and workers.