Physicist Assesses Effects Of Nuclear War

Press, Volume CII, Issue 30156, 13 June 1963, Page 12

Physicist Assesses Effects Of Nuclear War

A nuclear-free zone covering the whole of the Southern Hemisphere would protect the future of human life on this planet, because calculations of fall-out showed that a, nuclear war which could conceivably destroy nearly all human life in the temperate regions of the Northern Hemisphere would have relatively little effect in this hemisphere, Mr J. F. McCahon, senior physicist of the Dominion X-ray and Radium Laboratory, Department of Health, said yesterday.

Mr McCahon had been asked what fall-out New Zealand could expect from a nuclear war in the Northern Hemisphere.

“In view of claims that nuclear war anywhere on earth could wipe out life everywhere, and of stories such as ‘On The Beach.' which imply the same idea. I decided recently to see whether this was in fact likely,” said Mr McCahon. “Using figures published by the United Nations Scientific Committee on the Effects of Atomic Radiation, I found that it just would not happen.” The pattern of fall-out resulting from all bomb tests in the Northern Hemisphere up to 1960 indicated that an all-out nuclear war in that hemisphere would give, at a probable maximum, about four times as much exposure to human populations in the latitude of New Zealand during the following 40 years as was recommended as a limit by the International Com-

mission on Radiological Protection. This level would result in significant genetic damage, but not in disaster. The effect on the individual in the way of leukemia and other somatic ills should be negligible, ds the dose would be much below the maximum recommended by the commission for workers habitually exposed to ionising radiations.

"These figures are. I repeat, a probable maximum, assuming that all bombs are exploded in the atmosphere and not on the ground or in the sea. that all are fission bombs and not fusion, that they are let off In the northern tropics and not further north, and that the whole world stockpile assumed now to exist —a quoted figure is 40.000 megatons—is exploded.” said Mr McCahon. “What the stockpile really is. and what it may be in a few years, is, of course, the great unknown.

“It is much more likely that the ratio of fission to

fusion and of air burst to ground burst in the bombs exploded during the war. and the latitudes at which they were set off. would be much the same as in the tests and that the material detonated would be less than the stockpile. Fall-out would vary directly with the amount exploded

“On this basis, and assuming bombs rated at 10.0<K» megatons were exploded, the total genetic effect of the fallout in the southern temperate latitudes as a result of the war would be equal to an extra 10 years' natural background radiation spread over tihe first 40 years after the war. or to 28 years' natural radiation if a 20,000-year period is considered. These figures are well inside the safety levels proposed by the international commission. "New Zealand is in the peak radiation fall-out belt for the Southern Hemisphere Lower and higher latituaes would both get less fall-out than the temperate zone." Asked what the position would be in the northern temperate zone. Mr McCahon said this was anybody's guess, as most places in the zone would be within the plume of heavy contamination downwind of one or other of the explosions. Tn the few areas which missed this, the effect would be at least 10 times as great as in the corresponding Southern Hemisphere regions. After 40 years or so. the level in the Northern Hemisphere would have fallen to much the same as in the Southern Hemisphere. since most of the remaining radiation dose would come from the long-lived carbon-14, which by then would be spread fairly homogeneously through the carbon dioxide in the atmosphere.