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Salient: Victoria University Students' Paper. Vol. 28, No. 5. 1965.

Fallout Bogey Laid

page 11

Fallout Bogey Laid

It is impossible to discuss the ethics of nuclear testing in general or the proposed French tests in the Pacific in particular without some knowledge of their physical effects.

Since the countries most likely to be effected by the French tests are New Zealand and the Cook Islands, the Council of the Royal New Zealand Society set up a committee to study the effects of radiation from the explosions. It consisted of Dr. M. A. F. Burnett, Sir Ernest Marsden and Dr. A. M. O. Veale, and presented its findings in May, 1964.

The dispersal of radio-active substances from an atomic explosion depends on the size and position of the explosion. Should the test be low yield (that is, in the kiloton range) and at sea-level, the radio-active particles will remain in the troposphere, the envelope of air surrounding the earth. Within a few weeks these particle will be removed from the atmosphere by rain and, carried by the prevailing winds, may be deposited within a radius of 1000 miles.

Should the test be at sea-level and approach or exceed the megaton range, besides what remains in the troposphere a significant quantity of radio-active dust will be injected into the stratosphere, or upper atmosphere. The dust may re-enter the troposphere either at the polar regions, where, in the winter months, there are large sinking masses of air, or through a discontinuity in the tropopauses occurring in the temperate latitudes. Thus fallout front an autumn explosion in high latitudes will be deposited within a few months; but if the explosion is in the tropics it will take some years for fallout to mix with air from the troposphere in the temperate latitudes.

The length of time between the exploding of an atomic bomb and the depositing of radio-active substances varies then according to the size and position of the explosion. Radio-active substances with a short half life (a short period of time, that is, in which the frequency of radiations fall to half their original value) are unlikely to have a significant effect as stratospheric fallout. However, such substances as strontium 90 (half life—27.7 years), caesium 127 (half life—30 years) and carbon 14 (half life— 5700 years) will scarcely be affected by some years in the stratosphere, and may make a considerable contribution to radiation levels when they reach the troposphere and are deposited.

Hitherto most atmospheric testing has been carried out in the northern hemisphere, so that there is a higher concentration of radio-active material there than in the southern hemisphere. Though material from the higher concentration area will tend to drift towards the lower concentration area, fallout will continue to be less this side of the equator unless extensive further testing is carried out.

In fact, measurements taken at the National Radiation Laboratory and the Institute of Nuclear Science at Gracefield indicate that at present New Zealand has only one-quarter of the fallout of the corresponding northern latitude; and increases in radiation levels, at first sight alarming, are meaningful only if seen in relation to naturally-occurring background radiation. This includes cosmic radiation, radiation from rocks, medical treatments and luminous dials of watches. Everywhere it is large compared to the fallout from an atomic explosion, except in the immediate vicinity of the blast. There are many places where for generations the natural level has been 100 per cent higher than the average background value; in New Zealand and the Cook Islands, when due allowance has been made for the French tests, the overall radiation effects are not likely to exceed 5 per cent of the average background level.

For the reasons mentioned above, only the longer-living isotopes—strontium 90, caesium 147, and carbon 14—are likely to retain their radiation long enough to harm New Zealanders. Strontium 90 alone directly damages the health, producing the diseases widely associated with radioactive fallout—the various types of amnesia, for example. But such harm occurs only where an extremely large amount of radiation is received. The increase in the incidence of disease would be statistically undetectable in New Zealand.

Caesium 147 and carbon 14 are known to act on the gonads to affect the chemical nature of genes and hence produce mutations. Naturally-occurring mutation rates in man average about 15 mutations per million genes per generation (approximately 1 person in 50,000). If background radiation, which accounts for only 10 per cent of naturally-occurring mutations were doubled by fallout, the mutation rate would rise by no more than 10 per cent. However, the present rate of fallout in the United Kingdom would have to be continued indefinitely to produce an increase of 1 per cent. Even after the French tests the level in New Zealand is unlikely to approach the British figure.

If the tests in the Pacific are, as is probable, low yield, they are unlikely to affect the radiation level in New Zealand at all. Unless they are carried out between January and May, a season of westerly winds and high rainfall, they are extremely unlikely to affect the Cook Islands. If the tests are in the megaton range, the risk to either New Zealand or the Cook Islands is as described above, and harm will be statistically undetectable.

The report concludes that with care, accurate meteorological advice and patience, it is possible to avoid significant contamination of inhabited areas. The committee adds, however, that this conclusion is in no way to carry the inference that it favours the testing or considers it of little concern to New Zealand. It has considered solely the physical aspects of testing and has not discussed its psychological aspects. It feels that the chief danger lies in the use of weapons so developed in a global war.

Subsequently Sir Ernest Marsden has said that if the French use substances which lead to the presence of radio lend and plutonium in the construction material of the bomb, already present in the southern hemisphere from USA and USSR tests, the French explosion will not be as harmless as had previously been expected. These substances, which contribute towards lung cancer, may be left out of the bomb. The findings have been conveyed to the New Zealand Government and the Radiation National Committee of the countries concerned.

—A. M. Bisley.