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62
From the bombs released in North Russia a cloud of fall-out rose,
passing in an easterly direction to reach this country some days later. At
this stage radio-active iodine is the most important component. In the
Spring of 1962 there will be further danger. By this time the radio-active
iodine which has a half-life of only eight days will have disintegrated and
the dangerous components will be the strontium 90 which has a half-life of
many years. The contamination in the Spring will come about because the
radio-active cloud which has risen into the stratosphere will descend in the
troposphere gap. Although the largest amounts of radio-active dust from
this series of bombs will be expected to fall in the Spring of 1962, there
will be further, though smaller falls, each Spring for at least ten more
years.
The degree to which this country is exposed to contamination from
this series of bombs set off in the locality they were, depends partly on the
height at which they were released and partly on the composition of the
bombs. Deposition from large explosions is most rapid when debris is
released into the lower stratosphere in high altitudes during the autumn
and on such factors as latitude and the time of the year. The largest are of
the fission-fusion-fission type. The first fission element is to set-off the
rest of the bomb. The dirtiness of an individual bomb depends on the
extent to which it is made up of the dirty fission element as compared
with the cleaner fusion part.
When it became apparent that the new series of explosions might
lead to appreciable amounts of radio-active elements in the air, the
Agricultural Research Council Radiobiological Laboratory started
examining milk from eight depots or farms located in different parts of
England and Wales, Scotland and Northern Ireland. This was later
expanded to collections from twenty sites. Most of the samples were
examined daily for iodine 131, and were also examined for strontium 90.
The results of the earlier examinations suggested that if larger bombs
were released, the amounts of radio-active iodine in the milk might reach
dangerous levels and be a danger to infants under one year of age consuming
such milk. Those of about six months of age would be at greatest
risk because they would be the greatest consumers of the milk. The
Government therefore made arrangements for supplies of dried milk,
sufficient to be able to provide 1½ pints of reconstituted milk daily for
each child under one year of age, to be available. In point of fact at no
stage did the amount of radio-active iodine in milk reach a sufficiently
high level as to be at all dangerous. The highest level reached was
sufficiently low that it would have been necessary for milk containing that
contamination to be consumed for six months before it became dangerous.
This could come about of course only if the bombs were released continously
over this period. That the later larger bombs did not present the
danger apprehended from the consideration of the fall-out from the
earlier smaller ones, might have been due to the larger ones being release
at greater heights, but also probably because they were cleaner bombs.