Work On Fall-out In U.K. Described By Scientist

Press, Volume CI, Issue 29722, 16 January 1962, Page 13

Work On Fall-out In U.K. Described By Scientist

While in the United Kingdom under a Nuffield Foundation fellowship Dr. T. M. Morrison, senior lecturer in the plant science department at Lincoln College, worked for a short time on the measurement of radioactive iodine fall-out after the recent series of Russian bomb tests. This work was done at the Agricultural Research Council’s radiobiological laboratory at Wantage, in Berkshire.

Dr. Morrison said that the laboratory, which was responsible for measurement of radioactivity in agricultural products, had been taking milk samples daily from all over Britain for analysis for iodine 131.

The milk was made into what was virtually a cheese and this was cut up to fit a counting device known as a multi-channel analyser. This device was able to separate out the emissions of activity according to their energy, and by setting it on an energy appropriate for measuring iodine it was possible to detect all of the iodine activity.

"It is essentially a simple device but in operation it is anything but simple,” said Dr. Morrison.

An example of how quickly and efficiently this laboratory was producing results was given by Dr. Morrison. At a meeting in London which was discussing this programme the director of the institute was able at afternoon tea to tell those present the amount of radioactive iodine there was in the milk they were having with their tea.

Drop in Level When winter came on and the cows were taken inside for feeding. Dr. Morrison said, the level of iodine in the milk suddenly fell off. This decline was also due to the natural decay of the iodine in the fall-out

Dr. Morrison said that radioactive iodine decayed quickly—it had a "half - life of only about eight days. Therefore most of the initial energy from fall-out was iodine 131.

Its importance was due to its concentrating in the thyroid of particularly young children under one year who were taken off mothers' milk and put on to cows’ milk. A permissible level of iodine had been settled on assuming that a child drank so much milk a day and ate no food, and allowing a considerable safety factor. It was the duty of the laboratory to see that over a year the level did not exceed the permissible figure as it was possible for persons to stand a high dosage tor a.short time. Noting that milk powder had been stored up for feeding to young children if the levels became too high. Dr. Morrison said that because of the quick decay of radioactive iodine it would be possible to hold fresh milk for two weeks, after which it would be quite safe again, with milk powder being fed in the interim period. Big Bomb

Dr. Morrison said that there was no more iodine in the fall-out after the 75 megaton bomb than there had been from some of the earlier bombs of one megaton and less. This was possibly because it had been set off at a great height so that less dust had been sucked up to return to earth in radioactive form. “The initial scare is now over,” said Dr. Morrison. “The iodine has now all decayed and now they are getting the other isotopes coming in—mainly strontium 90.” Discussing the dangers of radioactive fall-out Dr. Morrison said an important point was that the whole population could stand a level of activity a great deal higher

than any small group. However, any activity would cause some damage so it was obviously necessary to steer a middle course. When damage became significant would vary from individual to individual and depending on

circumstances. There had always been a background of radioactivity and the level people were now getting from tests was actually less than the total background. While he might be exceptional, Dr. Morrison said that Sir Ernest Marsden, who had worked with radioactivity for a very long time and had been exposed to very high radiation, was one of the fittest men that he knew. Dr. Morrison’s interest in radioactivity is in the use of isotopes as tracers in following the absorption of mineral nutriments by plants. At Wantage he was looking into the absorption by plants of radioactive thorium, one of the decay products of uranium.