I.. J. DWYER, J. H. MARTI\ AND E. W. TITTERTOX 



from ^^^I, ceases to be an appreciable fraction of that from ^•''^I in mixed 

 fission-products after seven days. The contribution from isomeric ^^^Xe, 

 although increasing for a short time, is not appreciable at any stage. 



Experiments conducted by Bustad et al.^ entailed the continuous feeding of 

 radioiodine to sheep over entire lifetimes. They observed no biological 

 damage to sheep fed 150 m[j,C daily for life, and only slight damage to those 

 fed 5000 mfxC daily. On these results it would seem reasonable to assume 

 that the maximum daily ingestion for no damage would be about 1000 vc\\xC, 

 which would lead to a mean lifetime concentration of radioiodine of some 

 600 m[j,C/g of thyroid. 



The maximum integrated dose to sheep thyroid glands from the transient 

 contamination resulting from Operation 'Antler' is very small compared 

 with the dose required to produce biological damage. 



RADIO-STRONTIUM IN AUSTRALIA 



In May 1957 the Australian Atomic Weapons Tests Safety Committee, in 

 co-operation with the United Kingdom Atomic Weapons Research Establish- 

 ment, planned a continuing survey of Australian biological and geophysical 

 materials for ^"Sr. Since facilities are only now being developed in Australia 

 to carry out these difficult measurements, the Committee at the outset 

 of its survey accepted the offer of the Atomic Energy Research Establish- 

 ment to perform the analyses in the United Kingdom. 



The programme was designed to monitor various phases of the uptake of 

 the radio-isotope — the surface contamination, the levels in a number of 

 food materials and in human bone. Samples of soil, powdered milk, cabbage, 

 and human bones have been collected from the locality of the five population 

 centres, namely Perth, Adelaide, Melbourne, Sydney and Brisbane. Some 

 difficulty was anticipated in arranging for an adequate supply of human bone 

 tissue, particularly from infants, so long bones from sheep grazing close to 

 the five population centres, as well as from 1 1 other sites in central and 

 eastern Australia, were included in the first stage of the programme. The 

 levels of ^°Sr in animal bones are known to depend markedly on the chemis- 

 try of the pasture soil, and with the established wide variations of this 

 property the results cannot be easily interpreted to throw light on human 

 experience without much additional data. Since a supply of human bone 

 tissue is now assured, the collection of sheep bones has been discontinued. 



Soil, cabbages and powdered milk were sampled in September 1957 and 

 1958. Powdered milk was also obtained in March 1958 to give some idea of 

 seasonal variation. Human bone tissue has been collected throughout 1958; 

 142 samples, of age from stillborn to 80 years, are now being analysed. 

 Sheep bones were provided from the 16 sites in September 1957 and 1958. 



The results so far to hand are too few to allow of an unequivocal evaluation 

 of the situation. The available soil data, however, confirm the expectation 

 that levels in the Southern Hemisphere are lower by a factor of three or four 

 than those in the Northern Hemisphere. Table 2 shows Australian accumu- 

 lated surface deposition for mid- 1957 reported by the United Nations 

 Scientific Committee^, as well as some United States Atomic Energy Com- 

 mission data for early 1958 and our own results for September 1957. The 

 agreement between the sets of data is within the estimated errors. These 



143 



