No Health Hazard From Radioactive Fallout

Press, Volume CX, Issue 32351, 17 July 1970, Page 7

No Health Hazard From Radioactive Fallout

Radioactive fallout levels in New Zealand during 1969 were a small fraction of the permissible levels for continuous consumption and did not constitute a health hazard, the director of the National Radiation Laboratory in Christchurch (Mr G. E. Roth) said in his annual report for that year released this week. However, the levels of long-; lived fission products, such as! Sfrontium-90 increased during last year by about 50 per cent over the 1968 average, j “This increase has been due to the French nuclear tests in the South Pacific and in particular the 1968 tests. The deposition in 1969, however.; was only one-third of the peak deposition in 1964,” the re-! port said. The 1964 peak was caused! mainly by the Russian and American nuclear tests .in 1961 and 1962, the report! said.

During last year there were j no nuclear explosions in the! atmosphere of the Southern! Hemisphere, but the expected ; decrease in the levels of fission product activity after the 1968 French tests (which, for! the first time, culminated in the explosion of two hydrogen bombs) occurred more slowly than the decrease in levels after French tests in the previous two years.

Longer Period “This delay undoubtedly resulted from the stratospheric! injection of hydrogen bomb! debris. The subsequent deposition of the debris was thus

extended over a longer period,” the report said. Levels of total beta activity in air filter and rainwater samples decreased significantly during 1969, according to the report, but Stron-tium-90 levels in milk increased about 30 per cent, and the caesium-137 levels in milk increased about 22 per cent over the 1968 levels. “The levels in milk in 1969, however, were only about one half of the peak levels in 1965. In 1965 and 1969 the levels of Strontium-90 in milk were 4.3 per cent and 2.5 per cent of the permissible level respectively: and the levels of caesium-137 in milk were about 0.9 per cent and 0.4 per cent of the permissible levels respectively,” the report said. Further Deposits Of the analysis carried out on strontium - 89 and strontium-90 in rainwater, the

report said that the half-time of the material measured in the rainwater after the 1966 and 1967 tests was of less than 50 days, which is the half-life of strontium-89. The low half-time was probably due to the washout of debris produced by the low yield nuclear devices tested by the French combined with further deposits of strontium-90 from the stratospheric reservoir built up in the past by testing mainly in the Northern Hemisphere. During 1968 and 1969, however, the ratio decreased initially and then built up to a half-time of more than 50 days. This was consistent with a combination of fallout from the French tests giving a lower half-time and the eventual higher half-time could be due to debris of the high yield Chinese explosion on December 27, 1968, the report said.