Trace Of Radio-Activity Recorded In N.Z. Fall-Out

Press, Volume CI, Issue 29749, 16 February 1962, Page 5

Trace Of Radio-Activity Recorded In N.Z. Fall-Out

A slight trace of radioactivity in the barium fraction of nuclear fall-out, possibly from last year’s Russian tests, is now being recorded at the Institute of Nuclear Sciences, Department of Scientific and Industrial Research, Lower Hutt,

‘'The activity is so small that we cannot determine the half-life of the isotope responsible, but it could be barium-140,” said Mr R. N Woodward. who is making the observations. “The amount is, in any case, such that it is of academic interest only. We find it quite intriguing, however, since if the fall-out were coming through the stratosphere in the normal way the expectation would be that the amount recorded would increase as time went on; but it is not increasing Perhaps it is coming through the troposphere (lower atmosphere). or perhaps we have not yet taken enough readings to get a clear picture,” Mr Woodward said. ”Barium-140 has a half-life of 12.8 days and will soon be no longer traceable from the Russian tests in any case so, unless a new test series starts, we shall soon be looking instead for cerium--141. which has a half-life of 30 days. ‘We are still checking routinely for strontium-90, caesium-137. and cerium-144. which we assume come from the tests of 1958 and earlier tn the equatorial regions. The amounts of each of these being detected are now fairly steady. The decay of material sent into the upper atmosphere by these earlier tests should now just be overcoming the increase in the rate of deposition,” he said.

“The proposed American tests at Christmas Island will give a lot of fall-out in the New Zealand area if the size of the explosions is at all comparable with those the Russians let off. It would oe better, in my personal opinion, if the Americans carried out their tests in Alaska, where fewer people are likely to be in the area affected by the local and most intense part of the fallout,” Mr Woodward said.

The acting director of the Dominion X-ray and Radium Laboratory, Christchurch (Mr H. J. Yeabsley), said that no increase in radio-activity in rainwater had so far been observed at Christchurch. Tests were not yet complete, however, on the falls of the last two or three days.