STUDIES IN RADIOACTIVE FALLOUT IN NEW ZEALAND. PART 2. THE TOTAL BETA ACTIVITY OF RAINWATER (SEPTEMBER 1956-JUNE 1959)
The decay rate of the total BETA activity has been measured from monthly rainwater samples collected at six New Zealand sites from September 1956 to June 1959. By comparison of this rate with the rate of decay of the slow neutron fission products of U/sup 235/, an estimate was made of the month in which the fission products in each sample were formed. From the relative ages of successive samples, it was concluded that about 10 successive waves of fresher fission product activity were deposited in the rainwater over the 2-yr period. Possible nuclear test series which caused these waves are suggested. A greatly increased amount of short-lived radioactive material was deposited in the north of New Zealand after the U.K. test series in Australia in 1957, although the U.K. Pacific tests in May contributed most of the total BETA activity in the latter half of 1957. The next major influxes of debris came from the latter half of 1958 from U.S. and U.K. Pacific tests. The relative aging of the 1959 samples is supported by Srsup 90/ and Ce/sup 144/ determinations. It is possible that some U.S.S.R. October 1958 debris was detected in March-June 1959. If this deduction is valid, upper limits of 25% and 9% have been calculated for the Sr/ sup 90/ deposition at Auckland (37 deg S) from this source during the period January-June 1959, depending on whether data for thermal fission of U/sup 235/, or for 14 Mev fission of U/sup 238/ are used. The estimated upper limits for Russian Sr/sup 90/ deposited at Wellington (4l deg S) in the same period is probably not more than 2/3 of this. The accumulated deposition of total BETA activity over the 2-yr period was approximately proportional to the amount of rainfall at the collection site, although there was a decrease of 35% in the specific activity of the rain from the most northerly site to that furthest south. Age measurements suggest that this might be due in part to the longer time taken for the debris to travel further south, rather than solely due to a dilution phenomenon. (auth)
- Research Organization:
- Inst. of Nuclear Sciences, Hutt, New Zealand
- NSA Number:
- NSA-17-005758
- OSTI ID:
- 4751591
- Journal Information:
- New Zealand J. Sci., Journal Name: New Zealand J. Sci. Vol. Vol: 5
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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