Determination of the Ratios of 239Pu and 240Pu to 241Am for Nuclear Weapons Test Sites in Australia

Abstract

Recent measurements of the plutonium contamination at former nuclear weapons test sites in Australia have used the 59.5 keV gamma ray from the 241Am impurity to estimate levels of 239Pu and 240Pu. Measurements of the activity ratio of 239Pu to 241Am are presented for sites where suitable samples could be collected. Measurements of 240Pu were also made when interferences from fission products were absent. All measurements were made using a planar Ge detector of sufficient resolution to separate the 51.6 keV 239Pu gamma ray from the Ge K x-ray escape peaks and Compton scattering continuum from the much stronger 59.5 keV 241Am gamma ray. Results are given for most of the plutonium-contaminated sites in Australia.

Studies of Plutonium Aerosol Resuspension at the Time of the Maralinga Cleanup

“…We found good agreement between the Pu/Am ratios observed by LLNL during the 1996-1997 investigations and those recommended by Williams, 1993, for Taranaki sites in the IAEA dose assessment report. These measurements were a little different, in that the Pu/Am ratio from LLNL alpha spectroscopy was 239,240 Pu to 241 Am while Burns et al, 1994, were able to separate 239 Pu and 240 Pu, however, the results should be fairly comparable. The ratio of 239 Pu to 241 Am from Williams, 1993, is the Pu/Am reference value shown in Table 2.…”

“…The Pu/Am ratio as observed is defined as the ratio of 239,240 Pu to 241 Am, and had been earlier determined in the soil by ARPANSA (Burns et al, 1994). The technical advisory group considered these Pu/Am ratios when the cleanup criteria were adopted.…”

“…A considerable amount of research had been conducted at Maralinga by the Australian Radiation Laboratory, now the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), prior to the cleanup (Johnston et al, 1992, Williams 1993, Johnston et al 1993, Burns et al 1994, Burns et al 1995. ARPANSA staff made major contributions to delineate the areas with Pu in the soil, to determine the degree of secondary soil contamination by fission products from nuclear testing, to measure Pu resuspension by wind erosion of the undisturbed soil, and to prepare assessments of the human health risk from residual soil Pu.…”

Development and performance of the vehicle-mounted radiation monitoring equipment used in the Maralinga rehabilitation project

“…Therefore, if the ratio of 239 Pu to 241 Am is known, the quantitative detection of this gamma ray may be used as a surrogate in the measurement of plutonium contamination levels. This ratio, for several areas at Maralinga, has been measured using gamma ray spectrometry (Burns et al, 1994) and was 7 for Taranaki and TM101, and 20 for TM100 and Wewak.…”