Studing the effects of 1974 French Atomic Tests series in the Pacific on Australian atmosphere - a novel approach to nuclear metrology

Full text: PRINCIPLE: A novel approach for nuclear metrology has been selected to study the effects of French Atomic Tests in the Pacific of 1974 on the Australian atmosphere. This is to investigate the changes in the elemental concentrations of the atmospheric particulates collected in Australia just before and after the onset of the atomic tests in the Pacific. Any additional radioactivity due to the tests would either be still there or would decay into stable isotopes. If by some very sensitive techniques one could determine the elemental / isotopic composition of the air particulate, one can work backwards in estimating the sort and quantity of activities that could have existed just after conducting of the tests. We decided to use the technique of charged-particle activation analysis to estimate the elemental / isotopic concentrations of the Australian Atmosphere. This technique has the potential to provide concentrations in the ppb and sub ppb regions. METHOD: The atmospheric particulates were collected on Polystyrene filters in high-volume air samplers placed all along the Australian East Coast at locations in Port Moresby (New Guinea), Townsville, Brisbane, Sydney, Melbourne and Hobart. The filters were cut into small pieces and placed in the grove of an Al-Target holder, covered by a thin Al-foil, which was cooled by liquid nitrogen. The samples were irradiated for one hour each with 8.5 MeV proton beam at an intensity of 1 μA. After waiting period of one hour the irradiated samples were counted with a high resolution and high sensitivity Germanium detector. Suitably prepared 'Standards', for quantifying the absolute concentrations, were also irradiated in identical fashion and their induced activities were measured. RESULTS AND DISCUSSION: A number of elements, like S, Ca, Ti, Cr, Fe, Ni, Cu, Zn, Se and Hg, were detected in the two types of samples- one taken just before the Atomic Tests started and the other set taken just after the finishing of the tests. Their concentration of different elements ranged from 0.001- 3.27 μg/m3. Certain changes in the concentrations of different elements were observed in the two sets. However, these changes were attributed to synoptic effects rather than due to Nuclear Fall-out Effects. The ease, strength and potential of this sort of approach for nuclear metrology will be discussed. (author)