ABSTRACT
Of particular value, over longer time-scales, will be the plutonium isotopes ratios. With a 238Pu half-life of 87.7 years, the 239+240pu/ 238Pu quotient will continue to change, providing a very useful dating technique. Its value, however, will depend on careful analyses of contemporary samples because the Pu a-isotope quotient is far from constant. The average quotient in weapon's fallout was at least 40, and may have been as high as 50, but the actual values are less than this, globally, because they have been affected by the input from the USA satellite SNAP 9A which burned up some 46 km above the Mozambique channel shortly after take off in April 1964. This contained plutonium metal, primarily 238Pu, as a source of heat to provide power through thermo-electric converters. The SNAP (Systems for Nuclear Auxiliary Power) device contained about 0.63 PBq of 238Pu and 0.48 TBq of 239Pu. It is estimated that 73% was eventually deposited in the southern hemisphere, the ground-level period of maximum deposition being 1966-67i depletion from the atmosphere was essentially completed by about 1971(0. The effect this had on the ratios of the cumulative deposition of Pu isotopes up until this time is given in Table 2.
