Two opposite types of radionuclide fractionation have been found in the highly radioactive fallout particles which originated from the first Chinese nuclear test explosion carried out on 16 October 1964. The first type was quite similar to the fractionation that was observed in the highly radioactive fallout particles which originated from the large scale air-bursts carried out by the U.S.S.R. in the autumns of 1961 and 1962. The radiochemical composition of the particles fractionated in this type was always much enriched in 95Zr + 95Nb and impoverished in 103Ru, taking a middle position for most of other nuclides. The particles fractionated in the second type were, just contrary to those fractionated in the first type, much enriched in 103Ru and impoverished in 95Zr + 95Nb. The second type of fractionation was never found in the Russian particles that were examined. The fractionation factors as EDVARSON et al. defined were measured for some fallout samples. It was found that the particles having exceedingly higher activities among the collected 300 particles were all fractionated in the second type and that the others were fractionated in different degrees, some being fractionated in the first type and others in the second type. The difference in fractionation behavior between the Chinese and the Russian particles may be considered to be ascribed to the fact that the former were produced in a small scale land surface burst, while the latter were produced in large scale air-bursts.
(C)1966Health Physics Society