Studies on chemical compositions of spherules separated from deep sea sediment dredged off Hawaii island and Antarctic ice by instrumental neutron activation analysis

Chemical compositions of spherules separated from deep sea sediment dredged off Hawaii island and from Antarctic ice were measured by INAA (Instrumental Neutron Activation Analysis) using KUR (Kyoto University Reactor). Iron, cobalt, nickel, iridium, scandium and manganese contents in those spherules were determined to be 7.3-84.4 %, 33-6100 ppm, 0.20-29.8 %, 0.31-42.1 ppm, 2.31-46.7 ppm and 3-5700 ppm, respectively. The spherules in which iridium was detected turned out to be extraterrestrial origin because iridium is depleted on the earth's surface relative to extraterrestrial matters. From the analysis of the results, it was also found that the origin of spherules could be pursued by the following new criteria; manganese contents, the detection of nickel, and the correlation between iron and cobalt contents in spherules. Furthermore, the formation mechanism of spherules was investigated from the correlation between nickel and iridium contents in extraterrestrial spherules and the variation of iron contents between iridium-rich spherules and scandium-rich ones. It may be suggested that the iridium-rich spherules are formed from the evaporated part of meteorites and scandium-rich ones from the evaporation residue of those in atmospheric entry. Further studies along this line are currently in progress in our group.