Cosmochemical Studies on Enstatite Chondrites.

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One of the chondrite group called enstatite chondrite is well known for their unique chemical and mineralogical compositions. In order to study the origin of such chondrites, the distribution of rare earth elements among composed mineral phases has been determined. Experiments were mainly performed by radiochemical thermal neutron activation analysis. and found that most of rare earths were exists in water soluble sulfide minerals as already described. However enstatites also contain about 10 % or more of them. From above results and other our former investigations, it was assumed that enstatite chondrites were formed in rather near sun, say, between Mercury and Venus, while other chondrites believed to form in asteroid belt. Further, size of parent body or bodies of enstatite chondrite should be quite small which hard to produce coagulation heat in their lives. Of course, this is not the final conclusion, it is necessary to study more, for example, the determination of cosmic-ray-produced nuclides and of solidification ages using several nuclides pairs, and why or how oxygen deficient conditions had been introduced in their histories.During preparation of the apparatus measuring very weak <gamma> -rays for study the enstatite chondrites, a new chondrite shower fell in Shikoku Japan. We had switched immediately to measure cosmic-ray-produced radioactive nuclides from 5.6 days half-lives of <^(52)Mn> to 7.16x <10^5> years of <^(26)Al> in several specimens collected different places. It was found that <^(54)Mn> and <^(22)Na> are very sensitive for the size, shape and position of parent body of each specimen.