Cosmochemical Studies on Enstatite Chondrites.

顽火辉石球粒陨石以其独特的化学和矿物组成而闻名。为了研究这类钙钛矿的成因，测定了稀土元素在组成矿物相中的分布。实验主要采用放化热中子活化分析。发现稀土元素大多存在于水溶性硫化物矿物中。然而顽火辉石也含有约10%或更多的它们。根据上述结果和我们以前的研究，我们认为顽火辉石类的形成地离太阳较近，如水星和金星之间，而顽火辉石类的形成地则被认为是小行星带。顽火辉石球粒陨石的母体或体的尺寸应很小，在其生命过程中很难产生凝结热。当然，这还不是最后的结论，还需要进一步的研究，例如，宇宙射线产生的核素的测定和用几种核素对测定凝固年龄，以及为什么或如何在它们的历史中引入缺氧条件。在为研究顽火辉石而准备测量极弱射线的仪器期间<gamma>，日本四国地区出现了一个新的球粒陨石雨。我们立即转换到测量宇宙射线产生的放射性核素，从&lt;^（52）Mn&gt;的5.6天半衰期到&lt;^（26）Al&gt;的7.16 x &lt;10^5&gt;年。发现&lt;^（54）Mn&gt;和&lt;^（22）Na&gt;对每个样品母体的大小、形状和位置都很敏感。

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.