Chemical composition of the Kobe meteorite; Neutron-induced prompt gamma ray analysis study

抄録

Neutron-induced prompt gamma ray analysis (PGA) was applied to several lump samples of the Kobe meteorites, along with powdered sample and separated chondrules, and a total of 15 elements (H, B, Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Mn, Fe, Co and Ni) were determined non-destructively. Except for chondrule samples, uniformity in chemical composition is remarkable for most elements. Exceptions are B and Cl, which appear to be heterogeneously distributed in the Kobe meteorite. Comparing Mg/Si, Al/Si, Ca/Si and Ti/Si ratios among carbonaceous chondrites (CI, CM, CV, CO and CK), CK chondrites are characterized by the highest Mg/Si ratio. Abundances of S and Zn were observed to coincidently change among carbonaceous chondrites, as suggested by similar condensation temperatures. Boron abundances in CK are even lower than those for S and Zn, being contrary to the prediction from thermodynamic calculation. For the classification of carbonaceous chondrites, we propose a S/Mn vs. Al/Mn diagram, on which individual groups of CI, CM, CV, CO and CK cluster with discrete locality. These three key elements are all determined for voluminous and irregularly shaped chondrite samples by PGA, showing that PGA has a great merit in analyzing new fall meteorites like Kobe.