Cosmogenic radionuclides in the recently fallen Kobe (CK4) meteorite

Abstract

Cosmogenic radionuclides in the Kobe chondrite (CK4) fell on September 26th, 1999, have been measured immediately after the fall (21 hours) using a ultra low-background Ge-detector. Nineteen cosmogenic nuclides including the very short-lived 24Na were detected and their activities place constrains on the exposure history of the meteorite and reflect effect of solar modulation of galactic cosmic rays during solar maximum. Two nuclides, 28Mg and 43K were possibly detected for the first time and signals probably due to 56Ni and 57Ni were present although statistical uncertainties were very large. On the other hand, low activities of 60Co (~1 dpm/kg) and 26Al (~38 dpm/kg) mainly suggest a small preatmospheric size (≤10 cm) of the Kobe meteorite.