Cosmogenic radionuclides in the recently fallen Kobe (CK4) meteorite

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 Na-24 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, Mg-28 and K-43 were possibly detected for the first time and signals probably due to Ni-56 and Ni-57 were present although statistical uncertainties were very large. On the other hand, low activities of Co-60 (similar to1 dpm/kg) and Al-26 (similar to38 dpm/kg) mainly suggest a small preatmospheric size (less than or equal to10 cm) of the Kobe meteorite.