Cosmogenic radionuclides in the recently fallen Kobe (CK4) meteorite

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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.