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Cosmogenic effects in Mbale, L5/6 chondrite
Author(s) -
MURTY S. V. S.,
BHANDARI N.,
SUTHAR K. M.,
CLEMENT C. J.,
BONINO G.,
CASTAGNOLI G. CINI
Publication year - 1998
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.1998.tb01315.x
Subject(s) - chondrite , meteoroid , meteorite , radionuclide , radiochemistry , analytical chemistry (journal) , geology , mineralogy , chemistry , astrobiology , physics , nuclear physics , environmental chemistry
— Measurements of particle tracks, cosmogenic radionuclides, and rare gas isotopes in Mbale indicate that the meteoroid had a simple, one‐stage exposure for 30.2 Ma in interplanetary space. On the basis of the measured track production rates and 60 Co and 26 Al activities, the meteoroid is estimated to be a sphere with a radius of ∼36 cm. The activities of several cosmogenic radionuclides ( i.e. , 57 Co, 54 Mn, 22 Na, 44 Ti, and 26 Al) in two fragments having different shielding, as estimated by their track density and 60 Co activity, provide the depth variation in their production rates. Cobalt‐57, 54 Mn and 22 Na activities agree with the production that is expected around the maximum of the solar cycle 22 as calculated from the Sunspot numbers. The U, Th‐ 4 He and K‐ 40 Ar ages are measured to be 0.54 Ga indicating a late thermal event which is in agreement with the thermal history of some other L group chondrites. The trapped N has δ 15 N of −57 ± 4%o, which is much lighter than the average L‐group chondrite value; this indicates the presence of an isotopically anomalous light N component.