Cosmogenic radioisotopes in Almahata Sitta meteorite

C. Taricco(1), N. Bhandari(2), P. Colombetti(1), A. Romero(1), G. Vivaldo(1), P. Jenniskens(3), 1 Dipartimento di Fisica Generale, University of Torino and Istituto di Fisica dello Spazio Interplanetario (IFSI, INAF), Torino, Italy; 2 Basic Sciences Research Institute, Navrangpura, Ahmedabad, India; 3 SETI Institute, Mountain View, CA.

A fragment (#15, weighing 75g) of Almahata Sitta meteorite, which has a well determined orbit and fell in October 2008, was measured non destructively by whole rock counting method on a sensitive gamma-ray spectrometer. The gamma ray spectrum shows well developed peaks of cosmic ray produced 46Sc (half life, 83.8d), 57Co (271.35d), 54Mn (312.2d), 22Na (2.6y), and 26Al (7.4x104y), in addition to the neutron produced 60Co (5.27y). 22Na/26Al activity ratio is extremely high, probably due to unusually prolonged solar minimum before the fall. Large value of 60Co is consistent with the large size of the meteoroid.