Exposure history of meteorites as deduced by sub-nanogram of53Mn radiochemical neutron activation analysis

Radiochemical neutron activation analysis is the only method to determine the galactic cosmic ray (GCR) produced radionuclide53Mn (T=3.8·106) in small meteorite samples. A large number of such samples was analyzed using extremely thermalized neutrons of the DIDO reactor at the KFA Jülich. The detection limit of 10−14 g/g was recently achieved in our laboratory through the improvement of pre- and postirradiation chemistry. The main purpose of our studies of meteorite finds from Antarctica and the Southwestern United States is to establish their exposure ages up to 12·106 a by means of53Mn. Especially in the case of Antarctic meteorites terrestrial ages up to several 105 years have been observed by combining53Mn and26Al (T=7.2·105 a) measurements.