Conditions of the cosmic ray exposure of the Jilin chondrite

Nine documented samples from the main mass, Jilin 1, and three samples from different locations of the strewn field have been analyzed for cosmogenic 26Al (Tsub(1/2) = 0.716 Myr), 60Co (Tsub(1/2) = 5.27 yr) and 22Na (Tsub(1/2) = 2.6 yr). 53Mn (Tsub(1/2) = 3.7 Myr) has been determined in seven of the same documented samples and in two further documented samples. The pre-atmospheric size of Jilin was reconstructed from the documented sample positions and from the measured 60Co activities. Jilin was almost spherical and has a pre-atmospheric radius of about 85 cm. The cosmogenic nuclides in Jilin can be explained by a two-stage exposure history. The first stage occurred near the surface of the parent body in 2π geometry and lasted about 10 Myr. Jilin was then expelled from its parent body and exposed to cosmic rays in a second (4π) stage lasting approximately 0.4 Myr. The measured concentration profiles of spallogenic nuclides are compared to calculated production rates. (orig.)