Exposure history of H5 chondrite Gujargaon

Abstract

Cosmic-ray-produced tracks, He and Ne isotopes, and radionuclides have been studied in the recently fallen H5 chondrite Gujargaon. The results indicate an exposure age of about 7 Ma. The high track production rates of 0.25 to 0.69 × 10⁶ cm^-2 Ma^-1 suggest that the Gujargaon meteoroid had a small size, (R_E = 9-10 cm) in space and suffered 1-3 cm ablation in the atmosphere. The conclusion about the meteoroid size is supported by the low activity of neutron capture isotope ⁶⁰Co and high spallogenic ²²Ne/²¹Ne ratio of about 1.25. The data on long lived isotopes ¹⁰Be, ⁵³Mn, and ²⁶Al are used to derive production rates of these isotopes in a rock having a radius of 9 cm, and the activity levels of the short lived isotopes ²²Na and ⁵⁴Mn are used to estimate the effect of modulation of galactic cosmic rays at the time of solar maximum of 1982.