ABSTRACT

Activities of two cosmic ray produced radionuclides, ¹¹Be and ²⁶Al, were determined for the Norton County achondrite. ¹¹Be, ²²Na, ²⁶Al, ⁴⁴Ti, ⁵³Mn and ⁶⁰Co were determined for the Peace River chondrite. Except for ¹⁰Be and ⁵³Mn, these activities were measured employing a low level β-γ coincidence method. Combining these data with those reported for stable rare gases, the radiation age of Norton County was calculated to be (120±20) × 10⁶ y which is significantly lower than previous estimations by a factor ranging from 2 to 5. The results for Peace River were compared with other experiments which appeared in literature, and the shielding effect was discussed.