Evidence for244Pu fission tracks in hibonites from Murchison carbonaceous chondrite

We have developed a technique for revealing nuclear tracks in the mineral hibonite (CaAl₁₂O₁₉), found in the refractory inclusions from carbonaceous chondrites. The tracks in hibonitesfrom Murchison carbonaous chondrite are dominated by fission tracks from²⁴⁴Pu (constituting more than 90% of the total). The measured uranium contents in these crystals range from 1.2 to 62 ppb. We deduce that the average value for the²⁴⁴Pu/²³⁸U ratio in most of the Murchison hibonites at the time of track retention is0.022 ± 0.011.