Abstract
ABSTRACT The absence of excesses of fission tracks along the boundaries between olivine crystals and metal grains indicates that the concentration of fissioning superheavy elements in the metal must have been less than about 2.5 × 10−15 kg kg−1 and 2.5 × 10−13 kg kg−1 in the chondritic meteorites Wold Cottage and Alta'ameem respectively. The abundance of 244Pu fission tracks in phosphates from each meteorite suggests that track retention could not have commenced later than about 4 × 109 y ago. Superheavy element concentrations of such magnitudes would not provide a sufficient heat source to drive a lunar core dynamo.
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