The presence of ^(146)Sm in the early solar system and implications for its nucleosynthesis

Abstract

The presence of the p-process nucleus ^(146)Sm (mean life, r = 149 x 10^6 yr) in the early solar system and its in situ ɑ-decay into ^(142)Nd is demonstrated by the correlation of ^(142)Nd/^(144)Nd with ^(144)Sm/^(144)Nd in two meteorites which have a large range in ^(144)Sm/^(144)Nd in their constituent mineral phases. Clear excesses of ^(142)Nd/^(144)Nd, relative to the solar system value, are present in high Sm/Nd phases and a clear deficit of ^(142)Nd/^(144)Nd is observed in one sample with low Sm/Nd. The inferred abundance of ^(146)Sm/^(144)Sm is 0.008 at the time of the last equilibration of each meteorite at 4.47 AE ago, which yields ^(146)Sm/^(144)Sm ~0.015 at the time of formation of the solar system, 4.56 AE ago. These results confirm the presence of ^(146)Sm and provide a well defined initial abundance for ^(146)Sm. The abundance of ^(146)Sm is compatible with the p-process production rate estimates but not with the production rate for ^(146)Sm based on a photodisintegration model for the production of p-process nuclides.