Neutron Capture Effects and Radionuclei in the Early Solar Nebula

Abstract

We consider the particle radiation environment in the early solar system that might result from low-energy cosmic-ray acceleration in active star-forming regions and explore the possibility that neutron capture-produced radionuclei could account for some of the fossil isotopic anomalies in meteorites. We calculate the effects of possible low-energy cosmic-ray nuclear interactions 4.56 Gyr ago on the evolving solar nebula and compare the predictions with the fossil records of possible neutron-induced fission products and extinct radionuclides observed in meteorites. We conclude that the external irradiation of the early solar nebula by low-energy cosmic-ray particle fluxes generated by supernovae in a star formation region cannot produce the neutron fluences of about 3 × 1016 n cm-2 that would be required to account for the possible neutron capture isotopic anomalies in meteoritic samples.