Measurement of the Half-Life of 60Fe for Stellar and Early Solar System Models Using the Direct Decay of 60mCo and Accelerator Mass Spectrometry

Radioisotopes, produced in stars and ejected through core collapse supernovae (SNe), are important for constraining stellar and early Solar System (ESS) models. The presence of these isotopes (specifically 60Fe) can identify progenitors of SNe, give evidence for nearby SNe, and can be used as a chronometer for ESS events. The 60Fe half-life, which has been in dispute in recent years, can impact calculations for the timing of ESS events, the distance to nearby SNe, and the brightness of individual, non-steady state 60Fe gamma-ray sources in the Galaxy. To measure such a long half-life, one needs to simultaneously determine the number of atoms in, and the activity of, an 60Fe sample. We have undertaken a half-life measurement at the University of Notre Dame. This thesis gives results of both an activity measurement and an Accelerator Mass Spectrometry (AMS) measurement on an 60Fe sample. This is the first time that the AMS technique is coupled with the direct isomeric day of 60Co instead of the ground state decay of 60Co. The resulting half-life from this work is (2.55 +/- 0.15) million years, agreeing with the two most recent measurements. This is substantially longer than the previously accepted value of (1.49 +/- 0.27) million years published in 1984.