New 59Fe Stellar Decay Rate with Implications for the 60Fe Radioactivity in Massive Stars

The discrepancy between observations from γ -ray astronomy of the 60Fe/26 Al γ-ray flux ratio and recent calculations is an unresolved puzzle in nuclear astrophysics. The stellar β -decay rate of 59 Fe is one of the major nuclear uncertainties impeding us from a precise prediction. The important Gamow-Teller strengths from the low-lying states in 59Fe to the 59Co ground state are measured for the first time using the exclusive measurement of the 59Co (t, 3He + γ)59 Fe charge-exchange reaction. The new stellar decay rate of 59Fe is a factor of 3.5 ± 1.1 larger than the currently adopted rate at T = 1.2 GK. Stellar evolution calculations show that the 60Fe production yield of an 18 solar mass star is decreased significantly by 40% when using the new rate. Our result eliminates one of the major nuclear uncertainties in the predicted yield of 60Fe and alleviates the existing discrepancy of the 60Fe/26 Al ratio.