Isomeric state of 80Y and its role in the astrophysical rp-process

A careful investigation of the isomeric transition of the long-lived state at 228.5 keV excitation energy in ⁸⁰Y has been done. The HIGISOL facility at the Jyv?skyl? isochronous cyclotron has been used. We used the electron magnetic transporter to prepare an appropriate source and to measure the electron spectra in clean background conditions. The measured internal conversion coefficient α_K = 0.50±0.07 allows unambiguous 1^- identification for the 228.5 keV first excited isomeric state in ⁸⁰Y. With a “bare" half-life of 6.8±0.5 s found in this work, this state is strongly populated in the rp-process during X-ray bursts and has therefore to be taken into account in X-ray burst model calculations. However, because of the similarity of the β-decay half-lives of isomeric and ground states, we find a maximum reduction in the effective β-decay lifetime of ⁸⁰Y of only 17±2%. Our results pave the way for a future investigation of the impact of the isomeric state on the “effective" ⁸⁰Y proton capture rate. Received: 14 March 2001 / Accepted: 10 July 2001