Isomeric state of Y-80 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 Y-80 has been done. The HIGISOL facility at the Jyvaskyla isochronous cyclotron has been used. We used the electron magnetic transporter to prepare an appropriate source and to measure the el ectron spectra in clean background conditions. The measured internal conver sion coefficient alpha (K) = 0.50 +/- 0.07 allows unambiguous 1(-) identifi cation for the 228.5 keV first excited isomeric state in Y-80. With a "bare " half-life of 6.8 +/- 0.5 s found in this work, this state is strongly pop ulated 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 sim ilarity of the beta -decay half-lives of isomeric and ground states, we fin d a maximum reduction in the effective beta -decay lifetime of Y-80 of only 17 +/- 2%. Our results pave the way for a future investigation of the impa ct of the isomeric state on the "effective" Y-80 proton capture rate.