Fine structure in the α  decay of 179Hg and 177Au.

The α -decay fine structure of 179 Hg and 177 Au was studied by means of decay spectroscopy. Two experiments were performed at the Accelerator Laboratory of the University of Jyväskylä (JYFL), Finland, utilizing the recoil separator RITU and a digital data acquisition system. The heavy-ion induced fusion-evaporation reactions 36 82 Kr + 44 100 Ru and 38 88 Kr + 42 92 Mo were used to produce the 179 Hg and 177 Au nuclei, respectively. Studying the evaporation residues (ER, recoils)- α 1 - α 2 correlations and α - γ coincidences, a new α decay with E α = 6156(10) keV was observed from 179 Hg. This decay populates the (9/2 - ) excited state at an excitation energy of 131.3(5) keV in 175 Pt. The internal conversion coefficient for the 131.3(5) keV transition de-exciting this state was measured for the first time. Regarding the 177 Au nucleus, a new α decay with E α = 5998(9) keV was observed to populate the 156.1(6) keV excited state in 173 Ir. Two de-excitation paths were observed from this excited state. Moreover, a new 215.7(13) keV transition was observed to depopulate the 424.4(13) keV excited state in 173 Ir. Properties of the 179 Hg and 177 Au α decays were examined in a framework of reduced widths and hindrance factors. For clarity and simplicity, the spin and parity assignments (e.g. J π ) are presented without brackets throughout the text.