Shape coexistence in odd-mass Au isotopes: Determination of the excitation energy of the lowest intruder state in 179Au

Abstract Phenomenon of the shape coexistence has been investigated in 179 79 Au 100 . This very neutron-deficient isotope, 18 neutrons away from the stable gold isotope 197 79 Au 118 , was studied by a combination of α -decay and isomer-decay spectroscopy employing the ritu gas-filled separator and the great focal-plane spectrometer at the University of Jyvaskyla. A new isomer with t 1 / 2 = 328 ( 2 ) ns was observed and states associated with π d 3 / 2 − 1 , π s 1 / 2 − 1 , π f 7 / 2 + 1 and π h 9 / 2 + 1 structures were revealed. The implications of these results on the systematics of π h 9 / 2 + 1 and π f 7 / 2 + 1 intruder structures in the odd-mass gold isotopes are discussed. The minimum of the parabolic trend is at N = 104 , i.e. exactly at the mid-shell point and the π f 7 / 2 + 1 structure is dropping in energy relative to the π h 9 / 2 + 1 with decreasing mass number.