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

Phenomenon of the shape coexistence has been investigated in 17979Au100. This very neutron-deficient isotope, 18 neutrons away from the stable gold isotope 19779Au118, 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 Jyväskylä. A new isomer with t1/2=328(2) ns was observed and states associated with πd3/2−1, πs1/2−1, πf7/2+1 and πh9/2+1 structures were revealed. The implications of these results on the systematics of πh9/2+1 and πf7/2+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 πf7/2+1 structure is dropping in energy relative to the πh9/2+1 with decreasing mass number.