Decay Studies of 178Au and Its Daughter 174Ir

Historically, the region near the proton Z=82 shell closure and in the neutron midshell at N=104 has displayed numerous examples of shape coexistence and shape evolution. Here, multiple oblate, prolate and spherical configurations are found at low excitation energies. This effect can be manifested as large changes in the mean square charge radius of nuclei within this region, the most well-known example being the shape staggering observed in the mercury isotopes. Over the past several years, multiple studies by means of in-source laser spectroscopy for the isotopic chains of gold, astatine, mercury and bismuth have been carried out at the CERN ISOLDE facility by the Windmill-RILIS-ISOLTRAP IDS collaboration. Relevant to the present work, in the xperiment dedicated to studies of the long chain of gold isotopes, two alpha-decaying states were identified in 178Au. The results from the laser-spectroscopy measurement showed that both of these states in 178Au were proved to be strongly deformed. To shed further light on this phenomenon, a dedicated in-beam gamma-ray and alpha-decay study was performed at the gas-filled separator, RITU, at the Accelerator Laboratory in Jyvaskyla, Finland. The 178Au nuclei were produced in the fusion-evaporation reaction 92Mo(88Sr, np)178Au. A combination of the JUROGAM II gamma-ray array and the RITU gas-filled separator was used, complemented by the GREAT spectrometer at the focal plane of RITU. The nucleus 174Ir, the alpha-decay daughter of 178Au, was also studied. The much higher statistics obtained in the RITU investigation, in comparison to the complementary study of 178Au performed at ISOLDE, allowed to detect several new fine structure alpha decays in (178gs;is)Au. This knowledge provides further input in respect of the puzzling discovery in the ISOLDE experiment of three unhindered alpha-decays of 178Au, which is a situation, hardly known for any other nuclei. Furthermore, the present study identified two sub-microsecond isomeric transitions in 178Au. These are built on top of both alpha-decaying ground and isomeric states in 178Au. The identification of these isomeric states considerably simplifies the construction of rotational bands in this nucleus, the first examples of which are presented in this work.