Ponente
Descripción
Neutron-deficient Pb nuclei feature unique shape coexistence with oblate, prolate and spherical shapes coexisting with few hundred keV in $^{186}$Pb. Not much is known in lighter Pb isotopes, with the spectroscopic knowledge vanishing at $^{178}$Pb. The structure of Pb isotopes with A<186 will allow one to understand the evolution of shape coexistence towards the lighter half of the N=82-126 space. The proposal is to perform isomer decay spectroscopy of the semi-magic $^{178-184}$Pb isotopes. Isomers have been observed all along the isotopic line until $^{188}$Pb: the high spins (12$^+$, 19$^-$ and 8$^-$) of these isomers allows the measurement of the low-lying level structure populating yrast and yrare states indicating the respective energy positions of the oblate and prolate intruder states.
Moreover, in this region the first systematic violation of Geiger-Nuttall law was observed in the alpha decay of Po isotopes. Its origin remains an open question but extending alpha-decay measurements to $^{184}$Po would help to understand at least the extent of the violation.
To populate the nuclei of interest we propose to exploit the intense primary $^{238}$U beam from the RIBF facility, using a cocktail secondary beam produced by the BigRips separator. The separated fragmentation products will be implanted in the WAS3ABI Si array. The $\beta$-delayed $\gamma$-rays as well as the isomer decays will be studied with the HPGe array. Fast-timing measurement might be interesting if an array is available.
