Shapes of medium-mass nuclei studied by Monte Carlo shell model calculations

The nuclear shape is one of the fundamental properties of nuclear structure and related to nuclear shell structure and other properties.
Monte Carlo shell model can describe nuclear intrinsic shapes as well as other properties such as energies, electromagnetic moments and transitions.
We performed Monte Carlo shell model (MCSM) calculations for nuclei around Ni (Z=28) isotopes and so on.
Nuclei in Ni region are calculated with the fine-tuned effective interaction in the model space composed of pf shell and 0g9/2, 1d5/2 orbits
and the results agree with the experimental data well.
Calculations of heavier nuclei are more challenging and need large model space in order to describe deformation.
We can calculate in these large model spaces without any particle-hole truncation, as an advantage of MCSM.
Shape coexistence and shape evolution in these regions are discussed by using "T-plot",
a method to visualize the information of nuclear intrinsic shape of the states calculated by Monte Carlo shell model.
In Ni isotopes around doubly-magic 68Ni, there are oblate and prolate deformed bands as well as the spherical ground state from the calculation.
Such shape coexistence can be explained by introducing the mechanism called Type II shell evolution,
driven by changes of configurations within the same nucleus mainly due to the tensor force. Other nuclei are discussed as well.