We analyze systematically the effective order parameters in nuclear shape phase transition both in experiments and in the interacting boson model. We find that energy ratios and B(E2) ratios can distinguish the first from the second-order phase transition in theory above a certain boson number N (about 50), but in experiments, only those quantities, such as E(L1+)/E(02+) and B(E2; (L+2)1 → L1)/B(E2; 21 → 01), etc., of which the monotonous transitional behavior in the second-order phase transition is broken in the first order phase transition independent of N, are qualified as the effective order parameters. By implementing the originally proposed effective order parameters and the new ones, we find that the isotones with neutron number Nn = 62 are a trajectory of the second order phase transition. In addition, we predict that the transitional behavior of isomer shifts of Xe, Ba isotopes and Nn = 62 isotones is approximately monotonous due to the finiteness of nuclear system.
ZHANG Yu1,2, HOU ZhanFeng2 & LIU YuXin2,3 1Department of Physics, Liaoning Normal University, Dalian 116029, China
The properties of the low-lying energy states for the l00 Mo isotope is investigated within the framework of the proton-neutron interacting model IBM2. By considering the relative energy of the d proton boson to be different from that of the neutron boson and taking into account the dipole interacting among like-boson Lπ·Lπ and Lπ·Lπ, the low-lying energy spectrum is reproduced well. Particularly, the relative position of the energies for 2＋1, 0＋2, 2＋2 and 4＋1 states shifted correctly fit the experimental data. The electromagnetic properties, including the key observable B（E2） reduced transition branching ratios and the E2 reduced matrix elements of the experimental data, are well described. Our calculations show possible shape coexistence in the l00Mo nucleus.
