Wu Yiheng

Lifetime Measurement of the Low Lying Yrast States in 189Pt

High-spin states in 189Pt are populated through the heavy-ion fusion-evaporation reaction176Yb (18O, 5n)189Pt at 87MeV beam energy. An array consisting of 13 HPGe detectors is used in conjunction with the plunger device in CIAE. The lifetimes of two levels in the yrast band are determined by using the recoil distance Doppler shift method. The transition quadrupole moments Qt are extracted. The results show that the state has a much larger Qt value than that of the ground state, whereas the value deceases quickly with spin increasing. This may contribute to the shape driving effect of the quasi-neutron from the i13/2 orbital.

High-Spin States in the Odd-Odd Nucleus 92Nb

High spin states of the odd-odd nucleus 92Nb are investigated using the 82Se (14N, 4n)92Nb reaction at a beam energy of 54 MeV. The level scheme of the 92Nb was extended up to Jπ =(16+) at about 7.3 MeV and Jπ=(21−) at about 9.7 MeV. According to systematic analyses and a comparison with the neighboring nucleus, the higher spin states could be interpreted by the multi-particle excitations in the π(f5/2,p3/2,p1/2,g9/2)⊗ν(p1/2,g9/2,d5/2, g7/2) configuration space.

New high spin level scheme of 87Sr

High spin states of the odd-A 87Sr were populated by the fusion-evaporation reaction 82Se(9Be,4n) 87Sr at a beam energy of 46 MeV. Excited levels of 87Sr have been extended up to an excitation energy of 7.4 MeV at spin 31/2ħ. The coupling of a g9/2 neutron hole to the yrast states of the 88Sr core can account for the low-lying states in 87Sr. The structure of the higher spin states is discussed by analogy with those of the neighboring odd-A N = 49 isotones and possible configurations are proposed.

A capacitance servo control plunger for accurate lifetime measurement

The recoil distance Doppler shift method has been widely used in the study of nuclear structure to determine the level lifetime and absolute transition probabilities. A capacitance servo control plunger based on this method has been successfully developed by the Nuclear Structure Group of the China Institute of Atomic Energy. Three microscopes were employed to check the parallelism and can therefore guarantee a delicate measurement of the distance between the target and the stopper. This new plunger made a successful performance in the test experiment and the measured lifetime of the 2 + →0 + transition in 78 Kr is in agreement with the previous value.