Li Cong-Bo

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 Level Scheme of 120I

Excited states in 120I are investigated utilizing in-beam gamma-ray spectroscopy following the 114Cd(11B,5n) reaction at 70 MeV bombarding energy. A level scheme is constructed with states up to 9 MeV. The levels are classified into several bands and their possible configurations at low spins are discussed briefly Based on the linking transitions between different bands at higher spins, the excitation energy of the previously reported T1/2 = 53 min isomer is ascertained to be 72 keV. Evidence showing the existence of an isomer at an excitation energy of 6.4 MeV is presented.

Near-Yrast Structures in Odd-Odd 122I Nucleus

Excited states of the odd-odd nucleus 122I are investigated via the fusion-evaporation reaction 116Cd(11B,5n) at a beam energy of 68 MeV. The two most strongly populated bands in 122I are observed up to excitation energies around 10.5 MeV. Their possible configurations at lower spins are assigned to πh11/2 ⊗ vh11/2 and πh11/2 ⊗ vd5/2 based on the observed population, B(M1)/B(E2) values, alignments and signature splitting. E1 transitions are observed connecting the πh11/2 ⊗ vd5/2 band to the πh11/2 ⊗ vh11/2 band, which may be evidence of octupole collectivity. Band terminations caused by the full alignment of the valence nucleons outside the 114Sn core are observed in both bands.

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.

Description of the shape evolution in the yrast states of 186Pt

186Pt was tested in the framework of IBM-1 and the X(3) model. The results show that 186Pt is located close to the shape phase transition point, but the B(E2) values little agree with the X(3) model. The shape evolution in the yrast states of 186Pt is also discussed in detail. TRS calculation exhibits a flat bottomed potential at low spin states, but a relatively deep minimum at high spin states. It suggests that a shape evolution from vibrational mode to rotational mode happens in 186Pt. The result is in agreement with the E-GOS calculation.186Pt was tested in the framework of IBM-1 and the X(3) model. The results show that 186Pt is located close to the shape phase transition point, but the B(E2) values little agree with the X(3) model. The shape evolution in the yrast states of 186Pt is also discussed in detail. TRS calculation exhibits a at bottomed potential at low spin states, but a relatively deep minimum at high spin states. It suggests that a shape evolution from vibrational mode to rotational mode happens in 186Pt. The result is in agreement with the E-GOS calculation.

Yrast Band in 122I and Band Termination

High spin states of the odd-odd nucleus 122I have been investigated via the fusion-evaporation reaction 116Cd(11B, 5n) at a beam energy of 68 MeV. The yrast band is extended up to Iπ = (29+). The band termination at Iπ = (22+) reported in previous studies is confirmed and interpreted as arising from a shape change from collective prolate to noncollective oblate according to Total-Routhian-Surface (TRS) calculations. In addition, the Iπ=(29+) state is assigned to the [πh11/2(πg7/2)2]23/2-⊗[(νh11/2)3(νd5/2)2]35/2− configuration corresponding to the full alignment of all valance nucleons outside the semi-closed shell.

Yrast Band in 122 I and Band Termination

High spin states of the odd-odd nucleus 122I have been investigated via the fusion-evaporation reaction 116Cd(11B, 5n) at a beam energy of 68 MeV. The yrast band is extended up to Iπ = (29+). The band termination at Iπ = (22+) reported in previous studies is confirmed and interpreted as arising from a shape change from collective prolate to noncollective oblate according to Total-Routhian-Surface (TRS) calculations. In addition, the Iπ=(29+) state is assigned to the [πh11/2(πg7/2)2]23/2-⊗[(νh11/2)3(νd5/2)2]35/2− configuration corresponding to the full alignment of all valance nucleons outside the semi-closed shell.