X. G. Lei

7Be, 8B+208Pb Elastic Scattering at Above-Barrier Energies

Angular distributions for the elastic scattering of 7Be and 8B by an enriched 208Pb target were measured at the Radioactive Ion Beam Line at Lanzhou (RIBLL). The incident energies of the radioactive beams were about three times the respective Coulomb barriers. A suppressed Coulomb-nuclear Interference Peak (CNIP) is not observed for 8B, a pronounced proton halo nucleus. Optical model fits were performed using Woods-Saxon potentials and the total reaction cross sections deduced. The results are discussed.

Low-spin signature inversion in the {pi}h{sub 9/2}x{nu}i{sub 13/2} oblate band of {sup 190}Tl

High-spin states in {sup 190}Tl have been studied experimentally by using the {sup 160}Gd({sup 35}Cl,5n) fusion-evaporation reaction at beam energies of 167 and 175 MeV. A rotational band built on the {pi}h{sub 9/2}x{nu}i{sub 13/2} configuration with oblate deformation has been established for {sup 190}Tl. Spin values are assigned by adopting the results from {alpha}-{gamma} decay work for {sup 194}Bi found in the literature. With the configuration and spin-parity assignments, the low-spin signature inversion has been revealed for the {pi}h{sub 9/2}x{nu}i{sub 13/2} oblate band in {sup 190}Tl. It is the first experimental observation of low-spin signature inversion for a band associated with the oblate {pi}h{sub 9/2}x{nu}i{sub 13/2} configuration. The low-spin signature inversion for the oblate {pi}h{sub 9/2}x{nu}i{sub 13/2} band can be interpreted by the two-quasiparticle-plus-rotor model including a J-dependent p-n residual interaction.High-spin states in Tl-190 have been studied experimentally by using the Gd-160(Cl-35,5n) fusion-evaporation reaction at beam energies of 167 and 175 MeV. A rotational band built on the pi h(9/2)circle times nu i(13/2) configuration with oblate deformation has been established for Tl-190. Spin values are assigned by adopting the results from alpha-gamma decay work for Bi-194 found in the literature. With the configuration and spin-parity assignments, the low-spin signature inversion has been revealed for the pi h(9/2)circle times nu i(13/2) oblate band in Tl-190. It is the first experimental observation of low-spin signature inversion for a band associated with the oblate pi h(9/2)circle times nu i(13/2) configuration. The low-spin signature inversion for the oblate pi h(9/2)circle times nu i(13/2) band can be interpreted by the two-quasiparticle-plus-rotor model including a J-dependent p-n residual interaction.

Quasi-elastic scattering of 10,11C and 10B from a natPb target

Angular distributions of the differential cross sections for the quasi-elastic scattering from a Pb-nat target by C-10 at 226 and 256 MeV, by C-11 at 222 MeV and 226 MeV, and by B-10 at 173 MeV were measured at the Heavy Ion Research Facility in Lanzhou, Radioactive Ion Beam Line in Lanzhou (HIRFL-RIBLL). Contributions from the inelastic scattering channels to these data are found to be negligibly small with coupled-channel calculations within the angular range covered by this experiment. These data can be well reproduced by optical model calculations with systematic nucleus-nucleus potentials. The reduced total reaction cross sections were compared with other existing data

High-spin level scheme of {sup 183}Au

High-spin states in {sup 183}Au have been studied experimentally using the {sup 159}Tb({sup 29}Si,5n){sup 183}Au reaction at a beam energy of 140 MeV. Three- or higherfold {gamma}-ray coincidences have been measured using the detector array of GASP. The level scheme of {sup 183}Au was revised and extended. A rotational band proposed as the unfavored signature branch of the {pi}i{sub 13/2} band has been observed for {sup 183}Au. Interaction properties between the two negative-signature bands of the {pi}h{sub 9/2}-{pi}f{sub 7/2} system have been discussed for the light odd-A Au nuclei.

High-spin states of an odd-odd 184Au nucleus

High-spin band structures in 184Au have been re-investigated using the multidetector array of GASP following the 149Sm(29Si, 4nγ)184Au reaction. Four previously observed bands built on prolate configurations have been extended significantly up to high spins and two weakly populated bands are newly identified. Structure properties of these bands are briefly discussed.

Characteristics of a CsI(Tl) Compton-suppressed clover detector

The performance of a four fold segmented clover detector coupled to a CsI-suppressed shield has been tested using several standard radioactive sources. The summing characteristics, hit patterns and absolute efficiency were measured in both crystal and clover modes. Peak-to-total ratios of 57.3% and 45.6% in suppressed clover mode have been determined for 137Cs and 60Co sources, respectively. A Geant4 simulation of the suppressed clover detector, including the segmentation of the germanium crystals, has been created, and the simulation results agreed very well with the experimental data.

SEARCH FOR SIGNATURE INVERSION IN THE πi13/2 ⊗ νi13/2 BANDS IN 182,184,186Au

Search for low-spin signature inversion in the πi13/2 ⊗ νi13/2 bands in odd-odd 182,184,186Au has been conducted through the standard in-beam γ-spectroscopy techniques. The experiments for 182Au and 186Au have been performed in the Japan Atomic Energy Agency (JAEA) via the 152Sm(35Cl,5n)182Au and 172Yb(19F,5n)186Au reactions, respectively. A study of 184Au has been made using a multi-detector array GASP in LNL, Italy, via the 159Tb(29Si,4n)184Au reaction. The πi13/2 ⊗ νi13/2 bands in these three nuclei have been identified and extended up to high-spin states. In particular, the inter-band connection between the πi13/2 ⊗ νi13/2 band and the ground-state band in 184Au has been established, leading to a firm spin-and-parity assignment for the πi13/2 ⊗ νi13/2 band. The low-spin signature inversion is found in the πi13/2 ⊗ νi13/2 bands in 182,184,186Au according to our spin-assignment and the signature crossing observed at high-spin states.

High-spin level scheme and decay of the 67-{mu}s isomer in {sup 142}Pm

Excited states in Pm-142 are investigated via the Te-128(F-19, 5n) Pm-142 reaction at beam energies from 75 to 95 Me V by using techniques of in-beam gamma-ray spectroscopy. Measurements of gamma-ray excitation function, X-gamma and gamma-gamma-t coincidences are performed with 10 BGO(AC)HPGe detectors. Decay of the previously known 67-mus isomer in Pm-142 is observed and added into the new level scheme. This isomer is definitely placed at the excitation energy of 2828.5keV. The spin of this isomer is suggested to be 13h according to the measured gamma-ray anisotropies.

Half-Lives of Low-Lying Isomeric States in 169Ta

Two low-lying isomeric states in 169Ta have been identified via 159Tb(16O, 6nγ)169Ta reaction. Their half-lives are measured to be 28 ± 5 ns for the 9/2- level and 17 ± 4 ns for the 5/2- level by using the delayed γ-γ coincidence method. These two isomeric states are considered to be the bandheads with 9/2-[514] and 1/2-[541] configurations, respectively. Possible neutron quasiparticle configuration for the ground state of 169W is discussed.

Experimental Study of Two-alpha Emission from High-lying Excited States of 17,18 Ne

The experiments of two-alpha emission from Ne-17,Ne-18 excited levels were performed at the HIRFL-RIBLL facility of the Institute of Modern Physics, Lanzhou. The beams of Ne-17 at the energy of 49.9 MeV/u and Ne-18 at 51.8 MeV/u bombarded a Au-197 target to populate excited states of Ne-17,Ne-18 via Coulomb excitation. Complete kinematics measurements were achieved by the detectors of a silicon strip and CsI+PIN array. The experimental results combined with simple MC simulations show the characteristic of sequential two-alpha emission via O-14 excited states for Ne-18. The results of two-alpha emission from Ne-17 are preliminary and need further analyses.