N. T. Zhang

A proposed direct measurement of cross section at Gamow window for key reaction 19F(p,α) 16O in Asymptotic Giant Branch stars with a planned accelerator in CJPL

In 2014, the National Natural Science Foundation of China (NSFC) approved the Jinping Underground Nuclear Astrophysics laboratory (JUNA) project, which aims at direct cross-section measurements of four key stellar nuclear reactions right down to the Gamow windows. In order to solve the observed fluorine overabundances in Asymptotic Giant Branch (AGB) stars, measuring the key 19F(p,α)16O reaction at effective burning energies (i.e., at Gamow window) is established as one of the scientific research sub-projects. The present paper describes this sub-project in details, including motivation, status, experimental setup, yield and background estimation, aboveground test, as well as other relevant reactions.

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.

Two measurements of the 22Na+p resonant scattering via thick-target inverse-kinematics method

Na-22 is an important isotope for the study of extinct radioactivity, meanwhile its sufficiently long half life provides the possibility to observe live Na-22 in nearby nova explosions. The Na-22(p,gamma)Mg-23 is one of the key reactions that influence the Na-22 abundance in nova ejecta. To study the proton resonant states in Mg-23 relevant to the astrophysical Na-22(p,gamma)Mg-23 reaction rates, two measurements have been carried out at the CRIB separator of University of Tokyo, and the RIBLL secondary beamline in Lanzhou, respectively. The Na-22 secondary beam was produced via the H-1(Ne-22,Na-22) n charge exchange reaction. Thick-target inverse-kinematics method is applied to obtain the excitation function of Na-22+ p elastic scattering. Extended gas target and solid state polyethylene foil were used in the two measurements, respectively, to map the different excitation energy region of the compound nucleus Mg-23. Several new resonant levels are observed and their contribution to the Na-22(p,gamma)Mg-23 reaction rate is evaluated.

Rotational band properties in {sup 165}Er

High-spin states in {sup 165}Er have been studied experimentally using the {sup 160}Gd({sup 9}Be, 4n) reaction at beam energies of 42 and 45 MeV. The previously known bands based on the 5/2{sup +}[642], 5/2{sup -}[523], and 11/2{sup -}[505] configurations are extended to (49/2{sup +}), (45/2{sup -}), and (31/2{sup -}) states, respectively. The rotational bands in {sup 165}Er generally show gradual alignment processes, indicating strong band interactions associated with the i{sub 13/2} neutron alignments. The band properties are compared with those in the neighboring nuclei and discussed within the framework of the cranked shell model.

Properties of the rotational bands in {sup 161}Er

High-spin states in {sup 161}Er have been studied experimentally using the {sup 150}Nd({sup 16}O,5n) reaction at a beam energy of 86 MeV. The 5/2{sup +}[642], 3/2{sup -}[521], and 11/2{sup -}[505] bands are extended up to high-spin states, and particularly the {alpha}=-1/2 branch of the ground state 3/2{sup -}[521] band is revised significantly. The relatively enhanced E1 transitions from the 3/2{sup -}[521] band to the 5/2{sup +}[642] band are observed. The band properties are analyzed within the framework of a triaxial particle-rotor model, and near-prolate shape and triaxial deformation are proposed to the 3/2{sup -}[521] and 5/2{sup +}[642] bands, respectively. Signature inversion occurs in the 3/2{sup -}[521] band after the band crossing in {sup 161}Er, and the systematics of the signature inversion associated with the 3/2{sup -}[521] configuration are discussed. By analyzing the properties of the relatively enhanced E1 transitions, it is found that the R(E1/E2) values show angular momentum dependence before the band crossing, and these enhanced E1 transitions could be attributed to octupole softness.

Identification of the {gamma}-vibrational band built on the 11/2{sup -}[505] orbital in {sup 165}Er

Excited states in {sup 165}Er have been populated using the {sup 160}Gd({sup 9}Be, 4n) reaction at beam energies of 42 and 45 MeV. A band consisting of two levels at excitation energies of 1317.6 and 1505.9 keV, both of which decay strongly to the 11/2{sup -}[505] band, is observed and assigned as the {gamma}-vibrational band built on the 11/2{sup -}[505] configuration. In addition, a newly identified level is proposed as a three-quasiparticle state.

Band properties of the transitional nucleus 189Pt

High‐spin states in 189Pt have been studied with the in‐beam γ‐spectroscopy method via the 176Yb(18O,5n) reaction at beam energies of 88 MeV and 95 MeV. A new level scheme of 189Pt has been established. Rotational bands based on the υi13/2−1, υf5/2(p3/2) and υi13/2−2υf5esol2(p3/2) configurations, as well as several structures with irregular level spacings, have been observed. Properties of rotational bands have been analyzed in the framework of triaxial particle‐rotor model. A γ~−30° triaxial shape and a near prolate shape have been proposed to the υi13/2−1 and υf5/2(p3/2) bands, respectively. Two ΔI = 2 transition sequences with similar energies have been observed, and they have been proposed to be associated with the υi13/2−2υf5/2(p3/2) configuration. According to the relevant Nilsson orbitals, the bands built on the υi13/2−2υf5/2(p3/2) configuration could be interpreted as a pair of pseudo‐spin partner.