A new multi-detector array named HALIMA (Hybrid Array for LIfetime MeAsurement) has been developed at Lanzhou for nuclear structure studies in fission. The array comprises eight BGO-shielded High-Purity Germanium detectors and twenty fast Ce-doped Lanthanum Bromide [LaBr _3 (Ce)] detectors shielded with CsI(Tl). HALIMA is further complemented by two ancillary detector systems: fission fragment (FF) detectors and β detectors. This configuration enables precise sub-nanosecond lifetime measurements using the fourfold FF/ β -Ge-LaBr _3 (Ce)-LaBr _3 (Ce) coincidence technique. The performance and specifications of the detectors, associated electronics, and the data acquisition system are presented in detail. The advantage of FF selectivity is emphasized, which significantly enhances sensitivity to specific fission channels. Using this approach, the lifetimes of the nuclear excited states populated in the spontaneous fission of ^252 Cf were measured, showing good agreement with the established literature values.

A state-of-the-art detector array with a digital data acquisition system has been developed for charged-particle decay studies, including β -delayed protons, α decay, and direct proton emissions from exotic proton-rich nuclei. The digital data acquisition system enables precise synchronization and processing of complex signals from various detectors, such as plastic scintillators, silicon detectors, and germanium γ detectors. The system’s performance was evaluated using the β decay of ^32 Ar and its neighboring nuclei, produced via projectile fragmentation at the first Radioactive Ion Beam Line in Lanzhou (RIBLL1). Key measurements, including the half-life, charged-particle spectrum, and γ -ray spectrum, were obtained and compared with previous results for validation. Using the implantation–decay method, the isotopes of interest were implanted into two double-sided silicon strip detectors, where their subsequent decays were measured and correlated with preceding implantations using both position and time information. This detection system has potential for further applications, including the study of β -delayed charged-particle decay and direct proton emissions from even more exotic proton-rich nuclei.

The measurement of low-level radioactivity using high-purity germanium (HPGe) detectors is important in applications such as environmental background radiation, material screening, and rare decays. The dead layers, dead zones, aluminum shell thickness, and diameter of Ge crystals are the most influential factors affecting the performance of HPGe detectors; hence, precise modeling of the physical conditions of the detectors is highly desirable. In this study, the GEANT4 simulation framework with an optimized detector geometry adequately replicated the experimentally recorded spectrum. These detector simulations explored the idea of realizing a dead zone (an inactive volume) at the backend of an n-type coaxial Ge-crystal. Using multigamma sources, the effect of true coincidence summing (TCS) on the full energy peak (FEP) efficiency calibration of an HPGe detector was investigated as a function of sample-to-detector distance. Good agreements between the simulated and experimental efficiencies as well as the simulated and analytically calculated summing coincidence correction coefficients were achieved. At a short distance between the source and detector, calculating the correction factors for a strong source posed challenges owing to significant deadtime and pile-up effects of the detection system. The described methodology can efficiently determine summing peak probabilities at short sample-to-detector distances.

The lifetimes of the first 2+ states in 116,118Te were measured by means of the recoil distance Doppler -shift technique with the CIAE-plunger coupled to a HPGe array via 107Ag(12C, 3n) and 110Pd(12C, p3n) reactions, respectively. The spectra are analyzed using the differential decay curve method. An improved precision for the lifetime of the 2+1 state in 118Te was obtained, tau(2+1) = 8.2(5) ps, as well as a first measurement of the 2+1 state in 116Te, tau(2+1) = 5.1(3) ps. The lifetime values complete the systematic data near midshell and contribute to the understanding of how quadrupole collectivity evolves in this mass region. The resulting B(E2, 0+1 -> 2+1 ) transitions strength are discussed in relation to the systematics of the previously reported B(E2, 0+1 -> 2+1 ) values in the Te isotopes and compared to the predictions of several models.

The near-symmetric complete fusion reaction 78Kr + 107Ag -> 185Bi & lowast; was studied at the gas-filled recoil separator SHANS with an attempt to synthesize the extremely neutron-deficient proton-unbound 182,183Bi isotopes. No decay events which could be attributed to them were observed. The two- and three-particle evaporation residues 180,179Hg (alpha p, alpha pn) and 183,182Pb (pn, p2n) were identified. Their production cross sections have been measured at two bombarding energies. Based on the yields of 182,183Pb in the present work and the systematics of the ratios between the cross sections of p(x-1)n and xn evaporation channels for the most neutron-deficient odd-Z nuclei above lead, the upper limits for the half-lives of 182,183Bi were estimated to be less than 0.3 mu s.

High-spin states in Sn-112 were investigated using the Rh-103(C-12, 1p2n) reaction at a beam energy of 62 MeV. Six electric dipole E1 transitions linking positive- and negative-parity intruder bands have been identified in Sn-112(50) through gamma -ray spectroscopy. The experimental reduced E1 transition probabilities B(E1), derived from level lifetimes by means of the Doppler-shift attenuation method, are of the order of 10(-4) W.u., which gives evidence for the octupole correlation in Sn-112. The systematics of the reduced E1 transition probabilities and neutron energy levels of 5/2(+) and 11/2(-) in Xe isotopes suggest an enhanced octupole correlation at neutron number N = 62, which is supported by the relativistic Hartree-Bogoliubov calculations.

High-spin states of 67Ga have been studied via the 58Ni(12C, 3p) 67Ga fusion-evaporation reaction at a beam energy of 50.4 MeV. Three negative-parity bands and three positive-parity bands in 67Ga are established. The observation of one new E3 transition linking the positive-parity pi 1g9/2 band and negative-parity pi 2p3/2 band provides evidence of octupole correlations in 67Ga. The characteristics of octupole correlations in the 67Ga are discussed in terms of the reflection-asymmetric triaxial particle rotor model and microscopic relativistic mean field + Bardeen-Cooper-Schrieffer model.

Excited states of 207Rn have been investigated with the 197Au(14N, 4n) 207Rn reaction at a beam energies of 78 MeV. The level scheme of 207Rn was revised and expanded considerably by the gamma -gamma coincidence measurement. A large-scale shell-model calculation was performed for the purpose of improving the understanding of some levels of 207Rn. A rotational-like band has been observed in 207Rn and the microscopic three-dimensional tilted axis cranking covariant density functional theory (3DTAC-CDFT) was applied to explain it. The calculated results indicate the weak oblate deformation and emergence of principal axis rotation for 207Rn. This band is suggested to be a collective oblate band.

High-spin states of Nb-94 have been studied by in-beam gamma-ray spectroscopic methods using the Se-82(O-18, p5n)Nb-94 reaction at beam energies of 82 and 88 MeV. Particle-gamma-gamma coincidence measurements using CsI and high-purity germanium arrays are employed to gain selectivity to Nb isotopic products. The level scheme of Nb-94 has been extended up to excitation energy approximate to 11 MeV and spin 24h with the addition of 20 new gamma transitions, and the placement of some of the previously known transitions has been revised. The energy spectrum bears signature of core breaking, viz., presence of high energy (E-gamma approximate to 2 MeV) gamma rays originating due to excitation of nucleons across the shell gaps. The proposed level scheme is compared with large basis spherical shell model calculations using the GWBXG and SNET interactions.

Charge-changing cross-sections (CCCSs) of 11−16C, 13−17N and 15−18O on a carbon target have been determined at energies around 300 MeV/nucleon. A nucleon separation energy-dependent correction factor has been introduced to the Glauber model calculation for extracting the nuclear charge radii from the experimental CCCSs. The charge radii of 11C, 13,16N and 15O thus were determined for the first time. With the new radii, we studied the experimental mirror-difference charge radii (ΔRchmirror) of 11B-11C, 13C-13N, 15N-15O, 17N-17Ne pairs for the first time. We find that the ΔRchmirror values of 13C-13N and 15N-15O pairs follow well the empirical relation to the isospin asymmetry predicted by the ab initio calculations, while ΔRchmirror of 11B-11C and 17N-17Ne pairs deviate from such relation by more than two standard deviations.

Zero-field magnetization switching (ZFS) driven by current-induced spin-orbit torque (SOT) holds significant importance in spintronic applications. The introduction of a lateral asymmetric structure (LAS) through oblique deposition proves to be an effective strategy for breaking inversion symmetry, thereby enabling SOT-driven ZFS. However, the coexistence of wedge thickness structure and slanted columnar microstructure in the obliquely deposited films poses challenges in distinguishing their respective effects. In this study, we conducted a comparative investigation of the perpendicular magnetic properties and current-induced switching in W/Co40Fe40B20/MgO films by oblique sputtering of the W underlayer at a fixed tilting angle and at two opposite tilting angles with its wedge thickness compensated. We have found that the perpendicular magnetic properties of the Co40Fe40B20 layer are significantly altered at large tilting angles, irrespective of whether the W wedge thickness is compensated. Notably, at a tilting angle of 50 degrees, ZFS is realized for both the conventional oblique sample and the compensating oblique sample, with the switching polarity contingent on the final tilting direction of the W layer. We have identified a gradient in perpendicular magnetic anisotropy in these samples, attributed to the laterally varying roughness associated with the slanted columnar microstructure of the W underlayer. This study underscores the dominant role of microscopic LAS in obliquely deposited films in breaking SOT symmetry. Our research sheds light on the impact of the slanted columnar microstructure on the magnetic and magneto-transport properties of films, offering valuable insights for advancing spintronic device research.

The compensated ferrimagnetic insulator Gd3Fe5O12 (GdIG) with a magnetization compensation point (TM ∼ 286 K) near room temperature has recently gained significant attention because of its long spin transmission length and absence of Ohmic loss. However, previously reported GdIG films with perpendicular magnetic anisotropy have a TM far below room temperature, which is unfavorable for practical applications. Here, we show the tuning of TM from 268 to 303.7 K in perpendicularly magnetized 15 nm GdIG films epitaxially grown on (111) Gd3Sc2Ga3O12 by manipulating the epitaxial strain through controlling the rapid cooling temperature during the annealing process. By varying the film thickness between 5 and 40 nm, the TM of the film can be further extended to a range of 246–380 K. We have also demonstrated highly efficient switching of the GdIG spin-sublattices driven by current at room temperature in the GdIG/Pt heterostructures with various TM values, especially with TM slightly higher than 300 K. Our findings reveal potential opportunities for insulating compensated ferrimagnetic films of GdIG in the development of high-density, high-speed, and energy-efficient spintronic devices.

In the pedestal region of the Experimental Advanced Superconducting Tokamak (EAST) during high confinement mode plasma operations with radio-frequency heating, two distinct fluctuations are observed: high-frequency fluctuations (HFFs) and edge harmonic oscillation-like (EHO-like) modes. The HFFs are characterized by intermittent fluctuations with a broadband frequency range of 1 - 3 MHz and a poloidal wave number ( k theta ) greater than 0.9 c m - 1 . On the other hand, the EHO-like mode exhibits characteristics similar to magnetohydrodynamics (MHD)-like modes with n = 1-5 and lower poloidal wave numbers ( k theta <= 0.12 c m - 1 ). During the pedestal establishing phase following the L-H transition, a significant concurrent presence of HFF and EHO-like modes in high-density pedestal regions has been noted. In this phase, the EHO-like mode not only modulates the amplitude of the HFF but also engages in nonlinear interactions. The occurrence of EHO-like mode and HFF is associated with particle transport toward the divertor, though it is notably less than that caused by edge coherent modes. During the inter-edge localized mode (ELM) period, a significant decrease in the D alpha baseline is observed whenever the low frequency fluctuation (LFF) weakens and the HFF grows, prior to each large ELM. One possible explanation is that the rapid increase of E x B shear stabilizes the LFF and destabilizes the HFF, which lowers the pedestal transport and enables the further growth of the pedestal until the onset of the ELM.

In the present work, the Doppler Shift Attenuation method (DSAM) was used to analyze the observed lineshapes of transitions from excited states in 45Sc, populated in the reaction 36Ar + 12C at a beam energy of 145 MeV. The interpretation and comparison of the experimental results have been performed with large-scale shell model calculations, involving different interactions like: GX1A, GX1J, FPD6, KB3 and ZBM2. KB3 and FPD6 (present work) interactions in the negative parity states, and in positive parity states ZBM2 are most pre-eminent in reproducing the results, due to the large configuration space describing strong collective effects. Furthermore, the present work also looks at the details of the shell model helping in improving the understanding for the occupancy of orbitals. The present investigation suggests the observation of stronger collectivity for positive parity states over negative parity states with predicted enhanced collectivity of states in 45Sc nucleus.

Received 14 March 2023DOI:https://doi.org/10.1103/PhysRevC.107.049901©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsElectromagnetic transitionsEnergy levels & level densitiesNuclear structure & decaysTransfer reactionsProperties150 ≤ A ≤ 189Nuclear Physics

通过重离子熔合蒸发反应82Se(18O，p5n)94Nb，布居了94Nb的高自旋态，实验中使用的18O束流由中国原子能科学研究院的HI-13串列加速器提供，束流能量为82MeV和88MeV。在前人工作的基础上发现了15条新的γ跃迁并调整了部分能级的摆放位置，丰富并完善了94Nb的能级纲图，结合DC0比值和线极化测量，确认了部分能级的自旋和宇称。在质子π(1f5/2, 2p3/2, 2p1/2, 1g9/2)和中子ν(2p1/2, 1g9/2, 1g7/2, 2d5/2)空间下对94Nb新的能级结构与壳模型计算进行了比较和讨论。

Received 26 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.039903©2023 American Physical Society