Simulation and test of the SLEGS TOF spectrometer at SSRF

The Shanghai laser electron gamma source(SLEGS)is a powerful tool for exploring photonuclear physics,such as giant dipole resonance(GDR)and pygmy dipole resonance,which are the main mechanisms of collective nuclear motion.The goal of the SLEGS neutron time-of-flight(TOF)spectrometer is to measure GDR and specific nuclear structures in the energy region above the neutron threshold.The SLEGS TOF spectrometer was designed to hold 20 sets of EJ301 and LaBr3 detectors.Geant4 was used to simulate the efficiency of each detector and the entire spectrometer,which provides a reference for the selection of detectors and layout of the SLEGS TOF spectrometer.Under the events of 208Pb,implementations of coincidence and time-of-flight technology for complex experiments are available;thus,and neutron decay events can be separated.The performance of SLEGS TOF spectrometer was systematically evaluated using offline experiments,in which the time resolution reached approximately 0.9 ns.

Unified mechanism behind the even-parity ground state and neutron halo of^(11)Be

Using the axially deformed relativistic Hartree-Fock-Bogoliubov(D-RHFB)model,we explore the mechanism behind the parity inversion and halo occurrence in^(11)Be,which are well reproduced by the RHF Lagrangian PKA1.It is illustrated that evidently enhanced deformation effects by theπ-pseudo-vector andρ-tensor couplings in PKA1 are crucial for correctly describing both the even-parity ground state(GS)and the neutron halo of^(11)Be.Coupling with the deformation,the intrude 1d_(5/2)component largely enhances the couplings between the evenparity orbit 1/2_(2)^(+)and the nuclear core to ensure an even-parity GS,whereas the 2s_(1/2)component therein dominates the halo formation in^(11)Be.Moreover,the deformed halo in^(11)Be is found to be stabilized by the attractive inherent correlations between the 1d_(5/2)and 2s_(1/2)components of the halo orbit 1/2_(2)^(+),instead of pairing correlations,which paves a new way for understanding the halo pictures in deformed unstable nuclei.

Restoration of pseudo-spin symmetry in N = 32 and N = 34 isotones described by relativistic Hartree-Fock theory

The restoration of pseudo-spin symmetry（PSS） along the N = 32 and N = 34 isotonic chains and the physics behind are studied by applying the relativistic Hartree-Fock theory with the effective Lagrangian PKA1. Taking the proton pseudo-spin partners(π2s1/2, π1d3/2) as candidates, the systematic restoration of PSS along both isotonic chains is found from sulphur（S） to nickel（Ni）, while an obvious PSS violation from silicon（Si） to sulphur is discovered near the drip lines. The effects of the tensor force components are investigated, introduced naturally by the Fock terms, which can only partially interpret the systematics from calcium to nickel, whereas they fail for the overall trends. Further analysis following the Schr?dinger-like equation of the lower component of Dirac spinor shows that contributions from the Hartree terms dominate the overall systematics of the PSS restoration. Such effects can be self-consistently interpreted by the evolution of the proton central density profiles along both isotonic chains. In particular, the PSS violation is found to tightly relate to the dramatic changes from the bubble-like density profiles in silicon to the central-bumped ones in sulphur.

Novel relativistic mean field Lagrangian guided by pseudo-spin symmetry restoration

The relativistic mean field(RMF)model has achieved great success in describing various nuclear phenomena.However,several serious defects are common.For instance,the pseudo-spin symmetry of high-l orbits is distinctly violated in general,leading to spurious shell closures N Z 58 and 92.This leads to problems in describing structure properties,including shell structures,nuclear masses,etc.Guided by the pseudo-spin symmetry restoration[Geng et al.,Phys.Rev.C,100:051301(2019)],a new RMF Lagrangian DD-LZ1 is developed by considering the density-dependent meson-nucleon coupling strengths.With the newly obtained RMF Lagrangian DD-LZ1,satisfactory descriptions can be obtained for the bulk properties of nuclear matter and finite nuclei.In particular,significant improvements on describing the single-particle spectra are achieved by DD-LZ1.In particular,the spurious shell closures Z 58 and 92,commonly found in previous RMF calculations,are eliminated by the new effective interaction DD-LZ1,and consistently the pseudo-spin symmetry(PSS)around the Fermi levels is reasonably restored for both low-l and high-l orbits.Moreover,the description of nuclear masses is also notably improved by DD-LZ1,as compared to the other RMF Lagrangians.