Charge Exchange Component of n-p Interactions

An extra term of n-p effective interaction containing charge exchange component is proposed and applied to treating odd-mass nuclei with shape coexistence. The energy spectra and some E2 transition branching ratios are calculated for odd-A nuclei ^113~125Sb,^115~127I. With the inclusion of new term, an overall agreement with experiment is much improved.     

Nuclear Level Density with Non-zero Angular Momentum

The statistical properties of interacting fermions have been studied for various angular momentum with the inclusion of pairing interaction. The dependence of the critical temperature on angular momentum for several nuclei, have been studied. The yrast energy as a function of angular momentum for 28Si and 24 Mg nuclei have been calculated up to 60.0 MeV of excitation energy. The computed limiting angular momenta are compared with the experimental results for ^26Al produced by ^12C＋ 14N reaction. The relevant nuclear level densities for non-zero angular momentum have been computed for ^44Ti and ^136 Ba nuclei. The results are compared with their corresponding values obtained from the approximate formulas.     

Neutron Halos in the Excited States of Spherical Nuclei Near the β-Stable Line

The newly discovered neutron halos in the excited states of nuclei ¹²B, ¹³C, and ²⁰⁹Pb are studied by the relativistic mean-field theory. The calculated binding energies are very close to the experimental ones. The experimentally extracted root-mean-square radii of the last neutron with different occupations in nuclei are well reproduced by calculations. New candidates for the neutron halos in excited states are predicted and are useful for further search of neutron halos in the excited states of stable nuclei.     

Magnetic moments of light nuclei

Magnetic moments of the nuclei ¹⁵N, ¹⁵O, ¹⁷O, ¹⁷F and ¹⁹F are investigated. The importance ; of configuration mixing as well as meson-exchange currents is discussed in detail. Meson-exchange currents are treated in the one-boson exchange limit. Short-range N-N correlations are obtained from solutions of the Bethe-Goldstone equation for doubly closed shell nuclei by the use of realistic N-N potentials which ensure a correct treatment of tensor correlations.     

Escape of charged particles at stopping annihilation of antiprotons in the heavy nuclei of nuclear photoemulsion

“Rare” annihilation channels for antiprotons stopping on heavy (Ag, Br) nuclei of photoemulsion, have been sought; 4872 stops of antiprotons on photoemulsion nuclei are analysed. Events of formation and decay of the hyperfragment _Λ⁴H, escape of ⁸He and ⁸Li nuclei, one-prong stars with the mean range 79.5±5.1 μm of secondary slow “b” particles are found among the annihilation stars at capture on nuclei (Ag, Br). The lower limits for the production probability of _Λ⁴H and ⁸He, ⁸Li nuclei per antiproton stopping in the nuclei (Ag, Br) are

W_Λ⁴H2×10⁻⁴ and W_⁸He,⁸Li=(1.3±0.6)×10⁻³.

The branching ratio for the production of one-prong stars with the secondary “b” particles is at least (1.3±0.6)×10⁻³. Possible mechanisms for a production of these events in annihilation processes are considered.     

Potassium tetracyanoplatinate (II) trihydrate (K2Pt(CN)4·3H2O) studied by high resolution solid state C MAS NMR

Prudent analysis of the solid state ¹³C MAS NMR spectra of polycrystalline K₂Pt(CN)₄ · 3H₂O (KTCP)⁻ reveals that in crystals of this compound there are two types of carbon nuclei with slightly different ¹³C chemical shift tensors, contrary to what is found for the solution NMR spectrum and previous static powder NMR studies on this compound and the high resolution solid state NMR studies on other similar compounds. The ¹³C MAS spectra measured at different rotor spinning speeds are satisfactorily simulated though the use of a newly developed computer program based on a novel density matrix formulation. The present method is eminently successful even though the spectra are rather complicated because of (1) the relatively large anisotropies of the chemical shift tensors; (2) the high-order dipolar interactions between ¹³C and ¹⁴N nuclei because of the strong quadrupolar coupling constants of ¹⁴N nuclei; and (3) the indirect J-coupling between the ¹³C and ¹⁹⁵Pt. The principal elements as well as their orientations of the two ¹³C chemical shift tensors are evaluated from the spectral simulations.     

Search for parity violation in the 1081 keV gamma transition of F

The weak neutral current results in a parity-violating one-pion-exchange potential in nuclei. A search for this force has been carried out with the 1081 keV γ-radiation of ¹⁸F, which is expected to be circularly polarized. Excited ¹⁸F nuclei were produced with the ¹⁶O(³He, p)¹⁸F reaction and the γ-ray polarization was measured with a multiple transmission polarimeter system. The experimental result P = (− 1.0 ± 1.8) × 10⁻³ is smaller than recent theoretical estimates.     

Intermediate Energy Pion-20Ne Elastic Scattering in the α+16O Model of 20Ne

We present an analysis of π-²⁰Ne elastic scattering at intermediate energy basing on the α+¹⁶O model of the ²⁰Ne nucleus and in the framework of Glauber multiple scattering theory. Satisfactory agreement with the general features of the experimental data of pion elastic scattering on the neighboring 4N-type nuclei is obtained without any free parameters. Compared with the experimental angular distributions of pion elastic scattering on ¹²C, ¹⁶O, ²⁴Mg, and ²⁸Si nuclei, the diffractive patterns and the positions of the dips and peaks in the angular distributions of π-²⁰Ne elastic scattering are reasonably predicted by the calculations.     

Simple Formula of β+-Decay Half-Lives of Nuclei Far From β-Stable Line

We generalize the formula of β⁺-decay half-lives [Phys. Rev. C 73 (2006) 014305] to include all available data of nuclei far from the β-stable line. Good agreement with experimental data is obtained by taking into account the even-odd (e-o) effect. It is shown that the e-o effect on β⁺-decay half-life is apparent for the allowed β⁺-transition, whereas it is not apparent for the first and second forbidden transitions. This demonstrates that the allowed β⁺-transition is more sensitive to the nuclear even-odd effect than the forbidden β⁺-transition. The underlying physics is discussed. This formula can be used to predict the β⁺-decay half-lives of the nuclei far from β-stability. It is useful to experimental physicists for analyzing the data of β⁺-decay.     

相对论平均场理论对Pt同位素形状演化的研究

利用形变约束的相对论平均场理论研究了Pt同位素偶-偶核的形状演化,比较了基态结合能和四极形变的理论计算值和实验值, 分析了这些核的位能曲线、单粒子能级及其随四极形变β₂ 的变化规律,发现从N=88到N=126, Pt同位素的基态变形从球形对称核经X(5)对称性核、演化为具有稳定形变的核,再演化为球形核的变化过程.其中, ^166-172Pt是近球形核, ¹⁷⁴Pt和^192-196Pt位于球形和稳定形变之间,可能具有X(5)对称性, ^176-190Pt具有稳定的变形, ^198-202Pt是近球形核, ²⁰⁴Pt是球形核,这些结果与实验一致.     

Ranges of 0.2-1.0 GeV/nucleon heavy ions in nuclear photoemulsion

Heavy nuclei transport in matter are studied experimentally and theoretically. Our experimental range and straggling values of 0.2 – 1.0 GeV/nucleon ²⁰Ne, ⁴⁰Ar, ⁵⁶Fe, ¹⁹⁷Au and ²³⁸U nuclei in BR-2 nuclear photoemulsion are presented and compared with model calculations carried out according to our RANGE-program and the PRAL-model (version of 1987) developed by Ziegler et al. The presented data analysis points at the necessity to take into account Z³-correction in Bete-Bloch formula when ionization losses of very heavy multicharge ions (for example ¹⁹⁷Au and ²³⁸U) are calculated. The comparison of experimental and calculated results showed that RANGE program can correctly calculate the ranges and straggling of heavy ions. The difference between experimental and theoretical data do not exceed 5% in all of the cases examined. PRAL model describes the heavy ion ranges quite adequately, but overestimates the particle range straggling.     

H NMR study of YT2-hydride (T = Fe, Mn)

In the hydrides YMn₂H_3.0, the nuclear magnetic resonance of ¹H nuclei has been measured under external fields up to 50 kOe at 4.2 K and three ¹H NMR signals have been observed. The ¹H hyperfine fields corresponding to these NMR signals can be discussed in terms of the dipole interaction between the H nuclei and the localized moments of the Mn(or Fe) atoms surrounding H atoms.     

Study of cluster decay of heavy nuclei

The last results of studying radioactive decay of heavy nuclei ²³²Th, ²³⁶U, ²³⁶Pu and ²⁴²Cm using different dielectric detector types and methods of their development have presented.     

香港大学在束伽玛谱学研究与新一代伽玛探测器阵列(英文)

探索原子核的壳层演化,验证奇特核的幻数结构是香港大学核物理研究的重要方向。目前,科研团队利用在束伽玛谱学技术已经研究了30Ne的N=20幻数消失和78Ni（Z=28,N=50）附近原子核的双幻数结构,而即将开展的53,56Ca在束伽玛谱学实验会对新幻数N=34的定量研究,以及到N=40核的壳层演化提供重要的数据。下一步的研究目标是探索100Sn（N=Z=50）的奇特结构,特别是研究它的第一个2+激发态与其邻近原子核的低激发态性质。100Sn处于质子滴线以及核天体快质子俘获路径上,因此,它的幻数结构及其临近原子核单粒子性能研究将会极大增强对核力和核合成机制的认识。为了进一步提高物理实验统计,香港大学在数量上增加了30% NaI（Tl）晶体从而全面升级了DALI2伽玛探测阵列。此外,为了探索远离稳定线核区的新物理,开展更高精度在束伽玛谱学实验,香港大学与中国科学院近代物理研究所、中国原子能科学研究院计划合作研制基于溴化镧晶体的新一代伽玛探测器阵列。这套阵列主要在兰州重离子加速器（HIRFL）和将来建成的强流重离子加速器（HIAF）等大科学装置上开展实验,从而在奇特核研究方面取得大量重要的成果,促进科研人员全面认识、理解核力以及天体核合成过程。Exploring the evolution of shell closures and examining the magicity of extremely exotic nuclei are the main research interests of HKU (University of Hong Kong) experimental nuclear physics group. The group has employed in-beam gamma-ray spectroscopy technique to investigate the vanishing of N=20 magicity in 30Ne (N=20) and the strong magicity in nuclei around 78Ni (Z=28, N=50). The approved future's experiment on spectroscopy of 53,56Ca, proposed by HKU, will give quantitative information for the "magic index" of N=34 and shell evolution toward N=40. The next goal is to investigate the structure of 100Sn (N=Z=50), particularly the energy of the first 2+ state, and the low-lying states in the neighboring nuclei. 100Sn lies on the proton drip-line and on the astrophysical rp-process path. Characterizing the magicity of 100Sn and the nature of single-particle states in its neighboring nuclei is therefore essential to the fundamental understanding of nuclear forces and nucleo-synthesis. To significantly increase the data statistics for our physics goals, HKU group has prepared the upgrade of gamma-ray spectrometer DALI2 with 30% more NaI(Tl) detectors integrated into a new array configuration. On the other hand, next significant insights into the structure of nuclei would require new gamma-ray detection array capable for higher precision gamma-ray spectroscopy. HKU group in collaboration with IMP and CIAE therefore proposes to construct a new-generation gamma-ray detection array based on the novel scintillator LaBr₃(Ce) to explore the new physics in nuclei far from the valley of stability. Utilizing the radioactive beams at the Chinese large-scale facilities such as the Heavy Ion Research Facility in Lanzhou (HIRFL) in IMP and the future's High Intensity heavy-ion Accelerator Facility (HIAF), this novel LaBr₃(Ce) array would lead to a significant boost to the frontiers of exotic-nuclei research, which will guide scientists towards the comprehensive and even beyond-traditional understanding of nuclear forces and nucleosynthesis.     

EPR and ENDOR study of an oxygen-vacancy-associated Ti center in RbTiOPO4 crystals

The dominant Ti³⁺ trapped electron center in flux-grown RbTiOPO₄ (RTP) crystals has been characterized using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR). This center is produced during an X-ray irradiation at room temperature when a Ti⁴⁺ ion traps an electron and becomes a Ti³⁺ ion, and is best studied in the 30–40 K range. The EPR spectrum contains a three-line hyperfine pattern from two nearly equivalent neighboring ³¹P nuclei, along with hyperfine lines from the ⁴⁷Ti and ⁴⁹Ti nuclei. The g matrix, determined from the angular dependence of the EPR spectrum, has principal values of 1.819, 1.889, and 1.947. Hyperfine matrices for four ³¹P nuclei are obtained from the angular dependence of the ENDOR spectrum. The proposed model for this defect is a Ti³⁺ ion adjacent to an oxygen vacancy at an OT position. Analogies are made to a similar Ti³⁺ center in KTiOPO₄ (KTP) crystals.     

High spin states in doubly even pf-shell nuclei

High spin states of the yrast band in ⁵⁰Ti, ⁵²Cr, ⁵⁴ and ⁴⁶Ti are investigated in a microscopic approach allowing a coupling of rotations, vibrations and quasiparticle excitations. The lowering of the 6⁺ state in N = 28 nuclei is shown to originate mainly from proton K = 0 two-quasiparticle excitations. Using as a basis the entire pf-shell 8⁺ and 10⁺ states can be predicted for ⁵⁰Ti and ⁵⁴Fe.     

Rotational excitations in residual nuclei produced by stopped negative pions on targets of Ho, Lu, Lu, Hf, and Ta

Reactions produced by stopped negative pions on targets of ¹⁶⁵Ho, ¹⁷⁵Lu, ¹⁷⁶Lu, ¹⁷⁹Hf, and ¹⁸¹Ta are investigated by measuring photons coincident with the stopped pions. These photons were detected with an 80 cm³ Ge(Li) detector and identified as pionic X-rays or rotational γ-rays from the residual nuclei. Pion capture is found to result in the excitation of high-spin states. Yields for the residual nuclei are inferred from the observed γ-transitions and compared to calculations based on the exciton model for pre-equilibrium emission followed by particle evaporation. Preliminary results of a pion stop, γn coincidence experiment are presented and compared to the calculations.     

Macroscopic-microscopic calculations of fission potential surface of uranium isotopes in the three quadratic surfaces parametrization

Five-dimensional (5D) fission potential energy surfaces (PES) for uranium nuclei are investigated based on the macroscopic-microscopic Lublin-Strasbourg drop model in the three-quadratic-surface parametrization, and the heights of static fission barriers are obtained. Asymmetric and symmetric fission paths are presented on the 5D PES of ²³⁶U for different nuclear shapes. The calculated barrier heights, E_A and E_B, are quite consistent with the experimental data for all even-even nuclei of uranium isotopes, from ²³⁰U to ²⁴⁴U.     

A Detailed Study of Pre-scission γ Emission as a Probe of Nuclear Dissipation

Using a Langevin equation coupled with a statistical model, we calculate pre-scission giant dipole resonance （GDR） γ-ray multiplicity of nuclei 194 pb, 200Pb, 206Pb, and 200 Os. It is demonstrated that with increasing the isospin asymmetry of these fissioning nuclei the sensitivity of the emitted γ multiplicity to the nuclear viscosity coefficient is decreased significantly. For 200Os nuc/eus, this γ-ray emission is no longer sensitive to the magnitude of the viscosity coefficient. In addition, the effect of the isospin asymmetry on the γ rays as a probe of nuclear dissipation is reduced with increasing angular momentum. These results suggest that to obtain a more accurate information of the viscosity coemfficient by the measurement of pre-scission GDR γ-ray multiplicity it is better to choose those compound systems with small isospin asymmetry and low spin.