Large-scale shell model calculations for odd-odd <Superscript>58-62</Superscript>Mn isotopes

Large-scale shell model calculations have been carried out for odd-odd ^58-62Mn isotopes in two different model spaces. The first set of calculations has been carried out in full fp shell valence space with two recently derived fp shell interactions namely GXPF1A and KB3G treating ⁴⁰Ca as core. The second set of calculations has been performed in the fpg _9/2 valence space with the fpg interaction treating ⁴⁸Ca as core and imposing a truncation by allowing up to a total of six particle excitations from the 0f _7/2 orbital to the upper fp orbitals for protons and from the upper fp orbitals to the 0g _9/2 orbital for neutrons. For low-lying states in ⁵⁸Mn , KB3G and GXPF1A both predict good results and for ⁶⁰Mn , KB3G is much better than GXPF1A. For negative-parity and high-spin positive-parity states in both isotopes the fpg interaction is required. Experimental data on ⁶²Mn is sparse and therefore it is not possible to make any definite conclusions. More experimental data on negative-parity states is needed to ascertain the importance of 0g _9/2 and higher orbitals in neutron-rich Mn isotopes.     

Shell-model results in <Emphasis Type="Italic">fp</Emphasis> and <Emphasis Type="Italic">fpg</Emphasis><Subscript>9/2</Subscript> spaces for <Superscript>61,63,65</Superscript>Co isotopes

Low-lying spectra and several high-spin states of odd-even ^61,63,65Co isotopes are calculated in two different shell-model spaces. First set of calculations have been carried out in fp-shell valence space (full fp space for ^63,65Co and a truncated one for ⁶¹Co) using two recently derived fp-shell interactions, namely GXPF1A and KB3G, with ⁴⁰Ca as core. Similarly, the second set of calculations have been performed in fpg _9/2 valence space using an fpg effective interaction due to Sorlin et al., with ⁴⁸Ca as core and imposing a truncation. It is seen that the results of GXPF1A and KB3G are reasonable for ^61,63Co. For ⁶⁵Co, shell-model results show that the fpg interaction adopted in the study is inadequate and also points out that it is necessary to include orbitals higher than 1g _9/2 for neutron-rich Co isotopes.     

Extension of the spectroscopic Monte Carlo method to realistic effective interactions

We propose an extension of the spectroscopic Monte Carlo method to realistic effective interactions. The scheme is applied to the recently introduced GXPF1 interaction for fp nuclei for the ground state of ⁶⁰Fe, ⁵⁶Ni, ⁶⁴Ni and ⁶⁰Zn. The method hinges on the use of Hartree-Fock-Bogoliubov wave functions (properly projected before variation) and on a reformulation of the effective interaction so that it is a sum of negative squares of Hermitian one-quasi-particle operators, so the application of the Hubbard-Stratonovich transformation to the elementary propagator exp[- ] gives a functional integral over a Hermitian propagator. Limitations and difficulties encountered in the calculation are discussed.     

Self-consistent medium polarization in RPA

The standard random-phase approximation for finite systems is extended by including the effect of the exchange of the RPA phonons in the residual interaction selfconsistently. It is shown that this particle-hole interaction is strongly energy dependent due to the presence of poles corresponding to 2p2h (and more complex) excitations. The RPA eigenvalue problem with this energy-dependent residual interaction also provides solutions for these predominantly 2p2h-like states. In addition a modified normalization condition is obtained.This new scheme is applied to ⁵⁶Ni (⁵⁶Co) in a large (up to 7ħω) configuration space using a residual interaction of G-matrix type. It is shown that the lowest 2⁺ eigenvalue, which in the standard RPA becomes imaginary, is stabilized when the selfconsistent screening is taken into account. Another feature observed is the splitting of the M1 strength as an example of 1p1h and 2p2h mixing.     

KBn(n=1~10)团簇的结构和性质的密度泛函理论研究

应用密度泛函理论(DFT) B3LYP方法在6-311+G(d)水平上计算并分析了KBn(n=1~10)团簇的几何结构及电子性质和极化率.通过研究团簇的平均结合能、能级间隙、二阶能量差分分析了团簇的稳定性规律,研究表明: KBn(n=1~10)团簇基态多数为立体构型,能级间隙和二阶能量差分结果表明KB3与KB9是幻数团簇.对团簇基态的极化率研究表明KBn团簇的电子结构随B原子的增加趋于紧凑,基本形成了一定的堆积方式.静态第一超极化率研究表明KB8与KB4两种平面构型的团簇具有较好的非线性光学性能.     

基于壳模型对力加四极力研究sd和pf壳偶偶原子核

本文在原子核壳模型框架下基于唯象相互作用(对力加四极力)研究sd壳和pf壳的偶偶核低激发集体态。在提取了USDB和GXPF1相互作用的单粒子能量和单极相互作用的基础上,我们用一套统一参数计算重现了球形核和形变核的低激发谱;将对相互作用中的单极成分扣除后可以得到较好的结合能计算结果。同位旋标量的对相互作用对计算结果影响不大。单极相互作用在经验质子—中子相互作用、原子核对称能和Wigner能中产生重要贡献。     

The shell model and collective structures in54,55,56Fe

Extensive shell-model calculations have been performed on^54,55,56Fe. The results obtained in a model space with two and with up to threef _7/2 holes in the,⁵⁶Ni core are compared with experiment. The Surface Delta Interaction (SDI) and the Kuo Brown interaction (KB) have been used to calculate energy levels, spectroscopic factors and electromagnetic properties resulting especially for⁵⁶Fe in a remarkably good agreement with experiment. Admixtures of three-hole components in the wave functions are significant and increase with mass number. Properties of high-spin states withJ≦15 are discussed. Pronounced collective features derived microscopically are expected in⁵⁶Fe. Finally some suggestions for interesting experiments are given.     

Gamma-ray spectroscopy of the doubly magic nucleus 56Ni

The doubly magic N = Z nucleus ⁵⁶Ni has been investigated with two fusion-evaporation reactions; ⁴⁰Ca(²⁸Si, 3α)⁵⁶Ni at a beam energy of 122MeV and ²⁸Si(³²S, 2p2n)⁵⁶Ni at 130MeV. To detect γ-rays in coincidence with evaporated particles the Ge-detector array Gammasphere was used in conjunction with the charged-particle detector system, Microball and a 1π neutron detector array. Results include a significantly extended level scheme of ⁵⁶Ni, which is compared to large-scale shell model calculations in the fp shell. The experimental and theoretical results agree to a large extent, with one notable exception; the theoretical model fails to predict the proper sequence of the yrast and yrare 8⁺ states.     

密度泛函方法研究NiSin(n=1~13)团簇

基于第一性原理,利用密度泛函理论中的广义梯度近似(GGA)系统研究了NiSin(n=1～13)团簇,在充分考虑自旋多重度的基础上讨论了这些团簇的生长行为,电子性质及其磁性,结果表明:NiSin 1的基态结构是在NiSin的基态结构上带帽一个Si原子而得到;随着团簇尺寸的增大,Ni原子逐渐从吸附在sin团簇的表面位置移动到Sin团簇笼内;掺杂Ni原子提高了硅团簇的稳定性;NiSi10团簇的稳定性在所有团簇中是最高的;电子总是从si向Ni转移,Ni原子所带的电荷数不仅与Ni原子的配位数有关,还与Nisin团簇的基态结构密切相关;n=1～2时,团簇的自旋总磁矩为2 μB,当n≥3时,团簇的磁性消失,这可能与Ni原子内部较强的sp-d杂化以及si原子内部的s-p杂化有关.     

硝酸羟胺-(H_2O)_n复合物氢键相互作用的密度泛函研究

为研究硝酸羟胺-(H_2O)_n复合物的氢键作用,采用密度泛函B3LYP方法在6-311++G(d, p)基组水平上对硝酸羟胺-(H_2O)_n复合物的结构进行优化,采用MP2/6-311++G(d, p)方法,经基组叠加误差和零点能校正计算得到复合物的相互作用能.利用自然键轨道分析方法研究复合物氢键作用的本质,并对复合物中水分子的振动光谱进行分析.计算结果表明,硝酸羟胺-(H_2O)_n复合物存在着6个硝酸羟胺-H_2O稳定构型和8个硝酸羟胺-(H_2O)_2稳定构型,且最稳定构型的相互作用能分别为52.821 kJ·mol~(-1)和73.349 kJ·mol~(-1).在硝酸羟胺-(H_2O)_n复合物中,水中H-O伸缩振动频率明显红移,且红移增大的程度与复合物稳定化能的变化趋势基本一致.     

Coupled-cluster and configuration-interaction calculations for heavy nuclei

We compare coupled-cluster (CC) and configuration-interaction (CI) results for (56)Ni obtained in the pf-shell basis, focusing on practical CC approximations that can be applied to systems with dozens or hundreds of correlated fermions. The weight of the reference state and the strength of correlation effects are controlled by the gap between the f(7/2) orbit and the f(5/2), p(3/2), p(1/2) orbits. Independent of the gap, the CC method with 1p-1h and 2p-2h clusters and a noniterative treatment of 3p-3h clusters is as accurate as the more demanding CI approach truncated at the 4p-4h level.     

In-beam γ-ray spectroscopy on56Ni

Yrast levels in the doubly-magic nucleus⁵⁶Ni have been studied by in-beam gg-spectroscopy with the reaction⁵⁴Fe(α, 2n)⁵⁶Ni. A cascade of five γ -transitions is established. A shell model calculation of 2p2h, T=0 states, using empirical matrix elements, suggests the assignments 8⁺ and 10⁺ for the two highest levels.     

The Cross-Section Measurements and Evaluations for 58Ni(n,p),60Ni(n,p),62Ni(n,α) and 54Fe(n,p) Reactions

Activation techniques have been used to measure the cross-section for ⁵⁸Ni(n,p),⁶⁰Ni(n,p) and ⁶²Ni(n,α) reactions in the neutron energy range 13.6—17.8MeV.The uncertainty of measured data has been aculated from 3%—7%.The covariance matrixes for measurement error are calculated.Evaluations for ⁵⁸Ni(n,p),⁶⁰Ni(n,p),⁶²Ni(n,α) and ⁵⁴Fe(n,p) crpss-section are made.     

Sulfur at nickel-alumina interfaces: Molecular orbital theory

An atom superposition and electron delocalization molecular orbital study has been made of surface atomic layer relaxations in Ni(110) and Ni(111), the binding of p(2 × 2)S to Ni(111), S on Ni(100), and the binding of A1₂O₃ to clean Ni(111) and p(2 × 2)S covered Ni(111). Surface Ni atom relaxations for three-layer thick cluster models are calculated to be close to the experimental results and S heights of 1.68 Å on Ni(111) and 1.40 Å on Ni(100) are also in close agreement with experimental determinations, which indicates cluster models are suitable for determining surface properties. Al³⁺ in the basal plane of Al₂O₃ are predicted to support a low-lying surface state band in the O2p---A13s3p band gap. These orbitals are found to participate in strong Al---Ni bonds and Al---S bonds of intermediate strength at the interfaces with Ni(111) and p(2 × 2) S-covered Ni(111). Should such bonds form, they are expected to be too few in number to lead to strong adhesion. The strongest Al₂O₃---Ni bonding is predicted to occur when the Ni surface is oxidized. In this case, though Ni---O bonds are relatively weak, their number is high. It is concluded from the structure models that are studied that the segregation of impurity S in Ni to the interface will markedly decrease the adhesion of protective Al₂O₃ films that grow on NiAl based alloys.     

Calculations of Rydberg energy levels for Ni ⅩⅧ using the weakest bound electron potential model theory

Martin expression about the quantum defect of single-valence atoms is extended to many-valence atoms by identifying the weakest bound electron (WBE) under the weakest bound electron potential model(WBEPM) theory. Six Rydberg series energy levels of 2p6np2P°1/2 (n ≥ 3), 2p6np2P°3/2 (n ≥ 3), 2p6nd2D3/2(n ≥ 3), 2p6nd2D5/2 (n ≥ 3), 2p6nf2F°5/2 (n≥4), and 2p6nf2F°7/2 (n ≥ 4) for Ni ⅩⅧ are calculated by this method. The calculated results are in good agreement with the experimental results.     

Unusual superexchange pathways in an NiS2 triangular lattice with negative charge-transfer energy

We have studied the electronic structure of the Ni triangular lattice in NiGa(2)S(4) using photoemission spectroscopy and subsequent model calculations. The cluster-model analysis of the Ni 2p core-level spectrum shows that the S 3p to Ni 3d charge-transfer energy is approximately -1 eV and the ground state is dominated by the d(9)L configuration (L is a S 3p hole). Cell perturbation analysis for the NiS(2) triangular lattice indicates that the strong S 3p hole character of the ground state provides the enhanced superexchange interaction between the third-nearest-neighbor sites.     

X-ray photoelectron spectroscopy study of NiSi formation on shallow junctions

The influence of boron (B)/arsenic (As) on X-ray photoelectron spectroscopy (XPS) study of NiSi formation on shallow junctions is investigated in this paper. The Ni-silicide film was formed after 30 s soak anneal at 450 °C on ultra shallow p+/n or n+/p junctions. The atomic ratio of Ni/Si profile in depth was probed by XPS and the results show that a uniform NiSi layer forms on B-doped p+/n junction while a non-uniform, Ni-rich silicide layer forms on As-doped n+/p junction. It does not agree with the results of other independent phase identification methods such as X-ray diffraction, Rutherford backscattering spectroscopy, and Raman scattering spectroscopy, which all demonstrate the formation of NiSi on both n+/p and p+/n junctions. Comparing the raw binding energy spectra of Ni and Si for each silicide film, the similar spectra for Ni signals are revealed. But the Si signals with an obviously smaller intensity is found to be responsible for the apparent Ni rich silicide formation on As-doped n+/p junction. It indicates that As atoms in the silicide film can affect the sputtering yield of Ni and Si, while no noticeable effect is observed for B atoms. More As atoms than B atoms segregation into the silicide layer is indeed verified by secondary ion mass spectroscopy. And micro-Raman scattering spectroscopy further confirms that the degree of crystallinity for NiSi on n+/p junction is inferior to that on p+/n junction.     

Hypertriton and light nuclei production at Λ-production subthreshold energy in heavy-ion collisions

High-energy heavy-ion collisions produce abundant hyperons and nucleons. A dynamical coalescence model coupled with the ART model is employed to study the production probabilities of light clusters, deuteron (d), triton (t), helion (³He), and hypertriton (_Λ³H) at subthreshold energy of Λ production (≈ 1 GeV per nucleon). We study the dependence on the reaction system size of the coalescence penalty factor per additional nucleon and entropy per nucleon. The Strangeness Population Factor (S₃ / (³He × (Λ/p))) shows an extra suppression of hypertriton comparing to light clusters of the same mass number. This model predicts a hypertriton production cross-section of a few μb in ³⁶Ar+³⁶Ar, ⁴⁰Ca+⁴⁰Ca and ⁵⁶Ni+⁵⁶Ni in 1 A GeV reactions. The production rate is as high as a few hypertritons per million collisions, which shows that the fixed-target heavy-ion collisions at CSR (Lanzhou/China) at Λ subthreshold energy are suitable for breaking new ground in hypernuclear physics.