102Ru核振动到转动演化的微观研究

基于微观sdIBM-2方案和实验单粒子能量值,在最普遍的哈密顿量下,用两组不同的核子.核子等效相互作用参数,分别很好地再现了102Ru核的振动带能谱和转动带能谱及其演化过程.微观和唯象的研究指认:1)这两种激发模式的共存区是能态81 -121 (即Ex=2.500-4.000 MeV);态81 是振动模式占据优势的能态,态121 是转动模式占据优势的能态,而状态101 则是两种模式的中立能态;2)态121 是141 态退耦到态101 辐射光子相变后的中间能态;3)从基态起直到201 态的yrast态全都是集体态,而以后出现的第一个拆对顺排态很可能就是中子h11/2的两准粒子态;4)这种结构的过渡不是很剧烈的,而是通过玻色子结构常数在过渡区中不大的改变来实现的.     

转动诱发原字核量子相变的一种可能途径

基于微观IBM理论，提出转动诱导出玻色子量子相变的一种可能途径：一旦原子核在受到高能激发或作快速旋转时，假如外界提供的能量足以使玻色子完成拆对顺排，则核处于集体相与单粒子态的共存相，其特征是出现较密集的能谱；假如能量不足以完成拆对或顺排，可能发生两种情况之一，当核旋转达到某个临界转动频率ωc时，或者一个高角动量的玻色子脱离“集体”而“游离”出来，或者发生一个高角动量的玻色子转变为一个低角动量的玻色子，核仍旧处于集体相；均会伴随出现光辐射，产生基态带的一条能级——相变信号．正是这类玻色子相变导致了原子核的量子相变．本物理图像统一了玻色子拆对顺排相变和退耦释放光子相变的描述．以100^Pd核的141^＋，142^＋和143^＋态的产生机理为例，对模型作了仔细说明．     

102Ru核振动到转动演化的微观研究

基于微观sdIBM-2方案和实验单粒子能量值, 在最普遍的哈密顿量下, 用两组不同的核子-核子等效相互作用参数, 分别很好地再现了¹⁰²Ru核的振动带能谱和转动带能谱及其演化过程. 微观和唯象的研究指认: 1) 这两种激发模式的共存区是能态8⁺₁—12⁺₁(即E_x=2.500—4.000 MeV); 态 8⁺_{1关键词： 微观sdIBM-2方案 形状演化 玻色子 102Ru核')" href="#">¹⁰²Ru核}     

40Ar+197Au(25MeV/u)产生的热核激发能与核温度的关系

对25MeV/u ⁴⁰Ar+¹⁹⁷Au反应系统裂变与后角轻粒子发射进行了符合测量,用裂变碎片折叠角和裂变碎片的飞行时间再构转移到类熔合核的线性动量.通过对线性动量转移和轻带电粒子能谱测量,给出从中心碰撞到周边碰撞产生的类熔合核的初始激发能、角动量和核温度,讨论它们的关系.发现了中心碰撞形成的类复合核的核温度已经接近饱和状态,接近多重碎裂的“准相变区”.     

转动诱发原子核量子相变的一种可能途径

基于微观IBM理论,提出转动诱导出玻色子量子相变的一种可能途径:一旦原子核在受到高能激发或作快速旋转时,假如外界提供的能量足以使玻色子完成拆对顺排,则核处于集体相与单粒子态的共存相,其特征是出现较密集的能谱;假如能量不足以完成拆对或顺排,可能发生两种情况之一,当核旋转达到某个临界转动频率ω_c时,或者一个高角动量的玻色子脱离“集体”而“游离”出来,或者发生一个高角动量的玻色子转变为一个低角动量的玻色子,核仍旧处于集体相;均会伴随出现光辐射,产生基态带的一条能级——相变信号.正是这类玻色子相变导致了原子核的量子相变.本物理图像统一了玻色子拆对顺排相变和退耦释放光子相变的描述.以¹⁰⁰Pd核的14⁺₁,14⁺₂和14⁺₃态的产生机理为例,对模型作了仔细说明.     

稀土变形奇A核173,175Hf的多准粒子高K转动带的粒子数守恒分析

用处理推转壳模型的粒子数守恒方法分析了稀土奇A变形核^173,175Hf的3准粒子和5准粒子高K转动带,包括转动惯量、顺排角动量,以及推转Nilsson能级上的粒子填布几率随转动角频率的变化.计算中无自由参数.实验观测结果在计算中得到较好地重现.分析了多准粒子带与相邻偶偶核基态带的转动惯量变化规律不同的微观机制.在这里Fermi面邻近高j闯入态的堵塞效应起了举足轻重的作用.     

双准自旋模型的严格好准自旋态能谱

提出了两种新形式的约束哈特里-福克方法,并在SU(2)×SU(2)双准自旋模型中讨论了它们的解.研究了建立严格好准自旋态的对角化方法,并对好准自旋态能错的特点和近似带结构的划分进行了探讨.两种CHP能谱与严格能谱的比较表明,它们都具有转动谱的特征;在相互作用不太强的体系中,新方案是获得好准自旋态的、能产生多带能谱结构的有效方法.     

准粒子特征与奇奇核的能谱统计

用粒子转子理论模型计算奇奇核⁸⁴Y的能谱,通过分析能谱的最近邻能级间距分布函数和能谱刚性度的变化特点,研究了准粒子特征对奇奇核⁸⁴Y能谱统计特点的影响,发现奇奇核⁸⁴Y的能谱总体上接近混沌;在采用的理论模型中,准粒子特征通过反冲项和科氏力作用项影响能谱,同时能谱具有随着费米能和能隙参量的减小从接近混沌逐渐转变到接近规则的特点 关键词： 奇奇核 粒子转子模型 准粒子特征 能谱统计 NNS分布函数 能谱刚性度     

清华大学物理系原子核物理研究的新进展

在清华大学物理系成立80周年之际,对近年来清华大学物理系原子核物理研究的主要进展情况作一介绍,包括原子核高自旋态的实验研究,原子核结构的理论研究,高能核物理的理论研究.在高自旋态研究方面,内容包括在A～100丰中子核区核的集体振动转动带结构、新的准粒子带特性、新手征二重带等特性研究;在A～140丰中子核区核的八极形变及八级关联等特性研究;在A～130缺中子核区核的形状驱动效应,包括扁椭形变带、形状共存等特性研究.在原子核结构理论研究方面,内容包括用相互作用玻色子模型、推转壳模型、投影壳模型以及相对论平均场对原子核特性的研究;对原子核结构或其他量子系统的各种对称性和代数方法的研究,如动力学对称性、超对称性、势代数方法等;与对称性紧密联系的普通李代数和非线性李代数的表示,如普通李代数、李超代数、平方根型非线性李代数、多项式型非线性李代数等.在高能核物理研究方面,内容主要包括量子色动力学（QCD）在高温高密条件下的相变以及在相对论重离子碰撞中相变信号的研究.     

具有1~+、3~+带的转动区偶偶核的相互作用玻色子模型

本文在s、d IBM的SU(3)极限下,考虑了八极态,并对二准粒子激发作类玻色子处理,得到了非简并的1~+、3~+带.导出了能谱的解析表达式.对转动区中八种原子核的能谱的计算结果与实验值符合得相当好.     

Entropy and phase diagram of valence transition

The electronic and lattice entropies associated with the valence transition are estimated. The electronic entropy in metallic phase is evaluated based on the model which includes the mixing between ?-level and d-band states, and the d-band superimposes the hybridized ?-level. The quasiharmonic approximation together with the Debye approximation are used to calculate the lattice entropy. For the first order transition occurring at low temperature the entropy of semiconducting phase is found to be lower than that of metallic phase. The reverse situation is obtained for high transition temperature. This explains the experimental fact that the slope of the phase boundary of valence transition in SmS changes its sign with temperature. The specific heat calculated in this model shows a broad maximum at low temperature.     

Low temperature heat capacity of Rh-Cu alloys

Reported here are the low temperature heat capacity data on a series of single phase fcc Rh-Cu alloys. The electronic heat capacity coefficient, γ, decreases rapidly up to 20 at % of copper in Rh and then stays constant to ～60 at % Cu after which decreases smoothly to the pure Cu value. This is interpreted as due to the initial partial filling of the d-band after which the conduction electron of Cu goes into the s-band. An attempt is made to understand the origins of the curious anomalies in the Debye temperature and microhardness data.     

Heat capacity and magnetic susceptibility of ReO3

The specific heat and magnetic susceptibility of the transition metal oxide ReO₃ have been measured. The specific heat results give a Debye temperature Θ_D = 460 ± 10 K and an electronic specific heat coefficient γ = 6.45 ± 0.07 cal/mole K² which are in good agreement with similar measurements on the cubic sodium tungsten bronzes. The magnetic susceptibility and the electronic contribution to the specific heat are within a few percent of the corresponding parameters calculated from the free electron model with one electron per unit cell. Our results show that ReO₃ behaves much like a simple metal. No experimental evidence for narrow d-band effects was observed.     

Spectral property and its shape transition on 72—84Kr isotopes in microscopic core plus two—quasiparticle approach

By using a microscopic sdIBM-2+2q.p. approach, the levels of the ground-band, γ-band and partial two-quasi-particle bands for {}^{72-84}Kr isotopes are calculated. The data obtained are in good agreement with the recent experimental results, and successfully reproduce the nuclear shape phase transition of {}^{72-84}Kr isotopes at zero temperature. The ground-state band is described successfully up to J^π=18^+ and E_x=10.0MeV. Based on this model, the aligned requisite minimum energy has been deduced. The theoretical calculations indicate that no distinct change of nuclear states is caused by the abruptly broken pair of a boson, and predict that the first backbending of Kr isotopes may be the result of aligning of two quasi-neutrons in orbit g_{9/2}, which gains the new experimental support of the measurements of g factors in the {}^{78-86}Kr isotopes.     

Landau-Ginzburg treatment of nuclear matter at finite temperature

Based on recent studies of the temperature dependence of the energy and specific heat of liquid nuclear matter, a phase transition is suggested at a temperature ∼ 0.85 MeV. We apply the Landau-Ginzburg theory to this transition and determine the behaviour of the energy and specific heat close to the critical temperature in the condensed phase. Received: 29 July 2000 / Accepted: 20 October 2000     

Calorimetric baseline fitting: Application to titanite

In order to analyse calorimetric measurements of a phase transition, it is necessary to determine the baseline from which the excess specific heat is measured. In this study, this baseline is determined by using the constraint that the resulting heat capacity anomaly must be consistent with measurements of the phase transition by other techniques.

The method is particularly useful when other mechanisms make it difficult to predict the low-temperature behaviour of the baseline. Titanite provides an example of this, since the antiferroelectric transition temperature is close to the temperature at which the phonon contribution to the specific heat begins to fall rapidly.     

Phase transition and thermodynamic properties of SrS via first-principles calculations

The phase transition of SrS from NaCl structure （B1） to CsCl structure （B2） is investigated by means of ab initio plane-wave pseudopotential density functional theory, and the thermodynamic properties of the B1 and the B2 structures are obtained through the quasi-harmonic Debye model. It is found that the transition phase from the B1 to the B2 structures occurs at 17.9 GPa, which is in good agreement with experimental data and other calculated results. Moreover, the thermodynamic properties （including specific heat capacity, the Debye temperature, thermal expansion and Griineisen parameter） have also been obtained successfully.     

CHIRAL PHASE TRANSITION IN A MODEL WITH DYNAMICAL SPONTANEOUS-SYMMETRY-BREAKING AT FINITE TEMPERATURE AND DENSITY

The chiral-symmetry-restoring phase transition in a model with dynamical spontaneous-symmetry-breaking is discussed qualitatively,making use of an approximation method.The selfconsistency equation of the model is established.The condensation and mass of fermions as well as the temperature or density dependence of energy density and specific heat are obtained.It turns out that,in this approximation,the chiral-phase-transition is second order at zero chemical potential and finite temperature; and the transition is first order for both cases at finite temperature and density and at zero temperature and finite density,this moment.the transition temperature or density from broken phase to normal phase differs from that from normal phase to broken phase.     

Phase transition and thermodynamic properties of BiFeO3 from first-principles calculations

The first-principles projector-augmented wave method employing the quasi-harmonic Debye model,is applied to investigate the thermodynamic properties and the phase transition between the trigonal R3c structure and the orthorhombic Pnma structure.It is found that at ambient temperature,the phase transition from the trigonal R3c phase to the orthorhombic Pnma phase is a first-order antiferromagnetic-nonmagnetic and insulator-metal transition,and occurs at 10.56 GPa,which is in good agreement with experimental data.With increasing temperature,the transition pressure decreases almost linearly.Moreover,the thermodynamic properties including Grneisen parameter,heat capacity,entropy,and the dependences of thermal expansion coefficient on temperature and pressure are also obtained.     

Thermodynamic geometry of the Garfinkle-Horowitz-Strominger dilaton black hole

This paper studies the thermodynamic properties of the Garfinkle-Horowitz-Strominger dilaton black hole from the viewpoint of geometry. It calculates the heat capacity and the temperature of the black hole, Weinhold metric and Ruppeiner metric are also obtained respectively. It finds that they are both curved and the scalar curvature of the Weinhold geometry consists with the first-order transition point reproduced from the capacity, while the Ruppeiner one is both in accordance with the first-order and the second-order phase transition points reproduced from the capacity.