Despite long-term research, the origin of spin cutoff in the angular-momentum (spin) distribution of nuclear level densities remains incompletely elucidated. We demonstrate that this problem can be traced back to Bethe's assumption that nucleons in finite Fermi systems are independent random variables. By constructing a statistical ensemble that enforces rotational invariance through angular-momentum coupling, we obtain an analytical expression for the spin cutoff parameter, which includes a previously unidentified finite-population correction. Our results show that, even in the absence of interactions, nuclear many-body states exhibit non-negligible correlations arising from fermionic antisymmetry and angular-momentum coupling. From this perspective, spin cutoff may be interpreted as a quantitative measure of correlation imposed by symmetry in nuclear level statistics.
The unbound nature of pure neutron matter (PNM) requires intrinsic correlations between the symmetric nuclear matter (SNM) EOS parameters (incompressibility $K_0$, skewness $J_0$ and kurtosis $I_0$) and those (slope $L$, curvature $K_{\rm{sym}}$ and skewness $J_{\rm{sym}}$) characterizing the symmetry energy independent of any nuclear many-body theory. We investigate these intrinsic correlations and their applications in better constraining the poorly known high-density behavior of nuclear symmetry energy. Several novel correlations connecting the characteristics of SNM EOS with those of nucle…
The Hauser-Feshbach Fission Fragment Decay (HF$^3$D) model is extended to calculate the prompt fission neutron spectrum (PFNS) for the thermal neutron induced fission on $^{235}$U, where the evaporated neutrons from all possible fission fragment pairs are aggregated. By studying model parameter sensitivities on the calculated PFNS, as well as non-statistical behavior of low-lying discrete level spin distribution, we conclude that discrepancies between the aggregation calculation and the experimental PFNS seen at higher neutron emission energies can be attributed to both the primary fission fra…
Van der Waals Equation of State with Fermi Statistics for Nuclear Matter
范德华状态方程是描述具有排斥和吸引相互作用的粒子平衡系统中压力函数的一个简单而流行的模型。该方程预言了一级液-气相变的存在,并包含一个临界点。本文对VDW方程进行了两步扩展,使其适用于新的物理应用:1)巨正则系综表述; 2)引入量子统计。然后应用具有费米统计的VDW方程描述相互作用核子系统。VDW参数$a$和$b$被固定以再现核物质在饱和密度$n_0=0.16$ fm $^{-3}$和零温度下的性质。该模型预测了对称核物质在温度$T_c\cong 19.7$ MeV和核子数密度$n_c \cong 0.07$ fm $^{-3}$下临界点的位置。
Shape deformations and charge radii, basic properties of atomic nuclei, are influenced by both the global features of the nuclear force and the nucleonic shell structure. As functions of proton and neutron number, both quantities show regular patterns and, for nuclei away from magic numbers, they change very smoothly from nucleus to nucleus. In this paper, we explain how the local shell effects are impacting the statistical correlations between quadrupole deformations and charge radii in well-deformed even-even Er, Yb, and Hf isotopes. This implies, in turn, that sudden changes in correlations…
Microcanonical Thermostatistics, the basis for a New Thermodynamics, "heat can flow from cold to hot", and nuclear multifragmentation. The correct treatment of Phase Separation after 150 years of statistical mechanics
有限哈密顿系统的平衡统计基本上是由微正则系综(ME)描述的。正则或巨正则配分函数通过拉普拉斯变换由此推导出。只有在热力学极限下,它们才与均相系统的ME等价。因此,ME是唯一的非广泛/非均匀系统,如原子核或恒星,其中$\lim_{N\to \infty,ρ=N/V=const}$不存在。传统的正则热统计量不适用于非广延系统。这对于一般的热统计具有深远的基本和相当违反直觉的后果:一阶相变由$S(E,N,Z,...)$ \cite{gross174}的凸性发出信号。这里热容是{ \em负数}。在这些情况下,热量可以从冷流到热!热力学最初的任务,即描述热机中的沸水,现在可以处理了。这一基本特性的核统计以及一般的统计力学的基本理解的后果进行了讨论。热核实验以丰富的形式显示了所有这些新现象。将指出非均匀天体物理系统的密切相似性。\keyword{Microcanonical statistics, first order transitions, phase separation, steam engines, nuclear multifragmentation, negative heat capacity}
Equation of state with quantum statistics corrections is derived for a multi-component gas of particles interacting through the repulsive and attractive van der Waals (vdW) forces up to first few orders over a small parameter $δ\approx \hbar^3 n(mT)^{-3/2}[g(1- bn)]^{-1}$, where $n$ and $T$ are the particle number density and temperature, $m$ and $g$ the particle mass and degeneracy factor. The parameter $b$ corresponds to the vdW excluded volume. For interacting system of Fermi nucleon and Bose $α$ particles, a small impurity of $α$ particles to the nucleon system at leading first order in bo…
Non-extensive statistics, fluctuations and correlations in high energy nuclear collisions
从高能核-核碰撞不能用基本核子-核子相互作用的叠加描述的实验证据出发,分析了高能重离子碰撞中记忆效应和长程力隐含非广延统计机制的可能性.这些统计效应的相关性和它们与现有的实验数据的兼容性进行了讨论。特别是,我们表明,理论估计,在广义非广延热统计学的框架内获得的,可以重现的π介子横向质谱的形状和解释不同的物理起源的π介子的横向动量关联函数在中央Pb+Pb和在158 A GeV的p+p碰撞期间发射。
Understanding how matter behaves at the highest densities and temperatures is a major open problem in both nuclear physics and relativistic astrophysics. This physics is often encapsulated in the so-called high-temperature nuclear equation of state, which influences compact binary mergers, core-collapse supernovae, and many more phenomena. One such case is the type (either black hole or neutron star) and mass of the remnant of the core collapse of a massive star. For each of six candidate equations of state, we use a very large suite of spherically symmetric supernova models to generate a suit…
The nuclear matter parameters (NMPs), those underlie in the construction of the equation of state (EoS) of neutron star matter, are not directly accessible. The Bayesian approach is applied to reconstruct the posterior distributions of NMPs from the EoS of neutron star matter. The constraints on lower-order parameters as imposed by the finite nuclei observables are incorporated through appropriately chosen prior distributions. The calculations are performed with two sets of pseudo data on the EoS whose true models are known. The median values of second or higher order NMPs show sizeable deviat…
This is a concise introduction to the topic of nonextensive Tsallis statistics meant especially for those interested in its relation to high energy proton-proton, proton-nucleus, and nucleus-nucleus collisions. The three types of Tsallis statistics are reviewed. Only one of them is consistent with the fundamental hypothesis of equilibrium statistical mechanics. The single particle distributions associated with it, namely Boltzmann, Fermi-Dirac, and Bose-Einstein, are derived. These are not equilibrium solutions to the conventional Boltzmann transport equation which must be modified in a rather…
Statistical nuclear spectroscopy (also called spectral distribution method), introduced by J.B. French in late 60's and developed in detail in the later years by his group and many other groups, is based on the Gaussian forms for the state (eigenvalue) and transition strength densities in shell model spaces with their extension to partial densities defined over shell model subspaces. The Gaussian forms have their basis in embedded random matrix ensembles with nuclear Hamiltonians consisting of a mean-field one-body part and a residual two-body part. However, following the recent random matrix …