径向膨胀流的同位旋效应

利用同位旋相关的量子分子动力学模型,研究了¹²⁴Ba+¹²⁴Ba和¹²⁴Sn+¹²⁴Sn两个系统在不同入射能量下对心碰撞的径向膨胀流.发现丰中子系统¹²⁴Sn+¹²⁴Sn的径向膨胀流系统性地小于系统¹²⁴Ba+¹²⁴Ba的径向膨胀流.同时发现这种差别主要来自于核子–核子碰撞截面的同位旋相关性而几乎与对称能无关.     

Isospin dependent properties of the isotopic chains of Scandium and Titanium nuclei within the relativistic mean-field formalism

Density-dependent nuclear symmetry energy is directly related to isospin asymmetry for finite and infinite nuclear systems. It is critical to determine the coefficients of symmetry energy and their related observables because they hold great importance in different areas of nuclear physics, such as the analysis of the structure of ground state exotic nuclei and neutron star studies. The ground state bulk properties of Scandium (Z = 21) and Titanium (Z = 22) nuclei are calculated, such as their nuclear binding energy (\begin{document}$ B.E. $\end{document}), quadrupole deformation (\begin{document}$ \beta_2 $\end{document}), two-neutron separation energy (\begin{document}$ S_{ {2n}} $\end{document}), differential variation in the two-neutron separation energy (\begin{document}$ {\rm d}S_{ {2n}} $\end{document}), and root-mean-square charge radius (\begin{document}$ r_{\rm ch} $\end{document}). The isospin properties, namely the coefficient of nuclear symmetry energy and its components, such as the surface and volume symmetry energy of a finite isotopic chain, from the corresponding quantities of infinite nuclear matter, are also estimated. Finally, we correlate the neutron-skin thickness with the coefficient of symmetry energy and the related observables corresponding to the isotopic chains of these nuclei. The coherent density fluctuation model (CDFM) is used to estimate the isospin-dependent properties of finite nuclei, such as symmetry energy, surface symmetry energy, and volume symmetry energy, from their corresponding component in infinite nuclear matter. The relativistic mean-field (RMF) formalism with non-linear NL3 and relativistic-Hartree-Bogoliubov theory with density-dependent DD-ME2 interaction parameters are employed in the analysis. The weight function \begin{document}$ \vert {\cal{F}}(x) \vert^{2} $\end{document} is estimated using the total density of each nucleus, which in turn is used with the nuclear matter quantities to obtain the effective symmetry energy and its components in finite nuclei. We calculate the ground state bulk properties, such as nuclear binding energy, quadrupole deformation, two-neutron separation energy, differential variation in the two-neutron separation energy, and root-mean-square charge radius, for the Sc- and Ti- isotopic chains using the non-linear NL3 and density-dependent DD-ME2 parameter sets. Furthermore, the ground state density distributions are used within the CDFM to obtain the effective surface properties, such as symmetry energy and its components, namely volume and surface symmetry energy, for both the parameter sets. The calculated quantities are used to understand the isospin dependent structural properties of finite nuclei near and beyond the drip line, which broadens the scope of discovering new magicity along the isotopic chains. A shape transition is observed from spherical to prolate near \begin{document}$ N \geq $\end{document} 44 and \begin{document}$ N \geq $\end{document} 40 for the Sc- and Ti- isotopic chains, respectively. Notable signatures of shell and/or sub-shell closures are found for the magic neutron numbers N = 20 and 28 for both isotopic chains using the nuclear bulk and isospin quantities. In addition to these, a few shell/sub-shell closure signatures are observed near the drip-line region at N = 34 and 50 by following the surface/isospin dependent observables, namely symmetry energy and its component, for both the isotopic chain of odd-A Sc- and even-even Ti- nuclei.     

Isospin and mixed symmetry structure in ~(26)Mg

The isospin excitation states and electromagnetic transitions of the ²⁶Mg nucleus are studied with the isospin-dependent interacting boson model (IBM-3). The mixed symmetry states at low spin and the main components of the wave function for some states are also analyzed. The results show good agreement with the available experimental data. From the IBM-3 Hamiltonian expressed in Casimir operator form, the ²⁶Mg is also proved to be a transition nuclei from U(5) to SU(3).     

Isospin dependence of nuclear multifragmentation in statistical model

The evolution of nuclear disintegration mechanisms with increasing excitation energy, from compound nucleus to multifragmentation, has been studied by using the Statistical Multifragmentation Model (SMM) within a micro-canonical ensemble. We discuss the observable characteristics as functions of excitation energy in multifragmentation, concentrating on the isospin dependence of the model in its decaying mechanism and break-up fragment configuration by comparing the A₀=200, Z₀=78 and A₀=200, Z₀=100 systems. The calculations indicate that the neutron-rich system (Z₀=78) translates to a fission-like process from evaporation later than the symmetric nucleus at a lower excitation energy, but gets a larger average multiplicity as the excitation energy increases above 1.0 MeV/u.     

重离子反应中核子前平衡发射的同位旋效应

考虑了同位旋相关的对称能、库仑能及核子—核子碰撞截面，对反应４０Ａｒ＋４０Ａｒ（Ｅ＝２５ＭｅＶ／ｕ，ｂ＝０）进行了量子分子动力学模拟，讨论了同位旋效应对核子发射的影响．观察到前平衡发射的中子和质子的比率大于反应系统的中质比，发现对称能有利于中子的发射而阻碍质子的发射，而同位旋相关的核子—核子碰撞截面对中子和质子的发射都有利，但似乎更有利于质子的发射。     

同位旋和动量依赖的相互作用在重离子碰撞中的同位旋效应

引入同位旋自由度将同位旋无关的动量相关作用改造成同位旋和动量依赖的相互作用. 利用同位旋依赖的量子分子动力学理论研究了同位旋和动量依赖的相互作用对中能重离子碰撞中动量耗散和同位旋分馏的作用. 计算结果表明动量相关作用具有重要的同位旋效应，尽管它没有明显的改变原子核阻止(动量耗散)对于两体碰撞截面和同位旋分馏强度对于对称势的灵敏依赖性，但它对于以上两种灵敏性产生了明显的减弱作用. 故动量相关作用中同位旋效应研究对于定量的研究和确定同位旋非对称核物质状态方程是重要的.     

放射性核束引起反应中轻带电粒子发射的同位旋效应

研究了69MeV/u³⁶Ar轰击Be靶的碎裂产物与Si靶反应引起的前角区轻带电粒子的发射产额与原子核同位旋、原子核序数的关系.发现前角区轻带电粒子发射产额对于丰质子核的结构非常敏感,与同位旋存在一种指数关系.因此可以把前角区轻带电粒子发射产额作为探测丰质子核结构的一种手段,也是一种新的验证一个核是否具有质子晕结构的实验证据.     

Isospin violations in largeP T pion inclusive processes in perturbative quantum chromodynamics

We investigate the asymmetries arising due to electromagnetic interactions in largeP _T pion inclusive processes. The hardqcd processes that contribute to such asymmetries areq+g→q+γ,q+q→g+γ etc. which are suspected to be substantial, as indicated by theqcd predictions for a significant and increasingγ/π ^o ratio at largeP _T. We calculate the expected isospin related asymmetries and propose tests that might detect them. Our estimates indicate that the effects are much smaller than may be naively expected. We also observe a remarkable scaling of asymmetries in the variableP _T/(s)^1/2.     

Comparison ofβ-decay and Charge-exchange Reactions in Mirror T =2 Nuclei and Isospin Mixing

We have carried out β decay studies of proton rich nuclei in the fp shell at different laboratories.Here we present our recent results on the decay of Tz =-2 nuclei performed at GANIL and compare them with the Charge Exchange reactions on their stable, mirror-partner targets, performed at RCNP. In one of the cases, the 56Zn - 56Fe pair, a strong isospin mixing has been observed. The results are well reproduced in the framework of Shell Model calculations     

Number of states with given spin I and isospin T for n fermions in a j orbit

In this study, we investigate formulas of the number of states with a given total spin I and isospin T for n nucleons in a single-j shell denoted by \begin{document}$ D_{IT} (j, n) $\end{document}. Talmi's recursion formulas for the number of states with a given z-axis projection of total spin are generalized by further considering the isospin couplings and are applied to derive explicit formulas of \begin{document}$ D_{IT} (j, n) $\end{document}.