近垒重离子熔合反应和超重核合成机制研究

本论文在同位旋相关的量子分子动力学(IQMD)模型基础上，对相互作用势、核子的费米子属性和两体碰撞做了系统改进，同时考虑原子核的壳效应，发展成为改进的同位旋相关的量子分子动力学(ImIQMD)模型。ImIQMD模型能够很好地描述大量核的基态性质，如结合能、均方根半径、密度分布、动量分布等，并使得基态核的稳定性有了很大提高。基于ImIQMD模型我们系统计算了一系列反应系统的熔合激发函数，并能够与已知实验数据相当好地符合，包括丰中子系统和幻数核系统；分析了各种动力学因素在熔合过程中的作用，发现动力学位垒、位垒分布、颈部动力学行为(颈部的成长，颈部中质比、颈部核子流)等对入射能量和系统的质量不对称度有着密切的依赖关系，分析了垒下熔合区域中壳效应的影响。运用ImIQMD模型，对重系统的俘获动力学过程做了分析，包括俘获截面、动力学位垒、颈部动力学行为等。基于双核系统概念，对熔合－蒸发反应合成超重核形成过程中的俘获、熔合和蒸发三个阶段分别采用了半经验耦合道模型、数值求解主方程(考虑了双核系统的衰变和重碎片的裂变)和统计蒸发理论做了描述，即为双核系统(DNS)模型。基于该模型对超重核的形成机制做了系统研究，并预言了进一步合成超重核最佳的弹靶组合和入射能量

超重核生成截面的研究

目前，人们在合成超重元素的研究中，做了大量的工作并已经取得了一些进展。这是一个有趣而又充满希望的方向。要在实验室合成超重元素，必须先做大量的理论工作。许多理论模型可以计算截面，但大多数理论模型没有考虑融合过程中准裂变的竞争。但实验证实，用重离子碰撞合成超重原子核时，准裂变对熔合的抑制是非常重要的。为了体现准裂变对熔合过程的影响，一种新的模型一双核模型被提出。双核模型假定在碰撞动能充分耗散后，弹靶组成双核系统，由轻核向重核转移核子而形成复合核。处于激发态的复合核通过发射中子和裂变竞争退激，形成稳定超重核。碰撞中双核系统间核子转移所形成的势能面称之为驱动势，它制约核子转移，因而决定熔合与准裂变的竞争。双核系统势能面还提供重离子碰撞合成超重原子核的最佳激发能和最佳弹靶组合的信息。驱动势制约由输运方程所支配的核子转移速率，因而确定双核系统形成复合核的几率。并由此可确定形成复合核所必须的最低激发能，即形成最稳定复合核的最佳激发能，我们计算了以208Pb为靶的一系列重离子熔合反应双核系统核子转移驱动势，得到了与已知实验值基本符合的结果。在双核系统框架下，用数值法解主方程描述双核间的核子跃迁全熔核形成几率；两碰撞核内部激发能由相对运动能损提供，则把核子转移过程与相对运动藕合起来。最后对一些以208Pb为靶的形成超重核的冷熔合反应，计算了最佳激发能，形成双核系统的俘获截面，复合核形成几率，及存活几率等，最终所得到的形成超重核蒸发剩余截面与已知实验值符合较好。

基于重离子输运理论对超重核合成及非对称核物质状态方程的研究

本论文基于重离子输运理论模型对当前人们感兴趣的超重核合成及非对称核物质状态方程做了研究。基于双核系统概念建立了一个描述超重核合成的理论模型。这个模型中通过求解Fokker-Planck方程来描述重离子碰撞过程的能量、角动量以及形变等的弛豫过程，从而合理地包含了重离子熔合过程中的动力学效应。在求解弹靶的质量扩散时采用了数值求解主方程的方法，避免对势能面做任何近似，因此能够充分地体现重离子熔合过程中弹靶的结构效应。本文利用这一模型计算了重离子熔合形成超重元素的最佳激发能、熔合几率、复合核的存活几率以及蒸发剩余核截面等，并给出了合成超重核的最佳弹靶组合。计算了超重核形成的最佳激发能，在符合已有最佳激发能实验数据的基础上预言了基于冷熔合反应合成114，116和118号元素的最佳激发能。计算了重离子熔合反应的熔合几率。结果表明，随着反应系统变得越来越重，重离子的熔合几率呈指数规律下降，准裂变变得越来越严重。这解释了实验上观测到的超重剩余核截面随体系的变重而急剧下降的现象。研究了重离子熔合截面的弹靶相关性。结果表明弹靶的质量非对称度越高越有利于熔合生成复合核，同时重离子熔合截面还强烈地依赖于弹靶结构。重离子的熔合过程是合成超重元素的关键因素之一，另一个影响超重核合成的因素是超重复合核的存活几率。基于统计模型，系统的研究了超重复合核存活几率的质量、能量、角动量等相关性。计算了基于冷熔合反应的蒸发剩余截面，得到的结果与实验基本符合，并预言了基于冷熔合反应生成114，116和115号元素的截面。在研究超重核蒸发剩余截面的弹靶相关性的基础上给出了合成超重核的最佳弹靶组合。计算表明，在挑选弹靶组合时使得合成的超重复合核是奇A核则会得到更高的奇数中子蒸发剩余核截面。计算给出了超重复合核的自旋布居及其对裂变位垒和鞍点态形变的依赖性。发现超重复合核的自旋布居强烈地依赖于复合核的裂变位垒，高的裂变位垒会给出宽的自旋布居；而超重复合核的自旋布居对鞍点态形变不是很敏感。另外研究了多核子转移反应合成超重元素的可能性。结果表明基于多核子转移反应合成大于108号的元素是很困难的。非对称核物质状态方程由于其对天体物理及理解奇异核结构的重要性，因此是人们长期以来一直感兴趣的研究内容，然而直到现在人们对核物质状态方程特别是高密核物质和非对称核物质状态状态方程仍了解甚少。基于Skyrme-Hartree-Fock理论以及同位旋相关的量子分子动力学（IQMD）模型研究了非对称核物质的化学不稳定性，结果表明非对称核物质可以发生化学不稳定性，且化学不稳定性发生的条件依赖于单粒子势能的密度相关形式。同时计算表明化学不稳定性是可以发生在真实的重离子碰撞过程中的，且在入射能量较高时化学不稳定性会消失。另外首次研究了高密核物质的化学不稳定性及其发生的条件。由于实验室很难达到很高密度的核物质，而中子星是由致密的极丰中子物质组成，因此提供了研究高密非对称核物质的自然实验室。基于Skyrme-Hartree-Fock理论研究了两种典型的非对称核物质状态方程（软对称势和硬对称势）对中子星中质子百分比的影响。另外研究了热中子星中质子百分比的温度相关性，发现热中子星中质子百分比随温度的升高而减小。基于IQMD模型研究了同位旋相分化现象的产生机制。通过与MSU的实验数据比较指出核物质应该有软的对称势。研究了重离子碰撞过程中的径向流现象，及其同位旋效应。计算了径向流产生的能量闭，并给出了实验上利用径向流产生的能量闭来提取非对称核物质状态方程的方法。

Extracting single-particle information for the superheavy mass region by studying excited structure in transfermium nuclei

Recent experimental advances have made it possible to study spectroscopy in very heavy nuclei. We show that from the excited high-spin structure of transfermium isotopes, one may gain useful information on single-particle states for the superheavy mass region, which is the key to locating the anticipated 'island of stability'. In this work, we employ the Projected Shell Model for Cf, Fm, and No isotopes to study rotation alignment of the particles that occupy particular high-j intruder orbitals.

Alpha decay half-lives of heavy nuclei within a generalized liquid drop model

Theoretical alpha-decay half-lives of the heaviest nuclei are calculated using the experimental Q value. The barriers in the quasi-molecular shape path is determined within a Generalized Liquid Drop Model (GLDM) and the WKB approximation is used. The results are compared with calculations using the Density-Dependent, M3Y (DDM3Y) effective interaction and the Viola-Seaborg-Sobiczewski (VSS) formulae. The calculations provide consistent estimates for the half-lives of the a decay chains of these superheavy elements. The experimental data stand between the GLDM calculations and VSS ones in the most time.

Possible way to synthesize superheavy element Z=117

Within the framework of the dinuclear system model, the production of superheavy element Z = 117 in possible projectile-target combinations is analysed systematically. The calculated results show that the production cross sections are strongly dependent on the reaction systems. Optimal combinations, corresponding excitation energies and evaporation channels are proposed, such as the isotopes Bk-248,Bk-249 in Ca-48 induced reactions in 3n evaporation channels and the reactions Sc-45+Cm-246,Cm-248 in 3n and 4n channels, and the system V-51+Pu-244 in 3n channel.

Alpha decay half-lives of new superheavy elements through quasimolecular shapes

The lifetimes of alpha decays of the recently produced isotopes of the elements 112, 114, 116 and the element (294)118 and of some decay products have been calculated theoretically within the Wentzel-Kramers-Brillouin approximation. The alpha decay barriers have been determined in the quasimolecular shape path within a generalized liquid drop model including the proximity effects between nuclei in a neck, the mass and charge asymmetry and the precise nuclear radius. These calculations provide reasonable estimated for the observed alpha decay lifetimes. The calculated results have been compared with the results of the density-dependent M3Y effective interaction and the experimental data. It is indicated that the theoretical foundation of the generalized liquid drop model is as good as that of the microscopic DDM3Y model, at least in the sense of predicting the T-1/2 values as long as one uses a correct alpha decay energy. The half lives of these new nuclei are well tested from the consistence of the macroscopic, the microscopic and the experimental data.

Systematic study of properties of Hs nuclei

The ground-state properties of Hs nuclei are studied in the framework of the relativistic meanfield theory. We find that the more relatively stable isotopes are located on the proton abundant side of the isotopic chain. The last stable nucleus near the proton drip line is probably the (255)Hs nucleus. The alpha-decay half-lives of Hs nuclei are predicted, and together with the evaluation of the spontaneous-fission half-lives it is shown that the nuclei, which are possibly stable against spontaneous fission are (263-274)Hs. This is in coincidence with the larger binding energies per nucleon. If (271-274)Hs can be synthesized and identified, only those nuclei from the upper Z = 118 isotopic chain, which are lighter than the nucleus (294)118, and those nuclei in the corresponding alpha-decay chain lead to Hs nuclei. The most stable unknown Hs nucleus is (268)Hs. The density-dependent delta interaction pairing is used to improve the BCS pairing correction, which results in more reasonable single-particle energy level distributions and nucleon occupation probabilities. It is shown that the properties of nuclei in the superheavy region can be described with this interaction.

Alpha-decay for heavy nuclei in the ground and isomeric states

The alpha-decay half-lives of nuclei in the ground states and Isomeric states have been calculated within the WKB approximation and Royer's formulas. The barrier in the quasimolecular shape path is determined within a generalized liquid drop model (GLDM). in which the centrifugal potential energy has been introduced to study the unfavored a-decay The agreement between the calculated results and experimental data indicates the reliability of studying alpha-decay of isomeric states with the generalized liquid drop model We find that their is no significant difference of preformation probability between Isomeric states and the corresponding ground states generally in favored alpha-decay Additionally. we extended Royer's formulas by taking account of the role of centrifugal harrier to study the unfavored alpha-decay, and some predicts oil the a decay half-lives of Isomers are made Finally. the effects of angular momontum transfer and Q(alpha) on alpha-decay half-life have been discussed Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved

Effect of deprivation of vitamin A on the basic proteins of the nuclei of rat testes

The relative concentrations of the major histones, namely, H1, TH1, H2A, H2B, H3 and H4 are not significantly changed in the testes of the vitamin A-deficient rats, as compared to those in the normal controls. But the testis-specific protein, TP, which is synthesized at the mid-spermatid stage, is markedly reduced in the testes of the deficient rats. On supplementation of the deficient rats with retinyl acetate for 28 days, there was a 50% recovery in the relative concentration of the TP with respect to the total amounts of H1 and TH1.

Electrophoretic mobility of cell nuclei (EMN index) as a biomarker of the biological aging process: Considering the association between EMN index and age

The present study examined whether a specific property of cell microstructures may be useful as a biomarker of aging. Specifically, the association between age and changes of cellular structures reflected in electrophoretic mobility of cell nuclei index (EMN index) values across the adult lifespan was examined. This report considers findings from cross sections of females (n = 1273) aged 18–98 years, and males (n = 506) aged 19–93 years. A Biotest apparatus was used to perform intracellular microelectrophoresis on buccal epithelial cells collected from each individual. EMN index was calculated on the basis of the number of epithelial cells with mobile nuclei in reference to the cells with immobile nuclei per 100 cells. Regression analyses indicated a significant negative association between EMN index value and age for men (r = −0.71, p < 0.001) and women (r = −0.60, p < 0.001); demonstrating a key requirement that must be met by a biomarker of aging. The strength of association observed between EMN index and age for both men and women was encouraging and supports the potential use of EMN index for determining a biological age of an individual (or a group). In this study, a new attempt of complex explanation of cellular mechanisms contributing to age related changes of the EMN index was made. In this study, a new attempt of complex explanation of cellular mechanisms contributing to age related changes of the EMN index was made. EMN index has demonstrated potential to meet criteria proposed for biomarkers of aging and further investigations are necessary.

RNA polymerase activity in isolated nuclei of Nicotiana sanderae callus: Characteristics and modulation during differentiation

Isolated nuclei from differentiating cultures of Nicotiana sanderae showed increased levels of RNA polymerase activity as compared to the nuclei from callus cultures. The RNA synthetic activity was dependent on nucleotide triphosphates and Mg2+ and was destroyed by RNase. Maximum activity was obtained in the presence of 50 mM (NH4)2 SO4 and α-amanitin inhibited 40% and 55% of the activity in the nuclei from callus and differentiating tissue respectively. The nuclei from differentiating tissue elicited a 3-fold increase in RNA polymerase I and a 4-fold augmentation in RNA polymerase II activities.