2013年 第30卷 第3期
迄今为止，人们合成的超重核都是缺中子的，无论是熔合-裂变反应还是碎化过程都无法使产物达到周期表的“东北区域”。而重核之间(如U核之间) 的近垒大质量转移反应则可能是目前生成丰中子超重核和达到未知丰中子重核区域的唯一途径。在改进的量子分子动力学(ImQMD) 模型结合统计模型框架内，研究了U+U等反应体系的大质量转移反应，计算了反应产生的初生态碎片的质量和电荷分布，并成功再现了产物的终态质量和电荷分布。通过比较3 个反应136Xe+248Cm，48Ca+248Cm和238U+248Cm 产生的106号元素的截面大小，揭示了U+U等重核大质量转移反应对产生丰中子超重核是非常有利的。For elements with Z > 100 only neutron deficient isotopes have been synthesized so far. The “northeast area” of the nuclear map can be reached neither in fusion-fission reactions nor in fragmentation processes.The large mass transfer reactions in near barrier collisions of heavy (U-like) ions seem to be the only reaction mechanism allowing us to produce neutron rich heavy nuclei including those located at the superheavy(SH) island of stability and unexplored area of heavy neutron-rich nuclides. This study is extremely important for nuclear astrophysical investigations and, in particular, for the understanding of the r process. In this paper within the Improved Quantum Molecular Dynamics (ImQMD) model combining with the statistical-evaporation model, the large mass transfer reactions, like 238U+238U have been studied. The charge and mass distributions of transiently formed primary fragments are investigated within the ImQMD model and de-excitation processes of those primary fragments are described by the statistical decay model. The mass distribution of the final products in 238U+238U collisions is obtained and compared with the recent experimental data. Through compared the formation cross sections of transfermium element 106 by three reactions of 136Xe+248Cm, 48Ca+248Cm and 238U+248Cm, it is explored that the large mass transfer reactions, like U+U are very benefit for the production of SH nuclei.
首先回顾了描写核多体系统输运现象的一些主要模型和方法，然后介绍了输运现象微观动力学基础研究上一些新的结果，强调了单粒子运动动力学特征在建立集体输运方程和理解超重核合成机制上的重要作用。能量耗散和熵产生的数值计算结果表明，集体运动耗散过程可分为退相干、弛豫和定态等3 个阶段，弛豫过程通常表现为非常复杂的反常扩散过程。在这些理论工作的基础上，提出了一种自洽地分离核多体系统集体和单粒子变量的可能途径。In this article, I provide a simple review on conventional methods and models on the transport phenomenon of nuclear many-body systems. By exploiting the basic idea of time-dependent projection operator, I recommend a novel method to derive the transport equation for collective motion which is embedded on the microscopic dynamics of timedependent single-particle motion. It is emphasized that the microscopic dynamics of single-particle motion should play an important role for understanding the dynamics of nuclear reaction and the synthesis mechanisms of new superheavy elements. The numerical results of energy dissipation and entropy production indicate that the collective motion passes through three stages, such as dephasing/decoherence, statistical relaxation and stationary state. The statistical relaxation is a complex anomalous diffusion process in general. With the aid of above analysis and results, a possible way to define the collective and single-particle variables for the realistic nuclear many-body systems is proposed.
着重阐述推广的液滴模型(GLDM) 理论框架及其应用。基于原子核的质量数、质子数以及反应Q 值，GLDM考虑了质量和电荷的不对称性、形状演化、亲近势和温度等，很好地描述了重核和超重核的质子放射性、 衰变、重离子放射性、自发裂变的半衰期和重离子熔合反应截面，同时也研究了原子核的粒子(质子、 、重离子) 放射性与自发裂变的竞争。Recent theoretical achievements and challenges about the fusion and decay properties of heavy and superheavy nuclei are generally introduced. Especially, the Generalized Liquid Drop Model(GLDM) as well as its application are emphatically described. Based on the mass number, proton number and the reaction Q value, the GLDM has taken the mass and charge asymmetry, the shape evolution, the proximity potential, as well as the temperature of nucleus into account, well described the proton radioactivity, the decay, the heavy particle radioactivity, the half life of spontaneous fission of heavy nuclei and superheavy nuclei, and the cross-sections of heavy ion fusion. The competitions between the spontaneous fission and other decay modes such as proton and heavy particle radioactivity, the alpha decay, and so on are also studied.
本征值问题是自然科学中基本运算之一，对于超大矩阵的对角化是当今许多科学问题的瓶颈。在应用原子核壳模型理论研究较重的原子核结构时，因为壳模型组态太大，通常的方法是基于各种物理考虑做某些组态截断，另一个思路是利用新的算法和飞速发展的计算机资源对这些大矩阵对角化或者近似对角化。总结了本课题组近年来在壳模型哈密顿量本征值近似方面研究的主要结果，包括最低本征值半经验公式及多种外推方法、本征值与对角元的相关性等。The eigenvalue problem is one of the fundamental issues of sciences. Many research fields have been challenged by diagonalizing huge matrices. The nuclear structure theorists face this problem in studies of medium-heavy
nuclei in terms of the nuclear shell model, in which the configuration space is too gigantic to handle. Thus one usually truncates the nuclear shell model configuration space based on various considerations. Another approach is to make use of super computers by various algorithms, and/or to obtain approximate eigenvalues. In this paper we review our recent efforts in obtaining approximate eigenvalues of the nuclear shell model Hamiltonian, with the focus on our semi-empirical approach and a number of extrapolation approaches towards predicting the lowest eigenvalue, as well as strong correlation between the sorted eigenvalues and the diagonal matrix elements, and so on.
简要介绍超Fm 原子核谱学的实验和理论研究进展，并综述本研究组近期在超Fm 原子核谱学方面的一些理论研究工作，包括：利用转动谱公式系统研究了超Fm 核区偶偶核与奇A 核的转动。结果表明，在二参数公式中，相较于AB 公式和Harris 公式， ab 公式能够更好地描述偶偶核基态转动带；通过拟合超Fm 核区奇A 核的单粒子能级，提出了一组轨道角动量依赖的Nilsson 新参数；利用粒子数守恒方法处理对关联，基于推转壳模型，系统研究了超Fm 原子核转动谱，计算得到的转动惯量、角动量顺排等与实验符合；通过分析费米面附近Nilsson 能级的占据几率以及各条轨道对角动量顺排的贡献，解释了这个质量区原子核的转动带产生回弯(上弯) 的原因。进一步，利用这组新Nilsson 参数，研究了超重核的单粒子能级结构以及微观壳修正能量。计算表明，这组新Nilsson 参数预言的超重岛中心为Z = 120 和N = 182。Experimental and theoretical studies on the spectroscopy of the transfermium nuclei are briefly reviewed.Recent theoretical progresses made by us is introduced. Moreover, the structure of the superheavy nuclei is investigated.
The rotational spectra in even-even and odd-A nuclei in this mass region are systematically studied by using several empirical formulas. Our result shows that compared with the AB formula and the Harris formula, the ab formula can give
a better description for rotational spectra of ground-state bands in even-even nuclei in this mass region. By fitting the experimental single-particle spectra of the odd-A nuclei in this mass region, a new set of Nilsson parameters is proposed.The rotational bands of the transfermium nuclei are investigated systematically by using a cranked shell model with the pairing correlations treated by a particle number conserving method. The experimental kinematic moments of inertia and angular momentum alignments are reproduced quite well. By analyzing the occupation probability of each cranked Nilsson orbital near the Fermi surface and the contributions of valence orbitals in each major shell to the angular momentum alignment, the upbending mechanism in this mass region could be understood clearly. This new Nilsson parameter set is also used to investigate the shell effects and the microscopic shell correction energies of the superheavy nuclei. The calculated results predict that center of the superheavy island is Z = 120, N = 182.
利用最近发展起来的两步模型分析重离子核反应48Ca+254Es 的熔合过程。在这个模型中，熔合过程被分为前后独立的两个过程，即粘连过程和形成过程。本研究组计算了对应的粘连概率和形成概率，并结合适用于蒸发过程的统计蒸发模型，计算了该反应合成119 号超重元素的剩余截面，即当Elab = 250:2 MeV时，得到最大剩余截面为0.7 pb。Two-step model is adopted to analyze the fusion process of heavy-ion reaction 48Ca+254 Es. Based on this model, the fusion process is divided into two consecutive steps, i.e., the sticking step and the formation step, and corresponding sticking probability and formation probability are calculated. Combining the statistical evaporation model for the evaporation stage, the maximum evaporation residue cross section for reaction 48Ca+254 Es is 0.7 pb at 4n, Elab =250.2 MeV.
成几率的方法，并给出了理论计算值的系统误差。对于“超重稳定岛”附近的超重核，除了壳修正，准裂变势垒高度也会影响超重核的形成几率。基于Skyrme 能量密度泛函得到的准裂变势垒高度，提出了描述复合核形成几率的解析表达式。对于“超重稳定岛”附近的超重核，除了壳修正，准裂变势垒高度也会影响超重核的形成几率。与此同时，基于该方法预言了合成新的超重元素Z = 119 和120 的几个熔合体系的蒸发剩余截面。对于熔合反应50Ti+249Bk，计算出来的最佳蒸发剩余截面大约为35 fb。The fusion probability in “hot” fusion reactions leading to the synthesis of superheavy nuclei is investigated systematically. The quasi-fission barrier influences the formation of the superheavy nucleus around the “island of stability” in addition to the shell correction. Based on the quasi-fission barrier height obtained with the Skyrme energy-density functional, we propose an analytical expression for the description of the fusion probability, with which the measured evaporation residual cross sections can be reproduced acceptably well. Simultaneously, some special fusion reactions for synthesizing new elements 119 and 120 are studied. The predicted evaporation residual cross sections for 50Ti+249Bk are about 35 fb at energies around the entrance-channel Coulomb barrier. For the fusion reactions synthesizing element 120
with projectiles 54Cr and 58Fe, the cross sections fall to a few femtobarns which seems beyond the limit of the available facilities.
利用包含动力学势能面的双核模型对超重核的生成机制中的一些问题进行了研究。对双核系统的粒子交换势能面进行的计算结果表明，反应过程中原子核动力学形变对于粒子交换势能面的结构有显著的影响。进一步计算了生成超重核的熔合几率，结果显示，原子核的动力学形变导致内熔合位垒升高，进而明显降低了生成超重核的熔合几率。Some aspects in the fusion mechanism for the production of superheavy nuclei are investigated with the dinuclear system model with dynamical potential energy surface. The calculation results about the potential energy surface indicate that the inclusion of nuclear dynamical deformation affects the structure of potential energy surface significantly.The investigation on the fusion probability to synthesize superheavy nuclei indicates that the fusion probability decreases significantly due to the increase of the inner fusion barrier for the inclusion of the nuclear dynamical deformation.
在重离子熔合反应中，准裂变与熔合过程之间相互竞争。在双核模型中，常常在主方程中加入Kramers公式来描述准裂变。但只有当准裂变位垒足够高时，该公式才能成立。在本工作中，把弹靶核的间距作为独立的动力学变量，通过求解主方程来自洽地同时描述双核模型向全熔合和准裂变过程的演化，因此检验了Kramers 公式的适用条件。此外，在重离子熔合反应过程中，把动力学形变的演化和核子的转移过程都看成是耗散过程，在系统的势能面的约束下，同时求解含有动力学形变参量和质量不对称度参量的一系列主方程。研究显示了动力学形变对准裂变质量分布的直接影响，得到了与实验观测值符合得很好的计算结果。In heavy ion fusion reactions, the quasifission(QF) is competing with fusion, and which is often described by incorporating the Kramers formula(KRA-F) into the master equation(ME) within the Di-Nuclear System(DNS) model. However the KRA-F works well only if the QF barrier is high enough. Presently by taking
the relative distance of nuclei as an independent dynamical variable, the evolution of the DNS towards fusion and QF are both treated as a diffusion process in a consistent way by solving MEs. The validity of the KRA-F is thus
checked. Furthermore, the dynamical deformation and the nucleon transfer in heavy ion fusion reaction process are viewed simultaneously as a diffusion process, and are treated by solving a set of MEs with the variables of the
quadrupole deformation of each nucleus and the mass asymmetry variable in the potential energy surface(PES) of the system. The distinct influence of the dynamical deformation on the QF mass yield distribution is discussed,and the experimental observations can be well reproduced by the calculation.
采用密度依赖的结团模型研究了奇Z 超重核的禁戒α衰变， 粒子与子核之间的微观核势通过双折叠模型对M3Y 核子-核子相互作用势以及 粒子与子核的密度积分给出。 粒子与子核之间的库仑相互作用也通过 粒子与子核的电荷密度积分给出。计算发现，由于非零角动量带来的禁戒效应和小的α粒子预形成几率，奇Z 超重核的α衰变寿命会明显变长。We investigate the α-transition of odd-Z superheavy nuclei by the density-dependent cluster model (DDCM). The microscopic nuclear potential between the -particle and the daughter nucleus is evaluated numerically from the double-folding model with the standard M3Y nucleon-nucleon interaction. The Coulomb potential is also obtained from the double-folding integral of the proton-proton Coulomb interaction with the charge density distributions of α-particle and daughter nucleus. From our calculations, enhanced stability against
α-decays is found for the odd-Z superheavy nuclei due to the hindrance effect of non-zero angular momentum and the small preformation factor of the -particle.
通过总Routhian 面计算方法研究了Z = 102 号元素已实验合成的偶偶248-264No同位素的转动性质。计算的基态形变β2,β4 与前人的计算相符。252,245No 两核基态带的转动惯量特征能得到基本再现。偶偶248-264No同位素转动惯量系统上弯的现象可归因于带交叉。研究还表明，推转时质子与中子顺排有强烈竞争，在较轻的No同位素中j15/2 中子拆对顺排较为优先，而在较重的No 核中i13/2 质子顺排更加优先。The rotational properties of the synthesized even-even 248-264No isotopes have been investigated by means of total Routhian surface calculations. The calculated ground-state properties (e.g. β2; β4) are in agreement with previous calculations. The behaviors of moment of inertia of 252,254No are well reproduced by our calculations. The systematic upbending in moment of inertia is attributed to band crossing. It is found that the j15/2 neutron rotation-alignment is preferred for the lighter No isotopes, but the i13/2 proton alignment is favored in the heavier ones.
基于推广的液滴模型(GLDM) 理论框架，计算了292-310122 同位素链的 衰变和自发裂变的半衰期。计算时的基本输入量为两子核的质量数和电荷数以及反应Q 值。GLDM能很好地描述重核和超重核的 衰变和自发裂变过程。计算结果表明，A < 308 时在同位素链上N = 176~184 的区域α衰变为主要衰变模式。A > 308 时在同位素链上自发裂变为主要衰变模式。308122 是α衰变和自发裂变的分界点，暗示着N = 184 为中子幻数。Based on the framework of the Generalized Liquid Droplet Model (GLDM), alpha decay and spontaneous fission half-lives for 292-310122 isotopes are studied. The calculation of the basic inputs which only need the two fragment
mass numbers, charge numbers and the Q value. GLDM can describe alpha decay and spontaneous fission the nuclei. It is found that the alpha decay is the dominant mode of decay for isotopes with mass number A < 308, and for those with A > 308 spontaneous fission is dominant. The demarcation between alpha decay and spontaneous fission is at 308122, which shows the presence of a spherical neutron shell closure at N = 184.
该工作提出了一个同位旋依赖碎块判断方法用以描述重离子碰撞过程中的碎块形成。利用该方法可以改善输运理论对于核子以及轻带电粒子产额的描写，其在计算中降低了发射核子产额、增加碎块(特别是丰中子碎块) 的产额。对于丰中子轻带电粒子的增强主要出现在中心快度区。研究表明，该方法对于同位旋敏感的观测量，如，n/p,t/3He,Rmidyield 和isoscaling parameters 等，以及系统的平衡度的量度都会产生影响。We introduce isospin dependence in the cluster recognition algorithms used in the Quantum Molecular Dynamics model to describe fragment formation in heavy ion collisions. This change reduces the yields of emitted nucleons and enhances the yields of fragments, especially for heavier fragments. The enhancement of neutron-rich lighter fragments mainly occurs at mid-rapidity. Consequently, isospin dependent observables, such as isotope distributions, yield ratios of n/p,t/3He, Rmid yield and isoscaling parameters are affected. We also investigate how equilibration in heavy ion collisions is affected by this change.
两体碰撞等系统研究了INDRA 能区重离子碰撞后出射的自由核子及轻粒子的集体流和核阻止本领等观测量。研究发现，一个采用带动量依赖的软的状态方程及动量修正的密度依赖的核子核子弹性散射截面的动力学输运过程能够很好描述INDRA 全能域内实验获得的中心快度区的氢同位素的直接流。利用该套输运系统还研究了直接流平衡能对对称势能密度依赖强度因子的敏感性。发现，出射的自由中子平衡能敏感依赖于对称势能的密度依赖，而自由质子却不会。同时还发现，利用两Sn 同位素系列反应出射的自由中子直接流的平衡能与初始中子/质子比的关系可以很好地探测对称能的密度依赖。The terms of initialization, equation of state (EoS), and two-body collision in the updated ultrarelativistic quantum molecular dynamics (UrQMD) model are examined in details so as to systematically study the collective flows and the nuclear stopping of free nucleons and light clusters from heavy-ion collisions at INDRA energies. It is seen that at INDRA energies the dynamic transport with a soft EoS with momentum dependence and with the momentum-modified density-dependent nucleon-nucleon elastic cross sections describes the directed flow exhibited by hydrogen isotopes (Z= 1) emitted at midrapidity fairly well. The sensitivity of the balance energy (Ebal) of the directed flow to the strength parameter of the density dependence of symmetry potential energy is further studied with the same parameter set. It is found that the Ebal of neutrons from HICs is particularly sensitive to the density dependence of the symmetry potential energy, while that of protons is not. And, the initial neutron/proton ratio dependence of the balance energy of neutrons from Sn isotopes can be taken as a useful probe to constrain the stiffness of the nuclear symmetry energy.
基于裂变的随机模型，研究了能级密度参数在鞍点与其基态处的比值af/an在热核衰变过程中的作用。计算表明，af/an的大小能显著影响蒸发剩余截面及其自旋分布的大小以及裂变过程中热核的耗散行为。发现，能级密度参数对激发能的依赖性af/an(E*) 能改变断点处的激发能对摩擦强度的敏感性。最后指出了af/an随E* 的变化对超重核的稳定性和散裂反应退激阶段描述的意义。Based on the stochastic approach to fission, we have demonstrated that the ratio of level-density parameters at saddle to that at ground-state configuration, af/an, plays a significant role in the decay of an excited nucleus. It modifies not only the sensitivity of evaporation residue cross section and its spin distributions
to nuclear friction, but also the dissipation properties of hot nuclei. Furthermore, we find that af/an as a function of excitation energy appreciably affects the evolution of excitation energy at scission with the friction strength. A consequence of a change of af /an with E* on the stability of superheavy nuclei and on modelling de-excitation processes of spallation reactions is indicated.
在相互作用玻色子模型(IBM) 基础上用O(6) 高阶项代替传统的SU(3) 四极-四极相互作用来研
究原子核从振动到转动过渡区的量子相变行为。利用U(5)-SU(3) 和UQ 两种方案，在玻色子数分别为N = 8 和N = 20 不同情况下，研究了原子核的一些低激发态的能级比和电四极跃迁比。结果表明：随着玻色子数N 的增大，系统的量子相变行为得到加强；两种方案都可以用来描述从振动到转动过渡区的原子核的量子相变特征且O(6) 高阶项方案下量子相变行为更为明显。在此基础上，进一步应用这两种方案具体讨论了152Sm 核的低激发态能级和电四极跃迁性质并与实验数据进行对比分析。结果表明，用O(6) 高阶项可以更为合理地描述带内跃迁及不同带之间的带间跃迁性质。With the framework of Interacting Boson Model(IBM), transitional patterns from the spherical to the axially deformed limit of the IBM with a schematic Hamiltonian are studied by replacing the SU(3) quadrupole-quadrupole term with O(6) cubic interaction. But, we use the two schemes to investigate some energy ratios and B(E2) ratios for different bosons N = 8 and N = 20. The results show that with the increasing of the numbers of bosons, the transitional behaviors can be enhanced; the transitional behaviors are very similar in the two schemes. However, there are some distinctive differences for some quantities across the entire transitional region, such as energy levels and ratios, B(E2) values and ratios, and expectation values of the shape variables. Generally speaking, the transition is smoother and the nuclear shape is less well defined in the new scheme. Then we apply the two schemes to the critical point symmetry candidate, such as 152Sm, and find the overall fitting quality of the UQ scheme is better than that of the U(5)-SU(3) scheme, especially for the inter-band E2 transitions in 152Sm.
它们使用的基本假设不一样。讨论了原子核系统的特殊性，这些特殊性使得核温度的提取特别困难。重点比较了动力学近似的几种温度计：使用经典Maxwell-Boltzmann 近似的，和使用量子Fermi-Dirac近似的。使用氦锂温度计对照考虑费米子属性后的斜率温度计和涨落温度计，发现考虑费米属性后提取的核温度更接近于热力学温度。仍需更多的工作，从核体系的孤立性、有限性和费米子属性等方面来研究核系统热力学温度的提取方法。Nuclear thermometers based on different approaches are reviewed. Due to the different basic assumptions of these methods, the nuclear temperatures extracted by different thermometer approaches are not consistent. Moreover,
several problems which make the extraction of the nuclear temperatures even more difficult are discussed. The nuclear thermometers based on different kinetic approaches are compared. The nuclear temperatures extracted by methodsbased on quantum (Fermi-Dirac) kinetic approaches are compared to the double ratio temperatures THe; Li. Perspectives for future investigations of the thermal temperature are given.
物态方程，并考虑非牛顿引力效应影响，数值计算了由于CFS(Chandrasekhar-Friedmann-Schutz) 不稳定性引起的年轻热中子星的r-mode 不稳定窗口，给出了引力辐射时标和耗散时标随温度的变化关系。利用中子星观测对非牛顿引力参数的约束，给出了热中子星在高温区不稳定窗口边界的约束，并发现较大的非牛顿引力参数对应着较宽的r-mode 不稳定窗口。研究结果可为地面引力辐射探测提供有意义的参考。Theoritically, instable r-mode in neutron star may radiate detectable gravitational waves. In this work,considering the non-Newtonian gravity proposed in the grand unification theories, we numerically calculate the CFS instabilities of r-mode s in the hot neutron stars by using an equation of state with super-soft symmetry energies. The changes of the gravitational radiation time scales and the viscous time scales versus the stellar temperatures are obtained.And according to the constraint of the neutron star observation on the parameter of non-Newtonian gravity, the constraint on the boundary of the instability window is also given. It is found that a stronger non-Newtonian gravity corresponds with a wider r-mode instability window. These results may provide interesting reference for the gravitational wave detection.
利用动力学加统计模型对200Pb 系统的断前中子的发射进行了模拟。计算结果表明，在核耗散的形变关系(DDND) 确定的情况下，断前中子多重性会随着能级密度坐标关系(DDLDP) 的增强而减少，且该规律主要由第一阶段内断前中子的发射决定。此外，选定DDLDP 而采用核耗散的不同形变关系也都很好地重现了实验数据。为了解释上述现象，提出了研究热核退激的路径分析方法，其主要内容是把核耗散看成是实验粒子在拉伸维度上的阻尼力，而核裂变的动力学过程是该阻尼力和自由能产生的驱动力之间相互竞争的结果。利用该方法对200Pb 系统的断前中子多重性进行了分析，并指出在确定DDND时应考虑DDLDP。Within a certain deformation dependence of nuclear dissipation (DDND), the simulation results about the deexcitation process of 200Pb show that the prescission neutron multiplicities decrease with increasing deformation dependence of level density parameter (DDLDP). Moreover, this pattern is determined by the emission of prescission neutron in the first period of nuclear fission. On the other hand, all of the results from two kinds of different DDNDs can reproduce the experiment data perfectly with a certain DDLDP. In order to illustrate those phenomena, the pathwise analysis method (PAM) is presented in this paper. In the PAM, nuclear dissipation is treated as the damping force on the elongation dimension, whereas the fission dynamics process results from the competition between damping force and the driving force stemming from the nuclear free energy. The prescission neutron multiplicity in the deexcitation process of 200Pb is analyzed, and the results point out that the DDLDP needs to be taken into account in studying the DDND.
盒型硅(Si-box) 探测器阵列和反符合(Veto) 探测器3 部分。Si-box 探测器阵列是由3 块位置灵敏硅探测器(PSSD) 和8 块周边硅探测器(SSD) 构成，它对注入核的 衰变的探测效率达到80% 左右。Si-box 探测器阵列与TOF 探测器关联可以有效区分注入信号和 衰变信号。Veto 探测器与Si-box 探测器阵列和TOF 探测器关联可以反符合掉高能轻粒子对注入信号和 衰变信号的干扰。简要介绍了PSSD 的能量和位置刻度方法。这套探测器系统已经应用于40Ca+175Lu 和40Ca+169Tm 的实验。实验结果表明，该探测器系统具备很好的本底抑制能力，能够给出干净的a衰变能谱，结合能量-时间-位置关联测量方法可以实现对单原子的探测和鉴别，总体上达到了预期的设计要求。A new designed focal plane detection system was mounted at the gas-filled recoil separator at Institute of Modern Physics, Chinese Academy of Sciences, which consisted of a time-of-flight (TOF) detector, a silicon-box (Sibox) detector array and a silicon veto detector. Three position sensitive silicon detectors (PSSD) were surrounded by eight side silicon detectors (SSD) without position sensitive, forming a box of the detector open from the front side. The detection efficiency for -decays of implanted nuclei was about 80%. The anticoincidence condition for the signals from the TOF detector and Si-box detector array was used to distinguish between the pulses originating from the implanted nuclei and their -decays. The veto detector information was used to discriminate events due to high-energy charged particles．External energy calibration and position calibration of PSSD are described concisely in this work. This system
has been used in experiments of 40Ca+175Lu and 40Ca+169Tm. Clean a-decay spectra obtained in these reactions indicated the detection system has a good performance in background suppression. Evaporation residues can be identified by the energy-time-position correlation method. On the whole, the new designed focal plane detection system has achieved thedesign requirements.
得到参数化的势能表示形式。通过拟合不同测量方法得到的实验数据(经过评价) 获得3 组模型参数。3 组参数计算的碎片质量分布均很好地再现了不同能点的实验数据，除了基于动能法实验数据得到的参数外，其14 MeV的计算结果与实验数据符合较差。研究发现，不同入射中子能量的裂变碎片质量分布有4 个主要交叉点，在叉点之上的产额随入射中子能量增加减少，之下的产额则随入射中子能量上升；内侧(或外侧) 的两个交叉点质量数之和近似等于裂变复合核的质量数；不同裂变系统的重峰左侧的交叉点都保持在132 附近。Present model was based upon Brosa model, where macro energy，shell effect energy and its decreasing with system temperature were considered and parameterized. 3 sets of model parameters were obtained by fitting to 3 groups of evaluated experimental data, respectively, where the groups were classified by measured method: radiochemistry (RA) method, double kinetic energy (KE) method, and both (ALL). All the 3 sets of parameters could well reproduce the
measured mass distributions on different energies, except the KE set on 14 MeV. The result shows the mass distributions mainly had 4 trend turning points, above which the yield decreasing and below which the yield increasing with energy.The sum of the 1st and 4th (or 2nd and 3rd) point positions was equal to the compound nuclei mass approximately. And the 3rd point was kept at ~132 constantly for different fission systems n+233 U, n+235U, n+233Pu.
232Th 中子诱发裂变产额在Th/U 燃料循环的核能开发中具有重要的意义，在现有国际评价产
额数据库基础上，结合最新的实验数据，对产物核的质量分布和反应堆计算所需的重点产物核进行了比对。这些产物核包括95Mo，99Tc，101Ru，103Rh，109Ag，133Cs，147Sm，149Sm，150Sm，151Sm，152Sm，143Nd，145Nd 和153Eu 等，对有分歧的133Cs，152Sm 和153Eu 累积产额数据进行了评价调整。最后推荐给出了n+232Th 裂变的产额数据库，作为CENDL 库的组成部分。The yields of n+232Th fission are important in study of the Th/U fuel cycle. Based upon the evaluated nuclear data libraries and recent experimental data，comparison and evaluation for yield mass distribution and cumulative
yield were performed for those products are needed and important in reactor calculations，including 95Mo，99Tc，101Ru，103Rh，109Ag，133Cs，147Sm，149Sm，150Sm，151Sm，152Sm，143Nd，145Nd adn 153Eu etc. Adjustments were made for 133Cs, 152Sm and 153En which have discrepancies among the libraries. Database for n+233Th fission yield is recommended as a part of CENDL update.