Mass Distribution of Fission Fragments and Abundances of Heavy Nuclei Produced in the r-Process

Physics of Atomic Nuclei - Several models of the fission fragment distribution (FFD) with respect to mass that are used in calculating the nucleosynthesis of heavy elements are considered. Their...     

基于GEM工艺的裂变时间投影室中裂变碎片的讨论

基于GEM工艺的裂变时间投影室兼具GEM工艺的高计数率、高空间分辨本领等优点,我们拟通过裂变时间投影室在单次测量中准确获取裂变产物的核电荷数、质量数以及能量等多种信息。本文主要讨论了基于GEM工艺的裂变时间投影室中工作气体的种类、气压以及裂变碎片在气室中的能量损失和有效电荷问题,发现对于轻重两种裂变碎片的能量损失而言,重裂变碎片的分布宽度更窄。并针对裂变碎片在气室中的能量损失,提出了一种通过裂变碎片的有效电荷获取核电荷数的方法。这对于裂变时间投影室的研制工作以及实现裂变产物的多参量测量具有重要意义。     

重核自发裂变寿命的新公式

利用Swiatecki寿命公式及其推广形式系统计算了重核的自发裂变寿命，并提出一个新的四参数自发裂变寿命公式，公式计算结果和实验数据能够很好地符合. 对于Z≥90的重核存在一条N=Z+52的长寿命线. 新公式可以预言长寿命线附近的重核自发裂变寿命.     

Radioactive-Ion Beams for the Fission Study of Heavy Neutron-Rich Nuclei

Physics of Atomic Nuclei - Quasi-elastic, multi-nucleon transfer reactions induced by the radioactive-ion beams with energy 4–6 MeV/u allow one to produce moderately excited neutron-rich...     

轻中等质量核非对称裂变研究的新进展

介绍了轻中等质量核非对称裂变研究的新进展.通过对64,58Ni+12C和78,82,86Kr+12C反应复杂碎片的激发函数测量,发现流行的转动液滴模型和转动有限力程模型均不能复现实验的非对称裂变位垒数据.The excitation functions were measured for complex fragments with atomic number Z=4—25 emitted from the compound nuclei~(70,76)Se and~(90,94,98)Mo produced in the reactions~(64,58)Ni+~(12)C and~(78,82,86)Kr+~(12)C. The extracted mass asymmetric fission barriers have been compared with those calculated from macroscopic nuclear models.     

100,104Sn核在裂变过程中发射的轻粒子多重性

用扩散模型考察了轻的幻核¹⁰⁰Sn在裂变过程中蒸发的轻粒子多重性. 发现壳仅对质子的发射有很强的影响, 而对中子几乎没有影响, 这与¹³²Sn核的情况正好相反. 因此把这种现象归因于系统中质比(N/Z)的影响. 通过比较¹⁰⁴Sn和¹⁰⁰Sn发射的粒子, N/Z的 影响得到了进一步证实. 计算发现高激发能弱化了N/Z效应.     

重核裂变过程中阻尼对中子发射的效应

用{c,h,α}核表面方程描写重核的形变, 建立了含中子发射的裂变动力学的耦合Langevin方程, 完成了断点前中子蒸发多重性的蒙特卡罗计算. 比较了不同黏滞系数对结果的影响, 尤其是区分了裂变核系统首次通过鞍点和最后通过鞍点期间的中子发射分布.     

Fission Properties of Neutron-Rich Nuclei around the End Point of r-Process

We studied the fission properties of neutron-rich nuclei ^278,286Cf around the end point of r-process by microscopic self-consistent approaches. The fission barriers and potential energy surfaces are obtained by constrained static Skyrme Hartree–Fock-BCS calculations. Fission fragments are studied by dynamical time-dependent Hartree–Fock+BCS calculations. Results show that ²⁸⁶Cf has an octupole deformation at ground state, which can increase the fission barrier height by 1.1...     

The Application of Lie Algebra Method in Induced Heavy Nuclei Fission

The propagator method is efficient in solving the Fokker-Planck equation.with an inharmonic oscillator potential. The propagator is deri;ed by using the Lie algebra method. The fission rate of ²⁴⁰Pu is calculated based on the expression of the propagator. The numerical results show that the rate is reasonable.     

重核熔合与裂变位垒的动力学回流现象

用实验粒子多次通过位垒的方法计算重核熔合与裂变过程中的熔合几率和裂变速率,结果发现位垒附近存在着一种强烈的回流现象.研究还表明当鞍点后势变得平滑,则回流变大.这种效应降低了以往所用的实验粒子首次通过位垒方法得到的熔合几率和裂变速率,从而给出这两种量的正确描述     

近垒和垒下重离子熔合裂变碎片各向异性的异常

系统总结了研究近垒和垒下重离子熔合裂变反应碎片各向异性的异常的结果 ,提出一个新的预平衡裂变模型,成功地解释了碎片各向异性的异常现象 .但对异常宽峰结构不能说明 ,有待进一步研究. Systematic summary on the anomalous anisotropies of fission fragments in near and sub barrier fusion fission reactions is presented. A new version of the preequilibrium fission model is put forward to explain the anomalous anisotropies of fission fragments, except the bump of anomaly. Further study is still needed.     

Angular Anisotropy of the Fission Fragments in the Dinuclear System Mo del

A theoretical evaluation of the collective excitation spectra of nucleus at large deformations is possible within the framework of the dinuclear system (DNS) model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two-cluster configurations in a dynamical way, permitting exchange of nucleons between clusters. In this work the method of calculation of the potential energy and the collective spectrum of fissioning nucleus at scission point is presented. Combining the DNS model calculations and the statistical model of fission we calculate the angular distribution of fission fragments for the neutron–induced fission of 239Pu.     

Experimental Cross Sections of Fission Fragments of Thorium-232 Irradiated with Medium-Energy Protons

This paper is focused on fission of Th-232 nuclei induced by protons with energies ranging from 20 to 140 MeV. This energy range is the most informative for studying the competition between asymmetric and symmetric fission modes. Experimental cross sections of production of radionuclides in thorium targets have been determined a year after irradiation. The corresponding theoretical values are calculated using the cascade–evaporation–fission model. The theoretical and experimental cross sections (literature data included) are compared.     

热核衰变中轻粒子的发射时间

报道了25MeV/u ⁴⁰Ar+¹⁹⁷Au反应中裂片符合下的粒子—粒子关联函数及其发射时间.实验测得粒子的平均发射时间为200—300fm/c,表明轻粒子的裂前发射占主导.在平面发射和出平面发射的粒子发射时间相差很少,发射时间是随着粒子能量的改变而发生显著变化,从中速粒子的约300fm/c下降至类弹粒子的约30—100fm/c.     

裂变碎片靶室在直接测量重Λ超核寿命中的应用

介绍了一种新的直接测量重超核寿命的方法. 并对其中用到的一个重要探测设备——裂变碎片靶室——在托马斯.杰斐逊国家实验室用²⁵²Cf放射源进行了测试. 该靶室的单模块时间分辨率为～163ns. 在此分辨率的基础上, 计算机模拟表明用此方法测到的超核寿命误差将在9.6ps左右.     

裂变碎片靶室在直接测量重A超核寿命中的应用(英文)

介绍了一种新的直接测量重超核寿命的方法.并对其中用到的一个重要探测设备——裂变碎片靶室——在托马斯·杰斐逊国家实验室用~(252)Cf放射源进行了测试.该靶室的单模块时间分辨率为～163ns.在此分辨率的基础上,计算机模拟表明用此方法测到的超核寿命误差将在9.6ps左右.     

Stopping, Trapping and Cooling of Radioactive Fission Fragments in an Ion Catcher Device

An ion catcher as presented in this contribution is able to create cooled and very clean singly-charged ion pulses out of a ‘hot’ beam within a very short period of time. Precision measurements on shortlived radioactive nuclides become possible. This contribution describes experiments with a ²⁵²Cf fission source at the ‘gas-cooler’ at ATLAS (Argonne Tandem Linac Accelerating System) at the Argonne National Laboratories (ANL), Argonne, USA[1]. The system consists of a gas-cell to stop and thermalize the ions, two extraction radio frequency quadrupole structures (RFQ) to separate the ions from the buffer gas and a buncher RFQ to cool and accumulate the ions. The system and its performance is investigated with two independent measurements. The transported activity was measured to determine the efficiency of the system and time of flight measurements (TOF) were performed to determine the transported masses with respect to the transported activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Possibility of Delayed Fission of Nuclei in the Region of Superheavy Transuranium Elements

Delayed fission of atomic nuclei was discovered in 1966. It is observed primarily in odd–odd nuclei for which the energy released in beta decay (K capture) is commensurate with the fission barrier in the nucleus formed after this process. Delayed fission was found in four nuclide regions: neutrondeficient isotopes in the Pb region, neutron-deficient isotopes in the Ac and Pa regions, and neutrondeficient and neutron-rich isotopes of transuranium elements. In the wake of investigations into the properties of isotopes of superheavy transuranium elements, numerous calculations were performed in order to determine the masses of new nuclei and to predict their decay properties. Explored and predicted properties of superheavy-element nuclides, where, for some odd–odd nuclei of transuranium elements, the K-capture energy is commensurate with the fission barriers in the corresponding daughter nuclei formed after K capture, are analyzed. Estimates of the delayed-fission probability are presented for some isotopes of elements whose charge number Z ranges from 103 to 107.