共查询到19条相似文献,搜索用时 140 毫秒
1.
2.
3.
综述了基于改进的量子分子动力学模型对超重核合成中入射道静态势的研究,重点从静态势垒高及其与质量不对称度的关系说明弹靶组合不对称有利于熔合反应的发生,而接触点驱动势最大所对应的弹靶组合为合成超重元素的最佳选择。 相似文献
4.
5.
运用约化维数量子动力学理论,利用含时波包法,对反应D+CD4→CD3+D2进行了四维量子散射计算.将反应多原子CD4看作双原子D—CD 3,反应D+CD4→CD3+D2看作单原子-双原 子反应,把体系的反应简化为四维散射问题. 波函数的传播采用分裂算符法,为避免格点边界处含时波函数的边界反射,采用了光学吸收 势法,在格点边界处引入光学势,消除边界反射.根据CD4分子的C3v对称性, 选取了Jordan和Gilbert提出的半经验势能面.计算结果表明,反应概率随平动能的变化图像 ,呈现出显著的量子共振特性,这是很多提取反应的共同特征.而不同振动态下的反应概率 随平动能的变化表明,随振动量子数的增大,反应概率有明显提高,且反应阈能明显降低, 这说明反应分子的振动能对分子的碰撞反应有重要贡献.而对基态和第一振动激发态时散射 截面的计算,也证明了这一结论.同时,还分别通过计算量子数j,k,m对反应概率的影响, 对该反应的空间取向效应进行了研究,并与H+CH4→CH3+H2 sub>反应进行了比较.
关键词:
含时波包
量子散射
反应概率 相似文献
6.
使用离线γ测量技术在质心系25.0—40.5MeV的能区测量了12C+93Nb熔合反应产生的二中子和三中子蒸发道的激发函数。由于在相同的激发能下,蒸发道的相对截面比与复合核的角动量有很强的依赖关系,应用统计蒸发程序(CASCADE),从二中子和三中子蒸发道的截面中提取不同能量下的复合核平均角动量和熔合截面。同时从能很好地拟合熔合激发函数的简单耦合道模型(CCFUS)计算中提取复合核的平均角动量。两种方法得到的复合核平均角动量随入射能量的变化相自洽,表明耦合道模型
关键词: 相似文献
7.
在不同的核物质对称能下利用约束的Skyrme-Hartree-Fock-Bogolyubov计算得到了形变核的核子分布,基于此计算了RHIC能量下形变核碰撞产生的自由旁观者核子数及中质子产额比,并分析了中子皮和碰撞几何构型的影响。本工作发现,相比于其他碰撞构型,长椭球核的头对头碰撞和扁椭球核的腰对腰碰撞产生的自由旁观者核子数最少。旁观者中质子产额比敏感于中子皮的平均厚度,因此是对称能的良好探针,但不同碰撞几何构型所得到的产额比依赖于中子皮的极化角分布。在某些碰撞体系中,碰撞几何构型的效应大约为对称能效应的50%。由于238U和96Zr的特殊形变中子皮,相对于其他碰撞构型,旁观者中质子产额比对对称能的敏感性在头对头的238U+238U碰撞和腰对腰的96Zr+96Zr碰撞得到了增强。此研究可能开启新的研究方向,即通过筛选高能形变核碰撞的几何构型来研究形变的中子皮分布。 相似文献
8.
在原子核熔合反应或裂变反应的动力学过程中,颈部变量都起着非常重要的作用。通常情况下,模型中变量的定义根据各种描述宏观形变的参数的不同而不同。为了进一步研究颈部增长在核熔合反应中的作用,通过引入弹核和靶核的形变参量来拓展哑铃模型。在此框架下,计算了从两个接触核到生成一个复合核过程的核熔合反应系统在不同形变下的势能曲面,同时又对核熔合反应体系的惯性张量和粘滞张量进行了计算,这些物理量的计算都为以后的朗之万动力学研究打下了基础。计算结果表明,在改进后的五参数哑铃模型之中,颈部变量是不稳定度并在核反应中起重要作用。 相似文献
9.
通过用QMD模型研究晕核11Be+208Pb的近垒熔合反应,发现晕核引起的熔合反应中,并存着两种相互竞争的机制:一方面当入射晕核11Be靠近靶核时,由于11Be是弱束缚体系,与靶核的相互作用可使其很容易破裂或少数核子被靶核俘获形成核子转移反应,从而对于熔合表现出压制;另一方面当11Be的少数中子进入靶核并与靶核相互作用而使得靶核有些激发,而使局部半径增大,导致熔合势垒降低,熔合截面增强.用QMD模型计算出的熔合截面与实验值基本符合,垒附近表现出增强效应. 相似文献
10.
描述了50.4MeV/u的12N和42.3MeV/u的13N次级放射性束在28Si靶上引起的核反应总截面σr实验研究,结果发现12N的反应总截面σr比其相邻同位素核13N有着异常的增大.这可能是核形变及核子对效应造成的,试验中的测量误差也不可忽视.利用微观Glauber模型计算了12N在28Si靶上的核反应总截面,并与实验结果做了比较,发现理论计算与实验结果拟合较好
关键词:
质子晕
反应截面 相似文献
11.
G. Mandaglio G. Fazio G. Giardina F. Hanappe M. Manganaro A. I. Muminov A. K. Nasirov C. Saccá 《Physics of Atomic Nuclei》2009,72(10):1639-1650
The measured yield of evaporation residues in reactions with massive nuclei have been well reproduced by using the partial
fusion and quasifission cross sections obtained in the dinuclear-system model. The influence of the orientation angles of
the projectile- and target-nucleus symmetry axes relative to the beam direction on the production of the evaporation residues
is investigated for the 48Ca + 154Sm reaction as a function of the beam energy. At the low beam energies only the orientation angles close to αP = 30° (projectile) and αP = 0°–15° (target) can contribute to the formation of evaporation residues. At large beam energies (about E
c.m. = 140–180 MeV) the collisions at all values of orientation angles αP and α
T
of reactants can contribute to the evaporation residue cross section which ranges between 10–100 mb, while at E
c.m. > 185 MeV the evaporation residue cross section ranges between 0.1–1 mb because the fission barrier for the compound nucleus
decreases by increasing its excitation energy and angular momentum. 相似文献
12.
G Giardina P D’Agostino G Fazio M Herman AI Muninov A Nasirov G Oliva R Palamara R Ruggeri 《Pramana》1999,53(3):409-418
The fusion-fission reaction mechanism leading to the massive nucleus formation is studied. We investigate the superheavy nucleus
formation in heavy-ion induced reactions by analysing the evaporation residue (ER) production in order to study the fusion
dynamics and the decay properties of nuclei close to the stability island at Z=114. We consider the 61Ni+208Pb, 48Ca+238U and 48Ca+244Pu reactions that lead to the Z=110, 112 and 114 superheavy elements respectively.
By using the dinuclear system (DNS) concept of the two interacting nuclei we calculate the quasifission-fusion competition
in the entrance channel and the fission-evaporation competition along the de-excitation cascade of the compound nucleus. The
dynamics of the entrance channel allows us to determine the beam energy window which is favorable to the fusion, while the
dynamic evolution of the compound nucleus on the shell correction to the fission barrier and the dissipative effects influence
the fission-evaporation competition in order to obtain the residue nuclei from the superheavy nucleus formation. We also calculate
the τ
n
/τtot ratio at each step of the de-excitation cascade of the compound nucleus and we present a systematics of τ
n
/τtot (at first step of the cascade) for many reactions that lead to nuclei with Z=102–114. 相似文献
13.
S.?Heinz V.?Comas S.?Hofmann D.?Ackermann J.?Heredia F.?P.?He?berger J.?Khuyagbaatar B.?Kindler B.?Lommel R.?Mann 《The European Physical Journal A - Hadrons and Nuclei》2010,43(2):181-184
We investigated the capture stage and successive nucleon transfer from the projectile to the target in the superheavy system
64
28Ni + 207
82Pb (Z
proj. + Z
target = 110) . The target-like transfer products were detected at forward angles of (0±2) degrees, such, we selected nuclei resulting
from central collisions. The data reveal several analogies to cold fusion reactions leading to superheavy elements. The observations
are in accordance with the two-center shell model. The experiments have been performed at the velocity filter SHIP at GSI. 相似文献
14.
A. K. Nasirov A. I. Muminov R. K. Utamuratov G. Fazio G. Giardina F. Hanappe G. Mandaglio M. Manganaro W. Scheid 《The European Physical Journal A - Hadrons and Nuclei》2007,34(3):325-339
The anisotropy in the angular distribution of the fusion-fission and quasifission fragments for the 16O + 238U , 19F + 208Pb and 32S + 208Pb reactions is studied by analyzing the angular-momentum distributions of the dinuclear system and compound nucleus which
are formed after capture and complete fusion, respectively. The orientation angles of the axial symmetry axes of the colliding
nuclei relative to the beam direction are taken into account for the calculation of the variance of the projection of the
total spin onto the fission axis. It is shown that there is a large contribution of the quasifission fragments in the 32S + 208Pb reaction to the deviation of the experimental angular anisotropy from the statistical model results. Enhancement of anisotropy
at low energies in the 16O + 238U reaction is connected with the quasifission of the dinuclear system having low temperature and relatively small effective
moment of inertia. 相似文献
15.
G. Giardina G. Fazio A. Lamberto A. I. Muminov A. K. Nasirov U. T. Yakhshiev R. Palamara R. Ruggeri 《Acta Physica Hungarica A》2004,19(1-2):101-108
We study the effect of the entrance channel and the shell structure of reacting massive nuclei on the fusion mechanism and the formation of evaporation residues of heavy and superheavy nuclei. In the framework of the combined dinuclear system concept and advanced statistical model, we analyze the reactions 32S+182W, 48Ti+166Er and 60Ni+154Sm leading to 214Th*, and the reactions 48Ca+248Cm and the 48Ca+249Cf leading to the 296116 and 297118 compound nuclei, respectively. 相似文献
16.
G. G. Adamian N. V. Antonenko A. N. Bezbakh R. V. Jolos 《Physics of Particles and Nuclei》2016,47(3):387-455
Properties and stability of superheavy nuclei resulting from hot fusion are discussed. It is shown that the microscopic–macroscopic approach allows obtaining the closed proton shell at Z ≥ 120. Isotopic trends of K-isomeric states in superheavy nuclei are predicted. Evaporation residue cross sections in hot fusion reactions are calculated using the predicted properties of superheavy nuclei. Interruption of α decay chains by spontaneous fission is analyzed. Alpha decay chains through isomeric states are considered. Internal level densities in superheavy nuclei are microscopically calculated. 相似文献
17.
G. Fazio G. Giardina A. Lamberto R. Ruggeri C. Saccá R. Palamara A. I. Muminov A. K. Nasirov U. T. Yakhshiev F. Hanappe T. Materna L. Stuttgé 《The European Physical Journal A - Hadrons and Nuclei》2004,19(1):89-104
The effects of the entrance channel and shell structure on the experimental evaporation residues have been studied by analyzing the 32S + 182W, 48Ti + 166Er and 60Ni + 154Sm reactions leading to 214Th*; the 40Ar + 181Ta reaction leading to 221Pa*; the 48Ca + 243Am, 248Cm, 249Cf reactions leading to the 291115, 296116 and 297118 superheavy compound nuclei, respectively. The fusion mechanism and the formation of evaporation residues of heavy and superheavy nuclei have been studied. In calculations of the excitation functions for capture, fusion and evaporation residues we used such characteristics as mass asymmetry of nuclei in the entrance channel, binding energies and shape of colliding nuclei, potential energy surface, driving potential, partial-fusion cross-sections and survival probability of the compound nucleus,
ratio at each step along the de-excitation cascade of the compound nucleus. The calculations have allowed us to make useful conclusions about the mechanism of the fusion-fission process, which is in competition with the quasifission process, and the production of the evaporation residues.Received: 22 April 2003, Revised: 26 June 2003, Published online: 18 December 2003PACS:
25.70.Gh Compound nucleus - 25.70.-z Low and intermediate energy heavy-ion reactions - 27.80. + w
- 27.90. + b
相似文献
18.
A.?A.?Voinov collaboration JINR LLNL ORNL University of Tennessee Vanderbilt University Research Institute of Atomic Reactors 《Physics of Atomic Nuclei》2016,79(13):1519-1524
A survey of experiments at the Dubna gas-filled recoil separator (Laboratory of Nuclear Reactions, JINR, Dubna) aimed at the detection and study of the “island of stability” of superheavy nuclei produced in complete fusion reactions of 48Са ions and 238U–249Cf target nuclei is given. The problems of synthesis of superheavy nuclei, methods for their identification, and investigation of their decay properties, including the results of recent experiments at other separators (SHIP, BGS, TASCA) and chemical setups, are discussed. The studied properties of the new nuclei, the isotopes of elements 112–118, as well as the properties of their decay products, indicate substantial growth of stability of the heaviest nuclei with increasing number of neutrons in the nucleus as the magic number of neutrons N = 184 is approached. 相似文献
19.
Shi-Sheng Zhang Xu-Dong Xu Jin-Peng Peng 《The European Physical Journal A - Hadrons and Nuclei》2012,48(3):1-8
In experiments for the synthesis of superheavy elements at the velocity filter SHIP, GSI, we observed fission events, which could not be attributed to decay chains of superheavy isotopes from fusion reactions. Usually, the observation of spontaneous fission is a crucial first step for the detection of decay chains. In order to avoid random correlations and misidentifications of superheavy isotopes, it is therefore essential to know the features and cross-sections of fission events not originating from decay chains of superheavy nuclei. The special properties of the velocity filter allowed us to identify and study the ??background?? fission events as decay products of heavy target-like nuclides populated in nucleon transfer reactions. Here, we will discuss the results obtained in collisions of 20 48 Ca + 96 248 Cm, 24 54 Cr + 96 248 Cm and 28 64 Ni + 92 238 U, which were applied for the synthesis of elements Z = 116 and 120, respectively. 相似文献