共查询到18条相似文献,搜索用时 156 毫秒
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计算和比较了26Mg+244Cm, 27Al+243Am和32S+238U3个反应系统的俘获截面和复合核270Hs形成截面. 在俘获截面计算中, 考虑了靶核形变效应. 穿越库仑势垒后, 反应系统由熔合谷进入不对称裂变谷. 只有越过不对称裂变谷中的条件鞍点的事件才进入复合核组态. 我们用考虑中子流动和径向运动的二参量Smoluchowski扩散方程来处理中间阶段的动力学过程. 此外, 还计算了经4n蒸发形成超重核266Hs的截面. 研究表明, 入射道的势垒分布, 中间阶段的条件鞍点高度对俘获截面, 复合核形成几率, 以及最终的超重核形成截面有显著影响. 相似文献
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在双核模型的理论框架下系统研究了超重元素Z = 116 ~121 的蒸发剩余截面,计算过程中核子扩散由主方程描述,同时考虑了全熔合与准裂变的竞争。计算基本再现了利用热熔合反应48Ca+245Cm,48Ca+249Cf 和48Ca+249Bk 产生116~118 号同位素的合成截面。同样,分别以249Bk,249Cf 和243Am 为靶,以48Ca,50Ti 和58Fe 为炮弹,计算了Z = 119~ 121 号同位素的生成截面。结果表明,这些超重核的生成截面随着质子数的增大进一步变小。例如,利用58Fe+243Am 反应合成121 号同位素的最大蒸发剩余截面仅在fb 量级。基于对选择的几个反应系统的系统分析,发现双核系统在熔合蒸发过程中偶Z 奇N 和奇Z 偶N 复合核分别有强的3n 和4n 蒸发道。The production cross sections of superheavy elements with Z = 116~121 have been investigated systematically within the dinuclear system (DNS) concept, where the master equation is solved numerically to obtain the fusion probability. The competition between complete fusion and quasifission, which can strongly affect the cross section of the compound nucleus formation, is taken into account. The evaporation residue cross sections ER calculated for the hot fusion actinide-based reactions (48Ca+245Cm, 48Ca+249Cf and 48Ca+249Bk) are basically in agreement with the known experimental data within one order of magnitude. Similar calculations for the synthesis of superheavy elements up to Z = 121 are performed using the available 249Bk, 249Cf and 243Am as targets and 48Ca, 50Ti and 58Fe as projectiles. Their production cross sections are relatively small,especially for the 58Fe+243Am→301121 reaction. A systematic analysis indicates that the 3n and 4n channelsare respectively the most favorable fusion-evaporation channels in the synthesis of even- and odd-Z superheavy elements. 相似文献
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利用额外推力模型研究了48Ca+238U俘获和熔合过程中的靶核形变效应.计算表明,在近垒和垒下能区,靶核形变使俘获截面和熔合截面增强,形成的复合核自旋分布展宽. 相似文献
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使用离线γ测量技术在实验室系28.3MeV至45.7MeV的能区首次测量了12C+93Nb反应产生的8个核素及同质异能态的激发函数.使用包括非弹性激发和α转移道的简单耦合道模型,结合统计蒸发程序对实验结果进行拟合.计算结果能较好地重现强截面的中子蒸发道(xn)的激发函数.而对于弱的质子(xpyn)特别是α粒子(xαyn)蒸发道的截面,实验测量明显高于模型计算结果.α转移道与入射道耦合作为熔合反应的门庭态使垒下能区重离子熔合截面有很大的加强,实验测量与理论计算的比较表明对于12C+93Nb反应系统在垒下能区可能存在着很强的α转移截面. 相似文献
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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
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6Li, 9Be为弱束缚核. 通过弱束缚弹核6Li, 9Be轰击靶208Pb,208Be的实验熔合激发函数与理论预言的比较, 讨论了弱束缚弹核破裂对熔合过程
的影响. 比较结果显示, 弱束缚弹核与重靶核的完全熔合截面在垒上能区
明显压低. 由部分熔合截面与完全熔合截面之和得到总熔合截面. 研究结果
表明, 破裂对总熔合截面几乎没有影响. 由此可见, 弱束缚核的部分熔合
可能发生在强吸收区域附近. 最后还给出了全熔合截面与部分熔合截面
之间的关系. 相似文献
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Within the framework of the dinuclear system model,the capture of two colliding nuclei,and the formation and de-excitation process of a compound nucleus are described by using an empirical coupled channel model,solving the master equation numerically and the statistical evaporation model,respectively.In the process of heavy-ion capture and fusion to synthesize superheavy nuclei,the barrier distribution func-tion is introduced and averaging collision orientations are considered.Based on this model,the production cross sections of the cold fusion system 76-82Se+209Bi and the hot fusion systems 55Mn+238U,51V-+244Pu,59 Co+232 Th,48 Ca+247-249 Bk and 45 Sc+246-248 Cm are calculated.The isotopic dependence of the largest production cross sections is analyzed briefly,and the optimal projectile-target combination and excitation energy of the ln-4n evaporation channels are proposed.It is shown that the hot fusion systems 48Ca+247 249Bk in the3n evaporation channels and 45Sc+248Cm in the 2n-4n channels are optimal for synthesizing the superheavy element 117. 相似文献
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通过双核系统模型与其他模型对$Z\leqslant$ 118元素的计算结果与实验数据的比较,证明了不同模型预测超重核的产生截面是可靠的。对比分析了不同模型对Z=119和Z=120超重核的预言结果,我们认为合成超重核Z=119和Z=120的最佳弹靶组合分别为反应$^{48}{\rm{Ca}} + ^{{\rm{252}}}{\rm{Es}}$ 和$^{40}{\rm{Ca}} + ^{{\rm{257}}}{\rm{Fm}}$ ,并且Z=119新核素很有可能会先于Z=120新核素在实验上被合成。由于实验上Z>100锕系靶的限制,人们正尝试寻找比48Ca更重的弹核来合成超重核Z=121和Z=122,超重核Z=121可以通过反应V+Cf来合成,而超重核Z=122的产生截面已经非常小,要求将来在实验上提高探测及鉴别技术。希望本文的讨论可以在将来为实验及理论核物理工作者们提供一些参考。 相似文献
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Within the concept of the dinuclear system (DNS), a dynamical model is proposed for describing the formation of superheavy nuclei in complete fusion reactions by incorporating the coupling of the relative motion to the nucleon transfer process. The capture of two heavy colliding nuclei, the formation of the compound nucleus and the de-excitation process are calculated by using an empirical coupled channel model, solving a set of microscopically derived master equations numerically and applying statistical theory, respectively. Fusion-fission reactions and evaporation residue excitation functions of synthesizing superheavy nuclei (SHN) are investigated systematically and compared them with available experimental data. The possible factors that affecting the production cross sections of SHN are discussed in this workshop. 相似文献
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We investigate the dependence of the yield of superheavy nuclei with Z = 110, 112, 114 on the neutron excess of the projectile nucleus with a two-parameter Smoluchowski equation. It is confirmed that in some cases, the cold fusion reactions with less neutron excess are more favourable than those with more neutron excess. In order to probe the origin of these unexpected isotopic trends, we also investigate the probabilities of capture, fusion and survival in the cold fusion reactions in detail It is found that the maximal ER cross sections of the superheavy nuclei exponentially increase as a function of Bf - Sn with Bf being the fission barrier and Sn being the neutron separation energy. Although the probabilities of capture and fusion have some influences, the unexpected isotopic trends mainly due to the dependence of the ER cross sections on the Bf - Sn value. Therefore, the reactions with larger Bf - Sn values should be more favourable for synthesis of superheavy nuclei. 相似文献
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The superheavy nucleus 270 Hs iS expected to be a "double-magic" deformed nucleus.We have calculated its cross sections of evaporation residue for the reactions 248Cm(26Mg,4n)270Hs,244pu(30Si,4n)270Hs,238U(36S,4n)270Hs and 226Ra(48Ca,4n)270Hs using a two-parameter Smoluchowski equation.It is found from our results that 226Ra(48Ca,4n)270Hs and 238U(36S,4n)270Hs are two optimal reactions for the synthesis of the superheavy nucleus 270Hs due to their large negative Q-values. 相似文献
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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^248.249 Bk in ^48 Ca induced reactions in 3n evaporation channels and the reactions ^45Sc+246.248Cm in 3n and 4n channels, and the system ^51 V+ 244pu in 3n channel. 相似文献
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E A Cherepanov 《Pramana》1999,53(3):619-630
The dinuclear system concept of complete fusion of nuclei has been applied to the analysis of superheavy elements synthesis.
The optimal excitation energy of compound nuclei and production cross sections in the cold synthesis of heavy elements with
charge Z=102–112 have been calculated. The possibility of synthesizing the element with magic number Z=114 in cold and hot fusion reactions has been considered. 相似文献
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With the Skyrme energy-density functional theory, the nucleus–nucleus potential is calculated and the potential energy surface is obtained with different effective forces for accurately estimating the formation cross sections of superheavy nuclei in massive fusion reactions. The width and height of the potential pocket are influenced by the Skyrme effective forces SkM, SkM*, SkP, SIII, Ska, and SLy4, which correspond to the different equations of state for the isospin symmetry nuclear matter. It is found that the nucleus–nucleus potential is associated with the collision orientation and Skyrme forces. A more repulsive nuclear potential is pronounced with increasing the incompressible modulus of nuclear matter, which hinders the formation of superheavy nuclei. The available data in the fusion-evaporation reaction of 48Ca+238U are nicely reproduced with the SkM* parameter by implementing the potential into the dinuclear system model. 相似文献