直接鉴别超重元素Z和A的一种新的可能方法

随着合成的超重元素向超重岛逼近,合成截面越来越小,同时,合成的超重元素的寿命可能相对增长,这对利用α衰变链的传统方法鉴别超重元素是非常不利的。讨论了可能突破这个瓶颈的一种可以直接鉴别超重元素原子序数Z和质量A的新方法,即与RFQ离子阱技术相结合的激光多步共振电离方法,对实现这种方法的途径、该方法所面临的困难和挑战、需要进行的前期研究工作以及该方法的可能性和可行性进行了较详细的讨论。

新同位素~(265)Bh(Z=107)的合成证据

利用兰州重离子加速器提供的26Mg离子束轰击243Am靶, 产生了新同位素265Bh. 实验中用氦喷技术对产物进行传输, 并用一套具有数对探测器组的转轮收集探测系统对产物进行收集和测量. 通过观测265Bh与它的衰变子核261Db及257Lr之间的α衰变的关联, 实现了对新核素的鉴别. 实验测得265Bh的α衰变能量为(9. 24±0. 05)MeV, 半衰期为 0. 94+0. 70 0. 31 s.

~(265)Bh(Z=107)同位素的首次观测

在兰州的重离子加速器上用 2 6Mg离子束轰击 2 43 Am靶 ,产生了新同位素 2 65Bh .通过观测新同位素 2 65Bh和它的已知子核 2 61Db和 2 57Lr之间的α衰变的关联 ,实现了对新核素的鉴别 .实验中使用了一套新建立的具有数个探测器对的转轮收集探测系统 .将该系统用于特殊的母 -子核搜索模式 ,从而大大减少了本底 .共测得了 8个 2 65Bh的α衰变关联事件 ;同时 4个已知核 2 64Bh的衰变关联事件也被鉴别出来 .实验测得 2 65Bh的α衰变能量为 (9.2 4± 0 .0 5 )MeV ,半衰期为 0 .94 + 0 .70-0 .3 1s .

利用深部非弹反应对Z≈56,N≈80区核激发态的探索性研究

通过 4 1 0MeV82 Se轰击天然Ba靶引起的深部非弹反应布居产生了类弹和类靶余核的激发态 ,利用在束γ谱学方法测量了它们的退激γ .通过γ -γ符合测量估计了类弹、类靶余核激发态的产生截面 ,在多个类靶余核中观测到了新γ跃迁 ,并建立了136 Ba的新能级纲图 ,说明利用深部非弹反应研究Z≈ 56,N≈ 80区高自旋态是有效、可行的

Z=105质量数为259的新同位素的合成和鉴别(英文)

利用 1 2 0MeV的2 2 Ne离子束轰击2 41　Am靶 ,通过2 41　Am(2 2 Ne ,4n) 2 5 9　Db反应合成了一个Z =1 0 5,质量数为 2 59的新同位素 .反应产物是用氦喷嘴技术和转动轮装置传输收集的 .借助一系列金硅面垒探测器探测到了反应产物及其子核的α衰变 .新同位素的原子序数Z和质量数A是借助该同位素和已知的2 5 5 　Lr核之间的遗传关系得到了确定的鉴别 .新同位素2 5 9　Db的测量半衰期为 (0 51± 0 1 6)s;它的α粒子能量为 9 4 7MeV .由本实验导出的2 5 9　Db的Qα 值同理论预言结果能够较好地符合

25MeV/u ~(40)Ar+~(115)In,~(58)Ni,~(27)Al反应中前中角区碎片角分布和元素Z分布

测量了 ２５ＭｅＶ／ｕ４０　Ａｒ＋１１５　Ｉｎ，５８　Ｎｉ，２７　Ａ１反应前中角区出射碎片的角分布和 元素 Ｚ分布．用改进的量子分子动力学（ＭＱＭＤ）模型研究了碎片的角分布和 Ｚ 分布．理论计算值和实验值整体上符合得很好，但在前角区，ＭＱＭＤ模型低估 了碎片的产额，在中角区对于Ｚ接近弹核的碎片，理论计算值比实验值偏高．碎 片产物的角分布和Ｚ分布还与统计蒸发模型ＧＥＭＩＮＩ进行了比较，结果表明，在 前角区平衡蒸发成份所占的比例很小，中角区所占的比例有所增加，但仍然是较 小的比例．同时发现平衡蒸发成份随着出射碎片核电荷数Ｚ的减小而逐渐减 少．

Shell-model Hamiltonian from self-consistent mean-field model: N = Z nuclei

We propose a procedure to determine the effective nuclear shell-model Hamiltonian in a truncated space from a self-consistent mean-field model, e.g., the Skyrme model. The parameters of pairing plus quadrupole-quadrupole interaction with monopole force are obtained so that the potential energy surface of the Skyrme Hartree-Fock + BCS calculation is reproduced. We test our method for N = Z nuclei in the fpg- and sd-shell regions. It is shown that the calculated energy spectra with these parameters are in a good agreement with experimental data, in which the importance of the monopole interaction is discussed. This method may represent a practical way of defining the Hamiltonian for general shell-model calculations. (C) 2009 Elsevier B.V. All rights reserved.

Production of new superheavy Z=108-114 nuclei with U-238, Pu-244, and Cm-248,Cm-250 targets

Within the framework of the dinuclear system (DNS) model, production cross sections of new superheavy nuclei with charged numbers Z=108-114 are analyzed systematically. Possible combinations based on the actinide nuclides U-238, Pu-244, and Cm-248,Cm-250 with the optimal excitation energies and evaporation channels are pointed out to synthesize new isotopes that lie between the nuclides produced in the cold fusion reactions and the Ca-48-induced fusion reactions experimentally, which are feasible to be constructed experimentally. It is found that the production cross sections of superheavy nuclei decrease drastically with the charged numbers of compound nuclei. Larger mass asymmetries of the entrance channels enhance the cross sections in 2n-5n channels.

Half-Lives of Superheavy Nuclei in Z=113 Alpha Decay Chain

The generalized liquid drop model (GLDM), including the proximity effects and centrifugal potential, and the cluster model with Cosh potential are used to study the half-lives of some Z=113 isotopes and their alpha-decay products.The experimental half-lives of (284)113, (283)113, (282)113and their alpha-decay products are well reproduced by the two models when zero angular momenta transfer is assumed. For (278)113 and its alpha-decay products, both the GLDM andthe cluster model could provide satisfactory results if we assume the alpha particle carry five units of angular momenta, which indicates that possible non zero angular momenta transfer and need further experimental measurements with high precision. Finally, we show that half-lives of alpha-decay are quite sensitive to the angular momentum transfers, and a formula could be used to describe the correlation between alpha-decay half-life and angular momentum transfer successfully.

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.

Properties and structure of N = Z nuclei within relativistic mean field theory

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the proper-ties and structure of N=Z nuclei from Z=20 to Z=48. Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-squaxe (rms) radii of charge and neutron, and shell gaps have been calculated. The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38-42. The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43. The evolution of shell gaps with proton number Z can be clearly observed. Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region. In addition, we found that the Coulomb interaction is not strong enough to breakdown the shell structure of protons in the current region.

Investigation of two-proton emission from excited states of the odd-Z nucleus P-28 by complete-kinematics measurements

An experiment to study exotic two-proton emission from excited levels of the odd-Z nucleus P-28 was performed at the National Laboratory of Heavy Ion Research-Radioactive Ion Beam Line (HIRFL-RIBLL) facility. The projectile P-28 at the energy of 46.5 MeV/u was bombarding a Au-197 target to populate the excited states via Coulomb excitation. Complete-kinematics measurements were realized by the array of silicon strip detectors and the CsI + PIN telescope. Two-proton events were selected and the relativistic-kinematics reconstruction was carried out. The spectrum of relative momentum and opening angle between two protons was deduced from Monte Carlo simulations. Experimental results show that two-proton emission from P-28 excited states less than 17.0 MeV is mainly two-body sequential emission or three-body simultaneous decay in phase space. The present simulations cannot distinguish these two decay modes. No obvious diproton emission was found.

A novel approach to isoscaling: The role of the order parameter m = N-f-Z(f)/A(f)

Isoscaling is derived within a recently proposed modified Fisher model where the free energy near the critical point is described by the Landau O(m(6)) theory. In this model m = N-f-Z(f)/A(f) is the order parameter, a consequence of (one of) the symmetries of the nuclear Hamiltonian. Within this framework we show that isoscaling depends mainly on this order parameter through the 'external (conjugate) field' H. The external field is just given by the difference in chemical potentials of the neutrons and protons of the two sources. To distinguish from previously employed isoscaling relationships, this approach is dubbed: m-scaling. We discuss the relationship between this framework and the standard isoscaling formalism and point out some substantial differences in interpretation of experimental results which might result. These should be investigated further both theoretically and experimentally. (C) 2010 Elsevier B.V. All rights reserved.

Two-electron-one-photon M1 and E2 transitions between the states of the 2p(3) and 2s(2)2p odd configurations for B-like ions with 18 <= Z <= 92

Two-electron-one-photon (TEOP) M1 and E2 transition energies, line strengths and transition probabilities between the states of the 2p(3) and 2s(2)2p odd configurations for B-like ions with 18 <= Z <= 92 have been calculated using the GRASP2K package based on the multiconfiguration Dirac-Hartree-Fock (MCDHF) method. Employing active-space techniques to expand the configuration list, we have systematically considered the valence, core-valence and core-core electron correlation effects. Breit interaction and quantum electrodynamical (QED) effects were also included to correct atomic state wavefunctions and the corresponding energies. Influences of electron correlation, Breit interaction and QED effects on transition energies and line strengths of the TEOP M1 and E2 transitions were analysed in detail. The present results were also compared with other theoretical and experimental values.