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提出了一种从理论上检验壳效应的方法. 即在考虑了BCS近似的相对论平均场理论框架内, 通过计算粒子数的涨落, 发现涨落的大小和核的壳结构有紧密的关系, 由此从理论上证明了在滴线附近的丰中子区, 传统幻数N=28已经消失. 相似文献
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基于相对论平均场理论(RMF),采用TM1以及有效超子-核子和超子-超子相互作用,首先研究了16O和ΛΛ18O的单粒子能级受超子的影响情况,发现超子的加入使得核子能级能量降低.其次基于相对论无规位相近似方法 (RRPA),自洽地计算了16O和ΛΛ18O同位旋标量巨单极和四极共振态.发现相比于16O各巨共振的响应函数,超核的响应函数会发生改变.研究表明:这种改变主要来自于超子的加入导致的核子单粒子能级的改变,以及超子粒子-空穴组态跃迁的贡献,而超子-超子剩余相互作用对单极和四极共振在低能区的响应函数的影响比较小,特别对高能区的响应函数基本没有影响. 相似文献
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在相对论平均场的基态上自洽的相对论无规位相近似(RRPA)理论框架下,研究稳定核和不稳定核的巨共振性质.研究了稳定核208Pb,144Sm,116Sn,90Zr,40Ca,16O和不稳定核Ca同位素链同位旋标量和同位旋矢量集体巨共振激发,并讨论了Dirac海负能核子态和矢量介子空间分量对核的巨共振性质的影响.研究的结果表明,Dirac海负能核子态和矢量介子空间分量对同位旋标量激发有贡献,特别是对重核,而对轻核它的贡献减弱,对于同位旋矢量激发的贡献可忽略.几组常用的相对论平均场非线性模型参量,不仅能成功的描述有限核的基态性质,也能很好地描述核的巨共振激发.对于N/Z极端情况下,同位旋矢量巨偶极激发模式存在低能集体激发,它是由于费密面附近弱束缚核子的激发和同位旋混杂效应
关键词:
相对论无规位相近似
核巨共振 相似文献
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在约束形变的相对论平均场理论下,用NL3参数组系统地研究了Se,Kr,Sr和Zr四个同位素链中的偶-偶核,理论计算的基态束缚能和实验值符合得非常好.通过对这些核的位能曲面的分析,发现在此区域内有着丰富的形状共存现象,系统地指出可能存在形状共存现象的原子核,并且进一步指出在这些核的位能曲面上两个能量极小点的能量差.另外通过对位能曲面以及单中子能级的研究,提出在此区域内N=70可能是一个中子幻数.
关键词:
形状共存
相对论平均场
位能曲面
幻数 相似文献
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One-proton, two-proton, and α-particle transfer have been studied on nuclei with closed neutron shell N = 82 using 16O beams of 63 to 66.5 MeV incident energy. Transfer probabilities defined in a semiclassical model are derived for the different reaction channels. For this purpose the Q-value and angular dependence of the cross section are discussed. The two-proton transfer to the ground states shows an enhancement by a factor 20–25 compared to other nuclei, showing the effect of the proton pairing in these nuclei (they correspond to equivalent neutron configurations in 108, 110, 112Sn). The total transfer probability follows a common trend for all three target nuclei as a function of energy above the Coulomb barrier for the proton and two-proton transfer, respectively, but not for the four-nucleon transfer. 相似文献
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The energy dependence of forward double charge exchange (DCX) reaction is studied for the doubly closed shell nuclei 16O and 40Ca. A common characteristic of the two DCX reactions is a resonance-like peak around 50 MeV pion lab energy. While some authors have interpreted this peak as the evidence of a dibaryon resonance state, we show that it arises naturally in a two-step process in the conventional pion—nucleon system with proper handling of nuclear structure. The effects of nuclear structure are demonstrated through a comparison among different nuclear structure models: the symmetry model SU(4) ? SU(3), the single particle shell model and the «realistic” shell model. 相似文献
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Bao-An Bian Feng-Shou Zhang Hong-Yu Zhou 《The European Physical Journal A - Hadrons and Nuclei》2010,43(1):67-71
The fusion reactions are studied in the central collisions 82Se+ + 134Ba and 82Se+ + 138Ba by the improved isospin-dependent quantum molecular-dynamics model, where the nucleus 138Ba has a closed neutron shell N = 82 . Comparing the shell correction energies and fusion probabilities of these two reactions with the ones of other asymmetric
or more symmetric reaction systems that form the same compound nuclei, we find the dependence of the fusion reaction on the
nuclear shell structure of the colliding nuclei. The experimental data of the fusion probabilities are described well by the
present model. The result suggests that the neutron shell closure N = 82 promotes fusion. 相似文献
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Experimental studies of neutron drip line nuclei are introduced. The neutron drip line in the oxygen-magnesium region has been explored by the projectile fragmentation of a 48Ca beam. New neutron-rich isotopes, 34Ne and 37Na, have been observed together with some evidence for the particle instability of 33Ne and 36Na. Recent data on mass measurements of neutron-rich nuclei at GANIL and some characteristics of binding energies in this region are discussed. Nuclear binding energies are very sensitive to the existence of nuclear shells, and together with the measurements of instability of doubly magic nuclide 28O, they provide information on changes in neutron shell closures of very neutron-rich isotopes from carbon up to calcium. The conclusion about a rearrangement in neutron shell closures is given. The spectroscopic measurements can reveal details of the underlying microscopic structures; in-beam γ-ray spectroscopy is an effective tool to check for shell closures. The results on the γ-ray energies of the first 2+ level in even-even nuclei for the range N=12–32 are discussed. The strength of N=20 and N=28 shells is variable in the region from carbon up to magnesium. 相似文献
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G. A. Lalazissis S. E. Massen C. P. Panos 《Zeitschrift für Physik A Hadrons and Nuclei》1994,348(4):257-261
The inlfuence of state dependent short range correlations on the occupation numbers of the single particle shell model orbits of the doubly closed shell nuclei16O and40Ca is examined. The study shows that the effect of the state dependence of the short range correlations is rather small. The total depletion of the nuclear Fermi sea changes slightly compared with the one calculated by considering state independent short range correlations. 相似文献
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V. I. Zagrebaev S. G. Zemlyanoy E. M. Kozulin Yu. Kudryavtsev V. Fedosseev R. Bark Z. Janas H. A. Othman 《Hyperfine Interactions》2014,227(1-3):181-189
The present limits of the upper part of the nuclear map are very close to stability while the unexplored area of heavy neutron-rich nuclides along the neutron closed shell N = 126 is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleosynthesis. This area of the nuclear map can be reached neither in fusion–fission reactions nor in fragmentation processes widely used nowadays for the production of exotic nuclei. A new way was recently proposed for the production of these nuclei via low-energy multi-nucleon transfer reactions. The estimated yields of neutron-rich nuclei are found to be significantly high in such reactions and several tens of new nuclides can be produced, for example, in the near-barrier collision of 136Xe with 208Pb. A new setup is proposed to produce and study heavy neutron-rich nuclei located along the neutron closed shell N = 126. 相似文献
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I. N. Boboshin V. V. Varlamov B. S. Ishkhanov S. Yu. Komarov E. A. Romanovsky 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(3):283-288
Investigation of the structure of the upper shells of new magic nuclei revealed an empirical regularity with the following characteristic feature: closed proton and neutron subshells, with identically large total angular momenta (j = j coupling), are located near the Fermi energy and there is a closed subshell with j = 1/2 above one of them. The properties of the nuclei exhibiting this feature of closed upper proton and neutron subshells have been investigated in detail. Quantitative manifestation of the new magicity effects, depending on the occupancy of the corresponding subshells with nucleons, has been analyzed. Several nuclei have been found, which, obviously, also have magic properties, and all classical, new magic, and nonmagic oxygen isotopes 14–48O have been considered from the new point of view. 相似文献
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M. Thoennessen 《Acta Physica Hungarica A》2004,21(2-4):379-384
Reaching the limits of nuclear stability offers unique opportunities to understand basic nuclear properties. New shell structures close to the driplines can change the existence of neutron-rich nuclei. A new search for 16Be confirmed the previous limit for particle stable Be isotopes at A=14. Single proton knock-out reactions offer the potential for more sensitive searches of very weakly bound nuclei. In order to extend the knowledge of the neutron dripline beyond Z=8 requires new accelerator developments. The proposed new rare isotope accelerator has the potential to push the limit of the neutron dripline to at least Z=25. 相似文献
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In Order to extend the conventional shell model(SM) calculation with harmonic oscillator bases to halo nuclei, a self-similar, structure shell model(SSM) is proposed. The SSM is achieved by a rescaling of both the Kinetic and potential energy term of the harmonic oscillator and a mean field imitation, so that the single particle orbit in SSM has state (orbit) -dependent frequency. The large r. m. s. radius and the thick neutron skin for halo nuclei as well as the bound state properties of Borromean nuclei such as 6He, 11Li and 14Be can be reproduced. 相似文献
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We study the proton magic O, Ca, Ni, Zr, Sn, and Pb isotope chains from the proton drip line to the neutron drip line with
the relativistic continuum Hartree-Bogoliubov (RCHB) theory. Particulary, we study in detail the properties of even-even Ca
isotopes due to the appearance of giant halos in neutron rich Ca nuclei near the neutron drip line. The RCHB theory is able
to reproduce the experimental binding energiesE
b and two neutron separation energiesS
2n very well. The predicted neutron drip line nuclei are28O,72Ca,98Ni,136Zr,176Sn, and266Pb. Halo and giant halo properties predicted in Ca isotopes withA>60 are investigated in detail through analysis of two neutron separation energies, nucleon density distributions, single
particle energy levels, and the occupation probabilities of energy levels including continuum states. The spin-orbit splitting
and the diffuseness of nuclear potential in these Ca isotopes, as well as the neighboring lighter isotopes in the drip line
Ca region and find certain possibilities of giant halo nuclei in the Ne−Na−Mg drip line nuclei are also studied. 相似文献