重核大集团发射半衰期的计算

重核大集团（¹⁴C-³⁴Si）发射的半衰期在理论上用Wentzel-Kramers-Brillouin近似进行了计算.利用双折叠模型计算大集团和剩余子核间的核相互作用,在折叠积分中选取了密度依赖的、零力程交换项的核子-核子相互作用.计算得到的半衰期和液滴模型结果、系统公式的结果以及实验数据进行了比较,表明目前的计算能够很好地给出重核大集团（¹⁴C-³⁴Si）发射的寿命.这可为重核其他大集团（¹⁵N, ⁴⁶Ar,⁴⁸Ca等）的发射提供可靠的预测. 关键词： 半衰期 双折叠模型 集团发射     

Theory of molecular collective excitation in the scattering of identical nuclei

The excitation of nuclear molecules, formed in the scattering of ¹²C on ¹²C, is treated by the collective two-center model (CTCM). The model is referred to a rotating coordinate system and describes the continuous transition from the collective states of the separated nuclei to the states of the compound system. The diagonalization of the interaction between the nuclei leads to a splitting of the excitation energies as function of parity and angular momentum projection. The theory is applied for the explanation of the molecular resonances observed in the ¹²C-¹²C scattering.     

Shell-model structure of exotic nuclei beyond <Superscript>132</Superscript>Sn

We report on a study of exotic nuclei around doubly magic ¹³²Sn in terms of the shell model employing a realistic effective interaction derived from the CD-Bonn nucleon-nucleon potential. The short-range repulsion of the bare potential is renormalized by constructing a smooth low-momentum potential, V_low-k, that is used directly as input for the calculation of the effective interaction. In this paper we focus attention on the nuclei ¹³⁴Sn and ¹³⁵Sb which, with an N/Z ratio of 1.68 and 1.65, respectively, are at present the most exotic nuclei beyond ¹³²Sn for which information exists on excited states. Comparison shows that the calculated results for both nuclei are in very good agreement with the experimental data. We present our predictions of the hitherto unknown spectrum of ¹³⁶Sn.     

Classical simulations of heavy-ion fusion reactions and weakly-bound projectile breakup reactions

Heavy-ion collision simulations in various classical models are discussed. Heavy-ion reactions with spherical and deformed nuclei are simulated in a classical rigid-body dynamics (CRBD) model which takes into account the reorientation of the deformed projectile. It is found that the barrier parameters not only on the initial orientations of the deformed nucleus, but also on the collision energy and the moment of inertia of the deformed nucleus. Maximum reorientation effect occurs at near- and below-barrier energies for light deformed nuclei. Calculated fusion cross-sections for ²⁴Mg + ²⁰⁸Pb reaction are compared with a static-barrier-penetration model (SBPM) calculation to see the effect of reorientation. Heavy-ion reactions are also simulated in a 3-stage classical molecular dynamics (3S-CMD) model in which the rigid-body constraints are relaxed when the two nuclei are close to the barrier thus, taking into account all the rotational and vibrational degrees of freedom in the same calculation. This model is extended to simulate heavy-ion reactions such as⁶Li + ²⁰⁹Bi involving the weakly-bound projectile considered as a weakly-bound cluster of deuteron and ⁴He nuclei, thus, simulating a 3-body system in 3S-CMD model. All the essential features of breakup reactions, such as complete fusion, incomplete fusion, no-capture breakup and scattering are demonstrated.     

Pairing correlations and soft dipole excitations in nuclei on the neutron-drip line

Paring correlations and soft dipole excitations in weakly bound nuclei on the edge of neutrondrip line are studied by using a three-body model. A density-dependent contact interaction is employed to calculate the ground state of halo nuclei ⁶He and ¹¹Li, as well as a skin nucleus ²⁴O. Dipole excitations in these nuclei are also studied within the same model. We point out that the dineutron-type correlation plays a dominant role in the halo nuclei ⁶He and ¹¹Li having the coupled spin of the two neutrons S = 0, while the correlation similar to the BCS type is important in ²⁴O. Contributions of the spin S = 1 and S = 0 configurations are separately discussed in the low-energy dipole excitations. The calculated results are compared with recent experimental data of ⁶He and ¹¹Li. The text was submitted by the authors in English.     

Combined model of photonucleon reactions

A combination of the semimicroscopic, exciton, and evaporation models is used to describe photonucleon reactions induced in medium-mass and heavy nuclei by photons of energy below the mesonproduction threshold. Two mechanisms of the photoexcitation of nuclei are considered. These are the formation of a giant dipole resonance (GDR) at energies in the range E _γ ≲ 30 MeV and quasideuteron photoabsorption, which is dominant at energies in the region E _γ ≳ 40 MeV. The densities of particle-hole states appearing in the exciton model are calculated on the basis of the Fermi gas model. Our combined model takes into account the multiparticle emission of preequilibrium particles. The influence of isospin conservation and collective phenomena on photonucleon emission by giant dipole resonances is considered. The combined model is used to describe cross sections for photonucleon reactions proceeding on the ^40,48Ca, ⁹⁰Zr, ¹³⁹La, ¹⁴²Nd, and ¹⁸¹Ta nuclei, as well as difference (E _γmax = 85–55 MeV) bremsstrahlung photoneutron spectra for the ⁶³Cu, ¹¹⁵In, ¹¹⁸Sn, ¹⁸¹Ta, ²⁰⁷Pb, ²⁰⁹Bi, and ²³⁵U nuclei and bremsstrahlung photoproton spectra for the ⁹⁰Zr nucleus at the energies of E _γmax = 22, 25, and 34 MeV.     

Momentum distributions in halo nuclei

From the analogy between the break-up of weakly bound, neutron-rich nuclei and the phenomenon of optical diffraction, it is possible to formulate a model for the momentum distribution of both the core and the valence neutrons of halo nuclei which displays a simple dependence on nuclear structure parameters. The model is applied to the analysis of reactions where¹¹Be,¹¹Li and¹⁴Be impinge on¹²C, providing an overall account of the experimental findings and predictions for further measurements.     

Deformation and shape coexistence in medium mass nuclei

Emerging evidence for deformed structures in medium mass nuclei is reviewed. Included in this review are both nuclei that are ground state symmetric rotors and vibrational nuclei where there are deformed structures at excited energies (shape coexistence). For the first time. Nilsson configurations in odd-odd nuclei within the region of deformation are identified. Shape coexistence in nuclei that abut the medium mass region of deformation is also examined. Recent establishment of a four-particle, four-hole intruder band in the doublesubshell closure nucleus⁹⁶Zr₅₆ is presented and its relation to the Nuclear Vibron Model is discussed. Special attention is given to the N=59 nuclei where new data have led to the reanalysis of⁹⁷Sr and⁹⁹Zr and the presence of the [404 9/2] hole intruder state as isomers in these nuclei. The low energy levels of the N=59 nuclei from Z=38 to 50 are compared with recent quadrupole-phonon model calculations that can describe their transition from near-rotational to single closed shell nuclei. The odd-odd N=59 nuclei are discussed in the context of coexisting shape isomers based on the (p[303 5/2]n[404 9/2])2^– configuration. Ongoing in-beam (t.p conversion-electron) multiparameter measurements that have led to the determination of monopole matrix elements for even-even₄₂Mo nuclei are presented, and these are compared with initial estimates using lBA-2 calculations that allow mixing of normal and cross subshell excitations. Lastly, evidence for the neutron-proton³S₁ force's influence on the level structure of these nuclei is discussed within the context of recent quadrupole-phonon model calculations.Work supported by USDOE contract Nr.W-7405-Eng-48 and NATO Grant Nr.RGO565/82.     

Formation and decay of hot nuclei

Formation and decay properties of composite-like nuclei produced by ⁵⁸Ni projectiles bombarding ²³²Th target nuclei are investigated at different energies by means of fission fragment angular correlation measurements. Experimental results are compared to the excition model and excitation energies in the fissioning nuclei are deduced. By comparing the present data with the results on other systems, the influences of entrance channel conditions and composite-like nuclei temperatures are discussed to explain the evolution of the high linear momentum transfer region. The coexistence of both massive transfer mmechanism and head-on collisions followed by preequilibrium is suggested.     

Description of cross sections for photonuclear reactions in the energy range between 7 and 140 MeV

A combination of the exciton and evaporation models is used to describe photonuclear reactions induced in light, medium-mass, and heavy nuclei by photons of energy in the range 7 ≤ E _γ ≤ 140 MeV. Two mechanisms of the photoexcitation of nuclei are considered. These are the formation of a giant dipole resonance at energies in the range E _γ ? 30 MeV and quasideuteron photoabsorption, which is dominant at energies in the region E _γ ? 40 MeV. The density of particle-hole states, which appears in the exciton model, is calculated on the basis of the Fermi gas model. The emission of two preequilibrium particles is taken into account in describing the quasideuteron reaction channel. The effect of isospin conservation on giant-dipole-resonance decay accompanied by photonucleon emission is examined. The model in question is used to describe cross sections for photon-induced reactions on ²⁶Mg, ⁵⁴Fe, ^{112,118,119,124}Sn, and ¹⁸¹Ta nuclei.     

Estimate of large fragment yield forZ>56 nuclei

Summary Large fragment yields are calculated forZ>56 nuclei in the frame-work of abrasion/ablation model which includes a third-order correction for surface energy term. The results for 1.049 GeV/n¹⁹⁷Au₇₉ nuclei, 1.128 GeV/n¹⁶⁵Ho₆₇ nuclei, 1.88 GeV/n⁵⁶Fe₂₆ nuclei, 1.239 GeV¹³²Xe₅₄ nuclei and 1.489 GeV⁸⁴Kr₃₆ nuclei are compared with experimental data for different target combinations. The comparison shows that the theory provides a reasonable representation of elemental cross-section for all projectiles.     

Mass-surface predictions near the doubly magic nuclide 78Ni

The mass surface of nuclei close to the doubly magic nuclide ⁷⁸Ni is calculated by two methods. The first relies on the multiparticle shell model based on an effective interaction and a mean nuclear potential. The second employs the concept of so-called “magic crosses” and enables us to determine the masses of odd-odd nuclei close to ⁷⁸Ni by using similarity of the shell structure and neutron-proton interaction in the region of nuclei under consideration and in the region of heavy magic nuclides. The energies of the separation of one and two neutrons from nuclei close to ⁷⁸Ni and the energies of the β decay of these nuclei—recall that these quantities of astrophysical interest—are presented.     

Decay of heavy and superheavy nuclei

We present here, an overview and progress of the theoretical works on the isomeric state α decay, α decay fine structure of even–even, even–odd, odd–even and odd–odd nuclei, a study on the feasibility of observing α decay chains from the isotopes of the superheavy nuclei Z = 115 in the range 271 ≤A ≤ 294 and the isotopes of Z = 117 in the range 270 ≤A ≤ 301, within the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The computed half-lives of the favoured and unfavoured α decay of nuclei in the range 67 ≤Z ≤ 91 from both the ground state and isomeric state, are in good agreement with the experimental data and the standard deviation of half-life is found to be 0.44. From the α fine structure studies done on various ranges of nuclei, it is evident that, for nearly all the transitions, the theoretical values show good match with the experimental values. This reveals that CPPMDN is successful in explaining the fine structure of even–even, even–odd, odd–even and odd–odd nuclei. Our studies on the α decay of the superheavy nuclei ^271?294115 and ^270?301117 predict 4 α chains consistently from ^284,285,286115 nuclei and 5α chains and 3α chains consistently from ^288?291117 and ²⁹²117, respectively. We thus hope that these studies on ^284?286115 and ^288?292117 will be a guide to future experiments.     

Calculation of single-particle energies in the <Stack><Subscript>38</Subscript><Superscript>96</Superscript></Stack>Sr nucleus within the mean field model with the dispersive optical potential

Evaluated and experimental neutron single-particle energies of the ^{88, 94, 96}Sr and ^{90, 96, 98}Zr nuclei near the Fermi energy are compared. A possibility of formation of a considerable particle-hole gap in the ^{94, 96}Sr typical of traditional magic nuclei is investigated. Agreement is obtained between the single-particle energies calculated within the mean field model with the dispersive optical potential and the evaluated energies for the ^{94, 96}Sr nuclei.     

The low-energy level structure and the electromagnetic properties of191Ir and193Ir

TheM 1 andE 2 reduced transition probabilities in¹⁹¹Ir and¹⁹⁹Ir have been calculated on the weak particle-core coupling model. The static moments of the ground state and the first three low-lying excited states have been computed. The theoretical values are in good agreement with the experimental results, in particular, the existing discrepancy between the theoretical and the experimental value for the magnetic moment of the first excited 5/2⁺ state, in both these nuclei, has been removed. The predicted sign of the quadrupole moment of the 2⁺ state in the neighbouring even-even nuclei is consistent with the results reported for Platinum nuclei. The level structure of both these nuclei has been calculated assuming the particle-core interaction to be dipole-dipole and quadrupole-quadrupole type.     

Polarization phenomena in elastic proton scattering on odd nuclei

Polarization observables of elastic proton scattering on ¹³C and ¹³N nuclei are calculated by using the theory of multiple diffractive scattering and the α-cluster model with dispersion. The ¹³C and ¹³N nuclei are considered as those that consist of a deformed core and an additional cluster (nucleon) occurring with the highest probability inside the core. It is shown that this assumption on the structure of these nuclei makes it possible to match the calculated and measured observables without resort to adjustable parameters.