Description of α-decay half-lives of heaviest nuclei

The accuracy in describing α-decay half-lives T _α of heavy and superheavy nuclei is studied. A simple five-parameter phenomenological formula, expressing T _α as a function of the α-decay energy Q _α, is considered. It is found that such a formula can describe measured values of T _α within a factor of 1.3 for even-even, 2.1 for odd-even, 3.2 for even-odd, and 4.0 for odd-odd nuclei when measured values of Q _α are taken. This accuracy is decreased by a factor of about 4 when theoretical values of Q _α are used. The latter are obtained within a macroscopic-microscopic approach and reproduce the experimental values of Q _α of the same nuclei with an average accuracy of about 190 keV for even-even, 270 keV for odd-even, 260 keV for even-odd, and 330 keV for odd-odd nuclei. In the analysis, 201 nuclei with proton number Z = 84–111 and neutron number N = 128–161, with measured values of both Q _α and T _α, are taken. The text was submitted by the authors in English.     

光学平面绝对检验方法的研究

应用两种方法对三个高精度平面进行了测试。第一种方法是Fritz的三面互检法,它利用Zernike多项式的特性拟合三个面四次组合测量得到的干涉图,然后求出三个面的Zernike多项式系数,从而得到三个面的面形偏差。第二种方法是奇偶函数法,根据函数的奇偶性,把平面的面形函数分解为四类:偶奇、奇偶、偶偶和奇奇函数,分别求出各分量,从而得到三个面的三维面形偏差。对两种方法都编制了理论模拟和实测程序,并进行了实验,实现了无参考面的高精度平面面形测试。     

Generalization of the N(p)N(n)N(p)N(n) scheme and the structure of the valence space

The N(p)N(n) scheme, which has been extensively applied to even-even nuclei, is found to be a very good benchmark for odd-even, even-odd, and doubly-odd nuclei as well. There are no apparent shifts in the correlations for these four classes of nuclei. The compact correlations highlight the deviant behavior of the Z = 78 nuclei and are used to deduce effective valence proton numbers near Z = 64 as well as to study the evolution of the Z = 64 subshell gap.     

Intershell beta- and gamma-decay transition rates in the multiparticle shell model

In the framework of the two-group configuration model we obtain formulas for the reduced transition rates for beta and gamma transitions in even-even, odd-odd, even-odd, and odd-even nuclei. We explored dependencies of the transition rates on the occupancies of the involved subshells, as well as on the spin values of the initial and final states. The obtained formulas are useful for the qualitative spectroscopic analysis of experimental data, particulary in the regions of magicity, including the regions of the “remote” nuclei.     

Quadrupole collectivity of neutron-rich neon isotopes

The Angular Momentum Projected Generator Coordinate Method, with the quadrupole moment as collective coordinate and the Gogny force (D1S) as the effective interaction, is used to describe the properties of the ground state and low-lying excited states of the even-even neon isotopes ^20-34Ne, that is, from the stability valley up to the drip line. It is found that the ground state of the N = 20 nucleus ³⁰Ne is deformed but to a lesser extent than the N = 20 isotope of the magnesium. In the calculations, the isotope ³²Ne is at the drip line in good agreement with other theoretical predictions. On the other hand, rather good agreement with experimental data for many observables is obtained. Received: 19 Novemeber 2002 / Accepted: 24 January 2003 / Published online: 8 April 2003     

对力对希土原子核性质的影响

本文利用粒子数守恒方法分析对力对希土区变形偶偶核的各种性质的影响,其中包括低内部激发态(E≤2MeV)的激发机构、有关的β衰变和奇偶质量差等。为进行这些分析,本文先确定希土变形核内的单粒子能级。分析表明:适当改变参数μ和к以后的Nilsson能极,在考虑对力影响后,能较好地解释奇A核的低内部激发谱的自旋和宇称,并能近似地解释其能级间隔。参数μ,к,和η是由奇A核的实验能谱来确定的。在希土转动区中,к～0.067—0.072,η～4—4.6.     

Nuclear spectroscopy of neutron-richA=143 nuclei

A study of the beta decay of¹⁴³Cs and¹⁴³Ba fission products was undertaken by the use of two on-line mass-separators OSTIS and OSIRIS. Level schemes for¹⁴³Ba and¹⁴³La are deduced from gamma and conversion electron spectra,γ-γ andβ-γ coincidences.Q _β values and ground state beta feedings were also measured. The nuclei¹⁴³La and¹⁴³Ba are tentatively inserted in a systematic of odd-even nuclei aroundA=143 and even-odd nuclei with 87 neutrons respectively.     

Gamma band in transitional nuclei

The obstinate difficulty of the Davydov-Filippov model in obtaining the correct bunching of states in the γ-band of even-even mass transitional nuclei is explained in an extended version of the model which includes the 2-qp excitations and also the coupling between the 0- and 2-qp states. The important result is that the 0–2qp coupling for even spin states is much stronger than that for odd ones. Due to this effect the bunching of even-odd spin states in the Davydov-Filippov model is destroyed producing either an opposite bunching (now odd-even spin states) or a band wherein the states have similar energy spacings.     

Cluster radioactivities of odd-mass nuclei

The partial half-lives of the hypothetical even-even equivalent of an odd-mass nucleus for cluster transitions toward various excited states of the daughter, used as a reference to find the hindrance factor, can be calculated within analytical superasymmetric fission model, by taking into account the angular momentum of the emitted cluster. Detailed tables are presented for ¹⁴C radioactivity of ²²¹Fr, ^221,223Ra, ²²⁵Ac; ²⁴Ne radioactivity of ²³³U, ²³¹Pa, and ²³F decay of ²³¹Pa, showing that, except for ²²⁵Ac, the existing experimental evidences, do not exclude (moderate) hindered transitions to the ground states of the daugther nuclei.     

Core polarization effects on C4 form factors of sd-shell nuclei

Coulomb form factors of C4 transitions in even-even N = Z sd-shell nuclei ( ²⁰Ne, ²⁴Mg, ²⁸Si and ³²S) are discussed taking into account higher-energy configurations outside the sd-shell model space which are called core polarization effects. Higher configurations are taken into account through a microscopic theory, which allows particle-hole excitations from the 1s and 1p shells core orbits and also from the 2s1d-shell orbits to the higher allowed orbits with excitations up to 4 ω. The effect of core polarization is found essential in both the transition strengths and momentum transfer dependence of form factors, and gives a remarkably good agreement with the measured data with no adjustable parameters. The calculations are based on the Wildenthal interaction for the sd-shell model space and on the modified surface delta interaction (MSDI) for the core polarization effects. Received: 24 January 2002 / Accepted: 29 July 2002 / Published online: 6 March 2003 RID="a" ID="a"e-mail: baguniv@uruklink.net Communicated by P. Schuck     

Properties of universal functions in the Wigner mass formula for nuclei

The properties of the empirical functions in the Wigner mass formula for nuclei, which is based on SU(4) spin-isospin symmetry, are considered. It is shown that the origin of the odd-even effect in nuclei can be explained on the basis of an explicit analytic form of the second-degree Casimir operator for even-even and odd-odd nuclides and for nuclei of odd mass number. Experimental data in support of the proposed Wigner origin of the odd-even effect are presented.     

Search for M1 strength in 51V and the difference in 51V(e,e′) and 51V(p,p′) spectra

Following the studies of the distribution of M1 strength in the even-even N = 28 isotones ⁴⁸Ca, ⁵⁰Ti, ⁵²Cr and ⁵⁴Fe by inelastic electron scattering, the result of a search for M1 transitions in the odd-even N = 28 nucleus ⁵¹V is reported. No strong M1 excitation has been detected, in contrast to a recent (p, p') experiment. There is no immediate explanation for this discrepancy. Shell-model calculations indicate that a part of it might be accounted for by an interference between the spin and orbital term of the electromagnetic transition operator in the (e, e') experiment.     

The systematics of (n, α) reaction cross-sections at 14.5 MeV neutron energy

A comprehensive review of the experimental data for 14.5 MeV neutron induced reaction crosssections for (n, α) reaction has been made for the isotopes having Z up to 82. Two different parameter groups have been considered by the classification of nuclei into odd-mass and even-even nuclei. The empirical formulae with two parameters for the evaluation of (n, α) reaction cross-sections are discussed in the present study. The odd-even effects have been observed as the cross-sections of odd-mass nuclei are higher as compared to their neighboring even-even nuclei. The shell effects have also been established at magic nucleon numbers for these reaction cross-sections.     

The neutron drip line in the region of <Emphasis Type="Italic">N</Emphasis>=20 and <Emphasis Type="Italic">N</Emphasis>=28 closures

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.     

A Reliability Analysis of Calculated Results for Odd-Even and Odd-Odd Nuclei in Relativistic Mean-Field Theory

We calculate the binding energies of Ni, Cu, Xe, Cs, Pt, Au, Np, Pu isotope chains using two interaction parameter sets NL-3 and NL-Z, and compared the relative errors of the even-even nuclei with those of odd-even nuclei and odd-odd nuclei. We find that the errors of binding energy of odd-even and odd-odd nuclei are not bigger than the one of even-even nuclei. The result shows that comparing with even-even nuclei, there is no systematic error and approximation in the calculations of the binding energy of odd-even and odd-odd nuclei with relativistic mean-field theory. In addition, the result is explained theoretically.     

A Reliability Analysis of Calculated Results for Odd-Even and Odd-Odd Nuclei in Relativistic Mean-Field Theory

We calculate the binding energies of Ni, Cu, Xe, Cs, Pt, Au, Np, Pu isotope chains using two interaction parameter sets NL-3 and NL-Z, and compared the relative errors of the even-even nuclei with those of odd-even nuclei and odd-odd nuclei. We find that the errors of binding energy of odd-even and odd-odd nuclei are not bigger than the one of even-even nuclei. The result shows that comparing with even-even nuclei, there is no systematic error and approximation in the calculations of the binding energy of odd-even and odd-odd nuclei with relativistic mean-field theory. In addition,the result is explained theoretically.     

Nuclear Level Density and Thermodynamic Functions for Nuclei with Static Deformation

The level densities of even-odd and even-even isotopes^161,162Dy,^166Er and ^171,172Yb were calculated using microscopic theory of interacting fermions and compared with experiments.It is found that the data can be well reproduced with level density formalism for nuclei with static deformation.The nuclear temperature as well as the reproduced with level density formalism for nuclei with static deformation.The nuclear temperature as well as the entropy of nuclear system as a function of excitation energy has been extracted from the BCS theory.It is shown that the entropy exhibits an S-formed shape as a function of excitation energy.This is interpreted as a phase transition.Procedure of treating the even-odd and even-even nuclear systems has been presented and discussed.     

Suppression of band crossing in the neutron-rich nuclei 172, 173Yb due to the absence of a static pair field

High-spin states in the neutron-rich nuclei ^172,173Yb have been populated in a ¹⁷⁰Er(⁷Li,(p,d,t)xn) incomplete-fusion reaction and the emitted γ-radiation was detected with the GASP array. The signature partners of the 7/2⁺[633] rotational band of the odd-N ¹⁷³Yb isotope have been newly established and were observed up to spin values of (45/2⁺) and (43/2⁺), respectively. The ground-state band of the even-even nucleus ¹⁷²Yb has been observed up to a spin value of (22⁺). No band crossings were found in these bands. To explain this observation, it is proposed that the static pair field is absent, considering that the neutron odd-even mass differences reach for these nuclei very small values and that the band crossing is absent in cranked shell modell calculations without pairing. The results indicate, however, that strong dynamic correlations are still present.