原子核的形状相变

简要回顾原子核形状相变研究的现状，并将相干态理论与角动量投影方法相结合，在不区分质子玻色子和中子玻色子的相互作用玻色子模型（IBM-1）框架下，对角动量驱动的轴对称情况下的具有U（5）、SU（3）对称性以及两种对称性之间过渡区的原子核的形状相变进行了具体研究。We review the status of the research of nuclear shape phase transitions in this paper. Meanwhile, by taking the coherent state theory and angular momentum projection method, we study the shape phase transitions of axially symmetric even-even nuclei with U（5） symmetry, SU（3） symmetry and those in the transitional region of the two symmetries in the framework of Interacting Boson Model-1 （IBM-1）, which does not distinguish the proton bosons from neutron bosons.     

MEASUREMENTS OF ANGULAR MOMENTUM EFFECT OF FISSION BARRIER

The fission cross sections and the evaporation residue cross sections for ¹²C+²⁰⁹Bi and ¹⁴N+Pb reactions were measured with the gold surface barrier silicon detectors and the mica nuclear track detectors.The critical angular momentum l_er was deduced from the measured evaporation residue cross section σ_er on the basis of the sharp-off model.The fission barrier with the particular angular momentum i derived from the condition Γ_f/Γ_n=1 at l=l_e The angular momentum effect of the fission barrier was studied experimentally.     

A FURTHER EXPLORATION FOR MECHANISM OF ANGULAR MOMENTUM TRANSFER IN HEAVY ION REACTION

The difficulty of the classical dynamics in studing the mechanism of angular momentum transfer is discussed. According to the nuclear rotational concept formed in the study of the nuclear structure for a long time, we point out that it is convenient to divide the total angular momentum I transfered to the target and the projectile into two components-the nuclear collective angular momentum I_R and the rotational alignment angular momentum I_j.     

Correspondence between phenomenological and IBM-1 models of even isotopes of Yb

Energy levels and the reduced probability of E2–transitions for ytterbium isotopes with proton number Z=70 and neutron numbers between 100 and 106 have been calculated through phenomenological(Ph M)and interacting boson(IBM-1)models.The predicted low-lying levels(energies,spins and parities)and the reduced probability for E2–transitions results are reasonably consistent with the available experimental data.The predicted low-lying levels(gr–,β1–andγ1–band)produced in the Ph M are in good agreement with the experimental data compared with those by IBM-1 for all nuclei of interest.In addition,the phenomenological model was successful in predicting theβ2–,β3–,β4–,γ+2–and 1+–band while it was a failure with IBM-1.Also,the 3–band is predicted by the IBM-1 model for172Yb and174Yb nuclei.All calculations are compared with the available experimental data.     

ON THE IRREDUCIBLE REPRESENTATIONS OF THE COMPACT SIMPLE LIE GROUPS OF RANK 2(I)

In this paper, we analyse the commutation relations of the infintesimal opera-tors of the group SU₃ and find that the eight infinitesimal operators of the groupSU₃ can be written as a scalar operator A, three angular momentum operators (L₁,L_o, L_-1,)and two sets of the irreducible tensor operators of rank 1/2, （T_±1/2,V±1/2）By means of the commutation relations of these operators, all irreducible represen-tations of the group SU₃ can be easily obtained. In this pape, the matrices corresponding to these operators in the irreduciblerepresentation（λμ）, are given; therefore the irreducible representation and its re-presentation space R^λμ are completely defined. Besides, a method for calculatingthe scalar factors of the reduction coefficients and the symmetric relations of thosefactors are also given. As examples, the scalar factors of the reduction coefficientsof （λμ）×（10）, （λμ）×（01）, （λμ）×（20） and （λμ）×（11） are calculated. In the last part of this paper, we define the irreducible tensor operators ofthe group SU₃ and prove the corresponding Wigner-Eckart theory. The method used in the discussion of the group SU₃ be extended to allof the compact simple Lie groups of rank 2 and we shall discuss them in two suc-ceeding papers.     

A MICROSCOPIC ANALYSIS OF THE DIFFERENCE IN ANGULAR MOMENTUM BETWEEN EXCITED AND GROUND BANDS

An analysis for various components included in the difference of angular momentum between excited and ground bands, i(ω), is done carefully. It is pointed out that, generally, i(ω) should read as i(ω)=i_RAL(ω)+i_PR(ω)+i_SC(ω). And the i(ω). corresponding to s-band of the first backbanding in even-even nuclei is really not only the i_RAL(ω). The various components in i(ω) corresponding to s-band for three typical nuclei ¹⁶⁴Er, ¹⁸⁸Hg and ¹⁵⁶Er are estimated quantitatively and microscopicly by using cranked shell model. For well deformed nuclei, i_RAL plays the dominant role, but the contribution of pairing reduction, i_PR, can not be neglected. As for the soft nuclei like ¹⁸⁸Hg, the contribution from shape changes, i_SC, is very important. While for transitional nuclei as ¹⁵⁶Er, both pairing reduction and shape changes will play substantial role.     

A Time-Dependent Wavepacket Method for Photodissociation Dynamics of Triatomic Molecule

We report a time-dependent quantum wavepacket theory employed to interpret the photoabsorption spectrum of the N20 molecule in terms of the nuclear motion on the upper 21A＇ and 11A＂ potential energy surfaces. The N2-O bond breaks upon excitation leading to dissociation. The total angular momentum is treated correctly taking into account the vector property of the electric field of the exciting radiation.     

ANALYSIS OF THE MOMENTUM DISTRIBUTION WIDTH OF THE PREOJECTILE-LIKE-FRAGMENT FROM HEAVY ION COLLISIONS

A model taking into account both fragmentation and transfer process agrees well with experimental data on projectile-like-products momentum distribution resulting from heavy ion collisions in Fermi energy domain and in relativistic energy domain.The resulted reduced widths σ₀ are given for both fragmentation and transfer process respectively.     

A hartree-bose mean-field approximation for IBM-3

A Hartree-Bose mean-field approximation for the IBM-3 is presented. A Hartree-Bose transformation from the spherical to the deformed bosons with charge-dependent parameters is proposed which allows bosonic pair correlations and includes higher angular momentum bosons. The formalism contains previously proposed IBM-2 and IBM-3 intrinsic states as particular limits. Presented by J.E. García-Ramos at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997. This work has been supported in part by the Spanish DGICYT under contracts No. PB 95/0123 and PB95-0533, a DGICYT-IN2P3 agreement and by the European Commission under contract CI1*-CT94-0072.     

角动量的物理图象

根据角动量的定义，结合图形，分析和讨论角动量计算中各项以及各量的深刻意义，建立角动量的物理图象．明确对点的角动量和对轴的角动量的关系．     

M1 transition strength in the SU(3) limit of the generalized IBM-2

We generalize the SU(3) limit of the standard IBM-2 formalism of sd bosons to sdg…λ bosons, where λ denotes a boson of arbitrarily large, even angular momentum λ, and investigate the effect on the B(M1, 0₁⁺ → 1⁺) transition strength. In the SU(3) limit, all the M1 transition strength resides in a single 1⁺ state and is proportional to λ.     

SUq(2) Analysis of Nuclear Rotational Spectra

The validity of the quantum group SU_q(2) expression for the nuclear rotational spectrum is investigated thoroughly.Analyses (including the Mallmann plots,the relations for the I(I+1) expansion coefficients,energy spectra,etc.)definitely display a systematical deviation of the SU_q(2) prediction from the experimental data available for the even-even rare-earth and actinide nuclei.Only within a limited range of angular momentum the SU_q(2) expression is suitable for rotational spectra.A significant angular momentum dependence of q-deformation parameter is found.The q-deformation is derectly related to the nuclear softness.     

希土金属中的s-f相互作用

本文利用量子力学中角动量理论的代数方法,对希土金属的s-f相互作用模型作了比较仔细的讨论,导出了s-f电子间相互作用的哈密顿量的一般形式。用算符形式的微扰论方法,求得了通过s-f相互作用而导致的f电子间f-f间接作用的有效哈密顿量的一般表达式。在保留到二极小项的情况下,除各向同性的交换作用以外,还得到了赝偶极矩作用。在所得结果的基础上,初步讨论了希土金属铁磁相的磁晶各向异性。指出了以上的结果可能解释的一些实验事实。     

SOME PROBABLE APPROACHES TO THE PRODUCTION OF HYPERSYMMETRY STATES

The angular distributions of the strangeness exchange reations ⁹Be （K^-,π^-） ^_A9Be*and ¹³C（K^-,π^-）^_A13C with K^- in flight have been calculated on the basis of our pre-vious work^[2].In the framework of the plane-wave impulse approximation we havecalculated the relative rations of the differential cress-sections of the associated produc-tion reactions leading to the strangeness analoque states and the supersym-metric states of _A⁹Be and _A¹³C,and have estimated the absolute values of these dif-ferential cross-sections.The possibility of producing supersymmetric states bystrangeness exchange reactions and associated production reactions have been discus-sed on the basis of these calculations.     

Magnetic dipole moments of collective quadrupole excited states

Magnetic dipole moments for low-lying collective quadrupole excitations are studied in heavy and medium-heavy nuclei within the framework of the Interacting Boson Model (IBM-2). In the present study, we concentrate mainly on the fully symmetric representations of the U(6) group and their magnetic dipole moments. We shortly discuss the lowest non-symmetric 1⁺ level. Comparison with other collective model calculations of g_R and microscopic studies as well as with experimental data is performed.The authors are most grateful to A.E.L.Dieperink and coworkers for the generous help and permission to quote largely from their recent results on magnetic dipole moments in nuclei.They are also indebted to A.Richter,O.Scholten and Iachello for many stimulating discussions. They thank the NFWO,IIKW and the IWONL for financial support.     

EFFECTIVE MOMENT OF INERTIA OF MEDIUM MASS NUCLEI AT THE SADDLE POINT

The angular distributions of fission fragments are measured for systems of 120MeV ¹⁴N+¹¹⁸Sn with mica track detectors and gold-surfacebarrier silicon detectors. The measured angular distributions can be fitted by the standard theory of fission angular distributions on the basis of statistical model. The effective moments of inertia of fissioning nuclei at saddle point are derived from angular distribution anisotropies. The shapes of saddle point of fissioning nuclei in the region of Z²/A<30 are discussed.     

THE VERTICAL INTEGRATED MOMENTUM SPECTRUM OF THE MUON WITH MOMENTUM LARGER THAN 4 GeV/c AT 3220m ABOVE SEA-LEVEL

At an altitude of 3220 meters above sea level in Yunnan Province, we measured, by using a G-M counter-magnetic spectrometer, the vertical integratted momentum spectrum of the cosmic muon with momentum larger than 4 GeV/c. The spectrum obtained from this experiment is expressed by a power function in the form of I（>p）=Q （p+4）^-1.86±0.06(cm^-2·sr^-1·s^-1), where p is in GeV/c and Q is a constant. We also measured the charge ratio of muon in the 4—23 GeV/c momentum range. The result is N_μ/N_μ-=1.26±0.11. The error in the momentum measurement with spectrometer has been discussed and calculated.     

超导电子的角动量和磁通量子化

本文指出,磁通量子化应和超导电子的角动量量子化一致。分数角动量的存在必然导致分数磁通量子化,而分数磁通量子化和超导理论以及迄今为止的实验结果不相矛盾。我们提出和分析的一个新实验可以检测任意子和分数磁通量子。 关键词：     

MICROSCOPIC CALCULATION OF THE INERTIA IN HEAVY NUCLEI

A realistic calculation of the inertia for ²³⁶U fisson based on the linear response theory is presented, in which the single particle states are provided by Nilsson model. The dependence of the nuclear inertia M_δiδi on the collective variables δ₂, δ₄ is studied at the range of certain nuclear temperature (0—1 MeV). The pairing effect and the shell effect on the nuclear inertia are discussed. The calculated results show a very prominent structure at level crossing points and when acrossing the critical temperature.