Spin-current contributions to M2 excitations of 1p-shell nuclei

Microscopic analysis of spin-current contributions to magnetic quadrupole resonances in (e, e) cross sections has been performed using the particle-core coupling version of the shell model for 1p-shell nuclei. The contributions from spin-dipole and spin-octupole modes to M2 excitations of 1p-shell nuclei are traced up toq2.5 fm^–1.     

Influence of the separation energy on the radius of neutron rich nuclei

The intensive studies of equilibration processes in heavy ion reactions have produced a need for information on nuclear level densities at high energies. In a recent paper, it was concluded that standard Fermi gas formulas will be incorrect by exponential factors at energies above 100 MeV. Exact calculations of the nuclear level density in bases as large as 10³⁸ have been made and are compared with Fermi gas formulas. Two possible alternative forms are considered. Both forms produce much better agreement at high energies than does the Fermi gas model. All calculations reported are for non-interacting Fermions, but the effects expected from the two-body interaction are briefly examined. These considerations have consequences not only in heavy ion physics but also in astrophysics.     

Super-allowed beta decay of nuclei at the drip-line

We have investigated the continuous particle spectra following the beta decay of the neutron-rich nuclei that terminate the mass 6, 8, 9 and 11 isobaric chains. Strong beta transitions feeding the very top of the spectrum are found systematically. The favoured states are within a few MeV of the energy of the initial state. This phenomenon seems to be linked to the occurrence of a di-neutron structure or neutron halo in the drip-line nuclei.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

The influence of state dependent short range correlations on the depletion of the nuclear Fermi sea

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.     

Analysis of the results of calibrating meteoritic olivine crystals with238U nuclei at the Bevalac accelerator

The results are presented of calibrating the sensitivity of olivine crystals from meteorites by the²³⁸U nuclei produced at the Bevalac accelerator. The comparative studies of the spectra of the etchable track lengths due to the²³⁸U nuclei and to fossil tracks in these olivines have shown that the group of the 210 m fossil tracks observed in 1980 at the LNR, JINR is due to the galactic cosmic-ray nuclei of the Th-U group. As regards the origin of the 340–360 m group of fossil tracks which were considered in [2] to be candidates for superheavy nuclei in cosmic rays the presence of the track with a length of up to 360 m in the calibrating²³⁸U track length spectra indicates that the above interpretation has to be questioned. The possible ways of the unambiguous identification of the group of the abnormally long fossil tracks are discussed.In conclusion the authors express their deep gratitude to Academician G.N. Flerov for thoughtful guidance and permanent attention to this study. The authors wish to thank Dr. G.M. Ter-Akopian for very useful discussions and advice and also for his help during the calibrations on Bevalac, Dr. R.I. Petrova for her help in preparing olivine crystal mounts and for their subsequent annealing and etching, and Mrs. G.G. Bankova and G.P. Knyazeva for the thorough microscopic measurements of the²³⁸U track spectra.     

Nucleon pair structure of realistic many body wave functions

The scalar part of the two-body density is calculated for the²⁰Ne ground band and for the yrast 2⁺ state in⁶⁸Ge as obtained by solving the Hartree-Fock-Bogoliubov problem with symmetry-projection before the variation. The nucleon pair structure of these states is analysed and the results obtained with different effective Hamiltonians are compared.Work supported by the IPNE, Bucharest, Romania under Contract No. 60-92-7, the DFG and the Internationales Büro des KfK Karlsruhe, Germany     

On the formation mechanism of the exotic atom of light nuclei

Starting from the supposition that an exotic system constituted of a hadron, a nucleus, and an electron, which interact with each other by Coulomb pair forces, forms a quantum-mechanical system, the interaction potential between the hadron and the nucleus in the exotic system is analytically derived. It is shown that the structure of the additional potential depends on the three-body system charge structure, as well as on the isotopic one. It is precisely this asymmetry both in the electric charges and in the masses of the constituent particles that is responsible for the long lifetime of the exotic systems.     

Quenching of the spin-dependent scattering of weakly interacting massive particles on heavy nuclei

We present calculations of the quenching of the spin-dependent elastic scattering cross section for dark matter WIMPs on heavy nuclei. The theory of finite Fermi systems was used to describe the behavior of the nuclear spin matrix elements in the nuclear medium. The results of the calculations for planned dark matter detector nuclei are not only always smaller than corresponding single particle estimations but in some cases also differ from the ones obtained by using measured nuclear magnetic moments.One of the authors (M.A.N.) wants to thank the Max-Planck-Institut für Kernphysik (Heidelberg, Germany) for the hospitality during the time in which this work was carried out, and the Deutscher Akademischer Austauschdienst (DAAD) for financial support.     

The spin-orbit field in superdeformed nuclei: a relativistic investigation

Relativistic Mean Field (RMF) theory is used to investigate the behavior of the spin orbit potential,V _ls, in nuclear states of very large deformation and high angular velocity. As a by-product we present a set of parameters for an approximation of the relativistic scalar- and vector-potentialsS andV in the Dirac equation in terms of Saxon-Woods shapes. These reproduce more or less the same single particle specta as a full selfconsistent relativistic mean field calculation.Dedicated to Prof. Dr. H.J. Mang on the occasion of his 60th birthday     

Projected Tamm Dancoff theory for diabolical pair transfer in rotating nuclei

Angular momentum projected Tamm Dancoff theory in a realistic configuration space is used to investigate the occurrence of diabolical points and the connected Berry phase in the rotational spectra of well deformed Yb- and Hf-nuclei. Specific nuclei are predicted, where we expect diabolic pair transfer.Dedicated to Prof. Dr. H.J. Mang on the occasion of his 60th birthday     

Low energy orbital magnetic dipole excitations of heavy nonspherical nuclei

To clarify the physical nature of the orbital magnetic dipole excitations discussed widely in the past few years, a semiclassical model is presented and the nuclei¹⁵⁶Gd and¹⁶⁴Dy are investigated microscopically. The semi-classical model involves a consistent treatment of vibrational and rotational degrees of freedom; the microscopic results are obtained in quasiparticle-random-phase approximation (QRPA) with a realistic effective interaction. The results disagree with the picture of scissors modes or rotational vibrations.Dedicated to Prof. Dr. H.J. Mang on the occasion of his 60th birthday     

Approximation for shell-model level densities: Ergodicity

Using the supersymmetry method, we show that the maximum entropy approach for the calculation of nuclear shell-model partial and total level densities, developed in a previous paper, is ergodic.On leave from the Charles University, Prague, Czech Republic     

Approximation for shell-model level densities

The maximum entropy approach for the calculation of nuclear shell-model level densities developed in a previous paper is extended to the calculation of terms of higher order inN _k ^–1, whereN _K is the dimension of the shell-model subspaces of interest. We present terms of first and second order inN _k ^–1 , i.e. in the loop expansion, and the corresponding diagrams. We investigate the size of these contributions for several examples. We find that even for subspace dimensions as small as ten, the saddle-point approximation is quite reliable, the leading terms of the loop expansion are small, and the terms of next order are negligible.On leave from Department of Nuclear Physics, Charles University, S-18000 Prague 8, Czechoslovakia     

Scenario of charge distributions of f-p shell nuclei

Using the experimental occupation probabilities for the single particle states near the Fermi surface, the charge distribution of⁵⁴Fe,^58–64Ni and^64,66Zn have been calculated on the basis of an optimized one body potential. Excellent agreement with the experimental values have been found both in the case of single particle (-hole) energies and rms charge radii of the nuclei under consideration. Calculated values of Barrett moments and equivalent radii are in good agreement with the experiment. The details of the charge distributions have been evaluated by Fourier-Bessel analysis.The author wishes to thank the Research and Publication Committee of University of Botswana for a research grant. The interesting comments of the respected referee for the betterment of the paper is also acknowledged with thanks.     

Proton decay of spin isospin modes excited by the12C(6Li,6He)12N reaction

First investigations of the reaction¹²C(⁶Li,⁶He)-¹²N(p)¹¹C were used to study spin-isospin strength in the nucleus¹²N at E_Li=156 MeV. While the⁶He ejectiles were detected at _He=0° using a magnetic spectrograph, the decay protons were analysed in a wide range of backward angles (100°_p<170°) with=" an=" arrangement=" of=" semiconductor=" strip=" detectors.=" singles=" spectra=" were=" extracted=" as=" well=" as=" coincident=" excitation=" strength=" for=" the=" decay=" to=" low=" lying=" levels=">¹¹C. For the decay to the¹¹C ground state angular correlations were evaluated for six different energy regions in¹²N^*.The authors wish to thank the staff of the Karlsruhe Cyclotron Laboratory for their cooperation. This work has been funded by the German Federal Minister for Research and Technology (BMFT) under contract no. 06ER262I and by the Kernforschungs-zentrum Karlsruhe.     

From microscopic to macroscopic nuclear collective dynamics

We apply smoothing procedures to response functions for isoscalar vibrations. For collective motion, we find a transition from a structured strength distribution to one corresponding to one incoherent, strongly overdamped mode. It is argued that the latter may be interpreted as macroscopic motion exhibiting, to some extent, features of the hydrodynamical model. We discuss the physical origin of this behaviour, in particular its relation to the disappearance of shell structure.Supported in part by the Deutsche Forschungsgemeinschaft     

Supersymmetry in74Se,75Se,73As,and74As nuclei

New experimental data, obtained on⁷³As and⁷⁴As, were used to test the predictions of the U(6/12)U (6/12) supersymmetry scheme in its vibrational limit. The level spectra of ₃₄ ⁷⁴ Se₄₀, ₃₄ ⁷⁵ Se₄₁, ₃₃ ⁷³ AS₄₀ and ₃₃ ⁷⁴ As₄₁ supermultiplet nuclei have been calculated using a simple closed energy formula. 44 states in four different nuclei have been reasonably described using only 7 fitted parameters. The existence of supersymmetry was supported also by one-nucleon transfer reaction data, electromagnetic properties, and by a comparison between the supersymmetry and interacting boson-fermion-fermion model wave functions.     

One-quasiparticle strength functions in medium-heavy spherical nuclei

A method to describe quantitatively the one-quasiparticle strength functions is proposed which takes approximately into account the coupling of one-quasiparticle states to many-phonon configurations. The method is used to interpret the appropriate experimental data for medium-heavy spherical nuclei. The results are compared with the calculations made in different theoretical approaches.