High-resolution investigation of the 112Sn(p,p')112Sn reaction

The ¹¹²Sn(p, p') reaction was studied at proton energies of 20.51 and 25.0 MeV. The outgoing protons were momentum analysed with an Enge split-pole spectrograph and recorded with position-sensitive solid-state detectors with a total resolution between 10 and 15 keV. Excitation energies and angular distributions for states below 5.5 MeV excitation energy were obtained. The angular distributions were compared with macroscopic DWBA calculations in order to extract L-values and deformation parameters. Coupled-channels calculations were performed to investigate two-phonon excitations and the mixing between one- and two-phonon states. The results of the present experiment are compared with previous experimental results and with number-projected BCS calculations. The results for some of the excited states were compared with similar results for the other even Sn isotopes.     

Low-energy transitions in the 197Pb and 198Pb isotopes

The ¹⁹⁸Pb and ¹⁹⁷Pb isotopes are produced through the ¹⁸⁶W(¹⁶O, 4n, 5n) reactions. Conversion-electron, γ- and X-ray spectra are measured using the compound-nucleus recoil method. Conversion coefficients and multipolarities are deduced for a large number of transitions. Together with angular distribution measurements and the results of γγt multidimensional coincidences they lead to decay schemes for the two isotopes. Microscopic calculations, performed in the two- or three-quasiparticle approximation with a surface delta interaction, fail to reproduce completely the observed properties, showing similar defects for the odd and even isotope.     

Self-consistent study of triaxial deformations: Application to the isotopes of Kr,Sr, Zr and Mo

Self-consistent mean-field calculations of deformation energy surfaces have been performed for more than 30 exotic isotopes of the Kr, Sr, Zr and Mo elements. Our calculations extend to the proton drip line. We investigate the triaxial stability of the deformed ground states in the deformation regions N ≈ 38 and N ≈ 60. The results are in good agreement with the observed trends.     

Properties of Zr isotopes near the neutron drip line and beyond it

The properties of neutron-rich Zr isotopes up to the neutron drip line and beyond it have been investigated on the basis of the Hartree-Fock method with the Skyrme forces (Ska, Sly4), taking into account the deformation. By the example of chains of Zr isotopes, good agreement is shown for the two-neutron separation energies and mean-square radii with the known results of Hartree-Fock-Bogolyubov calculations with the Sly4 forces. For the extremely neutron-rich Zr isotopes, states with very large deformation parameters (β ≈ 0.4?0.45) of neutron and proton density distributions can be realized. Beyond the neutron drip line with respect to emission of two neutrons, the existence of ^150,152Zr isotopes, which are stable with respect to one-neutron emission, is predicted.     

Deformation properties of osmium,platinum, mercury isotopes from self-consistent calculations: Influence of the pairing treatment

The deformation properties of several isotopes of the elements Os, Pt and Hg have been computed by means of Hartree-Fock plus BCS calculations. The Hartree-Fock potential has been derived from the Skyrme interaction SIII. Two approximations have been used for the treatment of pairing correlations: the constant (versus deformation) gap method and the constant (versus deformation) pairing matrix element method. A good agreement with experimental data is obtained for ground state deformation properties except for the exact location of the prolate-oblate transition as a function of the neutron number. For one nucleus ¹⁸⁴Hg, the pairing matrix elements have been calculated from the Gogny interaction D1, in order to study their single-particle state — and deformation — dependence. From these results, the validity of the two approximations used for pairing correlations is discussed.     

Vibrations of excited molecules at combination and difference frequencies

In the context of the theory of molecular vibrations, by applying the direct product operation of matrices, an equation for the vibrations of vibrationally excited molecules at combination and difference frequencies is obtained. From the solution of this equation, elements of vibration patterns and expressions that can be used for the study of changes in the molecular structural parameters and the coefficients of kinematic interactions are determined. The formulas obtained are applied to the calculation of the anharmonic electro-optical parameters of the molecules of water H₂O and its two isotopes H₂ ¹⁷O and H₂ ¹⁸O. These calculations are performed in terms of the semiempirical quantum-chemical CNDO/2 method and by numerical differentiation of dipole moment functions by employing a cubic spline approximation.     

Temperature and angular momentum dependence of the quadrupole deformation in sd-shell

Temperature and angular momentum dependence of the quadrupole deformation is studied in the middle of the sd-shell for ²⁸Si and ²⁷Si isotopes using the spherical shell model approach. The shell model calculations have been performed using the standard universal sd-shell (USD) interaction and the canonical partition function constructed from the calculated eigensolutions. It is shown that the extracted average quadrupole moments show a transitional behaviour as a function of temperature and the infered transitional temperature is shown to vary with angular momentum. The quadrupole deformation of the individual eigenstate is also analysed.     

The (p, 2p) reaction for slightly deformed nuclei

A perturbation approach for the calculation of (p, 2p) angular correlations for slightly deformed nuclei is developed using the formalism of the distorted wave t-matrix approximation (DWTA) in the static limit where approximations that incorporate absorption and focussing effects are used for the spin-orbit independent optical-model waves. Using a finite-range off-shell t-matrix that fits p-p scattering at 90° to approximate the p-p interaction inside the nucleus, a zero-order calculation is performed and normalized to ¹⁹F(p, 2p)¹⁸O angular correlation data at 42.7 MeV. A rms study is undertaken in order to parametrize the bound-state and the sensitivity of the shape of the angular correlation to the rms value is observed. The deformation of the bound-state is introduced using normalized perturbation theory and calculations with various values of the deformation parameter β for prolate and oblate deformations are performed and the results are compared. The shape of the (p, 2p) angular correlation is shown to be highly sensitive to the degree of deformation and is consistent with the shape dependence of the correlation to the rms value of the bound-state wave function.     

Effects of channel non-orthogonality in (d,p) reactions

Coupled channel calculations for (d, p) reactions were performed in which a strong coupling between the d and p channels was assumed. Reactions investigated were ¹⁶O(d, p) ¹⁷O(2s) and ⁴⁰Ca(d, p) ⁴¹Ca(2p) at E_d =10.5 MeV and the related (d, d) and (p, p) scattering processes. The nonorthogonality of the d- and p-channels were taken into account. The results of these calculations are presented and are compared with the coupled channel calculations neglecting the channel nonorthogonality and also compared with the DWBA and optical model calculations.     

High-spin levels in the 199Pb and 200Pb isotopes

The de-excitation of the ²⁰⁰Pb and ¹⁹⁹Pb isotopes, produced through the ¹⁸⁶W(¹⁸O,4n, 5n) reactions, is investigated using γ-ray and conversion electron spectroscopy. The conversion coefficients are measured and the multipolarities deduced for a great number of transitions. The e⁻γ- and γγ-coincidences and the half-life measurements lead to several new levels in both level schemes; the ²⁰⁰Pb one is extended up to nearly 7 MeV, where an isomer is found. The experimental results are compared to those of microscopic calculations, performed in a two or three quasi-particle approximation, using a surface delta interaction with a reduced pairing component.     

Deformation of nuclei close to the two-neutron drip line in the Mg region

We present Hartree-Fock-Bogoliubov (HFB) calculations of the ground states of even Mg isotopes. A Skyrme force is used in the mean-field channel and a density-dependent zero-range force in the pairing channel. ⁴⁰Mg and ²⁰Mg are predicted to be at the two-neutron and two-proton drip lines respectively. A detailed study of the quadrupole deformation properties of all the isotopes shows that the ground states of ^36,38,40Mg are strongly deformed with significantly different deformations for the neutrons and protons. Our study supports the disappearance of the N = 28 shell gap in the Mg and Si isotopes.     

Ground-State Properties ,of C, O, and Ne Isotopes in Hartree——Fock-Bogoliubov Calculation with Gogny Interaction

Ground-state properties of C, O, and Ne isotopes are described in the framework of Hartree-Fock-Bogoliubov theory with density-dependent finite-range Gogny interaction D1S. We include all the contributions to the Hartree-Fock and pairing feld arising from Gogny and Coulomb interaction as well as the center of mass correction in the numerical calcu/ations. These ground-state properties of C, O, and Ne isotopes are compared with available experimental results, Hartree-Fock plus BCS, shell model and relativistic Hartree--Bogoliubov calculations. The agreement between experiments and our theoretical results is pretty well. The predicted drip-line is dependent strongly on the model and effective interaction due to their sensitivity to various theoretical details. The calculations predict no evidence for halo structure predicted for C,O, and Ne isotopes in a previous RHB study.     

In-trap decay of 61Mn and Coulomb excitation of 61Mn/61Fe

At ISOL (Isotope Separator On-Line) facilities, which utilize thick primary production targets, beams of neutron-rich iron isotopes are difficult to obtain due to the long extraction time of these isotopes out of the target matrix. At REX-ISOLDE, an exploratory experiment was carried out to investigate the possibility of producing a post-accelerated beam of neutron-rich iron isotopes by the in-trap decay of neutron-rich manganese isotopes, which are available at ISOLDE using the Resonance Ionization Laser Ion Source (RILIS). This production mechanism was tested for the first time at REX-ISOLDE with an intense and short-lived beam of ⁶¹Mn isotopes. In this work, the proof of principle of this method is demonstrated, although the technical details of the trapping process are currently not well understood and are still under investigation. The first physics results on the Coulomb excitation of ⁶¹Mn and ⁶¹Fe are presented and compared to shell model calculations.     

The (18O,16O) reaction on even tin isotopes

The two-neutron transfer reaction^ASn(¹⁸O,¹⁶O)^A+2Sn has been measured for the isotopes A=112, 116, 118, 120, 122 and 124 at bombarding energies of 57 and 60 MeV together with the elastic scattering. Angular distributions have been analysed for the transitions to the ground state and to the first excited 2⁺ state. The observed ground state transition is strongly enhanced. The theoretical DWBA analysis is performed with a finite range 2n-transfer form factor including recoil correction. The calculated cross section reproduces the observed systematic change over all isotopes. The absolute cross sections are normalized by a factor of 4.7 and 7.5, depending on the two different sets of 2n-wave functions used in the analysis. The results confirm the prediction of the pairing model that the transition strengths of a neutron pair between the ground states of even tin isotopes are the same.     

Étude des isotopes du plomb de masse 200, 198, 196 et 194 formés par réaction (ions lourds, xn)

The low-lying excited states of ^{194, 196, 198, 200}Pb have been studied through the de-excitation γ-rays following the reactions Os(¹²C, 4n), W(¹⁶O, 4n) and Re(¹⁴N, 5n). Prompt and delayed spectra, γ-γ coincidences, γ-ray angular distributions and γ-ray time distributions have been obtained. Half-lives were measured for the 12⁺ level in the four isotopes, for the 9^? level in ^{194, 196, 200}Pb, for the ^7? level in ²⁰⁰Pb and for the ^5? level in ^{196, 198}Pb. The results of microscopic calculations, performed with either a Gaussian interaction or a surface delta interaction, are compared to the experimental level schemes and transition probabilities, and discussed.     

Isotope effect in nuclear capture of negative muons in xenon

The lifetime of negative muons in the ¹²⁹Xe 1_s state was measured. The muon capture rate in ¹²⁹Xe is compared with that in the ^{132, 136}Xe isotopes. The capture rate was found to depend on the mass number of the cited isotopes. The experimental results are compared with the results of calculations by the semiempirical Goulard-Primakoff formula.     

Ground-State Properties of C, O, and Ne Isotopes in Hartree-Fock-Bogoliubov Calculation with Gogny Interaction

Ground-state.properties of C, O, and Ne isotopes are described in the framework of Hartree-FockBogoliubov theory with density-dependent finite-range Gogny interaction D1S. We include all the contributions to the Hartree-Fock and pairing field arising from Gogny and Coulomb interaction as well as the center of mass correction in the numerical calculations. These ground-state properties of C, O, and Ne isotopes are compared with available experimental results, Hartree-Fock plus BCS, shell model and relativistic Hartree-Bogoliubov calculations. The agreement between experiments and our theoretical results is pretty well. The predicted drip-line is dependent strongly on the model and effective interaction due to their sensitivity to various theoretical details. The calculations predict no evidence for halo structure predicted for C, O, and Ne isotopes in a previous RHB study.     

Self consistent calculations of a possible shape transition in neutron deficient mercury isotopes

Deformation energy curves of some mercury isotopes are calculated within the constrained Hartree-Fock method using a Skyrme effective interaction. These static calculations indicate clearly the possibility of a prolate-oblate transition around ¹⁸⁶Hg which could be an explanation of the anomalous isotopic shift observed from ¹⁸⁷Hg to ¹⁸⁵Hg. The appearance of a very well defined secondary minimum, at large deformation (β ～ 0.5) for ²⁰⁰Hg is also discussed.     

Cross section for the production of compound nuclei in <Emphasis Type="Italic">p</Emphasis>Bi interaction at energies in the range 20–100 MeV

A method for determining the cross section for compound-nucleus formation, σ _CN, in nuclear reactions initiated by protons of energy in the range 20–100 MeV is proposed. The method is based on measuring cross sections for the yield of isotopes maximally remote from the target nucleus. The applicability of the method is illustrated by applying it to the reaction ²⁰⁹Bi(p, xn), which is considered by way of example. Data obtained for the cross section σ _CN are compared with the results of calculations performed on the basis of the intranuclear-cascade model.