Complementary reaction analyses and the isospin mixing of the 4- states in 16O

Data from the inelastic scattering of electrons, and of intermediate energy protons and pions leading to ``stretched'' configuration 4- states near 19 MeV excitation in 16O as well as from charge exchange (p,n) scattering to an isobaric analogue (4-) state in 16F have been analyzed to ascertain the degree of isospin mixing contained within those states and of the amount of d_{5/2}-p_{3/2}^{-1} particle-hole excitation strength they exhaust. The electron and proton scattering data have been analyzed using microscopic models of the structure and reactions, with details constrained by analyses of elastic scattering data.Comment: 25 pages, 12 figure

Sum rules for isospin centroids in pick-up reactions on general multishell target states

Sum Rules equations for pick-up reactions are presented for the first time for the energy centroids of states both for the isospin T_< (\equiv T_0 - 1 \over 2) and T_> (\equiv T_0 + {1 \over 2}) of the final nucleus when a nucleon is picked up from a general multishell target state with isospin T_0. These equations contain two-body correlation terms, , which, at the present moment, are difficult to handle analytically. These terms are managed by combining these equations with the known stripping reactions equations. Sample applications of these equations to experimental data are presented.Comment: 11 pages, LaTe

Effects of the Spin-Orbit and Tensor Interactions on the M1M1 and E2E2 Excitations in Light Nuclei

The effects of varying the spin-orbit and tensor components of a realistic interaction on $M1$ excitation rates and $B(E2)'s$ are studied on nuclei in the $0p$ and $1s-0d$ shells. Not only the total $M1$ but also the spin and orbital parts separately are studied. The single-particle energies are first calculated with the same interaction that is used between the valence nucleons. Later this stringent condition is relaxed somewhat and the $1s$ level is raised relative to $0d$. For nuclei up to $^{28}Si$, much better results i.e stronger $B(M1)$ rates are obtained by increasing the strength of the spin-orbit interaction relative to the free value. This is probably also true for $^{32}S$, but $^{36}Ar$ presents some difficulties. The effects of weakening the tensor interaction are also studied. On a more subtle level, the optimum spin-orbit interaction in the lower half of the $s-d$ shell, as far as $M1$ excitations are concerned, is substantially larger than the difference $E(J=3/2^+)_1-E(J=5/2^+)_1=5.2~MeV$ in $^{17}O$. A larger spin-orbit splitting is also needed to destroy the triaxiality in $^{22}Ne$. Also studied are how much $M1$ orbital and spin strength lies in an observable region and how much is buried in the grass at higher energies. It is noted that for many nuclei the sum $B(M1)_{orbital}+B(M1)_{spin}$ is very close to $B(M1)_{total}$, indicating that the summed cross terms are very small.Comment: 39 pages, revtex 3.

A consistent analysis of (e,e'p) and (d,3He) experiments

The apparent discrepancy between spectroscopic factors obtained in (e,e'p) and (d,3He) experiments is investigated. This is performed first for 48Ca(e,e'p) and 48Ca(d,3He) experiments and then for other nuclei. It is shown that the discrepancy disappears if the (d,3He) experiments are re-analyzed with a non-local finite range DWBA analysis with a bound-state wave function that is obtained from (e,e'p) experiments.Comment: 23 pages, 7 figure

Double Beta Decay in pn-QRPA Model with Isospin and SU(4) Symmetry Constraints

The transition matrix elements for the $0^{+}\to 0^{+}$ double beta decays are calculated for $^{48}Ca$, $^{76}Ge$, $^{82}Se$, $^{100}Mo$, $^{128}Te$ and $^{130}Te$ nuclei, using a ${\delta}$-interaction. As a guide, to fix the particle-particle interaction strengths, we exploit the fact that the missing symmetries of the mean field approximation are restored in the random phase approximation by the residual interaction. Thus, the T=1, S=0 and T=0, S=1 coupling strengths have been estimated by invoking the partial restoration of the isospin and Wigner SU(4) symmetries, respectively. When this recipe is strictly applied, the calculation is consistent with the experimental limit for the $2\nu$ lifetime of $^{48}Ca$ and it also correctly reproduces the $2\nu$ lifetime of $^{82}Se$. In this way, however, the two-neutrino matrix elements for the remaining nuclei are either underestimated (for $^{76}Ge$ and $^{100}Mo$) or overestimated (for $^{128}Te$ and $^{130}Te$) approximately by a factor of 3. With a comparatively small variation ($<10$) of the spin-triplet parameter, near the value suggested by the SU(4) symmetry, it is possible to reproduce the measured $T_{1/2}^{2\nu}$ in all the cases. The upper limit for the effective neutrino mass, as obtained from the theoretical estimates of $0\nu$ matrix elements, is $\cong 1$ eV. The dependence of the nuclear matrix elements on the size of the configuration space has been also analyzed.Comment: 25 pages (LaTex) and 3 figures upon request, to be published in Nucl. Phys.

Shell Structure of the Superheavy Elements

Ground state properties of the superheavy elements (SHE) with Z from 108 to 128 and N from 150 to 192 are investigated using both the Skyrme-Hartree-Fock method with a density-independent contact pairing interaction and the macroscopic-microscopic approach with an average Woods-Saxon potential and a monopole pairing interaction. Detailed analysis of binding energies, separation energies, shell effects, single proton and neutron states, equilibrium deformations, alpha-decay energies, and other observables is given.Comment: 27 RevTeX pages, 22 figures available upon request to [email protected]

GABRIELA : a new detector array for gamma-ray and conversion electron spectroscopy of transfermium elements

With the aid of the Geant4 Monte Carlo simulation package a new detection system has been designed for the focal plane of the recoil separator VASSILISSA situated at the Flerov Laboratory of Nuclear Reactions, JINR, Dubna. GABRIELA (Gamma Alpha Beta Recoil Investigations with the Electromagnetic Analyser VASSILISSA) has been optimised to detect the arrival of reaction products and their subsequent radioactive decays involving the emission of alpha- and beta-particles, fission fragments, gamma- and X-rays, and conversion electrons. The new detector system is described and the results of the first commissioning experiments are presented.Comment: 24 pages, Submitted to NIM

La Privatizaci\uf3n en Venezuela y sus Conflictos Laborales. Caso: CANTV-VIASA 1990-1993

Para el desarrollo de la investigaci\uf3n, se procedi\uf3 al estudio de los efectos laborales surgidos como consecuencia de la privatizaci\uf3n de la Compa\uf1\ueda An\uf3nima Tel\ue9fonos de Venezuela (CANTV) y de la empresa Venezolana Internacional de Aviaci\uf3n, S.A. (VIASA), durante los a\uf1os de 1989 - 1993. Se crey\uf3 necesario tomar en consideraci\uf3n los conocimientos emitidos por expertos en materia laboral, respaldados por la ley del trabajo, para conocer los efectos laborales de los trabajadores de ambas empresas

A phenomenological spin-orbit and nuclear potential for \chem{^{208}Pb}

A local, state-independent nuclear single-particle potential for \chem{^{208}Pb} was developed by suitably shaping the nuclear central term and the related spin-orbit term of Thomas type. The aim was to reproduce accurately the excitation energies of the known single-particle states in \chem{^{207}Tl}, \chem{^{207}Pb}, \chem{^{209}Bi} and \chem{^{209}Pb} as well as the recently observed dependence of the spin-orbit splittings on angular momentum $\ell$ and principal quantum number $n$. As result, a set of orthogonal proton and neutron wave functions was obtained which were used for a consistent reanalysis of proton and neutron single-particle transfer reactions on \chem{^{208}Pb}. The quality of the description of measured angular distributions is comparable with that obtained originally with individual “best fit” potentials. The resulting single-particle spectroscopic factors amount on the average to $S\approx$ 0.7. Single- particle densities derived from these wave functions are in qualitative agreement with measured charge and mass densities for \chem{^{208}Pb}