Alberto Escuderos

Seniority conservation and seniority violation in the g9/2 shell

The g{sub 9/2} shell of identical particles is the first one for which one can have seniority-mixing effects. We consider three interactions: A delta interaction that conserves seniority, a quadrupole-quadrupole (Q{center_dot}Q) interaction that does not, and a third one consisting of two-body matrix elements taken from experiment ({sup 98}Cd) that also leads to some seniority mixing. We deal with proton holes relative to a Z=50,N=50 core. One surprising result is that, for a four-particle system with total angular momentum I=4, there is one state with seniority v=4 that is an eigenstate of any two-body interaction--seniority conserving or not. The other two states are mixtures of v=2 and v=4 for the seniority-mixing interactions. The same thing holds true for I=6. Another point of interest is that, in the single-j-shell approximation, the splittings {delta}E=E(I{sub max})-E(I{sub min}) are the same for three and five particles with a seniority conserving interaction (a well-known result), but are equal and opposite for a Q{center_dot}Q interaction. We also fit the spectra with a combination of the delta and Q{center_dot}Q interactions. The Z=40,N=40 core plus g{sub 9/2} neutrons (Zr isotopes) is also considered, although it is recognized that the core is deformed.

Odd- J pairing in nuclei

We point out a simplicity that arises when we use an interaction in which only an energy with odd J is non-zero. The emphasis is on J= J_{max} and in particular J=9+ in the g_{9/2} shell. It is noted that high overlaps can be deceptive. In many cases a single set of U9-j coefficients gives either an exact or a very good approximation to the wave function of a yrast state.

Shell model calculations ofB(E2)values, static quadrupole moments, andgfactors for a number ofN=Znuclei

In this work we look at the low lying nuclear structure of several N=Z nuclei residing between the doubly magic nucei ^{40} Ca and ^{100} Sn. Using large shell model codes we calculate and discuus the systematics of enegies. We show energy levels, B(E2)s, static quadrupule moments and g factors. In all cases we compare the results of 2 different interactions which yield significanly different occupation numbers. We compare with the simplest versions of the rotational and vibrational models. By examinnig B(E2)s and static quadrupole moments we make associations with collective models find that in the model space here considered ,{}^{88} Ru is oblate . The quadruple moment of ^{92} Pd is very small consistent with the vibrational model.

Isobaric analog states in thef7/2andg9/2shells

Calculations are performed for energies of isobaric analog states with isospins T=2 and T=3 in regions where they have been found experimentally e.g. f-p shell, and regions where they have not yet been found e.g. g_{9/2} near Z=50,N=50. We consider two approaches--one using binding energy formulas and Coulomb energies contained therein and the other using shell model calculations. It is noted that some (but not all) calculations yield very low excitation energies for the J=0^{+} T=2 isobaric analog state in ^{96} Ag.

Description of the two neutrino double β decay in deformed nuclei with projected spherical single particle basis

Using an angular momentum projected single particle basis, a pnQRPA approach is used to study the

Shell-model test of the rotational-model relation between static quadrupole moments Q(2+1), B(E2)'s, and orbital M1 transitions

2\nu\beta\beta

Full major shell calculation for states that were degenerate in a single j-shell calculation

properties of ten isotopes, exhibiting various quadrupole deformations. The mother and daughter nuclei exhibit different quadrupole deformations. Since the projected basis enables a unified description of deformed and spherical nuclei, situations where the nuclei involved in the double beta decay process are both spherical, both deformed or one spherical and another deformed, can be treated through a sole formalism. Dependence of single

Companion problems in quasispin and isospin

\beta^-

Partial conservation law in a schematic single j shell model

and

Large-jlimit for certain 9-jsymbols: Power law behavior

\beta^+