K. Sieja

\(\delta\)-pairing forces and collective pairing vibrations

Abstract.The collective pairing Hamiltonian is obtained in the framework of the generator coordinate method in the Gaussian overlap approximation with a slightly modified BCS function used as a generator function. The collective variable

Studies on the double-β decay nucleus Zn64 using the (d,He2) reaction

alpha

STATE DEPENDENT δ-PAIRING AND SPONTANEOUS FISSION

, measuring the monopole moment of the pairing field, and the gauge transformation angle

Collectivity in the light Xenon isotopes: A shell model study

phi

PARTICLE NUMBER CONSERVING APPROACH TO CORRELATIONS

are chosen as generator coordinates. The vibrational ground states are calculated by diagonalisation of the collective pairing Hamiltonian in the harmonic-oscillator basis.The eta-prime meson production in the reaction pp-->pp eta-prime has been studied at excess energies of Q = 26.5, 32.5 and 46.6 MeV using the internal beam facility COSY-11 at the cooler synchrotron COSY. The total cross sections as well as one angular distribution for the highest Q-value are presented. The excitation function of the near threshold data can be described by a pure s-wave phase space distribution with the inclusion of the proton-proton final state interaction and Coulomb effects. The obtained angular distribution of the eta-prime mesons is also consistent with pure s-wave production.

SUPERHEAVY NUCLEI IN DIFFERENT PAIRING MODELS

The (d, 2 He) charge-exchange reaction on the double-β decay (ββ) nucleus 64 Zn has been studied at an incident energy of 183 MeV. The two protons in the 1 S 0 state (indicated as 2 He) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. 2 He spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus 64 Cu with high precision. 64 Zn is one of the rare cases undergoing a ββ decay in β + direction. In the experiment presented here, Gamow-Teller (GT + ) transition strengths have been extracted. Together with the GT - transition strengths from 64 Ni( 3 He,t) data to the same intermediate nucleus 64 Cu, the nuclear matrix elements of the ββ decay of 64 Zn have been evaluated. Finally, the GT + distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell.

PROPERTIES OF SUPERHEAVY NUCLEI IN VARIOUS MACROSCOPIC-MICROSCOPIC MODELS

We examine the fission barriers, mass parameters and spontaneous fission half lives of Fermium isotopes within the framework of the macroscopic-microscopic model with a δ-pairing interaction. Four different macroscopic models are applied and studied. The results are compared to experimental data and to the ones of the corresponding monopole pairing approach. The half lives obtained in the δ-pairing model are comparable with experimental data.

PAIRING AND α-DECAY

known experimental data. Predictions are made for the (still unknown) N=Z nucleus 108 Xe. The results are interpreted in terms of the competition between the quadrupole correlations enhanced by the pseudo-SU(3) structure of the positive parity orbits and the pairing correlations brought in by the 0h11/2 orbit. We have studied as well the effect of the excitations from the 100 Sn core on our predictions. We show that the backbending in this region is due to the alignment of two particles in the 0h11/2 orbit. In the N=Z case, one neutron and one proton align to J=11 and T=0. In 110,112 Xe the alignment begins in the J=10 T=1 channel and it is dominantly of neutron neutron type. Approaching the band termination the alignment of a neutron and a proton to J=11 and T=0 takes over. In a more academic mood, we have explored the role of the isovector and isoscalar pairing correlations on the structure on the yrast bands of 108,110 Xe and examined the role of the

NEUTRON–PROTON PAIRING IN 64Ge

In the present work the so-called Higher Tamm-Dancoff Approximation method is presented for the generalized case of isovector and isoscalar residual interactions treated simultaneously. The role of different particle-hole excitations and of proton-neutron pairing correlations in the ground state of the self-conjugate 64Ge nucleus is discussed.

δ-PAIRING FORCES AND NUCLEAR MASSES

Pairing plays an important role in both mean-field and macroscopic-microscopic description of the fission process. We discuss two kinds of pairing models: monopole (g = const) and state dependent (δ-type force). As is known the BCS theory leads to the particle number symmetry braking. To restore the symmetry one uses a projection methods (projection before- or after variation) or one solves the Lipkin-Nogami equations. We apply all these methods in the case of monopole pairing. Fission barriers, inertia parameters and spontaneous fission half-lives are studied in the case of Z = 112 isotopes.