M. Axiotis

STRUCTURE OF NEUTRON–RICH NUCLEI FROM DEEP–INELASTIC REACTIONS

Neutron rich nuclei have been populated using the 82Se+192Os deep-inelastic reaction. New experimental results on 188W, 188,190Os target-like nuclei, as well as 74,76,78Ge beam-like nuclei are presented.

Investigation of the reaction 74Ge(p,gamma)75As using the in-beam method to improve reaction network predictions for p nuclei

A measurement of 74Ge(p,gamma)75As at low proton energies, inside the astrophysically relevant energy region, is important in several respects. The reaction is directly important as it is a bottleneck in the reaction flow which produces the lightest p nucleus 74Se. It is also an important addition to the data set required to test reaction-rate predictions and to allow an improvement in the global p+nucleus optical potential required in such calculations. An in-beam experiment was performed, making it possible to measure in the energy range between 2.1 and 3.7 MeV, which is for the most part inside the astrophysically relevant energy window. Angular distributions of the gamma-ray transitions were measured with high-purity germanium detectors at eight angles relative to the beam axis. In addition to the total cross sections, partial cross sections for the direct population of twelve levels were determined. The resulting cross sections were compared to Hauser-Feshbach calculations using the code SMARAGD. Only a constant renormalization factor of the calculated proton widths allowed a good reproduction of both total and partial cross sections. The accuracy of the calculation made it possible to check the spin assignment of some states in 75As. In the case of the 1075 keV state, a double state with spins and parities of 3/2- and 5/2- is needed to explain the experimental partial cross sections. A change in parity from 5/2+ to 5/2- is required for the state at 401 keV. Furthermore, in the case of 74Ge, studying the combination of total and partial cross sections made it possible to test the gamma width, which is essential in the calculation of the astrophysical 74

Test of the critical point symmetry X(5) in the mass A = 180 region

As(n,gamma)75As rate.

Gamma-decay study of 21Na and 21Ne, octupole bands in 21Ne

Based on the energy spectra and relative transition probabilities 176,178,180 Os turned out to be very promising candidates for testing the features of the critical point symmetry X(5). In order to also test absolute transition probabilities predicted in the framework of the X(5) symmetry lifetime measurements were performed at the Cologne FN tandem accelerator. The lifetimes of the first 2 + states in 176,178,180 Os were measured using electronic timing and in the case of 178 Os with the recoil distance Doppler shift (RDDS) technique using an 16 O-induced fusion evaporation reaction. In addition, a coincidence RDDS measurement was performed at the Laboratori Nazionali di Legnaro with the GASP spectrometer using the 154 Sm( 29 Si,5n) 178 Os reaction. The deduced transition quadrupole moments agree well with the X(5) predictions, thus further supporting an X(5) structure for 178 Os. The experimental data for 178 Os are compared to calculations in the framework of the interaction boson model (IBM) and of the general collective model (GCM).

The CLARA-PRISMA setup installed at LNL: first results

The reactions 16 O( 7 Li, 2n )a nd 16 O( 7 Li, np) populating 21 Na and 21 Ne have been studied at EL = 27 MeV using the GASP γ -detector array. The level scheme for 21 Na and 21 Ne has been extended to higher excitation energy. Spins and parities of the observed levels are assigned tentatively supporting th ei dentification of opposite parity structures connected by strong dipole transitions. The structure of these bands is interpreted as based on a reflection asymmetric cluster structure.

High-spin states populated in deep-inelastic reactions

CLARA is an array of 25 Clover (EUROBALL type) Ge detectors, placed at the target position of the large acceptance magnetic spectrometer PRISMA. Due to the granularity of the CLARA Ge array (100 crystals), the photopeak efficiency (≈3%) and the PRISMA large acceptance (≈80 msr, and 20% Δp/p), the setup is an excellent tool to investigate the structure of neutron-rich nuclei, populated in multinucleon transfer reactions and deep inelastic collisions with stable beams. Since March 2004 the setup is fully operational, and since then several experiments have been performed, with beams delivered by the LNL XTU-Tandem and the ALPI linac. In this contribution the preliminary outcome of the first experiments is shown.

Transition rates and nuclear structure changes in mirror nuclei 47 Cr and 47 V

High spin states in the neutron rich 188Os and 190Os nuclei have been populated using the 82Se + 192Os deepinelastic reaction. The level schemes are extended up to spin I »21. The observed new structures are tentatively interpreted as fragments of rotational bands built on multi-quasiparticle configurations.

Yrast states in 188, 190Os nuclei

Lifetime measurements in the mirror nuclei

Intruder configurations in neutron-rich P and S isotopes

{}^{47}\mathrm{Cr}

Toward the N = 40 sub-shell closure in Co isotopes and the new island of inversion

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