C. Rossi Alvarez

Split analogue of the 2.02 MeV state of 47Ca

Abstract The elastic scattering of protons by 46 Ca has been measured at seven angles for E p = 1.82−1.90 MeV. Thirteen resonances are observed and interpreted as components of the split analogue of the 47 Ca first excited state. The resonance parameters are extracted and the proton width of the IAS is determined. The partial reduced widths are fitted to the Robson one-level formula and the pertinent parameters are deduced. In addition, γ-rays from the 46 Ca(p, γ) 47 Sc reaction were detected; the decay scheme and Γ γ are deduced. The summed M1 strength for the IAS is 1.0 W.u. Hindrance of the M1 decay is explained as resulting from the polarization due to the spin-isospin interaction, which is especially strong for the analogue-to-antianalogue transitions.

Isospin Symmetry Along The N=Z Line In The sd Shell

Excited states have been studied in sd‐shell nuclei following the 16O (70 MeV) + 24Mg (400 μg/cm2) fusion‐evaporation reaction. The GASP spectrometer in conjunction with the charged‐particle detector ISIS and the Neutron ring allowed the detection of the γ‐rays in coincidence with evaporated light particles. New data on the mirror pairs A=31 and A=35 have been obtained. In particular, the comparison between the level schemes of 35Ar and 35Cl has confirmed the importance of the electromagnetic spin‐orbit term, which explains the large Mirror Energy Difference values. Evidence of isospin mixing can be deduced from the E1 transitions.

Lifetime measurements in light barium isotopes

The transition strenghts for the low—lying levels of 122,124Ba have been determined analysing the Recoil Distance Doppler Shift data by the Differential Decay Curve Method. The trend of normalised B(E2) reveals a drop in correspondance of the 81+ state. This feature is also present in 122Ba: entering the backbending region the interplay between collective and quasiparticle degrees of freedom have to be carefully taken into account.

High spin studies of 64Ge with EUROBALL

The high-spin states of the N=Z nucleus 64Ge have been investigated using the EUROBALL array coupled to the ISIS Si-ball and to a highly efficient n-Wall. Spins and parities were assigned on the basis of a DCO and of a polarization analysis.

MARS - A NOVEL γ-RAY DETECTOR ARRAY

MARS Mini ARray of Segmented detectors is the Italian effort to explore the feasibility of building a high performance 4π array for γ-ray spectroscopy based on γ-ray tracking. The most advanced present arrays, EUROBALL and GAMMASPHERE, are built of Compton suppressed HPGe spectrometers arranged in tightly packed spherical configurations. Despite the fact that these arrays are already composed of more than 100 detectors, their performance is limited to an efficiency of only about 10% and a response function (P/T-ratio) with about 60% of the total intensity in the full energy peak at 1 MeV. The good P/Tratio is achieved rejecting the signal from the detector when the surrounding BGO shield detects γ-rays Compton scattered out of the Ge crystal. However, the use of the suppression shields prevents to cover more than one half of the solid angle with Ge detectors limiting the achievable efficiency considerably to the present values. It is an established fact that an array with better performance cannot be obtained by simply increasing the number of detectors.

Absence of blocking effect in the N=Z odd-odd nucleus 62Ga: A new signature of the n-p pairing?

The high-spin structure of the N≃Z nuclei 62,64,65Ga have been investigated using the EUROBALL array coupled to the ISIS Si-ball. The collective bands of such nuclei are then compared showing an unexpected behavior.

High spin studies of 64Gewith EUROBALL

The high-spin states of the N=Z nucleus 64Ge have been investigated using the EUROBALL array coupled to the ISIS Si-ball and to a highly efficient n-Wall. Spins and parities were assigned on the basis of a DCO and of a polarization analysis.

Shape changes induced by quasiparticle alignment

Mean lifetimes of high-spin states of {sup 74}Kr have been determined using the Doppler shift attenuation method (DSAM). The high-spin states were studied using the {sup 40}Ca({sup 40}Ca,{alpha}2p) reaction at a beam energy of 160 MeV with the GASP array. The investigated ground state band and negative parity side band show the presence of three different configurations in terms of transitional quadrupole deformations. The deduced quadrupole deformation changes are well reproduced by cranked Woods-Saxon Strutinsky calculations.

Decay out of the highly-deformed bands in the A=130 mass region and experimental Δν for Nd nuclei

A review of the results on the decay out of highly-deformed bands in the A=130 mass region is presented, including new experimental information on the decay out of two highly-deformed bands in 132Nd and 134Nd. The previously observed E2 linking transitions are explained by the crossing with observed nonyrast bands of normal deformation. Large interaction matrix elements and mixing amplitudes between the interacting highly-deformed and normal-deformed bands are deduced. The large normal-deformed admixture into the lowest observed highly-deformed states explains why the decay out occurs at a certain spin along the band and shows that the barrier between the highly-deformed and normal-deformed minima disappears at low spins. Results on the decay out of the highly-deformed band of 136Nd are reported and the extraction of Δν for the highly-deformed Nd nuclei is discussed.

Fragmentation of the two-phonon γ-vibration in166Er

Two-phonon γ-vibrational states in166Er have been populated using Coulomb excitation. The Kπ=4+ component of the vibration appears to be fragmented over several states, whereas only one Kπ=0+ state is observed.