G. Lo Bianco

One- and two-phonon wobbling excitations in triaxial 165Lu

High-spin states in Lu-165 have been investigated by in-beam gamma-ray coincidence spectroscopy using the EUROBALL spectrometer array. Two new excited rotational bands have been discovered with features similar to a previously known triaxial superdeformed band in that nucleus. Comparison of the decay pattern of these bands, in particular the unusually large E2 transition strength from the first excited to the yrast superdeformed band, to theoretical calculations shows that they belong to a family of wobbling excitations with phonon numbers n(w) = 0, 1 and 2. These results, together with evidence for nuclear wobbling in the neighbouring isotopes Lu-163 and Lu-167, firmly establish this mode of excitation in the A = 165 mass region. The observation of wobbling is a unique signature of stable nuclear triaxiality

Investigation of an electromagnetic calorimeter based on liquid krypton

Abstract Effects determining the energy and spatial resolution of a calorimeter based on liquid krypton have been studied. With cathode strips of 10 mm a spatial resolution of 0.4 mm has been obtained in a cosmic rays test. The energy resolution of the calorimeter (0.4 ton of krypton) has been measured with positrons, achieving a rms of 5.7% at E = 130 MeV and 1.7% at E = 1200 MeV. The measurements are compared to Monte Carlo simulations.

Liquid krypton calorimeter for KEDR detector

Abstract A description of the liquid krypton calorimeter for the KEDR detector and experimental results on energy and position resolution obtained with prototypes are presented.

Liquid krypton electromagnetic calorimeter

Abstract A calorimeter using 30 tons of liquid krypton for the KEDR detector is being constructed. The main effects which determine the energy and space resolution have been studied. An energy resolution of 1.7% at 1.2 GeV was obtained with the prototype. A space resolution of 0.4 mm for relativistic particles has been reached with the prototype.

Quantum tunneling of the excited rotational bands in the superdeformed nucleus 143Eu

The properties of the thermally excited rotational motion up to the region of rotational damping are studied experimentally in the superdeformed nucleus 143 Eu. The effective lifetime of the excited discrete rotational bands forming ridge structures in ‐ matrices is measured at the EUROBALL array using the DSAM technique, giving a quadrupole momentQt 10 e b, consistent with the deformation of the superdeformed yrast band. In addition, the effective number of excited superdeformed bands is extracted by a statistical analysis of the ridge structure, for transition energies down to the region where the effect of the decay-out into the normal deformed well shows up. The experimental data are compared with microscopic cranked shell model calculations including a residual interaction of surface delta type. Satisfactory agreement between data and theory is obtained when the quantum tunneling of the excited superdeformed states is included in the model.

The rotational γ-continuum in the mass region A≈110

Abstract Unresolved γ transitions of 114 Te and of 112 Sn sorted into one-dimensional and two-dimensional spectra have been studied. The reaction 64 Ni + 54 Cr at bombarding energies 230, 240, 250, 260, 270 MeV was used and the γ -rays were detected with the EUROBALL array. In the case of the nucleus 114 Te the values of the multiplicity as a function of bombarding energy and of the moment of inertia were obtained. The effective moment of inertia was found to be almost constant in the interval I=20 – 40 ℏ , in contrast to the decreasing behaviour of the dynamic moment of inertia for the terminating yrast band. The ridge valley structures in E γ 1 ×E γ 2 spectra of 114 Te and of 112 Sn were analysed with the fluctuation analysis technique. The analysis of the two nuclei are compared to simulations based on microscopic cranking calculations with residual interactions included. A rather good agreement is found between data and predictions.

Rotation induced octupole correlations in the neutron-deficient 109Te nucleus

High spin states in the neutron deficient nucleus 109Te have been populated with the 58Ni+54Fe reaction at 220 MeV and investigated through γ-spectroscopy methods at the GASP spectrometer making use of reaction channel selection with the ISIS Si-ball. The level scheme has been extended up to an excitation energy of ≈12.1 MeV. The spins and parities of the observed levels are assigned tentatively supporting the identification of two bands of opposite parity connected by strong dipole transitions inferred to be of E1 character. Octupole correlations in 109Te induced by rotation are suggested as the cause of this effect.

The response of a HPGe detector with a BGO shield to high energy γ-rays

Abstract The response of a HPGe (82%) detector with a BGO anti-Compton shield has been studied for the 15.1 MeV γ-rays produced by the reaction D( 11 B,nγ) 12 C and for the 6.13 MeV γ-rays produced by a 238 Pu 13 C source. The energy deposited in the HPGe and in the BGO was measured for each detected γ-ray. The sum energy and the spectra of the HPGe in anticoincidence with the BGO were obtained and compared to simulated spectra calculated with the GEANT libraries. The measured energy resolution for the 15.1 MeV γ-rays emitted by 12 C is 209 keV. Due to the velocity ( β = 0.05) of 12 C, the Doppler broadening contribution to the measured FWHM is 140 keV. For the 6.13 MeV γ-rays emitted by the 238 Pu 13 C source, the measured energy resolution was 132 keV.

RDDS coincidence lifetime measurement for two superdeformed states in 192Hg

Lifetimes of two superdeformed states in 192Hg were measured with the recoil distance Doppler shift coincidence method, using the 160Gd(36S,4n)192Hg reaction at a beam energy of 168 MeV. The experiment was performed with the GASP set-up at the LNL, Legnaro. The obtained transitional quadrupole moments are in accordance with those obtained previously for the higher members of the superdeformed band.

Levels in 130Cs and the IBFFM

Abstract Three collective bands have been identified in the odd-odd 130 Cs nucleus by in-beam γ and electron spectroscopy. Spins and parities have been assigned. The interpretation of the level scheme has been performed in the framework of the interacting boson-fermion-fermion model.