D. Bazzacco

Sum-up and pile-up contribution to cross-over peaks in coincidence γ spectroscopy

Abstract High-efficiency arrays for γ spectroscopy, now available in several Laboratories, make possible the measurement of very weak cross-over transitions of high potential interest. A limit to the measurement possibilities comes, however, from the simultaneous detection of two γ-rays of a stop-over cascade (or “sum-up”), which cannot be distinguished from the true detection of the cross-over transition. We propose a new method to measure (and correct for) the sum-up effect, which can be used with symmetric γ detector arrays (like GASP and GAMMASPHERE), and discuss the possible techniques for identifying and estimating quantitatively the contribution of random pile-up, which can be sizeable at high counting rate. These ideas have been experimented at GASP in a dedicated measurement with a radioactive source of 52 Mn . The results of this measurement are presented and discussed. Moreover, as a significant example, the method is applied to deduce the intensity of the E3 cross-over transition from the lowest 3− state of 148 Gd .

Decay of superdeformed structures studied with GASP

Abstract Some studies on the subject of superdeformation, performed using the γ detector array GASP, are presented. The attention is focussed to the problem of the decay of the superdeformed bands. The cases of 133Nd, where the decay proceeds by discrete transitions, and of 194Pb, where the decay proceeds in a statistical way, are presented.

Study of the soft dipole modes in 140Ce via inelastic scattering of 17O

The main aim of this study was a deeper understanding of the nuclear structure properties of the soft dipole modes in 140 Ce, excited via inelastic scattering of weakly bound 17 O projectiles. An important aim was to investigate the ‘splitting’ of the PDR into two parts: a low-energy isoscalar component dominated by neutron-skin oscillations and a higher-energy component lying on the tail of the giant dipole resonance of a rather isovector character. This was already observed for this nucleus, investigated in (α, α′) and (γ, γ′) experiments. The experiment was performed at Laboratori Nazionali di Legnaro, Italy. Inelastic scattering of 17 O ion beam at − 2 0M eV A 1 was