G. Vedovato

Linking transitions between the highly deformed states and the yrast states of normal deformation in 133Nd

Abstract Transitions linking the highly deformed band to low deformation states have been unambiguously established in 133 Nd in the very first experiment performed with the GASP array. the highly deformed band becomes yrast at 29 2 + , where it mixes with the positive parity band built upon the [404] 7 2 Nilsson state. The experimentally deduced interaction amounts to 13 keV. The measurement of the spins in the highly deformed intruder band sheds some light upon the reported backbend anomaly in this mass region.

Alpha particles in coincidence with the superdeformed band in 150Tb

Abstract Alpha particle spectra in coincidence both with normal deformed (ND) and superdeformed (SD) bands of 150 Tb have been measured using the reaction 120 Sn( 37 Cl,α3n) at 187 MeV bombarding energy. A clear difference is observed between the two spectra, that in coincidence with the SD states being shifted to lower energies. This effect is understood in terms of different angular momentum regions from which the ND and SD states orginate. The standard statistical model fails to describe the angular momentum dependence of the alpha particle energies.

Study of the Mo-Ba partition in 252Cf spontaneous fission

Abstract: Measurements of fission fragment yields and neutron multiplicities have been carried out for the Mo-Ba fragment pairs in the spontaneous fission of 252Cf, using the γ-ray spectroscopy technique to analyze γ-γ-γ coincidence data. Prompt γ -ray multiplicities were also measured as a function of the number of neutrons emitted in the fission process leading to the Mo-Ba partition. We do not observe the enhancement in the yields of events with high neutron emission multiplicity (νn > 7) that has been associated to a second fission mode leading to the production of hyperdeformed Ba fragments, as reported in some earlier studies. The average γ-ray multiplicity is found to be rather weakly dependent on the number of neutrons emitted in the fission process.

Alpha particle emission, incomplete fusion and population of high-spin states in the reaction 120 MeV 19F + 181Ta

Abstract The reaction 120 MeV 19 F + 181 Ta has been studied by charged particle-γ-ray coincidence techniques. An incomplete fusion component has been identified in coincidence with 192,191 Hg residues which are populated in the αxn channels. Evidence has been found that the feeding of high spin states in final residues is enhanced when the coincidence is required with alpha particles emitted at forward angles, where the incomplete fusion component dominates.

Shape change along the highly-deformed band in 137Nd☆

Abstract Lifetimes of states of the highly-deformed (HD) band in 137Nd have been measured using the Doppler shift attenuation method. A line-shape analysis has been carried out for individual states, resulting in transition quadrupole moments which decrease with increasing spin. This represents the first confirmation of previous total routhian surface (TRS) calculations that predicted a drift towards positive γ values of the HD minimum (at essentially constant β deformation). The lifetime data show a rather modest deformation of the HD band structure, indicating a softening of the nuclear potential at HD shape.

Double band crossing in the superdeformed nucleus 145Gd

Abstract The nuclear structure of 145Gd has been investigated via the 114Cd(36S,5n) reaction. Three superdeformed bands have been discovered, consisting of 17, 16 and 10 transitions, respectively. The first excited superdeformed band shows two band crossings which are assigned to the subsequent alignment of an i 13 2 proton pair and a crossing of the i 13 2 and i 11 2 neutron orbitals, respectively. Such a double band crossing has been observed for the first time. The second excited superdeformed band is assigned as the signature partner of the previous band but shows no band crossing in the observed frequency range. The band crossing behaviour of the SD bands has been described theoretically.

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.

Proton and neutron alignments in the doubly odd nucleus Br-76

High-spin states in the doubly odd nucleus Br-76 have been investigated using the Mn-55(Si-30,2 alpha n) reaction at a beam energy of 130 MeV. Five bands have been established to high spin. The features of the level scheme, particularly the signature inversion and the band crossings in the yrast band as well as proton and neutron alignments in the negative-parity bands, are discussed in the framework of the cranked shell model

Proton spectra in coincidence with super- and hyper-deformed structures in 152Dy

Abstract The hyperdeformed ridge structure recently observed in the reaction of 187 MeV 37 Cl on 120 Sn has been confirmed in a new proton-γ coincidence experiment at the GASP spectrometer and assigned to the nucleus 152 Dy. Proton spectra have been measured in coincidence with γ-rays belongings to the different structures in 152 Dy (oblate, prolate, super- and hyper-deformed). The deformation of the final evaporation residue affects only weakly the proton evaporation from the compound nucleus. Evidence has been found that the energy of the protons in coincidence with the hyperdeformed structure is larger than expected. This effect is discussed in the framework of the fission-evaporation competition.

The transputer based GA.SP data acquisition system

A description of the new data acquisition system for the GA.SP detector is presented. It is distributed system based on a network of 40 T800 and T222 transputers linked to a VME system used for histogram storage. A 100 Mb/s FDDI ring connects the system to UNIX workstations used for the experiment control, histogram display, and second-level data analysis. >