D. Prévost

Single step links of the superdeformed band in Pb-194 : A measure of the absolute excitation energy, spin and parity of the superdeformed states

Abstract The EUROGAM array has been used to investigate the decay out of the yrast superdeformed (SD) band in 194 Pb. Six single step decays from the lowest observed SD states to low-lying states at normal deformation (ND) have been identified. From this observation, the excitation energy of the SD band in 194 Pb is established at 4877 ± 1.5 keV for the 6 + SD state. The most probable spins and parities of all members of the SD band are also deduced assuming that the SD states have even spin and positive parity.

Observation of superdeformation in 82Sr

Abstract The EUROGAM Phase 2 array has been used to detect γ rays following the reaction of 30Si on 58Ni at 134 MeV. Two rotational cascades exhibiting characteristic superdeformed behaviour have been observed in 82Sr. Cranked Woods-Saxon calculations have been performed and these suggest that both bands have the ν52π51 intrinsic intruder configuration and that they differ in the signature component of the [431] 1 2 proton orbital which is occupied.

Neutron excitations across the N = 86 superdeformed shell gap

Abstract Based on data obtained with the Eurogam spectrometer, a systematic investigation of superdeformed bands built on single neutron excitations across the N = 86 shell gap has been carried out for gadolinium, terbium, and dysprosium isotopes with 85 ≤ N ≤ 87. In each nucleus, pairs of bands corresponding to degenerate signature partners have been observed. The effective alignment is constant and close to zero for many of the bands, in agreement with cranked shell model calculations for the [402]5/2 and [514]9/2 orbitals. Several bands exhibit non-zero alignments, indicating in some cases the influence of pairing correlations even at high spin and in other cases the occupancy of the [521]3/2 orbital.

The observation of a superdeformed structure in82Y

The58Ni(30Si,αpn)82Y reaction at a beam energy of 134 MeV was used to populate the odd-odd nucleus82Y and coincidentγ rays depopulating high spin states in the evaporation residues were detected with the EUROGAM Phase 2 array. A superdeformed structure has been observed with an intensity of 1.5±0.5%. The cascade of 9 coincidentγ rays has consecutive energy spacing of ∼160 keV. This corresponds to a dynamic moment of inertia which is almost constant at approx mately 25h2 MeV−1. The band is interpreted as a signature=0, negative parity SD band with aπ51V52 intrinsic intruder configuration.

Gamma-ray spectroscopy of 79Rb and 81Sr

High spin states in 79Rb and 81Sr were populated through the bombardment of a 58Ni target with a 30Si beam at 134 MeV. Gamma rays depopulating the excited states were detected using the EUROGAM phase-2 array. A band of nine transitions has been observed in 81Sr decaying to the α = −12 sequence built on the [303]52− Nilsson orbit. The decay schemes of several bands in both 79Rb and 81Sr have been extended to higher spin with angular correlation measurements providing firm spin assignments for a number of states. A fork is observed in 79Rb after a band crossing at hω ⋍ 0.72 MeV in the α = +12 sequence built on the [312]32− Nilsson orbit. A previously observed cascade of three γ-rays in 79Rb has been extended by the addition of ten transitions up to 16 MeV. This has been assigned as a positive parity band built on the [440]12+ Nilsson orbit.

High fold computer disk storage DATABASE for fast extended analysis of γ-rays events

Abstract Recently spectacular technical developments have been achieved to increase the resolving power of large γ-ray spectrometers. With these new eyes, physicists are able to study the intricate nature of atomic nuclei. Concurrently more and more complex multidimensional analyses are needed to investigate very weak phenomena. In this article, we first present a software (DATABASE) allowing high fold coincidences γ-rays events to be stored on hard disk. Then, a non-conventional method of analysis, anti-gating procedure, is described. Two physical examples are given to explain how it can be used and Monte Carlo simulations have been performed to test the validity of this method.

High spin states in the nucleus150Tb

Excited states in the nucleus150Tb have been investigated up to spin 39ħ and 13 MeV excitation energy using the130Te(27Al, 7n) reaction and the EUROGAM array. The theoretical interpretation of the observed states has been performed in the framework of the deformed independent particle model. The analysis of the decay out of the yrast superdeformed band indicates that normal-deformed states with spins between 24ħ and 28ħ are fed.

High-Spin States and Lifetime Measurements in

Abstract This paper describes the results of two complementary experiments which studied the properties of the well-deformed nucleus 171 Hf. The first experiment, with a thin self-supporting target, extended the rotational bands built upon the [633]7 / 2, [512]5 / 2 and [521]1 / 2 configurations up to spins of 73 / 2–85 /2ℏ . The configurations of these bands and observed band crossings are discussed within the framework of the cranked-shell model. The second experiment employed a backed target in order to measure the lifetimes, by the Doppler Shift Attenuation method, and thereby establish deformations for some of the states in the collective rotational bands. The extracted deformations are found to be consistent with those predicted from theoretical Total Routhian Surface calculations. These deformations provide strong evidence that the high-spin states in 171 Hf, and perhaps more importantly, in the region where the high- K ( K π =19/2 + and K π =23/2 − ) isomeric states decay, retain their well-deformed axial symmetry.

^171

Excited states in the 150, 151, 152 Tb isotopes have been investigated using the 130Te(27 Al, xn) reaction and the EUROGAM array. The theoretical interpretation of the level schemes has been performed in the framework of the deformed independent particle model. The feeding patterns of the normal-deformed states by the superdeformed bands in 150, 151 Tb istopes have also been established. The results indicate that the decay-out mechanism of the bands is not of purely statistical nature, but depends on the configurations of both normal- and superdeformed states.

Hf

Abstract Excited states in the nucleus 151 Tb have been investigated up to spin 91/2 ħ and energy 16.5 MeV using the 130 Te( 27 Al, 6n) reaction and the EUROGAM array. The theoretical interpretation of the level scheme has been performed in the framework of the deformed independent particle model. The feeding patterns of the normal-deformed states by both the yrast and first excited superdeformed bands have also been established. The results indicate that the decay-out mechanism of the bands is not of purely statistical nature, but depends on the configurations of both normal- and superdeformed states.