B. Roussière

Shape transition in neutron deficient Pt isotopes

Abstract Isotope shift (IS) and hyperfine structure (HFS) measurements have been performed for 185,187,189,191,195 Pt using the PILIS (Post ISOCELE Laser Isobar Separation) apparatus installed at the ISOCELE facility. Magnetic and quadrupole moments have been deduced from the HFS results. The change radius changes determined for these odd nuclei from the IS results, added to the δ r 2 > values of the even- A nuclei, are compared to the results of lattice Hartee-Fock+BCS calculations for asymmetric solutions. 185 Pt is confirmed to be prolate shaped whereas 187,189,191 Pt are likely triaxial in their ground states.

Laser spectroscopy of laser-desorbed gold isotopes

Abstract Changes in mean-square charge radius δ〈r2〉, and magnetic dipole moments μ1 have been measured for a series of neutron-deficient gold isotopes between A = 186 and 196, and for neutronrich 198,199Au, using the PILIS system on-line with the ISOCELE mass separator. These measurements confirm the existence of the shape transition between A = 186 and 187. The measured μ1 values have been compared with calculations using Nilsson, and symmetric-rotor-plus-quasiparticle models. The results are consistent with the interpretation that 186Au is prolate, and that the heavier isotopes have oblate, or possibly triaxial deformation.

Release properties of UCx and molten U targets

Abstract The release properties of UC x and molten U thick targets associated with a Nier–Bernas ion source have been studied. Two experimental methods are used to extract the release time. Results are presented and discussed for Kr, Cd, I and Xe.

Decay of 183Ir: Shape of 183Os and 185Pt in their low-spin states

Abstract The decay of 183 Ir has been studied with mass-separated sources from the ISOCELE facility. A level scheme of 183 Os has been established. It is discussed in the framework of an “axial-rotor + quasi-particle” model: all the states located below 700 keV are interpreted assuming a prolate shape of the nucleus. This study has shed a new light on the interpretation of the 185 Pt low-spin states. Highly converted transitions in 185 Pt are discussed.

Recent studies to improve release properties from thick isotope separator on-line fission targets

In the framework of the PARRNe program (Production d’Atomes Radioactifs Riches en Neutrons) of IPN Orsay, various techniques are currently used to characterize the release properties of elements of interest from a UCX target. On-line studies have been carried out with two plasma ion sources: a Nier–Bernas and a hot plasma ISOLDE-type (the ISOLDE collaboration kindly supplied us a MK5 ion source for these studies). In parallel, the analysis of the chemical and structure properties of some UCX samples as function of heating conditions has been carried out. Such data are essential to determine optimal conditions for the production of isotopes by the isotope separator on-line (ISOL) technique. First results are presented here for Kr and Ag. Investigations for other kinds of fission targets are planned.

Pilis: Post-ISOCELE laser isobar separation — an apparatus for laser spectroscopic studies of laser-desorbed atoms

Abstract An apparatus for laser spectroscopic studies of laser-desorbed radioactive atoms has been installed on-line at the ISOCELE isotope separator (IPN, Orsay). Mass-separated gold ions were first implanted onto a substrate, and then thermally desorbed by a Nd-YAG laser pulse. A three-step, two-resonance scheme was used to selectively ionize the desorbed gold atoms. The ions created were then mass-identified through a time-of-flight technique. The laser system used has a linewidth of 130 MHz, and an actual experimental resolution of 170 MHz for the stable 197Au was obtained. It has been demonstrated that with 1010 total implanted ions, several laser scans can be performed, and that a 5 × 10−5 ion conversion efficiency for the desorbed gold atoms was reached at resonance. On-line measurements of the isotope shift (IS) and hyperfine structure (HFS) for several gold isotopes were carried out. With the high-resolution capability, a negative sign for the magnetic moment of 192Au was obtained. The HFS of 187Au confirms an earlier laser spectroscopic study, and the sudden variation of IS between 187Au and 186Au was reproduced.

Decay of 183Au: Low-spin states of 183Pt

Abstract The decay of 183 Au (T 1 2 = 42 s ) has been studied with mass-separated sources from the ISOCELE facility. A level scheme of 183 Pt has been established. Most of the states located below 800 keV are interpreted assuming a prolate shape of the nucleus from comparison with isotones or isotopes.

Structure of doubly-odd nucleus 184Ir from the decay of 184Pt

Abstract States of 184 Ir populated through the β + /EC decay of 184 Pt were studied using mass-separated sources and on-line -γ-ray and e − spectroscopic techniques. A rather complete low-spin level scheme is established. Negative and positive parity structures are interpreted within the two-quasiparticle- plus-rotor model. They are mainly the \ gp h 9 2 ⊗ \ gn i 13 2 structure based on the 5 − ground state and the \ gph 9 2 ⊗ \ gn 1 2 − [521] system of states based on a 3 + isomer at 225.7 keV.

The low-spin states in the doubly odd 182Ir nucleus and the influence of the proton-neutron interaction

Abstract Low-spin states of 182 Ir populated through the β + EC decay of 182 Pt were studied using the ISOCELE facility. A low-spin level scheme has been established. Using a semi-microscopic rotor-plus-two-quasiparticle model developed in the context of the HF + BCS approximation, the influence of the V pn interaction on the relative energy location of excited states has been studied and the low-spin states located at low energy in 182 Ir have been identified. The α-decay energy of 186 Au has been corrected to 4907 ± 16 keV.

Spin and parity of isomeric and ground states of the doubly-odd nucleus184Au

Low-spin states in doubly-odd184Au have been populated in the β+/EC decay of184Hg produced by bombarding184Sm targets with an 185 MeV40Ar beam. Radioactive Hg nuclei were transported by a He jet system. A new level scheme has been established from γ-γ-t and X-γ-t coincidence measurements. Spin and parity values Iπ=5+, Iπ =2+ and Iπ=3− were assigned to the ground state and the two isomeric states of184Au, respectively. The structure of these states is discussed using B(E1) values.