J. Obert

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.

Exotic nuclei produced by fast neutrons in a liquid uranium target

Abstract The latest results of the research and development program Production dAtomes Radioactifs Riches en Neutrons (PARRNe) at Institut de Physique Nucleaire (IPN) Orsay are presented. The production of neutron rich isotopes by fast neutron induced fission in a liquid depleted uranium target was measured. A comparison of the production rates with a uranium carbide (UCx) target is given.

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.

Resonant ionization spectroscopy of laser‐desorbed gold isotopes

A system for laser spectroscopic studies on implanted radioactive samples has been developed and installed at the ISOCELE isotopes separator. Mass separated gold isotopes collected in a graphite substrate are desorbed by pulses from a Nd/YAG laser. Three synchronized dye laser pulses produce ions in a resonant ionization process; these are detected and identified in a time‐of‐flight mass spectrometer. Results of isotope shift and hyperfine structure measurements on gold isotopes with A=186, 187, 190, 192, 194, 195 and 196 are presented.

Detection of low‐energy conversion electrons and location of isomeric states

The detection of conversion electrons of short‐lived isotopes at ISOCELE has been extended to very low‐energy: a special tape‐transport system has been built which allows the slowing down of the incoming radioactive ions and the acceleration of the electrons detected on photographic film in a flat magnetic spectrograph. Results have been acquired for the decay of mercury with A=185,u2009186,u2009187,u2009189,u2009191, and of platinum with A=184, and 186. As examples the location of isomeric states deduced from our measurements are given to illustrate the power of high‐resolution electron detection.

Deformation change between isomeric and ground states in the 184Au and 183Pt isotones

Deformation changes δβ have been found out between isomeric and ground states of the 183Pt and 184Au isotones. Atomic spectroscopy measurements by laser were carried out using the COMPLIS setup. Hyperfine structure (HFS) spectra and isotope shift (IS) were obtained for the 5d96su200a3D3→5d96pu200a3P2 and 5d106su200a2S1/2→5d106pu200a2P3/2 optical transitions in Pt and Au atoms respectively, providing deformation parameters β and nuclear moments μ and Qs. The influence of the proton-neutron coupling on the δβ value in 184Au relatively to its isotone 183Pt has been determined. Besides, the h9/2 proton state that is decoupled from the core in 183,185Au, becomes the 3/2[532] state (h9/2 parentage) strongly coupled in the doubly-odd 184Au nucleus.

Decay of neutron-rich Ga isotopes near N = 50 at PARRNe

The PARRNe facility has been used to produce neutron-rich isotopes 83,84Gaby the ISOL method. Their decay has been studied, and β-γ coincidence and γ-γ coincidence data were collected as a function of time. The first two excited levels in 83Ge and the first excited level in 84Ge have been measured for the first time.