P. Kilcher

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.

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.

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.

Decays of , and low-spin states of 181Pt and 177,181Ir

Abstract The decay of 181 Au (T 1 2 = 11.4 s ) has been investigated using mass-separated radioactive sources produced by the ISOCELE facility. Level schemes of 177 Ir, 181 Ir and 181 Pt have been obtained. Most of the levels located at low excitation energy in 181 Ir and 181 Pt are identified as states corresponding to prolate-shaped nuclei. Numerous highly converted transitions have been found in 181 Pt.

Evidence for abnormal M1 transition in 187Pt

Abstract Gamma-gamma angular correlation measurements have been performed in 187 Pt in order to determine the spin values of the states connected by the highly converted transitions. For one of these transitions, we have determined that the spin values of the initial and final states are different, which implies abnormal M1 multipolarity for this highly converted transition. In that case the deduced penetration parameters have especially high absolute values. Moreover we have determined uniquely the spin value of most of the excited states below 800 keV. The occurence of highly converted transitions in 187 Pt is examined and the low-spin negative-parity levels are discussed in terms of shape coexistence.

Location of the181Os isomeric state

The decay of181Ir has been studied on-line with mass-separated sources from the ISOCELE facility. The level scheme of181 Os has been established. The isomeric state has been located at 48.9 keV above the ground state. Thus the isomeric and ground states are identified as the 7/2−(T1/2 =2.7 m) and 1/2−(T1/2=105 m) levels respectively.

Structure of low-spin states in 186Ir

Abstract Low-spin states of 186 Ir populated through the β + /EC decay of 186 Pt nuclei were studied using mass-separated sources and γ-ray and e − spectroscopic techniques. A completely new level scheme of 186 Ir is established. It is shown that the 2 − isomeric state is located at an energy less than 1.5 keV above the 5 + ground state. A very low-energy transition from the 2 − isomer to the 5 + ground state has to exist in order to explain the data, and its relative intensity has been estimated to be around 25% of the total decay of the 2 − state. Most of the experimental levels are interpreted within the two-quasiparticle-plus-rotor model.

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.