J.K.P. Lee

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.

Improvements in the injection system of the Canadian Penning trap mass spectrometer

Abstract The Canadian Penning Trap (CPT) mass spectrometer is designed to make precise mass measurements on a variety of stable and short-lived isotopes. Modifications to the injection system of the CPT have been implemented in recent months, the purpose being to more efficiently collect and transfer weakly-produced reaction products from the target to the Penning trap. These include a magnetic triplet situated after the target chamber to increase the acceptance of the Enge spectrograph, a velocity filter to more effectively separate the beam from the reaction products and the replacement of the Paul trap with a linear trap resulting in more efficient capture and accumulation of ions from the ion cooler. This paper will discuss these recent modifications and how they have increased our ability in making mass measurements on isotopes of low abundance, including those from a 252 Cf fission source.

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.

COMPLIS experiments: COllaboration for spectroscopy Measurements using a Pulsed Laser Ion Source

Laser spectroscopy measurements have been carried out on very neutron-deficient isotopes of Au, Pt and Ir, produced as daughter elements from a Hg ISOLDE beam. For these transitional region nuclides, the hyperfine structure (HFS) and isotope shift (IS) were measured by Resonance Ionization Spectroscopy (RIS). Magnetic moments μ, spectroscopic quadrupole moments Qs and changes of the nuclear mean square charge radius δ〈rc2〉along isotopic series have been extracted. For some results, a detailed comparison with theoretical predictions is presented.

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 using synchronized laser pulses

Abstract The resonant ionization of gold atoms has been investigated using two synchronized laser pulses — a heating pulse from a Nd-Yag laser to desorb atoms from the substrate, and a pulse from an excimer-laser-pumped dye laser for resonant ionization. The 532-nm beam was found to be most suitable for desorption. With a power density of 5 × 10 7 W cm −2 for the ionization beam, the linewidth for the [5d 10 6s → 5d 10 6p] transition in gold was measured to be 180±10 GHz. Using long-lived 194–196,198 Au isotopes evaporated onto a tantalum substrate, an overall ion-collection efficiency of (1.0±0.5)×10 −4 was obtained. Geometric constraints of the experimental setup account for a loss factor of 3×10 −3 , while the remaining reduction factor of 3.3×10 −2 is attributed to incomplete desorption into single atoms, non-saturation of the ionization process, low ion-collection efficiency, and losses due to ion-atom collisions.

Study of the ((π1g92)3 s = 1)(v2d52) multiplet in 94Tc AND 98Tc by use of the 94, 98Mo(3He, t)94, 98Tc reactions

Abstract The structures of 94 43 Tc 51 and 98 43 Tc 55 have been investigated by using the 94, 98 Mc( 3 He, t) 94, 98 Tc reactions. Tentative spin and parity assignments have been made on the basis of the known systematics of the ( 3 He, t) reaction. The low-lying positive parity states of 94 Tc are shown to belong to the ((π1 g 9 2 ) 3 s = 1)(v2 d 5 2 ) multiplet. Excellent agreement between theory and experiment has been obtained. On the other hand, the ((π1 g 9 2 ) 3 s = 1)(v2 d 5 2 ) −1 multiplet in 98 Tc has been found to be fragmented due to configuration mixing. This configuration mixing appears to give rise to some intruder states in the low excitation spectrum of 98 Tc. However, the high spin states of 5 + , 6 + and 7 + at low excitation show remarkably similar features to those of the (π1 g 9 2 ) (v2 d 5 2 ) −1 multiplets in 96 Nb. The negative parity states of 2 − and 3 − which presumably have dominant (π p 1 2 ) −1 (v d 5 2 ) ±1 configurations were also observed. The triton yields for these negative parity states were rather weak, and consequently the angular distributions had anomalous shapes.

Proton stripping reactions populating levels in 95,97,101Tc

The structure of the low-lying levels of 95,97,101Tc was investigated with the proton stripping (3He,d) reaction. The experimental angular distributions were compared with distorted-wave Born-approximation calculations, and l-values and spectroscopic factors were extracted. The proton configurations of the target ground states were deduced. The systematics of transition strength distributions are discussed.

The (d, α) reaction viewed as a two-step process☆

Abstract The 98, 97, 94Mo(d, α)96, 95, 92Nb and 93Nb(d, α)91Zr reactions have been studied at 12 MeV bombarding energy. A DWBA analysis using one- and two-step processes has been carried out. The two-step process is found, in general, to dominate the one-step and together give rise to cross-section predictions within a factor of 10 of experiment. The angular distribution patterns are found to be best reproduced by DWBA predictions based on certain L-transfers (“parity violating”) associated with only the two-step process and which play but a minor role in their contribution to the overall cross section.

States of 87Sr populated by deuteron pick-up from 89Y

Abstract The reaction 89 Y(d, α) 87 Sr has been observed at a bombarding energy of 12 MeV. Angular distributions of the emitted α-groups were recorded over the angular range 10° to 160° lab and compared with a DWBA analysis. Many levels in 87 Sr appear to be populated by proton pickup from the 2 p 3 2 orbit. The levels of 87 Sr populated in this reaction correspond to those observed in the 87 Rb(p, n) 87 Sr reaction but differ to a large extent from those seen in neutron stripping and pick-up reactions.