A. Wöhr

Beams of short lived nuclei produced by selective laser ionization in a gas cell

Abstract An on-line laser ion source has been developed for the production of elemental and isobaric pure beams of radioactive ions. It is based on selective resonant laser ionization of nuclear reaction products thermalized and neutralized in a noble gas at high pressure. The ion source has been tested in a wide range of recoil energies going from 1.3 MeV to ∼ 90 MeV. Efficient schemes of two step laser ionization through autoionizing states have been found for nickel, cobalt and rhodium. Residence times of the reaction products in a gas cell have been measured for helium and argon as buffer gas. Elementally pure beams of 54,55Ni and 54Co, produced in a light-ion induced fusion-evaporation reaction, and of 113Rh, produced in proton-induced fission of 238U, were obtained. An efficiency of the ion source of 6.6% for fusion reactions and of 0.22% for fission reactions has been obtained. A selectivity of the ion source of 300 for fusion and 50 for fission reactions has been achieved.

The SPIG, improvement of the efficiency and beam quality of an ion-guide based on-line isotope separator

Abstract A SPIG (Sextupole Ion Beam Guide) has been constructed and tested to couple an ion-guide based ion source to an on-line isotope separator. In comparison to a skimmer, the SPIG offers both an increased beam quality and the possibility to operate the ion-guide at higher buffer gas pressures.

Single-neutron states in Sn-133

The location of several single-neutron states in Sn-133 has been identified. The P-3/2, h(9/2), and f(5/2) states were found at 853.7, 1560.9, and 2004.6 keV, respectively, by measuring gamma rays in coincidence with delayed neutrons following the decay o

Elastic 2n-transfer in the 4He(6He,6He)4He scattering

The elastic scattering He-4(He-6,He-6)He-4 has been investigated at center-of-mass energies of 11.6 and 15.9 MeV. Differential cross sections are determined using a post-accelerated He-6 (T-1/2 = 0.807 s) beam in the center-of-mass angular range between 50 and 140 degrees. The comparison of the measured data with calculations using a double folding potential shows evidence for the 2n-transfer process in the He-4(He-6,He-6)He-4 elastic scattering

Production of radioactive Ag ion beams with a chemically selective laser ion source

Abstract We have developed a chemically selective laser ion source at the CERN-ISOLDE facility in order to study neutron-rich Ag nuclides. A pulsed laser system with high repetition rate has been used based on high-power coppe-vapour pump lasers and dye lasers. With this source significant reductions of the isobaric background has been achieved.

Beta decay of 103In: Evidence for the Gamow-Teller resonance near 100Sn

Abstract The β decay of the neutron-deficient isotope 103 In was investigated by using total absorption γ-ray spectrometry on mass-separated sources. The measurement reveals a high-lying resonance of the β-decay strength in striking disagreement with high-resolution γ-ray data. The result is discussed in comparison with shell-model predictions.

A new pulsed release method for element selective production of neutron rich isotopes near 208Pb

Abstract A new method to reduce the isobaric contamination problem for the production of neutron rich Bi, Pb and Tl nuclei at on-line mass separators, based on the pulsed release of these radioactive species, is presented. The results of a feasibility study are reported.

Determination of the Gamow–Teller strength function for the neutron-deficient isotopes 104–107In

Abstract The Gamow–Teller β decays of the neutron-deficient indium isotopes 104–107 In have been investigated by using total absorption γ -ray spectrometry on mass-separated sources. The experimental Gamow–Teller strength, deduced as a function of the excitation energy in the daughter nuclei 104–107 Cd, is compared to shell-model predictions.

Status of the laser ion source at the Leuven isotope separator online

An online laser ion source has been used at the Leuven isotope separator online for the production of pure beams of exotic nuclei. The operational principle of the ion source is based on the element-selective multistep laser resonance ionization of nuclear reaction products thermalized and neutralized in a high-pressure noble gas. A number of improvements has been carried out to obtain stable and reproducible operation. The ion source has been optimized for the production of beams of exotic nuclei, created in proton-induced fission reactions. The efficiency of the ion source has been improved by incorporating the sextupole ion guide to separate laser-produced ions from the gas jet and to transport them to the acceleration stage of the mass separator. A gas purification system has been installed to purify the noble gas down to ppb level. High selectivity and efficiency of the ion source allowed to collect nuclear spectroscopic information for the neutron deficient 54Ni and neutron-rich 68–74Ni isotopes.

Structure of Co-65,Co-67 studied through the beta decay of Fe-65,Fe-67 and a deep-inelastic reaction

The neutron-rich isotopes {sup 65,67}Fe and {sup 65}Co have been produced at the LISOL facility, Louvain-La-Neuve, in the proton-induced fission of {sup 238}U. Beams of these isotopes have been extracted with high selectivity by means of resonant laser ionization combined with mass separation. Yrast and near-yrast levels of {sup 65}Co have also been populated in the {sup 64}Ni+{sup 238}U reaction at Argonne National Laboratory. The level structure of {sup 65}Co could be investigated by combining all the information from both the {sup 65}Fe and {sup 65}Co{beta} decay and the deep-inelastic reaction. The {sup 65}Fe, {sup 65}Co, and {sup 67}Fe decay schemes and the {sup 65}Co yrast structure are fully established. The {sup 65,67}Co level structures can be interpreted as resulting from the coexistence of core-coupled states with levels based on a low-energy proton-intruder configuration.