B. Bruyneel

A gas cell for thermalizing, storing and transporting radioactive ions and atoms. Part II: On-line studies with a laser ion source

Abstract The application of a gas cell filled with noble gas (helium or argon) for thermalizing, storing and transporting trace radioactive ions and atoms has been studied in on-line conditions. Radioactive ions produced in nuclear reactions and stable energetic ions have been resonantly re-ionized by laser light via a two-step resonant process after thermalization and neutralization in high-pressure noble gas. The influence of the ion–electron density created by the projectile beam on the recombination of exotic ions has been investigated in different experimental conditions, including DC and RF electrical fields in the gas cell. Results for the laser ion source efficiency and selectivity for heavy-ion induced fusion reaction products are given. For the Rh isotopes the efficiency reaches up to 12%.

The Leuven isotope separator on-line laser ion source

An element-selective laser ion source has been used to produce beams of exotic radioactive nuclei and to study their decay properties. The operational principle of the ion source 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 installed at the Leuven Isotope Separator On-Line (LISOL), which is coupled on-line to the cyclotron accelerator at Louvain-la-Neuve. 54,55Ni and 54,55Co isotopes were produced in light-ion-induced fusion reactions. Exotic nickel, cobalt and copper nuclei were produced in proton-induced fission of 238U. The b decay of the 68–74Ni, 67–70Co, 70–75Cu and 110–114Rh isotopes has been studied by means of β–γ and γ–γ spectroscopy. Recently, the laser ion source has been used to produce neutron-deficient rhodium and ruthenium isotopes (91–95Rh, 98Rh, 90,91Ru) near the N=Z line in heavy ion-induced fusion reactions.

A detector setup to study the decay properties of exotic nuclei

Abstract General features of a detector setup for decay studies at on-line mass-separators are discussed. The detection system was used for measurements of β-decay properties of exotic nuclei with A ≈70. Results of GEANT Monte-Carlo simulations of the detector setup generally confirm the measurements. Both measurements and simulations show that even in case of low multiplicity events the Ge detector efficiency and peak to total ratio of γ-lines are reduced by large factor due to summing. Steps to improve the detection system are discussed.

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

Resonant laser ionization in a gas cell has been implemented at the Leuven Isotope Separator On Line facility to produce beams of short lived radioactive nuclei and to study their decay characteristics. A description of the laser ion source is presented together with technical details on the laser system, the gas cell and the gas purification system. Results from off line as well as on line measurements are discussed. The new laser ion source has allowed β decay studies of neutron deficient (54Ni, 92Rh) as well as neutron rich (up to 74Ni and 70Co) isotopes.

Production of neutron-rich copper isotopes in 30-MeV proton-induced fission of 238U

Abstract The neutron-rich isotopes 70–76Cu have been produced in 30-MeV proton-induced fission of 238U using the Ion Guide Laser Ion Source (IGLIS) at LISOL. The production rates of the copper isotopes, and of the nickel and cobalt isotopes that were measured earlier, are compared to cross section calculations. Based on these new results an estimate for the cross section of 78Ni is given.

Short-lived fission products as a diagnostics tool for studying atom and ion behavior in a gas-based laser ion source

Abstract A striking difference between gamma spectra of neutron-rich Rh isotopes obtained with the laser ion source at the Leuven Isotope Separator On-Line facility has been observed depending on the mode of operation. Although the global production rate of 112Rhg,m nuclei decreases considerably, the ratio between the productions of 112Rhg and 112Rhm increases strongly when no laser ionisation is used. This effect is caused by 112Ru atoms which decay during gas evacuation of the ion source gas cell, thereby producing 112Rhg ions. The comparison in time behaviour of reaction produced ions, β-decay produced ions and laser produced ions makes it possible to study and characterise the different processes in the gas cell. The influence of these processes has to be considered when extracting nuclear information such as the relative feeding of different short-lived isomers and isotopes and fission cross-sections in a particular mass chain.

High-spin structure in40K

High-spin states of K-40 have been populated in the fusion-evaporation reaction C-12(Si-30,np)K-40 and studied by means of gamma-ray spectroscopy techniques using one triple-cluster detector of the ...

Electric quadrupole moments of the21+states inCd100,102,104

Using the REX-ISOLDE facility at CERN the Coulomb excitation cross sections for the 0(gs)(+)-> 2(1)(+) transition in the beta-unstable isotopes Cd-100,Cd-102,Cd-104 have been measured for the first time. Two different targets were used, which allows for the first extraction of the static electric quadrupole moments Q(2(1)(+)) in Cd-102,Cd-104. In addition to the B(E2) values in Cd-102,Cd-104, a first experimental limit for the B(E2) value in Cd-100 is presented. The data was analyzed using the maximum likelihood method. The provided probability distributions impose a test for theoretical predictions of the static and dynamic moments. The data are interpreted within the shell-model using realistic matrix elements obtained from a G-matrix renormalized CD-Bonn interaction. In view of recent results for the light Sn isotopes the data are discussed in the context of a renormalization of the neutron effective charge. This study is the first to use the reorientation effect for post-accelerated short-lived radioactive isotopes to simultaneously determine the B(E2) and the Q(2(1)(+)) values. (Less)

Gamow-Teller strength in the f7/2-nuclei 54Co and 42Sc studied through the beta decay of 54Ni and 42Ti

At the LISOL facility the neutron-deficient {sup 54}Ni isotope was produced via a {sup 3}He fusion-evaporation reaction on a {sup 54}Fe target positioned in the element-selective Ion-Guide Laser Ion Source (IGLIS). The {beta} decay of {sup 54}Ni was observed for the first time. The Gamow-Teller {beta}-decay strength associated with the (J{sup {pi}}=1{sup +}) level at 937.2 keV in the daughter nucleus {sup 54}Co was deduced. The Gamow-Teller {beta}-decay strength is in agreement with B(GT) obtained from (p,n) reaction studies. For the first time an experiment was performed using a heavy-ion beam in combination with the IGLIS in order to produce {sup 42}Ti.

Laser ion source for on-line production of exotic nuclei

An on-line laser ion source is used at the Leuven Isotope Separator On-Line (LISOL) for the production of pure beams of exotic nuclei. The operational principal 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 have been carried out to improve the ion source parameters.