J. Van Roosbroeck

On-line yields obtained with the ISOLDE RILIS

The ISOLDE resonance ionization laser ion source (RILIS) allows to ionize efficiently and selectively many metallic elements. In recent yield surveys and on-line experiments with the ISOLDE RILIS we observed 23–34 Mg, 26–34 Al, 98–132 Cd, 149 Tb, 155–177 Yb, 179–200 Tl, 183–215 Pb and 188–218 Bi. The obtained yields are presented together with measured release parameters which allow to extrapolate the release efficiency towards more exotic (short-lived) nuclides of the same elements. 2002 Elsevier Science B.V. All rights reserved.

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.

Isomer separation and measurement of nuclear moments with the ISOLDE RILIS

Short-lived radioisotopes are element selectively ionized by the resonance ionization laser ion source (RILIS) of the on-line isotope separator ISOLDE (CERN). The relative production of low and high spin isomers can be significantly changed when a narrow-bandwidth laser is used to scan through the atomic hyperfine structure. This allows the assignment of gamma ray transitions to the decay of the individual isomers. Moreover, the measurement of the hyperfine splitting provides a very sensitive method for the determination of magnetic moments of exotic isotopes. The technical developments are discussed for the example of copper.

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.

beta-decay study of Cu-77

A beta-decay study of Cu-77 has been performed at the ISOLDE mass separator with the aim to deduce its beta-decay properties and to obtain spectroscopic information on Zn-77. Neutron-rich copper isotopes were produced by means of proton- or neutron-induced fission reactions on U-238. After the production, Cu-77 was selectively laser ionized, mass separated and sent to different detection systems where beta-gamma and beta-n coincidence data were collected. We report on the deduced half-live, decay scheme, and possible spin assignment of 77Cu.

β-decay study of Cu77

A beta-decay study of Cu-77 has been performed at the ISOLDE mass separator with the aim to deduce its beta-decay properties and to obtain spectroscopic information on Zn-77. Neutron-rich copper isotopes were produced by means of proton- or neutron-induced fission reactions on U-238. After the production, Cu-77 was selectively laser ionized, mass separated and sent to different detection systems where beta-gamma and beta-n coincidence data were collected. We report on the deduced half-live, decay scheme, and possible spin assignment of 77Cu.

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.

{beta}-decay properties of {sup 72}Ni and {sup 72}Cu

The {beta}-decay properties of {sub 28}{sup 72}Ni{sub 44} and {sub 29}{sup 72}Cu{sub 43} have been studied at the LISOL facility of Louvain-La-Neuve and at the CERN-ISOLDE facility, respectively. These neutron-rich nuclei have been produced in the proton-induced fission of {sup 238}U. Their decay schemes are presented and the lifetime T{sub 1/2}=6.63(3) s of {sup 72}Cu was measured. No {beta}-decaying isomeric state was found in {sup 72}Cu, in line with a suggested spin (2) for its ground state. Spin and parity assignments of the observed excited states in the odd-odd nucleus {sup 72}Cu are proposed and discussed in terms of coupling between the valence proton and neutrons. Comparison is made with a schematic shell-model picture of {sup 72}Cu and with large-scale shell-model calculations performed in the (2p{sub 3/2}1f{sub 5/2}2p{sub 1/2}1g{sub 9/2}) shell space outside the doubly magic {sub 28}{sup 56}Ni{sub 28} core.The {beta}-decay properties of {sub 28}{sup 72}Ni{sub 44} and {sub 29}{sup 72}Cu{sub 43} have been studied at the LISOL facility of Louvain-La-Neuve and at the CERN-ISOLDE facility, respectively. These neutron-rich nuclei have been produced in the proton-induced fission of {sup 238}U. Their decay schemes are presented and the lifetime T{sub 1/2}=6.63(3) s of {sup 72}Cu was measured. No {beta}-decaying isomeric state was found in {sup 72}Cu, in line with a suggested spin (2) for its ground state. Spin and parity assignments of the observed excited states in the odd-odd nucleus {sup 72}Cu are proposed and discussed in terms of coupling between the valence proton and neutrons. Comparison is made with a schematic shell-model picture of {sup 72}Cu and with large-scale shell-model calculations performed in the (2p{sub 3/2}1f{sub 5/2}2p{sub 1/2}1g{sub 9/2}) shell space outside the doubly magic {sub 28}{sup 56}Ni{sub 28} core.