M. Hellström

Efficiency and delay of the integrated target-ion source of OSIRIS

Abstract The new compact target and ion source system of the OSIRIS ISOL-facility at Studsvik has now been in use for about five years. The system is used for studies of short lived nuclei obtained through fission with reactor neutrons. The ion source can simply be switched between two modes of operation, one being (thermal) surface ionization and the other an electron impact induced plasma mode. The efficiency for most elements in the fission product region has been measured. The use of a substantial (gram quantity) amount of target material introduces a delay between a fission event and the subsequent ionization of the products. This delay in a U+C target has been analyzed for several elements. Some observations of nuclidic yields as a function of the target temperature are reported.

Gamma-ray and delayed neutron branching data for the new or little known isotopes84,85Ge and84,85As

The branchings (absolute intensities) of γ-rays following the decay of84,85Ge and84,85As have been determined using mass-separated samples. Our results include the first identification of85Ge and the first γ-ray data for84Ge. Values of the delayed neutron emission probabilities, Pn, of84Ge and85As were also deduced from the data, together with a lower limit of this quantity for85Ge. The deduced Pn of about 39 % for the important neutron emitter85As is substantially larger than the values of about 22–23 % obtained in previous indirect determinations.

The doubly closed shell nucleus 132Sn: Collectivity and p-h states

The angular momenta and parities of the low lying states of 132Sn have been firmly determined through studies of the β-decay of 132In. The lowest lying state with a negative parity is shown to have a collective octupole character. Several particle-hole multiplets have been identified, including the lowest lying proton excitation. Theoretical estimates of multiplet positions and multiplet splittings, based on the analogy with 208Pb, agree well with the data. More than about 20% of the theoretically estimated bound states of 132Sn have been identified.

Some studies of molecular ions obtained from a U + C target at > 2100°C

Abstract The OSIRIS ISOL-facility at Studsvik is used for studies of short lived products from reactor neutron induced fission. Several species of molecular ions are produced in the target, forming sidebands to the fission mass distribution. Other species are obtained when reactive gases are introduced into the target chamber. Observations of the temperature stability of molecular ions and their formation probabilities under different conditions are reported.

Detailed spectroscopy of doubly-magic 132Sn and its neighbours; Perspective for further studies at PIAFE

Abstract Experimental studies at the OSIRIS fission-product mass separator have yielded a wealth of new results on the doubly-magic region near 132 Sn. In the following we focus on two aspects of the new results: on the evidence for octupole collectivity of the 3 1 − state in 132 Sn and on the similarity of the 208 Pb and 132 Sn regions as evidenced from the modelling of the low excitations in 132 Sb. The Stage-I of the PIAFE facility recently proposed at Grenoble will offer exciting possibilities for even more detailed studies of the doubly magic regions near 132 Sn and 78 Ni (the latter for the first time).