ELSEVIER Nuclear Physics A621 (1997) 289c-292c NUCLEAR PHYSICS A Can the waiting-point nucleus 7SNi be studied at an on-line mass-separator? A. W5hr, A. Andreyev, N. Bijnens, J. Breitenbach S. Franchoo, M. Huyse, Y.A. Kudryavtsev, A. Pieehaczek, R. R Raabe, I. Reusen, L. Vermeeren and P. Van Duppen a ~Katholieke Universiteit Leuven, Instituut voor Kern- en Stralingsfysica Celestijnenlaan 200D, B-3001 Leuven, Belgium Short-lived nickel isotopes have been studied using a chemically selective Ion Guide Laser Ion Source (IGLIS) based on resonance ionisation of atoms at the Leuven Isotope Separator On-Line (LISOL) separator. The decay properties of different Ni isotopes have been studied using fLy'-coincidences. Experimental production rates of proton induced fission of 23sU are obtained for 69,nNi. These numbers are in a strong disagreement with Silberg-Tsao calculations. 1. Introduction Since decades neutron- and proton-rich nuclei are studied at on-line mass separators [1], revealing many interesting nuclear physics phenomena. One of the most interesting nuclei is the doubly magic nucleus 7SNi. Its level and decay properties at the doubly-closed shell and of the nuclei in its neighborhood form well defined test cases for various nuclear structure models and can be used to calculate e.g. residual interactions in a shell model picture. Also from astrophysics point of view, these nuclei are of interest as the neutron- capture probabilities and/~-decay properties influence the mass flow in the r-process path and thus the relative isotope abundances. The doubly magic nucleus 7SNi is considered as a "waiting-point" nucleus in the region of the A _~ 80 r-abundance peak. This nucleus was since long time looked for and has been identified at GSI-Darmstadt using the fragment separator [2]. At on-line isotope separators (ISOL), various attempts to observe the decay of 7SNi failed. The low produc- tion cross section of neutron or light-ion induced fission of 23sU or 232Th forms a difficult obstacle but is not a principal problem. Due to their chemical properties Nickel atoms tend to have a rather long delay time in modest temperature plasma ion sources. Due to the short half-life of the nuclei of interest the long delay time induces large losses. Furthermore, the fission reaction is not selective resulting in isobaric contaminations with order of magnitude larger beam intensities. The solution to these problems is an on-line ion source that ideally fulfills the following requirements: the ionization efficiency should be high (> 10 % ), the delay time short (< 10 ms) and the element selectivity should be high (> 100). For this purpose a laser ion source to ionize reaction products was developed, 0375-9474/97/$17.00 © 1997 - Elsevier Science B.V All rights reserved. PII: S0375-9474(97)00257-1