Bochum 1998 – wissenschaftliches Programm

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HK: Hadronen und Kerne

HK 70: Plenar

HK 70.2: Gruppenbericht

Freitag, 20. März 1998, 12:00–12:30, P

Selective laser ionisation for decay studies far from stability — •M. Huyse, S. Franchoo, K. Kruglov, Y. Kudryavtsev, W.F. Mueller, R. Raabe, I. Reusen, P. Van Duppen, L. Vermeeren, and A. Woehr — Instituut voor Kern- en Stralingsfysica, University of Leuven, Belgium

When studying nuclei far from stability, one generally is confronted with two problems. Isobaric contamination by neighbouring nuclei that are produced in overwhelmingly more abundant quantities and the short halflives of exotic nuclei that are of the order of one second or less, imply the need for an ion source that is fast, selective and efficient.

The Iglis Ion Guide Laser Ion Source tries to meet these requirements by combining the high efficiency and selectivity of resonant laser ionization with the fast evacuation times reached by the ion guide technique [1]. Recently this novel technique has been applied for the study of neutron-deficient and neutron-rich Ni nuclei.

The beta-delayed gamma decay of ⁵⁴Ni has for the first time been studied and information on the Fermi and Gamow-Teller strength distribution could be extracted. This will be compared with the strength distribution obtained from the p,n reaction on ⁵⁴Fe [2].The neutron rich nickel isotopes are of interest both for nuclear and astrophysics. From the nuclear physics point of view, they are singly closed shell nuclei on the way to ⁷⁸Ni. As to astrophysics, their decay properties can be crucial for calculating the nucleosynthesis r-process path. The ⁷⁸Ni isotope has been identified at GSI a few years ago [3] but the heaviest nickel isotope on which decay spectroscopic information was available remained ⁶⁹Ni [4]. The nuclei of interest are produced in a 30-MeV proton induced fission of ²³⁸U, after which they are thermalized and neutralized in 500 mbar of argon buffer gas, transported by the gas flow to the laser ionization region and finally injected into the high vacuum parts of the mass separator. The isotopes ⁶⁸Ni up to ⁷⁴Ni were studied by means of beta-gamma and gamma-gamma coincidences. New gamma rays from the decay of ⁷⁰Ni to ⁷³Ni have been identified, halflives were determined for ⁶⁸Ni to ⁷⁴Ni down to an accuracy of 5 to 20% and production cross sections were extracted and can be compared to recent calculations [5,6].

[1] Y. Kudryavtsev et al., Nucl. Instr. and Meth. B 114, 350 (1996)

[2] B.D. Anderson et al., Phys. Rev. C 41, 1474 (1990)

[3] C. Engelmann et al., Z. Phys. A352, 351 (1995)

[4] U. Bosch et al., Nucl. Phys. A477, 89 (1988)

[5] M. Huhta et al., Phys. Lett. B405, 230 (1997)

[6] V. Rubchenya, private communication