Freiburg 1999 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 10: Kernphysik II / Spektroskopie I

HK 10.8: Talk

Monday, March 22, 1999, 18:30–18:45, B

Study of Shape Coexistence in Nuclei around ¹⁴²Gd with EUROBALL — •R.M. Lieder^1,2, T. Rzaca-Urban², H. Brands¹, W. Gast¹, H.M. Jäger¹, L. Mihailescu¹, Z. Pytel², W. Urban², D. Bazzacco³, G. Falconi³, R. Menegazzo³, S. Lunardi³, C. Rossi-Alvarez³, G. de Angelis⁴, E. Farnea⁴, A. Gadea⁴, D.R. Napoli⁴, and Z. Podolyak⁴ — ¹Institut für Kernphysik, Forschungszentrum Jülich, D-52425 Jülich — ²Institute of Experimental Physics, University of Warsaw, PL-00-681 Warsaw — ³INFN, Sezione di Padova, I-35131 Padova — ⁴INFN, Laboratori Nazionali di Legnaro, I-35020 Legnaro

Extensive studies of high-spin rotational bands in the mass regions with A ≈ 130 and A ≈ 150 have shown the existence of highly-deformed bands (β₂ ≈ 0.35) in the former and superdeformed bands (β₂ ≈ 0.50) in the latter region. The nucleus ¹⁴²Gd lies in the intermediate region and no bands built on states of large quadrupole deformation are known in this nucleus, from which one could learn how the transition between these two regions takes place. Theoretical calculations for ¹⁴²Gd in the framework of the cranked Woods-Saxon-Strutinsky approach predict a coexistence of superdeformed (β₂ = 0.49) and highly-deformed (β₂ = 0.27) shapes. Furthermore, oblate shapes (β₂ = 0.15) are predicted. A study of high-spin states in nuclei around ¹⁴²Gd has, therefore, been carried out with the γ-detector array EUROBALL III. A ⁹⁹Ru target was bombarded with a ⁴⁸Ti beam of 240 MeV produced by the XTU tandem – linear accelerator (ALPI) combination of the Laboratori Nazionali di Legnaro, Italy. In this reaction ¹⁴²Gd is populated with a maximum cross section through the 2p3n channel but neighbouring Tb, Gd, Eu and Sm nuclei are also populated very strongly. In order to carry out an isotopic selection and to increase thus the selectivity of EUROBALL III the charged-particle detector array ISIS, consisting of 40 Si-detector telescopes, has been mounted in the center of the γ-detector array. Approximately 4.5 · 10⁹ high-fold γ-events have been collected, ≈ 60% of which are associated with one or more detected particles. In the analysis a full and particle-gated γ-γ-γ cubes have been sorted. The level scheme of ¹⁴²Gd has been considerably extended and a search for bands of large deformation has been carried out in the nuclei around ¹⁴²Gd. Various types of bands have been found. The previously observed [1] dipole bands in ¹⁴²Gd have been extended. The experiment and the results of the analysis will be described. (Supported by the EU, Volkswagen Foundation, FNP and KBN).

[1] M. Sugawara et al., Z. Phys. A358, 1 (1997)