DOI 10.1140/epja/i2003-10234-8 Eur. Phys. J. A 22, 231–239 (2004) THE EUROPEAN PHYSICAL JOURNAL A New bands and spin-parity assignments in 111 Ru W. Urban 1, a , T. Rz¸ aca-Urban 1 , Ch. Droste 1 , S.G. Rohozi´ nski 1 , J.L. Durell 2 , W.R. Phillips 2 , A.G. Smith 2 , B.J. Varley 2 , N. Schulz 3 , I. Ahmad 4 , and J.A. Pinston 5 1 Faculty of Physics, Warsaw University, ul. Ho˙ za 69, PL-00-681 Warsaw, Poland 2 Schuster Laboratory, Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK 3 Institut de Recherches Subatomiques UMR7500, CNRS-IN2P3 et Universit´e Louis Pasteur, F-67037 Strasbourg, France 4 Argonne National Laboratory, Argonne, IL 60439, USA 5 Laboratoire de Physique Subatomique et de Cosmologie, IN2P3-CNRS/Universit´e Joseph Fourier, F-38026 Grenoble Cedex, France Received: 8 July 2003 / Revised version: 18 May 2004 / Published online: 9 November 2004 – c  Societ` a Italiana di Fisica / Springer-Verlag 2004 Communicated by D. Schwalm Abstract. The 111 Ru nucleus, populated in the spontaneous fission of 248 Cm has been studied by means of prompt gamma spectroscopy using the EUROGAM2 array. Spin and parity assignments, based on angular correlations, linear polarization, and conversion coefficient measurements differ from those available in the literature. New bands are reported, which incorporate γ transitions seen previously but not placed in the scheme of 111 Ru or placed incorrectly. The bands are interpreted as neutron excitations into subshells originating predominantly from the h 11/2 , g 7/2 and s 1/2 spherical orbitals. The s 1/2 band, strongly mixed with the d 3/2 , d 5/2 and g 7/2 configurations, is observed for the first time in this region. PACS. 23.20.Lv γ transitions and level energies – 21.60.Cs Shell model – 25.85.Ca Spontaneous fission – 27.60.+j 90 ≤ A ≤ 149 1 Introduction In our previous study of the neutron-rich (N ∼ 70) Ru nuclei we have demonstrated that even-even Ru isotopes with masses from A = 108 up to A = 114 exhibit features characteristic of triaxial deformation [1]. Such a behavior is expected in the region between strongly deformed nu- clei around Z = 40 and spherical nuclei at Z = 50. Tran- sitional in character, ruthenium nuclei are moderately de- formed and susceptible to various distortions, depending on the details of the underlying single-particle structure. It is therefore of prime importance to identify single-particle levels near the Fermi level in these isotopes, before at- tempting any detailed theoretical interpretation. Information about single-particle levels can be ob- tained from studies of odd-A nuclei. Such studies require a good knowledge of experimental decay schemes as well as unique identification of spins and parities of excited levels. We have developed techniques, which provide such data for the neutron-rich fission-fragment nuclei [2,3]. In this paper we report on the experimental investigation of the single-particle structure of 111 Ru, where we have identi- fied bands based on orbitals close to the Fermi level in a e-mail: urban@fuw.edu.pl this nucleus. Among them there is a complex 1/2 + band, which is observed for the first time in this region. The new experimental data on 111 Ru provides grounds for further tests of the theoretical model used to describe even-even Ru isotopes, where pairing vibrations were in- troduced as a new degree of freedom, improving the de- scription of even-even Ru nuclei, as compared to previous pictures [1,4]. It is interesting to check how this model will perform in the odd-A ruthenium isotopes. 2 Data analysis and the results The level scheme of 111 Ru, first deduced from a prompt- gamma measurement [5], has been recently reinvestigated in five reports [6–10], which partially contradict each other. In the prompt-gamma study [6] the authors have extended the level scheme of 111 Ru reported in [5] and pro- posed that the observed scheme is related to the excitation of the νh 11/2 orbital, though they did not specify which subshell is active. Because of the similarity of 111 Ru level scheme to that of the better known 109 Ru, they guessed that the 392.1 keV level in 111 Ru has spin and parity I π = 11/2 - . No spin-parity assignments were proposed for the lower-lying levels. The authors reported some angular