Eur. Phys. J. A 16, 159-169 (2003)
DOI: 10.1140/epja/i2000-10158-9

Narrow elastic-scattering states at high excitation in 

K.-M. Källman¹, M. Brenner¹, V.Z. Goldberg², T. Lönnroth¹, P. Manngård¹, A.E. Pakhomov² and V.V. Pankratov<sup>2

1</sup>  Department of Physics, Åbo Akademi, FIN-20500 Turku, Finland
²  Russian Scientific Center "Kurchatov Institute", 123182 Moscow, Russia

kkallman@abo.fi

(Received: 26 June 2000 / Revised version: 13 June 2002 / Published online: 4 February 2003)

Abstract
The excitation function and angular distributions of elastic -particle scattering on have been measured in the laboratory energy range 6-28 MeV using a backscattering technique on a thick target, yielding a continuous energy distribution. More than 200 narrow states are observed, with widths in the range -100 keV at excitation energies E^* =13-32 MeV. Angular distributions at backward angles were measured, and angular momentum values of more than 83 states have been deduced. The analysis gives spin-parities , -partial widths and reduced widths of the narrow high-lying resonant states in . The experimentally observed states display both the negative- and the positive-parity rotational-like sequences with seemingly no parity splitting, a finding which is at variance with most potential-model predictions. The deduced effective moment of inertia indicates a more extended structure than the ground-state configuration. The observed strength of each -value is analyzed in terms of an underlying split doorway state of Lorentzian form, which yields an interpretation as fragmented rotational states.

PACS
21.10.Hw - Spin, parity, and isobaric spin.
24.10.-i - Nuclear-reaction models and methods.
24.30.-v - Resonance reactions.
25.55.-e - -, -, and -induced reactions.

© Società Italiana di Fisica, Springer-Verlag 2003