2018 Impact factor 2.481
Hadrons and Nuclei
Eur. Phys. J. A 16, 159-169 (2003)
DOI: 10.1140/epja/i2000-10158-9

Narrow $\chem{\alpha+ {}^{28}Si}$ elastic-scattering states at high excitation in  $\chem{^{32}S}$

K.-M. Källman1, M. Brenner1, V.Z. Goldberg2, T. Lönnroth1, P. Manngård1, A.E. Pakhomov2 and V.V. Pankratov2

1  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 $\alpha$-particle scattering on $\chem{^{28}Si}$ 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 $\sim 30$-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 $J^\pi$, $\alpha$-partial widths $\Gamma_\alpha$ and reduced widths of the narrow high-lying resonant states in $\chem{^{32}S}$. 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 $\ell$-value is analyzed in terms of an underlying split doorway state of Lorentzian form, which yields an interpretation as fragmented rotational $\alpha + \mathrm{^{28}Si}$ 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 - $\chem{^{3}H}$-, $\chem{^{3}He}$-, and $\chem{^{4}He}$-induced reactions.

© Società Italiana di Fisica, Springer-Verlag 2003