Bochum 1998 – scientific programme
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HK: Hadronen und Kerne
HK 43: Nuclear Forces III, Reactions, Resonances
HK 43.4: Group Report
Tuesday, March 17, 1998, 18:00–18:30, J
Interference of nuclear states via the continuum and giant resonances in hot nuclei* — •I. Rotter1,2, V.V. Sokolov3, D.V. Savin3, and M. M"uller4 — 1Technische Universit"at Dresden, Institut f"ur Theoretische Physik, D-01062 Dresden — 2Max-Planck-Institut f"ur Physik komplexer Systeme, D-01187 Dresden — 3Budker Institute of Nuclear Physics, 630090 Novosibirsk, Russia — 4Centro Internacional de Ciencias, Cuernavaca, Mexico
A phenomenological schematic model of multipole giant resonances is concidered [1] which treats the external interaction of the resonance states via common decay channels on the same footing as the internal residual interaction. The external coupling becomes important at high excitation energy (see e.g. [2]). Here, the cross section pattern is governed by the interplay of two types of collectivity, the internal and the external one. The interplay influences significantly the distribution of the dipole strength over the single states as well as their widths and positions in energy. In particular, an appreciable part of the dipole strength is transferred, at a critical value of the level density, to a narrow resonance state. This state as well as the resonance state on which the dipole strength was originally concentrated, are shifted to an energy below the energy of the giant dipole resonance.
The photoemission turns out to be most sensitive to this interplay of internal and external collectivity. The restructuring towards lower energy and apparent quenching of the dipole strength under critical conditions (realized at high excitation energy) are reflected in the photo-nuclear reaction cross section.
Both the shift down of a part of the dipole strength and the loss of
some part of the dipole strength itself are discussed at present
in connection with experimental results obtained for the excitation
of collective modes at about 250 MeV excitation energy in heavy
nuclei (see e.g. [3]). The different existing theoretical approaches can only
partly explain the experimental situation observed. The interference
phenomena due to the interaction via common decay channels, which is
discussed by us, point to a new mechanism which could
shed additional light on the saturation of the γ
multiplicity observed experimentally at high excitation energy.
[1] V.V. Sokolov, I. Rotter, D.V. Savin and M. Müller, Phys. Rev.
C 56, 1031 and 1044 (1997)
[2] M. Müller, F.M. Dittes, W. Iskra and I. Rotter, Phys. Rev. E 52, 5961
(1995)
[3] T. Suomijärvi et al., Phys. Rev. C 53, 2258 (1996)
*Supported by DFG (Ro 922) and DAAD