A Model Study of the Strength Distribution for a Collective State Coupled with Chaotic Back.pdf
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February 9, 2008
3 A Model Study of the Strength Distribution for a
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9 Collective State Coupled with Chaotic Background System
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N Hirokazu AIBA and Toru SUZUKI
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Koka Women’s College, 38 Kadono-cho Nisikyogoku, Ukyo-ku, 615 Kyoto, Japan
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4 ∗Research Center for Nuclear Physics, Osaka University, 567 Ibaraki, Japan
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u ABSTRACT
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i We consider a model in which a collective state couples to a large number of
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r background states. The background states can be chosen to have properties which
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are classically characterized as regular or chaotic. We found that the dynamical
nature of the background system considerably affects some fluctuation properties
of the strength function.
1. Introduction
Over the last twenty years a number of new giant resonances have been found
in a broad range of the nuclear table. They are coherent particle-hole excitations
carrying a large fraction of the energy weighted sum rules. In most cases they are
embedded in a continuum and are damped due to particle escape. At not much
high excitation energies, however, the damping of giant resonances is dominated by
spreading, i.e., by coupling to a huge number of background states. It is also known
that there is in some cases a mechanism which reduces the width of resonances [1].
In many theoretical calculations the spreading of a collective particle-hole state
is accounted for by coupling to more complicated states, e.g., two-particle two-hole
states. As the number of these states in heavy nuclei becomes enormously large it
is necessary t
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