A Model Study of the Strength Distribution for a Collective State Coupled with Chaotic Back.pdfVIP

February 9, 2008 3 A Model Study of the Strength Distribution for a 9 9 Collective State Coupled with Chaotic Background System 1 v o ∗ N Hirokazu AIBA and Toru SUZUKI 7 2 Koka Women’s College, 38 Kadono-cho Nisikyogoku, Ukyo-ku, 615 Kyoto, Japan 1 v 4 ∗Research Center for Nuclear Physics, Osaka University, 567 Ibaraki, Japan 3 0 1 1 3 9 / h t - l c u ABSTRACT n : v i We consider a model in which a collective state couples to a large number of X r background states. The background states can be chosen to have properties which a 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