SPring-8, the large synchrotron radiation facility

Date&Time: 16:00-17:00, 21 July,2004

Speaker: Prof. Harry Lipkin
Affiliation: Weizmann Institute of Science, Israel

Abstract:
　　The role of coherence and recoil effects in resonant nuclear scattering is reviewed in the light of more complicated new types of experiments that are being considered. These include the breakdown of the common expression f = exp (-k^2<x^2> and coherence effects when more than one excitation can occur in a given sample. The application of sum rules in the analysis of data is discussed.
　　An apparent contradiction between two equally valid descriptions of multiple excitation is clarified together with the difference between coherent and incoherent multiple excitations. When many nuclei in a given sample are excited independently, the radiation is known to decay exponentially with the normal lifetime. But a state with n-nuclei excited can also be considered as a single quantum state whose decay to a state with n-1 nuclei excited is described by time-dependent perturbation theory as an exponential decay with a lifetime n-times shorter than the normal lifetime.