Is Fermi’s Golden Rule Always True for Compton Scattering?

Abstract

We present an example of a situation where Fermi’s golden rule does not apply, even if an unstable quantum system decays exponentially. The work is inspired by the recent experiments by Chatzidimitriou-Dreismann and co-workers on reduction of the neutron Compton scattering cross-section in hydrogenated compounds. Although full quantitative explanation of these experimental results is still to be accomplished, our preliminary results show a possibility of strong modification of the scattering cross-section.