Ultrasound-induced echoes in the nuclear-exciton decay utilising synchrotron radiation Bragg-scattered by a quartz crystal

The time evolution of the coherent decay of the nuclear exciton induced by 14.4 keV synchrotron radiation was observed with a system of two stainless-steel resonance absorbers. In between these foils, the radiation was Bragg-scattered from a vibrating quartz crystal. The ultrasound-modulated radiation disrupts the coherent superposition of the radiation from both targets. However, at times corresponding to multiples of the ultrasound period, spikes or dips in the decay were observed which are interpreted as ultrasound-induced echoes.