Self-absorption with quasi-monochromatic photon beams

We present a new experimental technique to perform self-absorption experiments in combination with nuclear resonance fluorescence using a quasi-monochromatic photon beam for the determination of absolute level widths of excited low-spin states. By measuring simultaneously at two target positions the amount of absorbed photon intensity is directly measured in a single experiment, which strongly reduces systematic uncertainties and reduces the amount of needed beam time by a factor of two. In addition the method does not rely on a given shape of the energy profile of the photon beam and, thus, can also be applied with quasi-monochromatic beams produced via Laser-Compton-Backscattering (LCB). Due to the strongly reduced background with these kind of photon beams this new method in combination with LCB promises a highly improved sensitivity for self-absorption experiments compared to experiments using bremsstrahlung.