Investigation of nuclear scissors like vibration

The scissors mode is a collective, orbital M1 excitation found in deformed atomic nuclei, and is considered an oscillation of the protons against the neutrons in a scissors like fashion. In recent measurements of the scissors mode in radiative decay experiments, transition strengths were observed that were double that expected from systematics established from measurements using nuclear resonance fluorescence (NRF). Additional strength in NRF measurements can only be present as heretofore unobserved branching or fragmentation of the scissors mode. Such possibilities were investigated in a transmission NRF measurement on the deformed ¹⁸¹Ta using a quasi-monoenergetic γ-ray beam generated by laser Compton scattering at High Intensity γ-ray Source (HIγS) facility, Duke University. A large branching of fragmented small resonances to excited states was discovered. The results could reconcile the scissors mode strength observed in NRF measurements with the expectations for enhanced scissors mode strength from radiative decay experiment. (author)