Nuclear superradiance into anomalous emission channels
Hung, Nguyen V.
Hannon, James P.
Master of Arts
This thesis investigates the coherent spontaneous emission, or superradiance, of initial nuclear excitations into anomalous emission (Borrmann modes) for a perfect needle-shaped crystal sample. The anomalous emission effect, which suppresses the nonresonant photoelectric absorption of gamma rays emitted in the Borrmann modes without destroying the coupling of these modes with the nuclei, allows emission of gamma rays from Mossbauer emitters within a Borrmann depth from the crystal surface, greatly enhanced over the ordinary photoelectric absorption length. Two approaches are discussed. First we treat the superradiance emission semiclassically, solving Lamb's selfconsistent field equations for the emitted intensity in the superradiance limits rather than in the usual rate equation approximation in laser theory. Next we apply the quantum statistical theory developed by R. Bonifacio et al., after incorporating necessary modifications to allow for various multipole emission into Borrmann modes. Finally we attempt to determine criteria that would characterize a good isotope for superradiance.