Studies of nuclear levels around 7.4 MeV using a high resolution γ-monochromator

A variable-energy γ-source is obtained by nuclear resonance scattering of neutron-capture γ-rays through various scattering angles. An energy resolution of less than 10-6 is obtained. Pb and Cd targets were employed to scatter the 7.279 and 7.632 MeV photons, respectively, of the neutron capture γ-rays of Fe. Variation of the angle of the resonantly scattered photons between 600-1500 permits an energy scan of approximately 370 eV (for Pb) and approximately 760 eV (for Cd) in any absorber. Thus nuclear energy levels in 139La, Ce, Cd and 209Bi absorbers were photoexcited and the corresponding values of gGAMMA0 were extracted from the measured absorption curve. (Auth.)