Nuclear resonance scattering from the first excited states in ${\mathrm{F}}^{19}$ and ${\mathrm{Mn}}^{55}$ has been studied with the bent-diffraction-crystal monochromator. The experiment was performed by observing the scattered radiation from nuclei exposed to nearly monoenergetic x rays selected by crystal diffraction from the bremsstrahlung spectrum of an x-ray tube. Gamma rays scattered at 135° from samples of lithium fluoride and manganese placed in the diffracted beam were observed as a function of the incident photon wavelength. With the lithium fluoride sample three measurements were made under different experimental conditions. In each case pronounced resonance peaks 10 to 15% above background were observed. A least-squares analysis of the data gives 109.894±0.005 keV for the energy position of the first excited level in ${\mathrm{F}}^{19}$. From the observed yield the width of this level was deduced to be (5.1±0.7)×${10}^{-7\mathrm{}}$ eV. Measurements with a ${\mathrm{Mn}}^{55}$ scattering sample gave 125.95±0.01 keV for the position of the first excited level and (1.1±0.3)×${10}^{-6\mathrm{}}$ eV for the resonance width.

• Received 16 July 1962

DOI:https://doi.org/10.1103/PhysRev.128.2334