Anisotropy of ³⁹K binding in C₈K studied by nuclear resonance photon scattering

A new technique employing nuclear resonance photon scattering of bremsstrahlung has been used for studying the anisotropic binding of K atoms in the first-stage intercalated compound C₈K. The bremsstrahlung was obtained using an electron beam with E_e=8.5 MeV. The scattered intensities from the 5.262- and 6.334-MeV levels in ³⁹K and from the 4.439-MeV level in ¹²C were found to be dependent on the c-axis orientation of C₈K with respect to the photon beam in a nuclear self-absorption measurement. This behavior is interpreted in terms of the anisotropy in the Doppler broadenings of the ³⁹K and ¹²C nuclear levels caused by the zero-point energies of the C₈K vibrational modes along and perpendicular to the graphite basal planes. The measured anisotropy was found to be somewhat higher than that calculated from the known vibrational spectra in C₈K.