Abstract
Anisotropies of longitudinal and transverse ultrasonic attenuations in a pure single crystal of niobium were measured near H c 2 at temperatures above 4.2 K. Separation of the anisotropy due to the excitation spectrum of quasiparticles from the crystallographic anisotropy ( H c 2 -anisotropy) was made and the H c 2 -anisotropy measured by using 70 MHz longitudinal waves was found in qualitative agreement with theory regarding its angular and temperature dependences. The experimental data of the anisotropies of the longitudinal wave attenuations at 70 MHz agree qualitatively with both the theories of Maki-Kinder and Houghton-Maki at a lower temperature ( T / T 0 ≡ t =0.70) whereas at a higher temperature ( t =0.89) they do not resemble any of two theories. The anisotropies of the transverse wave attenuations differ from any of these two theories especially at higher temperature.
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