Anisotropy of the recoilless fraction

Although, as was seen in Section 3.7, a quadrupole split spectrum for a - i transition in a powdered absorber with random orientation should be 

The relative intensity /i//i of the lines involving the [ f and i levels of the excited state (also frequently written as / // ) depends on the angle 6 between the y-ray direction and the principal axis of the electric field gradient from Table 3.2 this can be written as 

However, if the recoilless radiation is anisotropic and the recoil-free fraction / is itself a function of 0, then 

In other words an anisotropic recoilless fraction should produce an asymmetry in the f - i quadrupole doublet which is not angular dependent. 

More recently a detailed study of Mc2SnF2 by Berber and Chandra has shown substantial anisotropy in the recoilless fraction [60]. The ellipsoids of vibration of the tin atom have been measured by X-ray diffraction methods, and the ratio F[/(6)] defined in equation 3.57 was calculated by a lattice dynamical treatment to be 0-72. The corresponding experimental value of 

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