On the texture problem in Mossbauer spectroscopy

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Abstract
The authors discuss the theory of preferred orientation, determined by Mossbauer spectroscopy using unpolarised dipole radiation in the case of axial hyperfine interaction. A previous expansion of the texture function D( theta , phi ) in a series of spherical harmonics, involving five independent parameters, can be reduced by convenient rotation of the reference axes: in any case, there is an orthogonal set of 'principal axes' for which texture respects D2h symmetry. As a consequence, any texture can be described through three angular parameters and three numbers Nx, Ny, Nz representing 'populations' of spins parallel to the principal axes (Nx+Ny+Nz=1). In addition, they give general methods of obtaining texture-free spectra. Examples are given.