The spectral-angular distribution of polarizational bremsstrahlung from relativistic electrons crossing a polycrystalline target is studied theoretically. The effect of substantial growth in the emission spectral density is predicted for photons emitted in the backward direction relative to emitting electron velocity.

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A dynamic diffraction theory of x-ray emission by relativistic electrons crossing a finite-thickness multilayer mirror (e.g., alternating layers of W and B4C) is developed, taking into account both diffracted transition and parametric radiation mechanisms. Simple formulas describing the characteristics of the total emission from either thin nonabsorbing or thick absorbing multilayers are derived. These formulas show that a multilayer radiator can be brighter and more efficient than crystalline ones. Good agreement between theory and prior experimental results is also shown. Thus the theory and its experimental verification demonstrate the possibility of a tunable quasimonochromatic x-ray source whose efficiency can be larger than that of other novel x-ray sources.

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