X-ray Energy Dependence of the Properties of the Focused Beams Produced by Polycapillary X-ray Lens

Abstract

We investigated x-ray energy distribution in an x-ray microbeam produced by a polycapillary x-ray lens in combination with a sealed-type x-ray tube. This polycapillary x-ray lens has an output focal distance (OFD) of approximately 15 mm. The size of the x-ray microbeam and its OFD were estimated by using a wire scanning method. In our case, the sizes of the x-ray microbeams at the output focal distance were 49 µm for Mo L_α, 36 µm for W L_α, and 28 µm for Mo K_α. The spot sizes depend on the energy of the x-ray fluorescence. The reason for the energy dependence is that x-ray capillary optics is based on the principle of propagation through glass capillaries by means of x-ray total external reflection. The evaluated OFD values of Mo L_α and Mo K_α were slightly changed in 17 µm. However, a deviation of 100 µm from the OFD caused only a 3% increase of the focal spot size. Therefore, we concluded that the OFD showed no significant dependence on x-ray energy.