X-ray microbeams based on Kumakhov polycapillary optics and its applications: Analytical consideration 27
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X-ray microbeams based on Kumakhov polycapillary optics and its applications: Analytical consideration 27

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At a distance of 10 mm from the exit face of a polycapillary, the diameter of the beam
dout = d0 + 2 finθcr = 17 + 2 × 10 mm × 4 mrad = 97 μm, and the factor of increase
in flux density is 4 × 10−3/48.5 × 10−6/(0.5 + 10 + 10) × 10−3 2 × 0.7 ≈ 2. At
a distance of 20 mm from the exit of a polycapillary, the diameter of a beam will be
17 μm + 2 × 20 mm × 4 mrad = 177 μm, and factor of increase in flux density is
4 × 10−3/88.5 × 10−6/(0.5 + 10 + 20) × 10−3 2 × 0.7 ≈ 1.33, and for a distance
of 40 mm the factor is 1.006. With a distance of 41 mm, the factor of increase will be
below 1.
 
The complete expression for an estimation of change of gain of radiation flux density
in the exit beam on distance from an exit will be
G = θcr ( fin + L + fout)
rbeam

2
× Tr = θcr ( fin + L + fout)
rout + foutθcr

2
× Tr, (12)
where rout = r0 + dcap + finθcr is the radius of the exit beam and r0 denotes the radius
of focal spot of the X-ray tube.