The Bremsstrahlung photons generated within the target material are attenuated as
they pass through, typically, 50 microns of target material. The beam is further
attenuated by the aluminum or beryllium vacuum window. The results are the
elimination of the low energy photons, 1 keV through 15 keV, and a significant
reduction in the portion of the spectrum from 15 keV through 50 keV. The spectrum
from an X-ray tube is further modified by the filtration caused by the selection of filters
used in the setup.