Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/X-ray filter

An X-ray filter is a device to block or filter out some or all wavelengths in the X-ray spectrum.

X-ray filters are used to block low-energy X-rays during medical x-ray imaging. Low energy X-rays are more likely to be absorbed by the patient's soft tissues. This causes non-stochastic radioactive effects, and does not contribute to image quality.

X-ray filters are used in X-ray crystallography, where crystalline lattice spacing can be determined using Bragg diffraction. The filters allow only a single X-ray wavelength to penetrate through to a target crystal, allowing the resulting scattering to determine the diffraction distance.

Various elemental effects

Results using a molybdenum x-ray generator:

Zirconium - Absorbs bremsstrahlung and K-Beta.
Iron - Absorbs the entire spectra.
Molybdenum - Absorbs bremsstrahlung - leaving K-Beta and K-Alpha.
Aluminium - 'Pinches' bremsstrahlung* and removes third generation peaks.
Silver - Same as aluminium, but to greater extent.
Indium - Same as iron, but to lesser extent.
Copper - Same as aluminium, leaving only first generation peaks.

• Bremsstrahlung pinching is due to the atomic mass. The denser the atom, the higher the X-Ray Absorption. Only the higher energy x-rays pass through the filter, appearing as if the bremsstrahlung continuum had been pinched.
• In this case, molybdenum (Mo) appears to leave K-Alpha and K-Beta alone while absorbing the bremsstrahlung. This is due to Mo absorbing all of the spectra's energy, but in doing so it produces the same characteristic peaks as generated by the target.