Filtration - hdbk110997

DOE-HDBK-1109-97

Radiological Safety Training for Radiation-Producing (X-Ray) Devices

Student's Guide

iii. Filtration.

Low- and high-energy photons are sometimes referred to as soft and hard X-rays,

respectively. Because hard X-rays are more penetrating, they are more desirable for

radiography (producing a photograph of the interior of the body or a piece of apparatus).

Soft X-rays are less useful for radiography because they are largely absorbed near the

surface of the body being X-rayed. However, there are medical applications where soft X-

rays are useful.

A filter, such as a few millimeters of aluminum, or copper may be used to harden the

beam by absorbing most of the low-energy photons. The remaining photons are more

penetrating and are more useful for radiography.

In X-ray analytical work (X-ray diffraction and fluorescence), filters with energy selective

absorption edges are not used to harden the beam, but to obtain a more monochromatic

beam (a beam with predominantly one energy). By choosing the right element, it is

possible to absorb a band of high-energy photons preferentially over an adjacent band of

low energy photons.

(Insert facility-specific examples of filtration.)