Filtration - DOE-HDBK-1109-97

DOE-HDBK-1109-97

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

Instructor's Guide

Lesson Plan

Instructor's Notes

second, and the useful beam region is several cm

away from the anode target. These design features

lower the dose rates of the useful X-ray beam

significantly. The dose rate in a typical X-ray beam

is estimated in Module 103 section E iii.

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