Filtration - hdbk110997

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