X-Ray Production - hdbk110997

DOE-HDBK-1109-97

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

Student's Guide

As discussed in Module 101, the distinction between X-rays and gamma rays is their

origin, or method of production. Gamma rays originate from within the nucleus; X-rays

originate from atomic electrons and from free electrons decelerating in the vicinity of

atoms (i.e., bremsstrahlung).

In addition, gamma photons often have more energy than X-ray photons. For example,

diagnostic X-rays are about 40 keV, whereas gammas from cobalt-60 are over 1 MeV.

However, there are many exceptions. For example, gammas from technicium-99m are

140 keV, and the energy of X-rays from a high-energy radiographic machine may be as

high as 10 MeV.

X-RAY PRODUCTION

Radiation-producing devices produce X-rays by accelerating electrons through an electrical

voltage potential and stopping them in a target. Many devices that use a high voltage and a

source of electrons produce X-rays as an unwanted byproduct of device operation. These are

called incidental X-rays.

Most X-ray devices emit electrons from a cathode, accelerate them with a voltage, and allow

them to hit an anode, which emits X-ray photons.

Bremsstrahlung.

When electrons hit the anode, they decelerate or brake emitting bremsstrahlung (meaning

braking radiation in German). Bremsstrahlung is produced most effectively when small

charged particles interact with large atoms such as when electrons hit a tungsten anode.

However, bremsstrahlung can be produced with any charged particles and any target. For

example, at research laboratories, bremsstrahlung has been produced by accelerating

protons and allowing them to hit hydrogen.