Scattering cont'd - 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

target, but a portion is radiated away as X-rays. As

stated previously, the electrical power of an

electrical circuit is given by:

P=VxI

P is the power in watts or joules/second, V is the

potential difference in volts, and I is the current in

amps.

The power developed in the anode of an X-ray tube

can be calculated using this relationship. Consider

a 150 kilovolt (kVp) machine, with a current of 50

milliamps (ma).

P = [150,000 (V)] [0.050 (I)] = 7500 W.

This is about the same heat load as would be found

in the heating element of an electric stove. This

power is delivered over a very short period of time,

typically less than 1 second. More powerful X-ray

machines use higher voltages and currents and may

develop power as high as 50,000 W or more.

Cooling the anode is a problem that must be

addressed in the design of X-ray machines.

Tungsten is used because of its high melting

temperature, and copper is used because of its

excellent thermal conductivity. These elements

may be used together, with a tungsten anode being

embedded in a large piece of copper.

The percentage of the power transformed to X-rays

can be estimated by the following relationship: