Effect of Voltage and Current on Photon Energy and Power

DOE-HDBK-1109-97

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

Instructor=s Guide

Lesson Plan

Instructor=s Notes

EFFECT OF VOLTAGE AND CURRENT ON

PHOTON ENERGY AND POWER

It is important to distinguish between the energy of

individual photons in an X-ray beam and the total

energy of all the photons in the beam. It is also

important to distinguish between average power and

peak power in a pulsed X-ray device.

Typically, the individual photon energy is given in

electron volts (eV), whereas the power of a beam is

given in watts (W). An individual 100 keV photon has

more energy than an individual 10 keV photon.

However, an X-ray beam consists of a spectrum (a

distribution) of photon energies and the rate at which

energy is delivered by a beam is determined by the

number of photons of each energy. If there are many

more low energy photons, it is possible for the low

energy component to deliver more energy.

The photon energy distribution may be varied by

changing the voltage. The number of photons emitted

may be varied by changing the current.

Voltage.

The power supplies for many X-ray devices do not

produce a constant potential (D.C.) high voltage but

instead energize the X-ray tube with a time varying

or pulsating high voltage. In addition, since the

bremsstrahlung X-rays produced are a spectrum of

energies up to a maximum equal to the electron

accelerating maximum voltage, the