Current - hdbk110997

DOE-HDBK-1109-97

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

Student's Guide

A voltage of 50 kVp will produce a spectrum of X-ray energies with the theoretical

maximum being 50 keV. The spectrum of energies is continuous from the maximum to

zero. However, X-ray beams are typically filtered to minimize the low-energy

component. Low-energy X-rays are not useful in radiography, but can deliver a

significant dose.

Many X-ray devices have meters to measure voltage. Whenever the voltage is on, a

device can produce some X-rays, even if the current is too low to read.

ii. Current.

The total number of photons produced by an X-ray device depends on the current, which

is measured in amperes, or amps (A). The current is controlled by increasing or

decreasing the number of electrons emitted from the cathode. The higher the electron

current, the more X-ray photons are emitted from the anode. Many X-ray devices have

meters to measure current. However, as mentioned above, X-rays can be produced by

voltage even if the current is too low to read on the meter. This is sometimes called dark

current. This situation can cause unnecessary exposure and should be addressed in SOPs

or work documents.

iii. Determining Electrical Power.

Power, which is measured in watts (W), equals voltage times current (P = V x I). For

example, a 10 kVp device with a current of 1 mA uses 10 W of power.

(Insert facility-specific examples for determining electrical power.)

INTERACTION WITH MATTER

Scattering.

When X-rays pass through any material, some will be transmitted, some will be absorbed,

and some will scatter. The proportions depend on the photon energy, the type of material

and its thickness.