Current - hdbk110997

DOE-HDBK-1109-97

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

Instructor=s Guide

Lesson Plan

Instructor=s Notes

accelerating voltage of the X-ray device is often

described in terms of the peak kilovoltage or kVp.

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.