Glossary cont'd - hdbk110997

DOE-HDBK-1109-97

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

Instructor=s Guide

installation and contains additional shielding such that the dose equivalent rate at any accessible area 2

inches (5 cm) from the outside surface of the enclosure shall not exceed 0.5 mrem in any 1 hour.

Exposure: A measure of the ionization produced in air by X-ray or gamma radiation defined up to 3

MeV. It is the sum of the electrical charges of all of the ions of one sign produced in air when all electrons

liberated by photons in a volume element of air are completely stopped in the air, divided by the mass of

the air in the volume element. The unit of exposure is the roentgen (R) and is defined for photons with

energy up to 3 MeV.

External surface: An outside surface of a cabinet X-ray system, including the high-voltage generator,

doors, access panels, latches, control knobs, and other permanently mounted hardware, and including the

plane across any aperture or port.

Fail-safe design: A design in which the failure of any single component that can be realistically

anticipated results in a condition in which personnel are safe from exposure to radiation. Such a design

should cause beam-port shutters to close, primary transformer electrical power to be interrupted, or

emergence of the primary X-ray beam to be otherwise prevented upon failure of the safety or warning

device.

Flash X-ray unit: A radiation-producing device that can produce nanosecond bursts of high-intensity X-

ray radiation.

Floor: In this context, the underside external surface of the cabinet.

Fluorescence analysis: Analysis of characteristic X-rays and the X-ray emission process.

Gauge: A device that produces ionizing radiation for the purpose of measuring particular properties of a

system.

Half-value layer (HVL): The thickness of a specified substance that, when introduced into a beam of

radiation, reduces the dose rate by one-half.