Radiation Detection Glossary

Alpha Radiation

Radiation that is expressed by a positively charged particle emitted from the nucleus during radioactive decay. Alpha radiation has low penetrating effect and a short range, but it can be harmful if it enters the body through inhalation, ingestion or open lesion.

Beta Radiation

Radiation expressed by a particle ejected from a radioactive atom during the process of atomic decay. Beta radiation particles are smaller and faster than alpha radiation and can penetrate some small distance into human tissue.

Background Radiation

Also known as Ambient Radiation it is radiation in the natural environment to which people are exposed every day.


A unit used to measure radioactivity. One Becquerel is the amount of a radioactive material which will undergo one transformation in one second.

Chronic Exposure

Cumulative exposure to a radioactive source over a long period of time, which can possibly resulting in negative health effects.

Cumulative Dose

The total dose resulting from repeated or continuous tissue exposures, to ionizing radiation.


A unit of measurement that describes how much radioactivity is contained in a sample of material. The curie unit is based on the rate of decay of one gram of radium.

Depleted Uranium

Uranium containing less than 0.7% uranium-235, the amount similar to that found in natural uranium.

Dirty Bomb

A device designed to spread radioactive material using a conventional explosive as dispersal vehicle. A dirty bomb kills or injures people less through the initial blast of the conventional explosive and more my spreading radioactive contamination over possibly a large area.


A general term for the quantity of radiation or energy absorbed. Rads represent the energy absorbed from the radiation in a gram of any material. The biological dose or dose equivalent is a measure of the biological damage to living tissue from the radiation exposure, and is measured in Rem or Sieverts.

Dose Equivalent

The product of absorbed dose in tissue multiplied by a quality factor expressed numerically in Rems or Sieverts.

Dose Rate

The ionizing radiation dose that is delivered per unit of time. It is often used to indicate the level of hazard from a radioactive source.


A small portable instrument for measuring and recording the total accumulated dose of ionizing radiation a person receives.

Electromagnetic Radiation

A traveling wave motion resulting from changing electric or magnetic fields. Types of electromagnetic radiation include x-rays, gamma rays, radar and radio waves.


A negatively charged particle orbiting the nucleus of an atom. Electrons determine the atom’s chemical properties.

Exposure rate

A measure of the ionization produced in air by x-rays or gamma rays per unit of time (frequently expressed in roentgens per hour).

Gamma Radiation

A type of electromagnetic radiation of the most penetrating variety. Gamma rays are produced during the process of nuclear decay.

Geiger counter or G-M Meter

An measuring instrument used to detect and measure radiation. It consists of a gas-filled tube containing electrodes. When ionizing radiation passes through the tube, it free electrons are collected producing a pulse of current that is measured or counted.


The international system unit of absorbed radiation dose.


An electrically charged atomic particle, atom or molecule. Such a particle is in an unbalanced state.


The process by which electrons are stripped from an atom, creating an ion.

Ionizing Radiation

Radiation capable of producing ions or charged particles. Ionizing radiation includes alpha, beta, gamma, and X-rays.

Non-Ionizing Radiation

Commonly utilized radiation which does not alter sub-atomic structure of matter it interacts with. Typical examples are microwaves, infrared radiation, and electromagnetic radiation.

Lethal Dose

A radiation dose expected to cause death to one-half of an exposed population within one month. Such a dosage ranges typically extends from 400 to 450 Rem (4 to 5 Sieverts) received over a short period of time.

Non-Ionizing Radiation

A type of radiation, which includes microwaves and visible light, and which does not have sufficient energy to strip electrons from their orbits around the nucleus.


An elementary particle with a positive charge located in the nucleus of an atom.


The unit of radiation absorbed dose, which represents the amount of energy derived from any type of ionizing radiation deposited into any material.


Energy emitted by atoms in a changing state. Radiation can take its form as electromagnetic waves, heat, light, X-rays, Gamma rays, or streams of alpha particles, beta particles, neutrons or protons.

Radioactive Decay

Change in an atom by the spontaneous emission of alpha, beta, or gamma radiation emission or by radioactive decay and radioactivity. The change results in a less energetic and more stable nucleus.


The spontaneous emission of atomic particles or high-energy radiation from the nucleus of an unstable atom.


Acronym that stands for “Roentgen Equivalent Man”. A unit measuring the effects of ionizing radiation on human tissue. The dose equivalent in rems is equal to the absorbed dose in rads multiplied by the coefficient of the type of radiation.


The unit measuring exposure to X-rays or gamma rays.


The tendency of some Geiger counters fail in the event of a reading that exceeds the maximum operating range of the instrument. Some instruments are rated with anti-saturation circuitry to 100 times the operating range, which is derived through an arithmetical calculation.


The Sievert is a unit used to derive a quantity called equivalent dose. This relates the absorbed dose in human tissue to the effective biological damage of the radiation. One Sv is equal to 100 rem.


A very high-energy type of penetrating electromagnetic radiation with a wavelength much shorter than visible light. They are related to Gamma rays, but at a slightly different wavelength. Their effect on human tissue is the same as Gamma.