RadNet
Glossary
Below are definitions for terms used in this manual. For a more expanded glossary of radiation terminology, visit http://www.epa.gov/radiation/glossary/index.html.
Alpha Radiation: Energetic, positively charged particles consisting of two protons and two neutrons. Alpha particles are commonly emitted in the radioactive decay of the heaviest radioactive elements such as uranium-238, radium-226, and polonium-210. Alpha particles have a very short range in air and are easily stopped by something as thin as a layer of skin or a piece of paper.
Ambient Radiation: Radiation that is naturally occurring or is already present in a specified area. Ambient radiation is sometimes referred to as “background radiation” or “environmental radiation.”
Beta Radiation: Fast moving electrons emitted from the nucleus during radioactive decay. Beta particles are emitted from man-made and natural radiation sources, such as tritium, carbon-14, and strontium-90.
Beta Particle Energy: In the form of speed, a beta particle has energy that causes harm to living cells. When transferred, this energy can break chemical bonds and form ions. The beta particle energy can be used like a fingerprint to help identify which radionuclide is being detected.
Cosmic Radiation: Radiation originating from outer space and the sun. Contributing about 9% of the background radiation level on Earth, cosmic radiation is part of our natural environment, and we are constantly exposed to a certain amount of ionizing radiation.
CPM: Counts Per Minute. The number of decays of radioactive material that are detected in one minute.
Deployable Monitor: Mobile monitors that can be moved for use during drills, alerts, or an emergency event.
Fixed Monitor: Permanently positioned and continuously operating monitors that sample radioactivity in the air.
Gamma Radiation: Weightless packets of energy called photons. Gamma rays often accompany the emission of alpha or beta particles from a nucleus. They have neither a charge nor a mass and are very penetrating. One source of gamma rays in the environment is naturally-occurring potassium-40. Man-made sources include cobalt-60 and cesium-137.
Gamma Radiation Energy: The energy of a gamma photon is approximately 10,000 times more energetic than a photon emitted in the visible range of the electromagnetic spectrum. Gamma rays can travel vast distances and penetrate entirely through the human body.
Gamma Spectroscopy: The analysis of photons (X-ray or Gamma) emitted from radioactive atoms as they undergo transformations to more stable isotopes. The NaI detector and multi-channel analyzer in a fixed RadNet monitor provide laboratory information on the quantity and energy of photons emitted by radioactive material captured on the air filter. These data may then be used by trained spectroscopists to identify unknown radioisotopes in the sample.
Gross: In this manual, the term “gross,” as in “Gross Count Rate,” is synonymous with “total.”
Half-life: A concept used to measure the rate of a nuclide’s radioactive decay. It is the time required for the disintegration of one half of the radioactive atoms that are present when the measurement starts.
Ionizing Radiation: Energy in the form of waves or particles that has enough force to remove electrons from atoms.
Progeny: As radioactive atoms decay, the compositions of their nuclei change. A change in the number of neutrons will transform the atom into an isotope of the same element. A change in the number of protons will cause the atom to change into a different element. These resultant transformed atoms are referred to as “progeny” of the parent element.
RadNet: The United States’ only comprehensive network for monitoring radioactivity and ionizing radiation in the environment with more than 200 sampling stations nationwide. Formerly known as the Environmental Radiation Ambient Monitoring System (ERAMS), RadNet has continuously monitored multiple media, including air, precipitation, drinking water, and milk since its inception in 1973. The RadNet CDX Public Web site provides access to the near real-time air monitoring component of RadNet. Other information regarding RadNet is available at http://www.epa.gov/narel/radnet/.
Region of Interest (ROI): A specific range of gamma energies. The fixed RadNet monitors’ computer system breaks the gamma energy spectrum into ten contiguous Regions of Interest.