ASNT IRRSP key terms

Radiation that carries enough energy to knock electrons out of atoms, creating charged ions. Alpha particles, beta particles, gamma rays, and x-rays are examples.

A particle made of two protons and two neutrons, emitted by some unstable nuclei. It travels only a few centimeters in air and is stopped by skin or paper but is harmful if inhaled or swallowed.

A fast-moving electron or positron emitted from a radioactive nucleus. It can travel several meters in air and a few millimeters into tissue, and is stopped by plastic, glass, or thin metal.

A packet of electromagnetic energy released by an unstable nucleus. It has no mass or charge, can travel long distances, and needs dense material such as lead or tungsten for effective shielding.

Electromagnetic radiation produced when fast electrons strike matter, usually inside a tube. X-rays behave like gamma rays but come from electron interactions rather than nuclear decay.

The time it takes for half the radioactive atoms in a sample to decay. Each radionuclide has a unique half-life, which determines how fast its activity falls.

The rate at which radioactive atoms decay, expressed as decays per second. The SI unit is the becquerel; the older unit, the curie, equals 3.7 × 10^10 becquerels.

A rule stating that radiation intensity from a point source falls off with the square of the distance. Doubling the distance cuts the dose rate to one quarter.

The thickness of a material that reduces a radiation beam to half its original intensity. HVLs are used to estimate shielding and calculate exposure rates behind barriers.

An interaction in which a photon strikes a loosely bound electron, gives it part of its energy, and continues in a new direction with less energy. It is important in tissue and shielding.

An interaction in which a photon gives all its energy to an inner electron, which is ejected, and the photon disappears. It dominates at low energies and in high-atomic-number materials.

X-rays produced when fast electrons are slowed or deflected by atomic nuclei. This braking radiation is more significant for high-energy beta emitters and for shielding made of heavy elements.

The energy deposited by radiation per unit mass of material. It is measured in grays, where one gray equals one joule per kilogram, or in rads, where one gray equals 100 rad.

A dose quantity that accounts for how damaging a radiation type is by multiplying absorbed dose by a radiation weighting factor. It is measured in sieverts or rem.

A dose quantity that combines equivalent doses to organs and tissues, weighted by their sensitivity to cancer and hereditary effects. It is used to express overall risk.

The principle of keeping radiation doses as low as reasonably achievable, taking into account economic and practical factors. It relies on good design, training, and work practices.

A health effect whose chance of occurring rises with dose, while its severity does not. Cancer and hereditary effects are treated as stochastic, with no assumed threshold dose.

A health effect that appears only above a threshold dose and becomes more severe as dose increases. Skin burns, cataracts, and acute radiation syndrome are examples.

A number that reflects the relative biological harm of a given radiation type. It is multiplied by absorbed dose to calculate equivalent dose; for example, 1 for gamma rays and 20 for alpha particles.

A device worn by a worker to measure cumulative radiation dose over a monitoring period. Common types are film badges, thermoluminescent dosimeters, and optically stimulated luminescence dosimeters.

A gas-filled detector that gives a large pulse for each ionizing event, making it very sensitive. It is useful for finding contamination but generally cannot measure dose rate accurately.

A gas-filled detector that measures the electric current produced by ionizing radiation. It has a relatively flat energy response and is often used for accurate survey measurements.

A small direct-reading device worn by a radiographer to show accumulated dose immediately. It must be recharged and checked regularly and is not a legal dose record.

The process of comparing an instrument's reading to a known radiation field and adjusting it if needed. Calibrations should be traceable to national standards and are usually required at set intervals.

The short interval after a detector responds to an event when it cannot register another event. Long dead time can cause low readings at high dose rates.

Radioactive material permanently enclosed in a capsule or bonded so it cannot escape. Industrial radiography commonly uses sealed sources of iridium-192, cobalt-60, or selenium-75.

A shield made of dense material that shapes the radiation beam and limits it to the area being examined. It reduces scatter and lowers dose to nearby people.

A flexible tube that carries the sealed source from the exposure device to the point where the radiograph is made. It must be checked for kinks, cuts, and wear.

A flexible cable used to push the sealed source out of the exposure device and through the guide tube, and to pull it back into the shielded position.

A shielded container that holds a radiographic sealed source when it is not in use. It usually has a lock, a source-position indicator, and a connection for the guide tube.

A check for radioactive contamination on or around a sealed source. A wipe sample is counted, and results above a set limit require the source to be removed from service.

The person responsible for carrying out a licensee's radiation protection program. Duties include training, surveys, dosimetry, recordkeeping, and ensuring compliance with regulations.

A worker who has voluntarily told her employer in writing that she is pregnant. The employer must then apply a lower dose limit to protect the embryo or fetus.

Records of the radiation doses received by monitored workers. They must be kept, reviewed, and made available to the worker and regulators as required.

An area where access is controlled to protect people from radiation hazards. Radiography exposures are normally performed inside a restricted area marked with signs and barriers.

A failure in which the sealed source separates from the drive cable and cannot be pulled back into the device. The area must be secured and emergency procedures followed.

A sealed source that is missing or not in its shielded container. It requires immediate notification, surveys, and emergency action to prevent harmful exposure.

The removal of radioactive material from people, equipment, or surfaces. It reduces the spread of contamination and lowers radiation dose to workers and the public.

A written set of procedures for handling radiation incidents such as stuck sources, lost sources, or overexposures. It assigns responsibilities and describes notification, evacuation, and recovery steps.