2 P.C Basic Radiation Protection – Key Vocabulary

A comprehensive set of vocabulary flashcards covering foundational terms, interactions, units, protection principles, and monitoring devices presented in the Basic Radiation Protection lecture.

Radiation

Emission or transmission of energy in the form of waves or particles through space or a medium.

Ionizing Radiation

Radiation with enough energy to remove (eject) an orbital electron from an atom or molecule, creating an ion.

Non-Ionizing Radiation

Radiation that does NOT have sufficient energy to ionize atoms (e.g., radio waves, microwaves).

Electromagnetic Radiation (EM)

Radiant energy consisting of coupled electric and magnetic waves that travel at the speed of light and have no mass or charge.

Particulate Radiation

Ionizing radiation composed of sub-atomic particles such as protons, neutrons, electrons, alpha and beta particles.

X-Rays

Artificially produced, mass-less, chargeless photons that are a form of electromagnetic radiation capable of ionization.

Gamma Rays

High-energy photons emitted from the nucleus of radioactive atoms; a form of electromagnetic ionizing radiation.

Wavelength (λ)

The physical length of one complete wave cycle, measured in meters; inversely related to frequency.

Frequency (f)

The number of wave cycles that pass a point per second, measured in hertz (Hz); inversely related to wavelength.

Electron Volt (eV)

The kinetic energy gained by an electron accelerated through 1 volt; unit used to express photon energy.

Bremmstrahlung Radiation

‘Braking’ radiation produced when high-speed electrons are decelerated near the nucleus, releasing X-ray photons.

Characteristic Radiation

X-rays produced when an inner-shell electron is ejected and an outer-shell electron fills the vacancy, emitting a photon of a characteristic energy.

Classic (Coherent) Scattering

Low-energy (<10 eV) interaction where an incident photon is absorbed and re-emitted with the same energy but different direction; no ionization.

Photoelectric Interaction

Interaction in which an inner-shell electron is ejected, the photon is totally absorbed, and characteristic X-rays may be emitted.

Compton Scattering

Interaction where an outer-shell electron is ejected (recoil electron) and the incident photon is deflected with reduced energy; dominant in radiotherapy energies.

Pair Production

High-energy (>1.022 MeV) interaction in which a photon disappears in the nuclear field and is replaced by a positron and an electron, each 0.511 MeV.

Photodisintegration

Interaction (≈10 MeV) where a photon is absorbed by the nucleus causing ejection of a nuclear fragment, often a neutron.

Roentgen (R)

Traditional unit of exposure measuring ionization produced in air (2.58×10⁻⁴ C/kg).

Coulomb per Kilogram (C/kg)

SI unit of exposure measuring charge produced in air.

Rad

Traditional unit of absorbed dose equal to 100 ergs per gram.

Gray (Gy)

SI unit of absorbed dose; 1 Gy = 1 J/kg = 100 rad.

Rem

Traditional unit of dose equivalent; absorbed dose (rad) multiplied by radiation quality factor.

Sievert (Sv)

SI unit of dose equivalent or effective dose; 1 Sv = 100 rem.

Curie (Ci)

Traditional unit of radioactivity equal to 3.7 × 10¹⁰ disintegrations per second.

Becquerel (Bq)

SI unit of activity; 1 disintegration per second.

Natural Background Radiation

Ionizing radiation constantly present from cosmic, terrestrial, and internal sources (~310 mrem/year U.S. average).

Radon

Radioactive gas from decay of uranium in soil; largest single contributor to natural background dose in the U.S.

ALARA Principle

Guiding philosophy to keep radiation exposures As Low As Reasonably Achievable, assuming a linear non-threshold risk model.

Cardinal Principles of Protection

Time, Distance, Shielding – core methods to reduce radiation exposure.

Time (Protection)

Reducing the duration spent near a radiation source lowers total dose received.

Distance (Protection)

Increasing separation from a source greatly reduces exposure; most effective principle.

Shielding (Protection)

Interposing absorbing material (e.g., lead) between source and person to reduce dose.

Inverse Square Law

Intensity of radiation is inversely proportional to the square of the distance from a point source (I₁/I₂ = D₂²/D₁²).

Primary Barrier

Structural shielding designed to intercept the primary X-ray beam (e.g., wall struck directly by beam).

Secondary Barrier

Shielding that protects against scatter and leakage radiation only.

Film Badge

Inexpensive personnel dosimeter using photographic film that darkens proportionally to radiation dose; monthly wear period.

OSL Dosimeter

Optically Stimulated Luminescence badge using aluminum oxide; accurate, re-readable, and now the most common occupational monitor.

TLD

(Thermoluminescent Dosimeter); Dosimeter with lithium fluoride crystals that emit light when heated after irradiation; reusable but not re-readable.

Pocket Dosimeter

Pen-shaped ion-chamber device providing immediate dose readout; expensive and no permanent record.

Survey Meter

Portable area monitor measuring radiation levels; includes ion chambers and GM counters.

Geiger-Müller Counter

Gas-filled detector sensitive to low levels of ionizing radiation; commonly used for contamination surveys.

Quality Factor (QF)

Multiplier used to convert absorbed dose to dose equivalent, accounting for differing biological effectiveness of radiation; QF for X-rays = 1.

Effective Dose Limit

Recommended maximum annual radiation dose to minimize stochastic risk (e.g., 50 mSv for radiation workers).

Declared Pregnant Worker Dose Limit

5 mSv (0.5 rem) for entire gestation; recommended 0.5 mSv per month.

Linear Accelerator (Linac)

Radiotherapy device that accelerates electrons to produce high-energy X-ray beams; output is heterogenous in energy.