| Word | Description |
| atom | A until of matter. An atom consists of a central charged nucleus (made up of neutrons and protrons) and electrons that surround the nucleus. |
| Absorbed Dose | In 1957 ICRU defined: “Absorbed dose of any ionizing radiation is the energy imparted to matter by ionizing particles per unit mass of irradiated material at the place of interest”. Note that, unlike the definition of exposure dose, this definition is neither restricted to a particular radiation type nor to a particular absorbing material. The traditional unit is “rad” (Radiation Absorbed Dose), and the SI unit is “Gy” (Gray): 100 rad = 1 Gy = 1 J/kg (Joule per kilogram, that is energy per mass) For photon radiation in air you can easily convert exposure to absorbed dose by applying the appropriate factor: absorbed dose [rad] = C x exposure [R], where C = 0.877 rad/R (in air) In water or tissue, C is within the range of 0.94 to 0.98 rad/R for photon energies ranging from 100 keV to 3 MeV. With other materials, other values for C apply. If you further wish to convert absorbed dose from rad to Gy, simply divide by 100: absorbed dose [Gy] = absorbed dose [rad] / 100. Within the SI system, absorbed dose in air measured in Gy is called air kerma (Ka). Air kerma is the common SI replacement for exposure because these two quantities only differ by a constant factor over a very wide range of photon energies: Ka [Gy] = 0.00877 Gy/R x exposure [R]. Air kerma can be regarded as the basic SI quantity. If conversion factors for other SI quantities such as dose equivalents are reported, those conversion factors usually refer to air kerma. |
| activity | A measure of the strength of a radioactive source. Activity is measured in becquerels. |
| acute radiation exposure | Exposure to a large dose of radiation in a short period of time. In radiography, this usually refers to the dose a person receives from coming very near a source. |
| acute radiation syndrome | The medical term for radiation sickness. |
| AECB | See “Atomic Energy Control Board”. |
| alarming dosimeter | A small electronic instrument that a person can wear. The dosimeter will sound an alarm when a high radiation dose rat is encountered or when a certain radiation does has been exceeded. |
| Atomic Energy Control Board | Federal agency responsible for regulating the development, application and use of atomic energy in Canada. |
| attenuation | The reduction in the intensity of radiation as it passes through any material, for example, through lead shielding. |
| background radiation | Radiation that is emitted from the naturally occurring radioactive materials in the earth and from cosmic rays that bombard the earth from outer space. |
| battery check | A function on a survey meter ised to verify the condition of the batteries. |
| becquerel | SI unit of activity equal to one disintegration per second. |
| calibration | Verification of a radiation survey meter to ensure it reads radiation dose rate accurately. A known radiation source must be used for proper calibration. |
| cancer | A disease in which rapidly multiplying cells grow in the body, interfering with its natural functions. Ionizing radiation may increase the probability that a person will get cancer. |
| cassette | The covering radiography film is placed in to prevent light from striking the film. |
| cataract | A medical term for the loss of transparency of the lens of the eye. |
| chromosomes | All the genetic material or genes contained in a living cell. Chromosomes control the reproduction of cells and the characteristics of the cells produced from the original cell. See “gene”. |
| cobalt 60 | A radioactive material used in radiography which is noted for very penetrating gamma radiation. It emits gamma radiation of energy 1.17 MeV and 1.33 MeV and has a half-life of 5.3 years. Symbols: Co 60, 60Co, Co 60. |
| collimator | A small radiation shield of lead or other heavy metal used in radiography. A collimator which is placed on the end of the guide tube has a small opening through which a narrow cone of radiation escapes when the source is cranked into the collimator. Use of a collimator can greatly reduce the size of the controlled area to which access must be restricted. |
| contamination | The spreading of radioactive materials which occurs when the source capsule is damaged and releases its content. |
| control cable | See “drive cable”. |
| crank or crank handle | The handle used to crank the source in or out in a cable-operated exposure device. |
| decay | The disintegration of atoms that have excess energy. Radiation is emitted in the process. |
| decay constant | A numerical constant that expresses the rate at which radioactive materials decay. |
| decay curve | A graph showing the decreasing radioactivity of a radioactive source as time passes. The term can also refer to the line or curve on the graph that indicates the activity. |
| delayed effects | Those effects caused by radiation that do not become evident until years after exposure to radiation. The possible delayed effects of radiation are cancer in the exposed persons and genetic defects in their children. |
| depleted uranium | Uranium having a smaller percentage of uranium 235 than that found in uranium as it occurs naturally. Depleted uranium us an excellent shielding material. |
| detector, radiation | The part of a radiation survey meter that is sensitive to radiation. |
| direct reading dosimeter | A small air-filled ionization chamber (about the size and shape of a cigar) that measures radiation dose by responding to ionization of the air contained in the chamber. Also called pocket dosimeter. |
| disintegration | The process during which an unstable atom loses excess energy. Radiation is emitted in the process. See “decay” and “becquerel”. |
| dose | Dose is the amount of radiation absorbed by the organism. |
| Dose Equivalent | Dose Equivalent Exposure and absorbed dose are general scientific quantities; they are not primarily related to protection of humans against radiation. With regard to radiological protection, we need a quantity that measures the biological effect on tissue. One might suppose that the absorbed dose in tissue could serve that purpose. In fact, it does in the case of photons and electrons (beta particles). For other radiation types, however, the same amount of absorbed dose has a different biological effect. Therefore, RBE-Dose (Relative Biological Effectiveness Dose) was introduced in the 1950's. The RBE-Dose is the absorbed dose in tissue measured in rad multiplied by a quality factor Q (formerly called RBE factor) accounting for the biological effect of different types of radiation. The corresponding traditional unit is “rem”. RBE-Dose [rem] = Q x absorbed dose in tissue [rad], where Q = 1 for photons and electrons. With neutrons or alphas, for example, Q may range up to 20. Both rem and rad represent energy per mass, so Q has no unit. Rem means “Rad Equivalent Man” indicating that one rem is the amount of any type of radiation that has a biological effect on human tissue equivalent to the effect of one rad of photon radiation. In other words, one rem of any type of radiation causes the same biological damage as one rad of photon radiation. If we use that equation for photon radiation (Q = 1) and substitute exposure for absorbed dose in tissue, we obtain RBE-Dose [rem] = C x exposure [R] (C <= 0.98 rad/R) Since C is close to 1, exposure dose is a good estimate for RBE-Dose originating from photons. It even slightly overestimates RBE-Dose. This reflects many years' practice to take the reading of instruments indicating exposure in R as the RBE-Dose of photons in rem. The advantage of an “equivalent” dose is obvious: If a person is exposed to different radiation types, you may add the equivalent dose values of those radiations to get the total amount of biological effect. This total amount, the “effective” dose, decides whether permissible limits are exceeded or not. Without dose equivalents one would need individual limiting values (expressed, for example, in rad or Gy) for all types of radiation. It took a long time for the dose equivalent to be widely accepted. In 1957 ICRU mentioned the RBE-Dose and the rem as “recognized symbols”, but did not define them as recommended quantity and unit. In the time thereafter a lot of work (and, unfortunately, a lot of modifications) on the dose equivalent concept was performed as documented in many publications of ICRU and ICRP (International Commission on Radiological Protection). One of the results is the SI unit “Sv” (Sievert) to replace the rem as unit for the dose equivalent: 1 Sv = 100 rem = 1 J/kg Now we have to confuse you a little bit. If 1 Sv = 1 J/kg, and 1 Gy = 1 J/kg (see above), then fundamental mathematics tell us that 1 Sv = 1 Gy. One might conclude that, if 1 Sv = 1 Gy, then dose equivalent is equal to absorbed dose. However, that conclusion is not correct. You cannot conclude that two quantities are equal just from the fact that they are measured with the same unit. A quantity and its unit are different things. For example, think of something else like electric currents. If the current flowing through one circuit is reported to be 1 Amp, and the current flowing through some other circuit is also reported to be 1 Amp, this does not necessarily mean that both currents are identical. One may be a direct current (DC), and the other may be an alternating one (AC). In other words, it is not sufficient to say that the current amounts to 1 Amp; you also have to specify how it was measured, that is you have to specify the quantity (direct current, root-mean-square value or peak value of an alternating current, and so on). This distinction is sometimes not clearly observed in the radiation business (in the early days even by experts), and we feel that among users a lot of confusion arises from neglecting this distinction. A good example for that confusion is the popular equation “Sv/Gy = 1.20 (for Cs-137)”. Since we just learned that 1 Sv = 1 Gy, how can then be Sv/Gy = 1.20 ? The answer is that “Sv/Gy = 1.20” is a short - but rather confusing - notation for the fact that H*(10) [Sv] = 1.20 x Ka [Gy] (for Cs-137). Correctly the popular equation would read “H*(10)/Ka = 1.20 (for Cs-137)”, because 1.2 is the ratio of the quantities, not the ratio of their units. Ka is air kerma, and H*(10) is a dose equivalent quantity that will be discussed later. Now that we are aware of distinguishing quantities and units, we may discuss different dose equivalent quantities (unfortunately there are more than one) that are all measured in Sv. |
| dose rate | A measure of how fast a radiation dose is being received. It is a dose per unit of time. For example, “the dose rate is 10 mSv/h”. |
| dosimeter | A device used to determine the radiation dose a person has received. It may be a direct reading dosimeter, a thermoluminescent dosimeter or in some cases, a photographic film dosimeter. |
| drive cable | A cable used to push out and retract a source in a cable-operated exposure device. Usually operated with a crank or push-pull mechanism. Also called control cable. |
| electromagnetic radiation | A term for radiation that travels as waves composed purely of electrical and magnetic energy. For example. Gamma radiation, Z-rays, microwaves, visible light and radio waves. |
| electron | A very light particle that rotates around the nucleus of an atom and carries a negative electric charge. Electricity is the flow of electrons. |
| element | A basic type of matter. Each element has distinct chemical properties. There are 92 different elements that are found in nature, for example, hydrogen oxygen, lead, uranium, carbon, tungsten, and iron. |
| exposure (radiation) | Being subjected to radiation. People can be exposed to a radiation source, or a film can receive an exposure to radiation. See “radiographic exposure”. |
| exposure device, beam-type | A radiographic exposure device where the radioactive source never leaves the device. The radiographic exposure is done by moving the source in front of an opening or by moving a piece of shielding away from the front of the source. |
| exposure device, cable operated | A radiographic exposure device where the source capsule assembly is cranked or pushed out of the shield to make the radiographic exposure. |
| exposure device, fixed | A radiographic exposure device that can be moved by pushing it on wheels. |
| exposure device, pipeline | A beam-type radiographic exposure device designed for radiographing pipelines. |
| exposure device, pneumatically operated | A radiographic exposure device where the flow of the air moves the source capsule out of the shield to make the radiographic exposure. |
| exposure device, portable | A radiographic exposure device that can be carried by hand. |
| exposure device, radiography | A shielding container designed to hold a gamma radiography source. A means is provided to move the source capsule assembly outside the shield or remove part of the shield to make the radiographic exposure. Also called a radiography camera. |
| Exposure Dose | Exposure Dose Back in 1928 the second ICRU (International Commission on Radiation Units and Measurements) congress defined the “Roentgen” to measure the “quantity of X-radiation”. The definition of that quantity, also known as “exposure” or “exposure dose”, is based upon the X-radiation's ability to produce electric charge in air. That definition was extended to gamma radiation in 1937, that is to photon radiation in general. In 1928 the symbol for the Roentgen unit was defined as “r”, and was changed to “R” in 1962 (surprisingly enough, you can still meet the “r”). The SI unit of exposure is C/kg of air, which converts to R as follows: 1 R = 2.58 E-4 C/kg (Coulomb per kilogram of air, that is charge per mass of air) The SI unit C/kg is hardly used in practice. Instead, the SI system prefers a quantity called “air kerma”, see the comments on absorbed dose. |
| fallout, radioactive | Radioactive debris from emissions of radioactive material in air that falls out of the atmosphere onto the earth. |
| gamma alarm | A radiation detector that sounds an alarm when it detects gamma radiation above a preset level. |
| gamma radiation | A type of penetrating radiation used in industrial radiography. Gamma radiation, which is similar to X-rays, comes from the nucleus of an atom when it decays. |
| gamma radiography | Industrial radiography using radioactive materials that emit gamma radiation. |
| gamma survey meter | A portable instrument that measures radiation dose rate. |
| gene | A part of a living cell that controls the reproduction of the cell and determines the characteristics that reproduced cells will have. See “chromosomes”. |
| genetic defect | A defect in a living organism caused by a deficiency in the genes of the original reproductive cells from which the organism was conceived. Genetic defects are passed on to the descendents of the person with the defect. |
| Gravitas | One with a noble stature. Latin Root |
| half-life | The time it takes for half the atoms in a radioactive source to decay. Half-lives vary from a fraction of a second to billions of years. The half-life of cobalt 60 and of iridium 192 are 5.3 years and 74.2 days, respectively. |
| half-value layer | The thickness of a material which reduces the amount of radiation to one half of its initial intensity. The thickness of the half-value layer will depend on the material and the energy of the gamma radiation. |
| head hose | See “source guide tube” |
| health physicist | A trained specialist working in radiation protection. |
| industrial radiography | The use of penetrating radiation, such as X-rays or gamma radiation, to inspect metal casting or welds for internal flaws. Industrial radiography does not include medical uses of radiation such as chest or dental X-rays. |
| internal contamination | The presence of radioactive material within a person’s body caused by inhaling or swallowing radioactive material. |
| inverse square law | A law of nature that states how the intensity of radiation decreases as a person moves away from a radiation source. The law states that the intensity will decrease proportionately to the distance squared. This means that moving twice as far from a source decreases the intensity of the source by a factor of two squared (22), or four. |
| ion | An atom that has gained or lost one or more electron or an electron that is not attached to an atom. Ions have an electrical charge and can be caused by radiation. |
| ion pair | A positively charged ion and an electron. The production of ion pairs is the method by which ionizing radiation gives up its energy. |
| ionization | The process of adding electrons to, or removing electrons from, atoms or molecules. This creates ions. |
| ionizing radiation | Any radiation that has enough energy to break apart chemical bonds and cause atoms to form ions (charged particles). For example, gamma radiation, X-rays, beta particles. |
| iridium 192 | A radioactive isotope of the element indium that emits gamma radiation of energies from 0.3 MeV to 0.61 MeV. It has a half-life of 74.2 days and is commonly used in gamma radiography. Symbols: Ir 192, 192 Ir, Ir192. |
| isotope | A particular form of an element. The isotopes of an element have the same chemical properties but different nuclear properties. One isotope is stable. |
| leak test | A test performed to verify if radioactive material is being released from the source capsule. See “contamination”. |
| lethal dose | The radiation dose that would result in death. This dose is approximately 5 Sv delivered to the whole body within a short period of time. |
| leukemia | An often fatal cancer characterized by excessive production of white blood cells. |
| licensee (radiography) | A company or person to whom a license has been issued by the AECB for the use and possession of an exposure device containing radioactive material. |
| lock box | The part of a radiographic exposure device that contains the mechanism used to lock the source capsule assembly into its safe shielded position. |
| locking ball | A ball which is a part of the source capsule assembly that prevents the source assembly from being pulled out of the exposure device. |
| man-made radiation | Radiation produced by man-made sources, such as X-ray machines and nuclear power plants. |
| molecule | The smallest unit of a chemical compound. For example, a water molecule consists of two hydrogen atoms combined with one oxygen atom. |
| natural radioactivity | The radioactivity from naturally occurring elements, for example radium, carbon 14, uranium, thorium and potassium 40. |
| negative electrical charge | An electrical charge that is attracted to positive electrical charges. Electricity is the movement of negative electrical charges (electrons). |
| non-ionizing radiation | Radiation that does not have enough energy to create ions (charged particles). For example, visible light, radio waves and microwaves. |
| Nondestructive testing (NDT) | The testing or examination of an object to verify that it is free from flaws. Industrial radiography, ultrasonic testing, magnetic particles testing, and dye penetrate testing are examples of nondestructive testing. |
| nozzle | Metal tip at the end of the source guide tube of a pneumatically operated exposure device. |
| nucleus | The inner core of an atom or a living cell. In an atom, the nucleus consists of neutrons and protons tightly bound together. In a living cell, the nucleus contains the genes of genetic material. |
| operating procedures | Instructions supplied by the licensee or company covering radiation safety and regulatory requirements related to the use and possession of radiographic exposure devices. |
| overexposure | Receiving a radiation dose in excess of legal regulatory limits. |
| overpack | An outer container for a radiographic exposure device used to meet transportation requirements. For example, an overpack can lower the radiation does rate at the surface of the package or add thermal protection for an inner package. |
| panoramic radiographic exposure | A radiographic exposure in which film is exposed on a 360 degree angle around the source. For example, if the source is in the center of a pipe, a panoramic exposure will radiograph the entire circumference of the pipe. |
| penetrameter | A piece of metal of specific thickness with holes or slots in it. It is placed in front of the radiographic film near the area being inspected to show what size defects can be detected. |
| photographic dosimeter | A dosimeter worn by a person to measure radiation dose which contains a film that responds to radiation. It has been replaced in most cases by a thermoluminescent dosimeter. |
| pigtail | The part of a radiographic source assembly that included the short cable and the connector, but not the source capsule. |
| placard | The sign on a vehicle that indicates the vehicle is carrying packages containing radioactive materials. |
| pocket dosimeter | See “direct reading dosimeter”. |
| positive electrical charge | An electrical charge that is attracted to electrons or other negative electrical charges. |
| prompt effects | The harmful health effects of radiation appearing within a day or a few weeks after receiving a large radiation dose. The prompt effects are usually radiation burns and radiation sickness. |
| pump | Device used to move the source capsule in a pneumatically operated exposure device. |
| “empty” label | A transportation label used when a container normally used for transporting radioactive material does not contain any radioactive material. |