In physics, attenuation or, in some contexts, extinction is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates.
In physics, the mean free path is the average distance travelled by a moving particle between successive impacts (collisions), which modifies its direction or energy or other particle properties. It is the mean distance travelled by an electron between scattering events.
The gray is a derived unit of ionizing radiation dose in the International System of Units (SI). It is defined as the absorption of one joule of radiation energy per kilogram of matter.
Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposure can be from a source of radiation external to the human body or due to internal irradiation caused by the ingestion of radioactive contamination.
Absorbed dose is a dose quantity which is the measure of the energy deposited in matter by ionizing radiation per unit mass. Absorbed dose is used in the calculation of dose uptake in living tissue in both radiation protection, and radiology. It is also used to directly compare the effect of radiation on inanimate matter such as in radiation hardening.
Tritium radioluminescence is the use of gaseous tritium, a radioactive isotope of hydrogen, to create visible light. Tritium emits electrons through beta decay and, when they interact with a phosphor material, light is emitted through the process of phosphorescence. The overall process of using a radioactive material to excite a phosphor and ultimately generate light is called radioluminescence. As tritium illumination requires no electrical energy, it has found wide use in applications such as emergency exit signs, illumination of wristwatches, and portable yet very reliable sources of low intensity light which won't degrade human night vision. Gun sights for night use and small lights used mostly by military personnel fall under the latter application.
Kerma is an acronym for "kinetic energy released per unit mass", defined as the sum of the initial kinetic energies of all the charged particles liberated by uncharged ionizing radiation in a sample of matter, divided by the mass of the sample. It is defined by the quotient .
An X-ray tube is a vacuum tube that converts electrical input power into X-rays. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation. In contrast to other sources of ionizing radiation, X-rays are only produced as long as the X-ray tube is energized. X-ray tubes are also used in CT scanners, airport luggage scanners, X-ray crystallography, material and structure analysis, and for industrial inspection.
A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction, or to cause the spatial cross section of the beam to become smaller.
In physics, absorption of electromagnetic radiation is how matter takes up a photon's energy — and so transforms electromagnetic energy into internal energy of the absorber. A notable effect is attenuation, or the gradual reduction of the intensity of light waves as they propagate through a medium. Although the absorption of waves does not usually depend on their intensity, in certain conditions (optics) the medium's transparency changes by a factor that varies as a function of wave intensity, and saturable absorption occurs.
An antireflective or anti-reflection (AR) coating is a type of optical coating applied to the surface of lenses and other optical elements to reduce reflection. In typical imaging systems, this improves the efficiency since less light is lost due to reflection. In complex systems such as telescopes and microscopes the reduction in reflections also improves the contrast of the image by elimination of stray light. This is especially important in planetary astronomy. In other applications, the primary benefit is the elimination of the reflection itself, such as a coating on eyeglass lenses that makes the eyes of the wearer more visible to others, or a coating to reduce the glint from a covert viewer's binoculars or telescopic sight.
Radiation-absorbent material, usually known as RAM, is a material which has been specially designed and shaped to absorb incident RF radiation, as effectively as possible, from as many incident directions as possible. The more effective the RAM, the lower the resulting level of reflected RF radiation. Many measurements in electromagnetic compatibility (EMC) and antenna radiation patterns require that spurious signals arising from the test setup, including reflections, are negligible to avoid the risk of causing measurement errors and ambiguities.
Grenz rays are part of the electromagnetic spectrum comprising low energy (ultrasoft) X-rays. These were first investigated by Gustav Bucky in 1923 using a cathode vacuum tube with a lithium borate glass window, which he labeled Grenz rays as he believed that the biological effects resembled those of UV light and traditional X-rays and hence were on the border between the two. These rays are also known as Bucky rays.
Industrial radiography is a modality of non-destructive testing that uses ionizing radiation to inspect materials and components with the objective of locating and quantifying defects and degradation in material properties that would lead to the failure of engineering structures. It plays an important role in the science and technology needed to ensure product quality and reliability.
The linear attenuation coefficient, attenuation coefficient, or narrow-beam attenuation coefficient characterizes how easily a volume of material can be penetrated by a beam of light, sound, particles, or other energy or matter. A large attenuation coefficient means that the beam is quickly "attenuated" (weakened) as it passes through the medium, and a small attenuation coefficient means that the medium is relatively transparent to the beam. The SI unit of attenuation coefficient is the reciprocal metre (m−1). Extinction coefficient is an old term for this quantity but is still used in meteorology and climatology. Most commonly, the quantity measures the value of downward e-folding distance of the original intensity as the energy of the intensity passes through a unit thickness of material, so that an attenuation coefficient of 1 m−1 means that after passing through 1 metre, the radiation will be reduced by a factor of e, and for material with a coefficient of 2 m−1, it will be reduced twice by e, or e2. Other measures may use a different factor than e, such as the decadic attenuation coefficient below. The broad-beam attenuation coefficient counts forward-scattered radiation as transmitted rather than attenuated, and is more applicable to radiation shielding.
A gamma ray, or gamma radiation, is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves and so imparts the highest photon energy. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation gamma rays based on their relatively strong penetration of matter; in 1900 he had already named two less penetrating types of decay radiation alpha rays and beta rays in ascending order of penetrating power.
Dose area product (DAP) is a quantity used in assessing the radiation risk from diagnostic X-ray examinations and interventional procedures. It is defined as the absorbed dose multiplied by the area irradiated, expressed in gray-centimetres squared. Manufacturers of DAP meters usually calibrate them in terms of absorbed dose to air. DAP reflects not only the dose within the radiation field but also the area of tissue irradiated. Therefore, it may be a better indicator of the overall risk of inducing cancer than the dose within the field. It also has the advantages of being easily measured, with the permanent installation of a DAP meter on the X-ray set. Due to the divergence of a beam emitted from a "point source", the area irradiated (A) increases with the square of distance from the source, while radiation intensity (I) decreases according to the inverse square of distance. Consequently, the product of intensity and area, and therefore DAP, is independent of distance from the source.
The roentgen or röntgen is a legacy unit of measurement for the exposure of X-rays and gamma rays, and is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air . In 1928, it was adopted as the first international measurement quantity for ionising radiation to be defined for radiation protection, as it was then the most easily replicated method of measuring air ionization by using ion chambers. It is named after the German physicist Wilhelm Röntgen, who discovered X-rays.
Mean glandular dose (MGD) is a quantity used to describe the absorbed dose of radiation to the breast in mammography. It is based on a measurement of air kerma and conversion factors. MGD can be calculated from measurements made with PMMA blocks. It is often used to compare typical doses to patients between different centres or internationally, and is the preferred measure of the potential risk from mammography.
Schwarzschild's equation is used to calculate radiative transfer – energy transfer – through a medium in local thermodynamic equilibrium that both absorbs and emits electromagnetic radiation.
