|
Dosimetry
Radiation dosimetry in the fields of health physics and radiation protection is the measurement, calculation and assessment of the ionizing radiation dose absorbed by an object, usually the human body. This applies both internally, due to ingested or inhaled radioactive substances, or externally due to irradiation by sources of radiation. Internal dosimetry assessment relies on a variety of monitoring, bio-assay or radiation imaging techniques, whilst external dosimetry is based on measurements with a dosimeter, or inferred from measurements made by other radiological protection instruments. Dosimetry is used extensively for radiation protection and is routinely applied to monitor occupational radiation workers, where irradiation is expected, or where radiation is unexpected, such as in the aftermath of the Three Mile Island, Chernobyl or Fukushima radiological release incidents. The public dose take-up is measured and calculated from a variety of indicators such as ambient me ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Absorbed Dose
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 (reduction of harmful effects), and radiology (potential beneficial effects for example in cancer treatment). It is also used to directly compare the effect of radiation on inanimate matter such as in radiation hardening. The SI unit of measure is the Gray (unit), gray (Gy), which is defined as one Joule of energy absorbed per kilogram of matter. The older, non-SI Centimetre–gram–second system of units, CGS unit rad (unit), rad, is sometimes also used, predominantly in the USA. Deterministic effects Conventionally, in radiation protection, unmodified absorbed dose is only used for indicating the immediate health effects due to high levels of acute dose. These are tissue effects, such as in acute radiation syndrome, which are also known as deterministic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dosimeter
A radiation dosimeter is a device that measures dose uptake of external ionizing radiation. It is worn by the person being monitored when used as a personal dosimeter, and is a record of the radiation dose received. Modern electronic personal dosimeters can give a continuous readout of cumulative dose and current dose rate, and can warn the wearer with an audible alarm when a specified dose rate or a cumulative dose is exceeded. Other dosimeters, such as thermoluminescent or film types, require processing after use to reveal the cumulative dose received, and cannot give a current indication of dose while being worn. Personal dosimeters The personal ionising radiation dosimeter is of fundamental importance in the disciplines of radiation dosimetry and radiation health physics and is primarily used to estimate the radiation dose deposited in an individual wearing the device. Ionising radiation damage to the human body is cumulative, and is related to the total dose received, for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gray (unit)
The gray (symbol: Gy) is the unit of ionizing radiation dose in the International System of Units (SI), defined as the absorption of one joule of radiation energy per kilogram of matter. It is used as a unit of the radiation quantity absorbed dose that measures the energy deposited by ionizing radiation in a unit mass of matter being irradiated, and is used for measuring the delivered dose in radiotherapy, food irradiation and radiation sterilization. It is important in predicting likely acute health effects, such as acute radiation syndrome and is used to calculate equivalent dose using the sievert, which is a measure of the stochastic health effect on the human body. The gray is also used in radiation metrology as a unit of the radiation quantity kerma; defined as the sum of the initial kinetic energies of all the charged particles liberated by uncharged ionizing radiation in a sample of matter per unit mass. The gray is an important unit in ionising radiation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gel Dosimetry
Gel dosimeters, also called Fricke gel dosimeters, are manufactured from radiation sensitive chemicals that, upon irradiation with ionising radiation, undergo a fundamental change in their properties as a function of the absorbed radiation dose. Over many years individuals have endeavoured to measure absorbed radiation dose distributions using gels. As long ago as 1950, the radiation-induced colour change in dyes was used to investigate radiation doses in gels. Further, in 1957 depth doses of photons and electrons in agar gels were investigated using spectrophotometry. Gel dosimetry today however, is founded mainly on the work of Gore ''et al'' who in 1984 demonstrated that changes due to ionising radiation in Fricke dosimetry solutions, developed in the 1920s, could be measured using nuclear magnetic resonance (NMR). Gel dosimeters generally consist of two types; Fricke and polymer gel dosimeters and are usually evaluated or 'read-out' using magnetic resonance imaging (MRI), optic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Internal Dosimetry
Internal dosimetry is the science and art of internal ionising radiation dose assessment due to radionuclides incorporated inside the human body. Radionuclides deposited within a body will irradiate tissues and organs and give rise to committed dose until they are excreted from the body or the radionuclide is completely decayed. The internal doses for workers or members of the public exposed to the intake of radioactive particulates can be estimated using bioassay data such as lung and body counter measurements, urine or faecal radioisotope concentration, etc. The International Commission on Radiological Protection (ICRP) biokinetic models are applied to establish a relationship between the individual intake and the bioassay measurements, and then to infer the internal dose. Committed dose The internal radiation dose due to injection, ingestion or inhalation radioactive substances is known as committed dose. The ICRP defines Committed effective dose, as the sum of the products ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kerma (physics)
In radiation physics, kerma is an acronym for "kinetic energy released per unit mass" (alternately, "kinetic energy released in matter", "kinetic energy released in material",, or "kinetic energy released in materials"), defined as the sum of the initial kinetic energies of all the charged particles liberated by uncharged ionizing radiation (i.e., indirectly ionizing radiation such as photons and neutrons) in a sample of matter, divided by the mass of the sample. It is defined by the quotient K = \operatorname\!E_\text/\operatorname\!m. Units The SI unit of kerma is the gray (Gy) (or joule per kilogram), the same as the unit of absorbed dose. However, kerma can be different from absorbed dose, depending on the energies involved. This is because ionization energy is not accounted for. While kerma approximately equals absorbed dose at low energies, kerma is much higher than absorbed dose at higher energies, because some energy escapes from the absorbing volume in the form of brem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radon
Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through which thorium and uranium slowly decay into various short-lived radioactive elements and lead. Radon itself is the immediate decay product of radium. Its most stable isotope, 222Rn, has a half-life of only 3.8 days, making it one of the rarest elements. Since thorium and uranium are two of the most common radioactive elements on Earth, while also having three isotopes with half-lives on the order of several billion years, radon will be present on Earth long into the future despite its short half-life. The decay of radon produces many other short-lived nuclides, known as "radon daughters", ending at stable isotopes of lead.+ ion is believed to form by the following reaction: : Rn (g) + 2 (s) → (s) + 2 (g) For this reason, antimon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Percentage Depth Dose Curve
In radiotherapy, a percentage depth dose curve (PDD) (sometimes ''percent'' depth dose curve) relates the absorbed dose deposited by a radiation beam into a medium as it varies with depth along the axis of the beam. The dose values are divided by the maximum dose, referred to as dmax, yielding a plot in terms of percentage of the maximum dose. Dose measurements are generally made in water or "water equivalent" plastic with an ionization chamber, since water is very similar to human tissue with regard to radiation scattering and absorption. Percent depth dose (PDD), which reflects the overall percentage of dose deposited as compared to the depth of maximum dose, depends on the depth of interest, beam energy, field size, and SSD (source to surface distance) as follows. Of note, PDD generally refers to depths greater than the depth of maximum dose * PDD ''decreases'' with increasing depth due to the inverse square law and due to attenuation of the radiation beam * PDD ''increases'' wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermoluminescent Dosimetry
A thermoluminescent dosimeter, or TLD, is a type of radiation dosimeter, consisting of a piece of a thermoluminescent crystalline material inside a radiolucent package. When a thermoluminescent crystal is exposed to ionizing radiation, it absorbs and traps some of the energy of the radiation in its crystal lattice. When heated, the crystal releases the trapped energy in the form of visible light, the intensity of which is proportional to the intensity of the ionizing radiation the crystal was exposed to. A specialized detector measures the intensity of the emitted light, and this measurement is used to calculate the dose of ionizing radiation the crystal was exposed to. Since the crystal density is similar to human soft tissue density, the dose measurement can be used to calculate absorbed dose. Materials exhibiting thermoluminescence in response to ionizing radiation include calcium fluoride, lithium fluoride, calcium sulfate, lithium borate, calcium borate, potassium bromide ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Film Badge Dosimeter
A film badge dosimeter or film badge is a personal dosimeter used for monitoring cumulative radiation dose due to ionizing radiation. The badge consists of two parts: photographic film and a holder. The film emulsion is black and white photographic film with varying grain size to affect its sensitivity to incident radiation such as gamma rays, X-rays and beta particles. After use by the wearer, the film is removed, developed, and examined to measure exposure. When the film is irradiated, an image of the protective case is projected on the film. Lower energy photons are attenuated preferentially by differing absorber materials. This property is used in film dosimetry to identify the energy of radiation to which the dosimeter was exposed. Some film dosimeters have two emulsions, one for low-dose and the other for high-dose measurements. These two emulsions can be on separate film substrates or on either side of a single substrate. Knowing the energy allows for accurate measur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dose Profile
In external beam Radiotherapy, transverse and longitudinal dose measurements are taken by a radiation detector in order to characterise the radiation beams from medical linear accelerators. Typically, an ionisation chamber and water phantom are used to create these radiation dose profiles. Water is used due to its tissue equivalence. Transverse dose measurements are performed in the x (crossplane) or y (inplane) directions perpendicular to the radiation beam, and at a given depth (z) in the phantom. These are known as dose profiles. Dose measurements taken along the z direction create radiation dose distribution known as a depth-dose curve. See also *Dosimetry *Percentage depth dose curve In radiotherapy, a percentage depth dose curve (PDD) (sometimes ''percent'' depth dose curve) relates the absorbed dose deposited by a radiation beam into a medium as it varies with depth along the axis of the beam. The dose values are divided by th ... References {{Reflist Cancer treatments ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equivalent Dose
Equivalent dose is a dose quantity '' H '' representing the stochastic health effects of low levels of ionizing radiation on the human body which represents the probability of radiation-induced cancer and genetic damage. It is derived from the physical quantity absorbed dose, but also takes into account the biological effectiveness of the radiation, which is dependent on the radiation type and energy. In the SI system of units, the unit of measure is the sievert (Sv). Application To enable consideration of stochastic health risk, calculations are performed to convert the physical quantity absorbed dose into equivalent dose, the details of which depend on the radiation type. For applications in radiation protection and dosimetry assessment, the International Commission on Radiological Protection (ICRP) and the International Commission on Radiation Units and Measurements (ICRU) have published recommendations and data on how to calculate equivalent dose from absorbed dose. Equ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
