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Half Value Layer
material's half-value layer (HVL), or half-value thickness, is the thickness of the material at which the intensity of radiation entering it is reduced by one half. HVL can also be expressed in terms of air kerma rate (AKR), rather than intensity: the half-value layer is the thickness of specified material that, "attenuates the beam of radiation to an extent such that the AKR is reduced to one-half of its original value. In this definition the contribution of all scattered radiation, other than any ..present initially in the beam concerned, is deemed to be excluded." Rather than AKR, measurements of air kerma, exposure, or exposure rate can be used to determine half value layer, as long as it is given in the description. Half-value layer refers to the first half-value layer, where subsequent (i.e. second) half-value layers refer to the amount of specified material that will reduce the air kerma rate by one-half after material has been inserted into the beam that is equal to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Intensity (physics)
In physics, the intensity or flux of radiant energy is the power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy. In the SI system, it has units watts per square metre (W/m2), or kg⋅ s−3 in base units. Intensity is used most frequently with waves such as acoustic waves (sound) or electromagnetic waves such as light or radio waves, in which case the ''average'' power transfer over one period of the wave is used. ''Intensity'' can be applied to other circumstances where energy is transferred. For example, one could calculate the intensity of the kinetic energy carried by drops of water from a garden sprinkler. The word "intensity" as used here is not synonymous with " strength", "amplitude", " magnitude", or " level", as it sometimes is in colloquial speech. Intensity can be found by taking the energy density (energy per unit volume) at a point in space and multiplying it by the velocity at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ) * '' particle radiation'', such as alpha radiation (α), beta radiation (β), proton radiation and neutron radiation (particles of non-zero rest energy) * '' acoustic radiation'', such as ultrasound, sound, and seismic waves (dependent on a physical transmission medium) * '' gravitational radiation'', that takes the form of gravitational waves, or ripples in the curvature of spacetime Radiation is often categorized as either '' ionizing'' or '' non-ionizing'' depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules and break chemical bonds. This is an important distinction due to the large ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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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] |
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Exposure (radiation)
Radiation is a moving form of energy, classified into ionizing and non-ionizing type. Ionizing radiation is further categorized into electromagnetic radiation (without matter) and particulate radiation (with matter). Electromagnetic radiation consists of photons, which can be thought of as energy packets, traveling in the form of a wave. Examples of electromagnetic radiation includes X-rays and gamma rays (see photo "Types of Electromagnetic Radiation"). These types of radiation can easily penetrate the human body because of high energy. Radiation exposure is a measure of the ionization of air due to ionizing radiation from photons. It is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air. Medical exposure is defined by the International Commission on Radiological Protection as exposure incurred by patients as part of their own medical or dental diagnosis or treatment; by persons, other than those occupationally expo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Mean Free Path
In physics, mean free path is the average distance over which a moving particle (such as an atom, a molecule, or a photon) travels before substantially changing its direction or energy (or, in a specific context, other properties), typically as a result of one or more successive collisions with other particles. Scattering theory Imagine a beam of particles being shot through a target, and consider an infinitesimally thin slab of the target (see the figure). The atoms (or particles) that might stop a beam particle are shown in red. The magnitude of the mean free path depends on the characteristics of the system. Assuming that all the target particles are at rest but only the beam particle is moving, that gives an expression for the mean free path: :\ell = (\sigma n)^, where is the mean free path, is the number of target particles per unit volume, and is the effective cross-sectional area for collision. The area of the slab is , and its volume is . The typical number of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Attenuation
In physics, attenuation (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. Hearing protectors help reduce acoustic flux from flowing into the ears. This phenomenon is called acoustic attenuation and is measured in decibels (dBs). In electrical engineering and telecommunications, attenuation affects the propagation of waves and signals in electrical circuits, in optical fibers, and in air. Electrical attenuators and optical attenuators are commonly manufactured components in this field. Background In many cases, attenuation is an exponential function of the path length through the medium. In optics and in chemical spectroscopy, this is known as the Beer–Lambert law. In engineering, attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc.) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Attenuation Coefficient
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 coefficient value that is large represents a beam becoming 'attenuated' as it passes through a given medium, while a small value represents that the medium had little effect on loss. The SI unit of attenuation coefficient is the reciprocal metre (m−1). Extinction coefficient is another term for this quantity, often used in meteorology and climatology. Most commonly, the quantity measures the exponential decay of intensity, that is, the value of downward ''e''-folding distance of the original intensity as the energy of the intensity passes through a unit (''e.g.'' one meter) 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Radiation Protection
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. Ionizing radiation is widely used in industry and medicine, and can present a significant health hazard by causing microscopic damage to living tissue. There are two main categories of ionizing radiation health effects. At high exposures, it can cause "tissue" effects, also called "deterministic" effects due to the certainty of them happening, conventionally indicated by the unit gray and resulting in acute radiation syndrome. For low level exposures there can be statistically elevated risks of radiation-induced cancer, called " stochastic effects" due to the uncertainty of them happenin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Radiation Health Effects
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ) * '' particle radiation'', such as alpha radiation (α), beta radiation (β), proton radiation and neutron radiation (particles of non-zero rest energy) * '' acoustic radiation'', such as ultrasound, sound, and seismic waves (dependent on a physical transmission medium) * '' gravitational radiation'', that takes the form of gravitational waves, or ripples in the curvature of spacetime Radiation is often categorized as either '' ionizing'' or '' non-ionizing'' depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules and break chemical bonds. This is an important distinction due to the large diff ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |