Mass Attenuation Coefficients
Mass attenuation coefficients are critical measurements that quantify how electromagnetic radiation, particularly x-rays and gamma rays, is absorbed or scattered by various materials. Attenuation refers to the loss of energy as these waves interact with substances, affecting their penetrating ability. This coefficient is influenced by the energy of the photons, as well as the material's density and thickness, making it a more standardized measure than the linear attenuation coefficient, which does not account for density.
In practice, mass attenuation coefficients are essential in fields like medical imaging and astrophysics. They help determine the required shielding materials to protect humans from harmful radiation and are also used to analyze astronomical phenomena through the study of gamma rays. Researchers rely on established tables of mass attenuation coefficients for various substances, such as lead and water, to facilitate their calculations and applications. Overall, understanding how different materials affect the attenuation of radiation underpins many scientific and practical applications, from healthcare to cosmic exploration.
Mass Attenuation Coefficients
FIELDS OF STUDY: Astrophysics; Theoretical Astrophysics
ABSTRACT: Mass attenuation coefficients are measurements of how waves of energy and sound are absorbed or scattered by various materials.
Attenuation and Penetration
Mass attenuation coefficients are measurements of how electromagnetic radiation is absorbed or scattered by various materials. "Attenuation" is the loss of energy from waves or particles due to interaction with another object. For example, x-rays attenuate when they come in contact with lead, and visible light attenuates when it comes in contact with darkened glass.
X-rays and gamma rays are two types of electromagnetic radiation. They are used in medical imaging and cosmology because they can penetrate better than other types of waves. The type of electromagnetic wave is determined by the wavelength. Gamma rays have the shortest wavelengths, followed by x-rays. Many waves, including visible light, can scatter when they hit an object. However, x-rays and gamma rays penetrate more deeply into the objects. Penetration is the opposite of attenuation.
Electromagnetic radiation has characteristics of both waves and particles, and it can be treated as either depending on the situation. Particles of electromagnetic radiation are called photons. The extent to which radiation will penetrate an object depends on the energy of its photons. It also depends on the attributes of the object it is penetrating, such as density or thickness. These factors all affect a material’s mass attenuation coefficient.
A related value is the linear attenuation coefficient, which also measures how much a particular type of energy can penetrate a certain material. However, it does not take into account the density of the material. The mass attenuation coefficient, which can be found by dividing the linear attenuation coefficient by the density of the material, can be used as a standard measurement.
Contributing Factors
In astrophysics, mass attenuation coefficients are most often used when studying x-rays and gamma rays. Various different interactions cause x-rays to attenuate, including Compton scattering, Rayleigh scattering, the photoelectric effect, pair production, and triplet production. Scientists calculate linear attenuation coefficients by taking all these probable interactions into account.
Attenuation can change depending on the density of the material the x-ray is passing through. For example, an x-ray passing through water vapor will attenuate differently from one passing through ice. Even though the two materials are chemically the same, they have different densities. Because of this, scientists often choose not to work with the linear attention coefficient. Instead, they work with the mass attenuation coefficient, which is measured in square centimeters per gram.
Determining Values
Scientists often work with tables of preestablished mass attenuation coefficients. These standard values were developed based on both observations and theoretical knowledge about various substances. Commonly used mass attenuation coefficients include lead, water, iron, and air.
To determine a mass attenuation coefficient via direct observation, a scientist would follow these steps: (1) direct a beam of photons with, all of the same energy, at a specific material; (2) measure the intensity of the photons before they enter the material; (3) measure the intensity of the photons after they exit the material; (4) compare the measurements to determine how many photons were absorbed and scattered; (5) take the density and thickness of the material into account.
Applications of Mass Attenuation Coefficients
The amount of energy that is absorbed by a particular material will determine where that energy goes and what it affects. Each layer of an object will attenuate the same percentage of photons. This means that the first layer will attenuate the most photons, while fewer and fewer photons will be attenuated with each successive layer that is penetrated. This phenomenon has a number of practical applications. For example, because x-rays can be harmful to humans, scientists must be careful when working with them. If they know how different materials attenuate x-rays, they can determine how much of which material is needed to shield people from harm.
Another application of mass attenuation coefficients is in astronomy. For example, gamma-ray astronomers observe gamma rays in the universe. Gamma rays travel at the speed of light and are unaffected by electric or magnetic fields, which makes them ideal tools for scientific observation. Their interactions with various materials in space help scientists gather data on celestial objects and the processes that may have shaped them. Studying how different materials attenuate gamma rays may also shed light on the origins of the radiation. Other forms of electromagnetic radiation, such as x-rays and bremsstrahlung, can be studied in this manner as well.
PRINCIPAL TERMS
- electromagnetic radiation: energy produced by the interaction of electric and magnetic fields that travels in the form of electromagnetic waves.
- wavelength: the distance between a point on one wave and the same point on the next wave.
Bibliography
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