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The detector efficiency depends on the radiation energy to be determined and the density and type of detector material. In XRF spectrometers three different types of X-ray detectors are used: gas-filled detectors, scintillation detectors and semiconductor detectors.
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X-ray detectors are devices used to measure the flux, spatial distribution, spectrum, and/or other properties of X-rays.
X-rays are a form of electromagnetic radiation, similar to visible light. Unlike light, however, x-rays have higher energy and can pass through most objects, including the body. Medical x-rays are used to generate images of tissues and structures inside the body.
- Overview
- Production of X-rays
- Detection of X-rays
There are three common mechanisms for the production of X-rays: the acceleration of a charged particle, atomic transitions between discrete energy levels, and the radioactive decay of some atomic nuclei. Each mechanism leads to a characteristic spectrum of X-ray radiation.
In the theory of classical electromagnetism, accelerating electric charges emit electromagnetic waves. In the most common terrestrial source of X-rays, the X-ray tube, a beam of high-energy electrons impinges on a solid target. As the fast-moving electrons in the beam interact with the electrons and nuclei of the target atoms, they are repeatedly deflected and slowed. During this abrupt deceleration, the beam electrons emit bremsstrahlung (German: “braking radiation”)—a continuous spectrum of electromagnetic radiation with a peak intensity in the X-ray region. Most of the energy radiated in an X-ray tube is contained in this continuous spectrum. Far more powerful (and far larger) sources of a continuum of X-rays are synchrotron particle accelerators and storage rings. In a synchrotron, charged particles (usually electrons or positrons) are accelerated to very high energies (typically billions of electron volts) and then confined to a closed orbit by strong magnets. When the charged particles are deflected by the magnetic fields (and hence accelerated via the change in their direction of motion), they emit so-called synchrotron radiation—a continuum whose intensity and frequency distribution are determined by the strength of the magnetic fields and the energy of the circulating particles. Specially designed synchrotron light sources are used worldwide for X-ray studies of materials.
In an X-ray tube, in addition to the continuous spectrum of radiation emitted by the decelerating electrons, there is also a spectrum of discrete X-ray emission lines that is characteristic of the target material. This “characteristic radiation” results from the excitation of the target atoms by collisions with the fast-moving electrons. Most commonly, a collision first causes a tightly bound inner-shell electron to be ejected from the atom; a loosely bound outer-shell electron then falls into the inner shell to fill the vacancy. In the process, a single photon is emitted by the atom with an energy equal to the difference between the inner-shell and outer-shell vacancy states. This energy difference usually corresponds to photon wavelengths in the X-ray region of the spectrum. Characteristic X-ray radiation can also be produced from a target material when it is exposed to a primary X-ray beam. In this case, the primary X-ray photons initiate the sequence of electron transitions that result in the emission of secondary X-ray photons.
In 1913 the English physicist Henry Moseley discovered a simple relationship between the wavelengths of the X-ray emission lines from a target and the atomic number of the target element—the wavelengths are inversely proportional to the square of the atomic number. Known as Moseley’s law, this relationship proved to be a definitive tool in the determination of atomic numbers in the early days of atomic physics. X-ray fluoresence techniques, in which the wavelengths of characteristic X-rays are recorded following the excitation of a target, are now commonly used to identify the elemental constituents of materials.
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There are three common mechanisms for the production of X-rays: the acceleration of a charged particle, atomic transitions between discrete energy levels, and the radioactive decay of some atomic nuclei. Each mechanism leads to a characteristic spectrum of X-ray radiation.
In the theory of classical electromagnetism, accelerating electric charges emit electromagnetic waves. In the most common terrestrial source of X-rays, the X-ray tube, a beam of high-energy electrons impinges on a solid target. As the fast-moving electrons in the beam interact with the electrons and nuclei of the target atoms, they are repeatedly deflected and slowed. During this abrupt deceleration, the beam electrons emit bremsstrahlung (German: “braking radiation”)—a continuous spectrum of electromagnetic radiation with a peak intensity in the X-ray region. Most of the energy radiated in an X-ray tube is contained in this continuous spectrum. Far more powerful (and far larger) sources of a continuum of X-rays are synchrotron particle accelerators and storage rings. In a synchrotron, charged particles (usually electrons or positrons) are accelerated to very high energies (typically billions of electron volts) and then confined to a closed orbit by strong magnets. When the charged particles are deflected by the magnetic fields (and hence accelerated via the change in their direction of motion), they emit so-called synchrotron radiation—a continuum whose intensity and frequency distribution are determined by the strength of the magnetic fields and the energy of the circulating particles. Specially designed synchrotron light sources are used worldwide for X-ray studies of materials.
In an X-ray tube, in addition to the continuous spectrum of radiation emitted by the decelerating electrons, there is also a spectrum of discrete X-ray emission lines that is characteristic of the target material. This “characteristic radiation” results from the excitation of the target atoms by collisions with the fast-moving electrons. Most commonly, a collision first causes a tightly bound inner-shell electron to be ejected from the atom; a loosely bound outer-shell electron then falls into the inner shell to fill the vacancy. In the process, a single photon is emitted by the atom with an energy equal to the difference between the inner-shell and outer-shell vacancy states. This energy difference usually corresponds to photon wavelengths in the X-ray region of the spectrum. Characteristic X-ray radiation can also be produced from a target material when it is exposed to a primary X-ray beam. In this case, the primary X-ray photons initiate the sequence of electron transitions that result in the emission of secondary X-ray photons.
In 1913 the English physicist Henry Moseley discovered a simple relationship between the wavelengths of the X-ray emission lines from a target and the atomic number of the target element—the wavelengths are inversely proportional to the square of the atomic number. Known as Moseley’s law, this relationship proved to be a definitive tool in the determination of atomic numbers in the early days of atomic physics. X-ray fluoresence techniques, in which the wavelengths of characteristic X-rays are recorded following the excitation of a target, are now commonly used to identify the elemental constituents of materials.
Britannica Quiz
Medical Conditions and Discoveries Quiz
Photographic film was used by Röntgen as one of the first X-ray detectors, and this simple technique remains in wide use in medical applications. The process of exposure is initiated by X-ray photons ionizing radiation-sensitive silver halide crystals in an emulsion on the film surface; the resulting photochemical change of the affected crystals darkens the exposed area (see radiation measurement: Photographic emulsions).
Photographic techniques, while much improved upon since the time of Röntgen and still extremely useful for qualitative applications, are not well-suited for more quantitative measurements of X-ray intensities and spectral content. A number of more effective detection methods have been developed. In a Geiger-Müller tube, or Geiger counter, incoming X-ray photons ionize atoms in a gas-filled volume. An applied high voltage induces further ionizations from collisions between liberated electrons and neutral atoms, creating an avalanche of charged particles and a large electrical pulse that is easily detected. More sophisticated detection schemes based on the ionization of gas atoms can discriminate between X-rays of different energies (see radiation measurement: Proportional counters). Other common detection schemes rely on the ability of X-rays to produce visible fluorescence in crystals (see scintillation counter) and charge separation in semiconductors (see radiation measurement: Semiconductor detectors).
An X-Ray Detector is a component of the X-ray/MRI system that is compatible with MRI systems and is used to capture digital images of anatomic structures during imaging procedures. AI generated definition based on: Biomedical Engineering in Gastrointestinal Surgery, 2017
An X-ray detector is a device that converts X-ray energy into visible light, allowing for the detection and imaging of X-rays in various applications such as medical equipment and industrial testing. AI generated definition based on: Materials Today Advances , 2022
Nov 18, 2020 · This new generation of hybrid detectors demonstrates low dark current under electric fields needed for high sensitivity X-ray imaging applications. The detectors have a linear response to...
