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Luminescent, Film, and Cryogenic Detectors
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
A charged particle passing through a dielectric material can cause the molecules along its path of travel to form dipoles, forming a segment of polarization. These molecules promptly return to the relaxed condition by the spontaneous emission of light, forming wavelets of light to propagate through the dielectric. If the particle is passing through the material at velocities below that of light in the same media, these successively released wavelets destructively interfere with each other, resulting in the suppression of luminescence. However, if the particle is traveling faster than the speed of light in the medium, these wavelets add constructively to produce a wavefront of light (depicted in Fig. 19.62, left). This pulse of light is known as Čerenkov (Cherenkov) radiation, after the Russian physicist who first observed the phenomenon in 1934 by noticing blue light emissions from water irradiated with gamma rays [Čerenkov 1934; see also Jelley 1955].39
Future Directions for SGRT
Published in Jeremy D. P. Hoisak, Adam B. Paxton, Benjamin Waghorn, Todd Pawlicki, Surface Guided Radiation Therapy, 2020
Cherenkov radiation occurs when a charged particle (e.g., an electron) moves with a phase velocity faster than the speed of light in a dielectric medium (e.g., the human body). Cherenkov radiation is emitted at wavelengths ranging from ultraviolet to the near infrared. The spectral intensity of the Cherenkov radiation is described by the Frank-Tamm’s formula (Equation 26.1): () dEdx=q24π∫vμ(ω)ω(1−c2v2n2(ω))dω
Basic Physics of X-ray Interactions in Matter
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
We should remember that light in a vacuum always travels at the same speed, c. As shown in Einstein's special relativity theory (Einstein 1905a), whenever light propagates in a vacuum, its speed possesses that exact value, no matter in which reference system it is measured. As we will see later, as light travels through materials it will slow down. For instance, the propagation or phase velocity, v, of light in water is only v = 3/4 · c. Therefore, it is not surprising that, in some dielectric (thus electrically polarizable) materials, light will propagate more slowly than high energetic charged particles such as electrons might do. This means that, under certain circumstances, the speed of electrons (although still less than c) can definitely outstrip the speed of light in these materials. If this is the case, so-called Cherenkov radiation (Cherenkov 1934) will be emitted. Although the Cherenkov effect is mostly used in high energy physics, nuclear physics, and astrophysics, more recently Cherenkov radiation has been used in in-vivo imaging for the detection of labeled biomolecules (Lui 2010).
Measuring time with high precision in particle physics
Published in Radiation Effects and Defects in Solids, 2022
B. Kaynak, S. Ozkorucuklu, A. Penzo
Methods to identify (charged) particles [determining their (rest) mass m] rely on the detection of Cherenkov radiation, which is emitted whenever charged particles pass through matter with a velocity v exceeding the speed (c/n) of light in the medium (with refraction index n). The Cherenkov detector is sensitive to β = v/c of the particle, whose rest mass m is identified by also determining its momentum p. Traditionally, three types of Cherenkov counters are defined (2): Threshold counters that measure the intensity of the Cherenkov radiation and are used to detect particles with velocities exceeding the threshold βth. The pulse height measured in the photon detector gives an estimate of the particle’s velocity above the threshold.Differential counters focus only Cherenkov photons with a certain emission angle onto the detector and, in this way, detect particles in a narrow interval of velocities.Imaging Cherenkov detectors make maximum use of the available information (Cherenkov angle and number of photons) and can be divided into two main categories: RICH (Ring Imaging Cherenkov) and DIRC (Detection of Internally Reflected Cherenkov light) devices.
The Effect of Wavelength Shifting Fibers on Cherenkov Glass Detectors for Gamma-Ray Measurements
Published in Nuclear Technology, 2022
Since the discovery of Cherenkov radiation in 1934, Cherenkov detectors have been developed and used in several fields, such as astrophysics experiments, radiochemistry, and biology.1 In these fields, the detectors have been used in many applications, like ring imaging Cherenkov detectors, time-of-flight positron emission tomography, detection of antineutrino by neutron sensing, threshold discrimination and particle identification, and X-ray imaging systems.1 Moreover, several types of Cherenkov detectors have been reported, including water, silica aerogel, gas, and glass. The most widely studied and used is the glass type, especially lead glass because of its high refractive index and high density. Cherenkov detectors have several advantages compared with other detector types, such as low noise due to the low-energy threshold of Cherenkov radiation and short decay constant. However, the yield of Cherenkov photons is low. Only several hundred Cherenkov photons can be generated per megaelectron-volt in several media, as shown in Fig. 1. This means about 10−3 of the particle’s energy is converted into Cherenkov photons, and this conversion is a factor of 100 smaller than scintillators.2