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Light Collection Devices
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
The basic design of a photomultiplier includes (1) a transparent envelope, typically constructed of glass, (2) a photocathode, (3) a series of dynodes, and (4) an anode. Each component, described in the following sections, plays an important role in the efficiency, timing, and ultimate energy resolution of the spectrometer. The photomultiplier is a simple device to understand. The basic PMT, depicted in Fig. 14.2, has a photocathode that is located so as to absorb light emissions from a light source such as a scintillating material. When photons of light strike the coating on the photocathode, they emit electrons that can diffuse through the coating to the surface facing the vacuum of the tube. A fraction of these diffusing electrons then escape the surface and enter the vacuum tube. A voltage applied to the tube guides the liberated electrons to an adjacent electrode called a dynode. As an electron approaches the dynode, it gains speed and energy from the electric field formed by the applied voltage. Hence, when it strikes the dynode, it again causes more electrons to become liberated into the tube. These newly liberated electrons are then guided by the electric field to the next dynode where more electrons are liberated and so on. As a result, the total number of electrons released is a function of the number of dynodes in the PMT and the photoefficiency of the photocathode and the dynodes.
Diamond Vacuum Electronics
Published in Mark A. Prelas, Galina Popovici, Louis K. Bigelow, Handbook of Industrial Diamonds and Diamond Films, 2018
When light levels are low, the photomultiplier tube is the detector of choice due to its unmatched sensitivity for visible or ultraviolet wavelength photons. A photomultiplier tube consists of a photocathode, a dynode chain (continuous or discrete), and an anode. If a photon of energy greater than the photocathode work function strikes the photocathode a photoelectron is emitted a fraction of the time. The dynode chain allows one to detect this single photoelectron by amplifying the emission event. An attractive potential difference is established between the photocathode, successive dynodes and the anode. The photoelectron is accelerated to the first dynode and the collision of the electron with the dynode causes additional electrons to be emitted. Common dynode materials emit approximately three secondary electrons per incident electron. The secondary electrons are accelerated to the next dynode, collide with the dynode and produce a new, amplified burst of electrons. After passing through roughly twelve dynodes, the initial photoelectron will have grown to a packet of 105 to 106 electrons. The anode collects the electron bunch and the signal is fed into appropriate signal processing electronics.
Detectors and Recording Materials
Published in Rajpal S. Sirohi, Optical Methods of Measurement, 2018
The series of dynodes constitutes a low-noise amplifier. These dynodes are at progressively higher positive potential. A photoelectron emitted from the cathode is accelerated toward the first dynode. Secondary electrons are ejected as a result of the collision of the photoelectron with the dynode surface. This is the first stage of amplification. These secondary electrons are accelerated toward the more positive dynode, and the process is repeated. The amplified electron beam is collected by the anode. The multiplication of electrons at each dynode or the electron gain A depends on the dynode material and the potential difference between the dynodes. The total gain G of the PMT is given by () G=An
Study of crystalline scintillator response with development of single-electron beam of 2–6 MeV at KU-FEL
Published in Journal of Nuclear Science and Technology, 2023
Yusuke Uozumi, Toshimasa Furuta, Yuji Yamaguchi, Heishun Zen, Toshiteru Kii, Hideaki Ohgaki, Elena Velicheva, Vladimir Kalinnikov, Zviadi Tsamalaidze, Petr Evtoukhovitch
Three scintillator crystals (PWO, LaBr3:Ce, and LYSO:Ce) were used as in our previous work. Each was covered by light-shielding tape and light-reflecting tape (Teflon sheet), and one of its faces was directly coupled to a photomultiplier tube (PMT) (R329–02; Hamamatsu Photonics, Japan) via lubricating silicone grease. The R329–02 PMT is a 12-stage-dynode type with a 51-mm-diameter bialkali photocathode [19], and it is built into a PMT assembly (H6410; Hamamatsu Photonics, Japan) [20] along with a voltage divider. When the anode peak current Ia exceeds a limit, the PMT gain decreases due to the space charge effect in the latter stages of the electron multiplier. The approximate expression for Ia [21] is given by
Occupational exposure to beryllium in French industries
Published in Journal of Occupational and Environmental Hygiene, 2019
Jérôme Devoy, Aurélie Martin Remy, Bénédicte La Rocca, Pascal Wild, Davy Rousset
Inductively Coupled Plasma Mass Spectrometer (ICP-MS, Varian 820-MS, Palo Alto, CA), with an external sample introduction assembly with a Peltier-cooled spray chamber, a concentric glass nebulizer, a peristaltic pump mounted outside the torch box and an SPS3 auto sampler, was used for airborne and urinary samples. A PFA Nebulizer and a spray chamber, as well as Pt skimmer and sampler cones, were used for the airborne and urinary samples (containing HF). A discrete dynode electron multiplier detector provided nine decades of dynamic range in an all-digital pulse design. The Varian 820-MS system also featured a Collision Reaction Interface (CRI) providing fast, flexible, interference-free analysis using simple collision and reaction gases.