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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 general expression for thermionic emission current density is described by the Richardson-Dushman equation J=A(1−αr)T2e−ϕm/kT, where T is the absolute temperature, αr is a reflection coefficient that quantifies the quantum mechanical reflection of the electron wave function at the barrier interface. The quantity A(1 − αr) is generally referred to as the “effective Richardson constant.” It is this thermionic emission that contributes most to the thermal noise, or “dark current,” of the PMT device. As described by Eq. (14.18), the dark current increases as ϕm decreases. However, at room temperature it turns out that the thermionic current is small and usually of little consequence. With careful attention to the selection of the photocathode material, the production of ultra-low-noise PMTs is possible.
Overview of Reliability Assessments
Published in Franklin R. Nash, Reliability Assessments, 2017
“In this physics-of-failure model, applicable to filament metals heated in vacuum, the life of the bulb is exponentially dependent on filament temperature, or correspondingly, inversely proportional to the metal vapor pressure P” [19, p. 294]. The pressure is given in Equation 1.1, where for tungsten the heat of vaporization, ΔHvap = 183 kcal/mol [19], R = the gas constant = 1.9872 cal/deg mole and T is the absolute temperature. The expression in Equation 1.1 applies as well for the vapor pressure of liquids [20]. The exponential temperature dependence is also found for the thermionic emission of electrons from metals, where the heat of vaporization is replaced by the work function [21]. P=Po exp [−ΔHvapRT]
Understanding the Role of CVD Nanodiamond Thin Films in Solar Energy Conversion
Published in Kuan Yew Cheong, Two-Dimensional Nanostructures for Energy-Related Applications, 2017
M. A. Fraga, L. A. A. Rodríguez, R. S. Pessoa, V. J. Trava-Airoldi
The main advantage of thermionic energy conversion technology is the relatively simple and low cost material requirements compared to photovoltaics and potential high conversion efficiency achievable when waste heat recovery is included (Cryan et al. 2015). Thermionic emission is the promotion of electrons to the vacuum from a hot surface of a conducting material. Thermionic energy conversion is a relatively unexplored technology for the efficient conversion of thermal energy directly to electrical energy. In recent years, thermionic emission properties of different cathode materials and its potential uses in solar energy conversion have been much discussed. There is a demand by cathode materials with low work function values (<2 eV) for low temperature thermionic electron emission, which is a key phenomenon for waste heat recovery applications (Sherehiy 2014). N-type diamond, doped with nitrogen, phosphorus and sulfur, meets this requirement.
Thermo-elasto-plasto-dynamics of ultrafast optical ablation in polycrystalline metals. Part I: Theoretical formulation
Published in Journal of Thermal Stresses, 2021
The target material being considered in the study has its irradiated face positioned at z = 0. Upon the illumination of a laser pulse, electrons of high kinetic energy breaks away from the potential energy barrier and subsequently escapes from the target surface via multiphoton photoemission and thermionic emission. The emission process is accompanied by an intense electron flux. At z = 0, the total surface emission rate is the sum of the multiphoton photoemission rate and the thermionic emission rate where N = 2,3,… denotes the two- or more photon emission. Thermal emission of the high-temperature electrons is prominent at the picosecond scale at which the increase of electron temperature is significant [34]. Thermal contribution to the ejected electron flux (the thermionic emission rate ) is expressed by the Richardson-Duschman equation, where =120 A/(cm2 K2) is the Richardson coefficient, is the electron temperature on the target surface, the work function =4.25 eV is the barrier height of electrons, and =1.38064852 × 10−23 JK−1 is the Boltzmann constant.