06_bolozonoya_two_pase - 616 A. I. Bolozdynya: Two-phase...

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1070-9878/06/$20.00 © 2006 IEEE 616 Two-phase Emission Detectors: Foundations and Applications Alexander I. Bolozdynya Department of Physics, Case Western Reserve University 10900 Euclid Avenue Cleveland, Ohio 44106-7079, U.S.A. ABSTRACT A new class of radiation detectors has recently been introduced into experimental practice. The detectors employ the effect of effective extraction of charge carriers from condensed non-polar dielectrics into the equilibrium gas phase under influence of an applied electric field. This approach makes possible to combine in one detector condensed detecting medium of a large mass, necessary for detecting rare events, with a rarefied phase, in which signals due to a few or even single electrons can be amplified and measured through the gas-discharge or electroluminescence processes. We will discuss properties of working media that can be used in emission detectors, the physics of charge carrier penetration through the inter-phase boundary and we will also review applications of two-phase dielectrics for detecting ionizing radiation and exotic particles. Index Terms Electron emission, ion emission, electroluminescence devices, radiation detectors, elementary particles, superconducting devices. 1 INTRODUCTION EXCESS electrons, liberated by ionizing radiation, i.e. chemically unbound to molecules of condensed nonploar dielectrics, can be efficiently transferred into the gas phase from quasi-free states in condensed Ar, Kr, Xe, CH 4 , solid Ne and some liquid saturated hydrocarbons, as well as from localized states in dielectrics with a positive ground state potential such as helium. Using the transition of electrons across phase boundaries allows effective amplification of weak signals in order to construct novel extremely sensitive radiation detectors. 2 CHARGE CARRIERS EMISSION FROM NON-POLAR DIELECTRICS Since the dielectric constant of non-polar dielectrics in the condensed phase is larger than that of the saturated gas, charge carriers experience an image potential A near the interface acting against their emission into the gas. The image potential is temperature dependent approaching zero at temperatures close to the critical temperature. At the electric field E , applied to extract electrons from the condensed dielectric, and the energy of the ground state of quasi-free electrons V o , the total potential energy of electrons in the vicinity of the inter-phase surface may be described in terms of a one-dimensional potential (Figure 1a). o V V(z) z 0 p dN /dp z z e e e (a) o V V(z) z 0 e 1 V (b) Figure 1. Potential energy near the interface of two-phase dielectrics favorable for emission of excess electrons from the quasi-free state (a) and from the localized state (b). Manuscript received on 15 September 2005, in final form 3 March 2006.
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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06_bolozonoya_two_pase - 616 A. I. Bolozdynya: Two-phase...

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