Post-print, re-edited for inclusion in T. Tabata, edited with commentary, The Collected Works of Tatsuo Tabata Volume 15, IDEA-TR 19 (2018), of the paper published in Radiation Physics and Chemistry Vollume 54, Issue 1, January 1999, Pages 11–18 (doi:10.1016/S0969-806X(97)00285-5) Copyright © 1999 by Elsevier Science Ltd. Fractional Energies of Backscattered Electrons and Photon Yields by Electrons Tatsuo Tabata a , Pedro Andreo b , Kunihiko Shinoda c a Research Institute for Advanced Science and Technology, Osaka Prefecture University, Sakai, Osaka 599-8570, Japan b Dosimetry Section RIHU, International Atomic Energy Agency, P.O. Box 200, A-1400 Vienna, Austria c Non-Destructive Inspection Co., Ltd., Nishi-ku, Osaka 550-0014, Japan (Received 1 August 1997; received in revised form 30 August 1997; accepted 6 September 1997) Abstract Fractional energies f BE of backscattered electrons and the photon yields Y from semi-infinite absorbers bombarded by electrons have been calculated with the ITS Monte Carlo system, and analytic expressions have been formulated for these pa- rameters. Besides the Monte Carlo results, experimental data collected from the literature have been used to determine the expression for f BE . The two expres- sions are applicable to absorbers of atomic numbers from 4 to 92. The region of incident-electron energy considered is from 5 keV to 100 MeV for f BE , and from 0.1 to 100 MeV for Y . 1. Introduction Estimates of the energy deposited in effectively semi-infinite absorbers irradiated by electrons are frequently based on the knowledge of the energy-backscattering coefficient η BE of electrons and the photon yield Y by electrons. The former, η BE , is defined as the ratio of the total energy carried away by backscattered electrons to the total incident energy. The photon yield Y is defined as the fraction of the initial energy T 0 of an electron that is converted into photon energy as the electron slows down to rest. In algorithms for energy deposition by electrons, η BE and Y are used to obtain a normalization factor f for the photon-free component (essentially equal to the collision component) of the energy deposition (Tabata and Ito, 1974; Tabata et al., 1990, 1991; see for a similar use, Attix, 1991): f =1 - η BE - Y. (1) It is therefore desirable to have a comprehensive set of data on η BE and Y or analytic expressions for these parameters. 1