Perspectives of Personnel External Dosimetry at Stanford Linear Accelerator Centre

Abstract

The need for providing personnel external monitoring for exposure to low energy photon (<150 keV) and beta radiation at the Stanford Linear Accelerator Center (SLAC) has been studied. At SLAC, a high energy electron accelerator facility, the major sources of low energy photons and betas (electrons and positrons) are from the induced activities in accelerator parts and components. Shower theory and measurements show that these induced activities are generally distributed deep inside the materials. Therefore, the low energy photons and betas will be significantly absorbed within the materials. Calculations based on the characteristics of the radionuclides produced by photonuclear reactions in several common materials have indicated that the beta doses on the material surface are small fractions of the photon doses. Field measurements at SLAC were made using Kodak type 2 films, Panasonic UD810 TLDs and a Victoreen 450 survey meter to determine the doses from low energy photons and betas, and then compared them with the doses from high energy photons. The X rays from the klystrons and the synchrotron radiation are also discussed. The results verify that the doses are small enough that, from the technical point of view, no personnel monitoring is needed for low energy photons and betas.