Photon activation analysis of the scraper in a 200-MeV electron accelerator using gamma-spectrometry depth profiling

Abstract

For a high energy electron facility, the estimates of induced radioactivity in materials are of major importance to keep exposure to personnel and to the environment as low as reasonably achievable. In addition, an accurate prediction of induced radioactivity is also essential for the design, operation and decommissioning of a high energy electron linear accelerator. The research of induced radioactivity focuses on the photonuclear reaction, whose giant resonance response in the copper is ranging from 10 MeV to 28 MeV. The 200 MeV electron linac of NSRL is one of the earliest high-energy electron linear accelerators in P. R. China. The electrons are accelerated to 200 MeV by five acceleration tubes and collimated by the scrapers made of copper. At present, it is the first retired high-energy electron linear accelerator in domestic. Its decommissioning provides an efficient way for the induced radioactivity research of such accelerators, and is a matter of great significance to the accumulation of the induced radioactivity experience. When the copper target is impacted by an 158 MeV electron beam, the number of photons generated whose energy are in the range of giant resonance response is the largest. Thus, this paper focuses on the induced radioactivity for a copper target impacted by the 158 MeV electron beam. The slicing method is applied in the research. The specific activity of each slice was measured at cooling times of ten months and the results were compared with the prediction from the Monte-Carlo program FLUKA. The simulation results are in good agreement with the measurement results. The method by Monte Carlo simulation in this paper gives a reasonable prediction of the induced radioactivity problem for the high-energy electron linear accelerators, laying a foundation for the accumulation of the induced radioactivity experience.