Activation of solid materials in a medical linear electron accelerator

Using the medical linear electron accelerator SL 75/20 supplied by Philips and employing a radiation time of 15 minutes with the 16 MeV high-energy photon stage, we measured the radioactivities induced by photons and neutrons, at the output elements (target, compensator body, wedge filter, diaphragms), at the positioning table of the patient and at a barium oxide concrete wall, via Ge(Li) spectrometry. The resulting local dose rates were determined. The radioactivity that is mainly caused by the nuclides W-187, Sb-120, Cu-64, Cu-62, Ni-57, Mn-56, Al-28, Mg-27 and Al-26m results (with the exception of the target) in a local γ-dose rate of the order of the 10 μSv/h, respectively. β radiation, however, is expected to markedly increase these values. The total dose rate of 15 mSv/h in the target region, which retains this indeed rather high level even 7 minutes after radiation has been discontinued, makes it imperative to control the local dose rate and if necessary - depending on the irradiation conditions - to introduce waiting times of several hours if manipulations in this area have to be performed. (orig.)