Control of X-ray hazard in femtosecond electron diffractometer

In a femtosecond electron diffractometer (FED) electrons are generated by a 266 nm laser beam with 8 μJ/pulse by hitting a gold-coated quartz disc (photocathode). The electrons are accelerated in an electric field up to 300 keV. 1 mm thick Silicon disk with a 400 μm hole is used as anode and also for collimation of the electron beam. The electrons passing through the hole will hit the sample and create the diffraction pattern. Due to the high voltage, a considerable amount of X-rays are produced inside the vacuum chamber of the diffractometer. The steel walls and the glass windows do not offer enough shielding to reduce the dose rate around the instrument to acceptable levels. In this paper we will present the engineering and administrative controls put in place to control the X-ray hazard and to comply with the requirements of the Ontario Ministry of Labour.