Cygnus precision dosimetry — Calibration and measurements

The Cygnus Dual Beam Radiographic Facility consists of two identical radiographic sources each with a dose rating of 4-rad at 1 m, and a 1-mm diameter spot size. The development of the rod pinch diode was responsible for the ability to meet these criteria¹. The rod pinch diode in a Cygnus machine uses a 0.75-mm diameter, tapered tip, tungsten anode rod extended through a 9-mm diameter, aluminum cathode aperture. When properly configured, the electron beam born off the aperture edge can self-insulate and pinch onto the tip of the rod creating an intense, small x-ray source. The Cygnus sources are utilized as the primary diagnostic on Subcritical Experiments that are single-shot, high-value events. In such an application, there is a necessity for reliability and reproducibility, as well as a precise measurement of these qualities. On Cygnus, the primary diagnostic for reliability and reproducibility is dosimetry. Thermoluinescent² dosimeters (TLDs) are used for time-integrated dose, and PIN diodes are used for time-resolved dose. Precision dosimetry calibration methods and results will be presented. Cygnus reliability and reproducibility using TLD dosimetry measurements will be given.