Calibration sources of Cerenkov radiation

We report on attempts to construct and simulate low intensity sources of Cerenkov radiation with accurately known spectral intensity. These sources will be used to calibrate photomulti-pliers for the Sudbury Neutrino Observatory. We have used ^Sr as a radioactive beta source located at the center of a sphere of ultraviolet transparent acrylic. The production of Cerenkov radiation by stopping electrons in acrylic has been calculated (by several methods) using the theory of Frank and Tamm. The systematic effects of the variation of the refractive index with frequency have also been considered. The propagation of the Cerenkov radiation out of the sphere has been studied with reference to the problem of total internal reflection. The total Cerenkov radiation output of these spheres from a single decay is calculated with a systematic uncertainty of a few percent. The amount of activity in each source also contributes to the uncertainty of the Cerenkov radiation intensity at the one percent level.