Abstract
One of the basic problems in the use of high energy therapy machines is the precise determination of the primary energy of the electron beam. A new way of estimating electron beam energy has been developed using Cerenkov radiation generated by relativistic electrons passing through a gas. Carbon dioxide and air, which have threshold values of 17.0 and 22 MeV at S.T.P. were studied. The detector consists of a gas filled pipe with a thin brass window at the front and a mirror set at 45 degrees to the beam at the far end which reflects the Cerenkov radiation onto the cathode of a photomultiplier tube. Energies of electrons from a 32 MeV linear accelerator, determined by this method agree within the limits of experimental error with those from the range energy method.