Measurements of RF Cavity Voltages by X-ray Spectrum Measurements
  Measurement of the endpoints of X-ray spectra emitted from RF cavities is a useful non-invasive technique for measuring peak voltages within the cavities. The matching of calculated X-ray spectra to measured spectra is described, with emphasis upon the endpoint region. 
J.P. Duke, A.P. Letchford and D.J.S. Findlay