Energy calibration of charged particle detectors using discrete and continuous energy spectra of 137Cs.

An improved method for energy calibration of particle detectors is presented utilizing both the discrete and continuous spectra from the conversion electrons and beta particles of a radioisotope of  137Cs. This method considers the instrument response against the discrete spectrum from the conversion electrons at 624.22 keV and the continuous spectrum from the beta particles emitted by the unique first forbidden transition in the energy range of approximately 120-513 keV. The instrument response is determined by fitting model functions to the measurements, from which the energy scale and energy resolution of the instrument are derived. Inclusion of the beta particles in this method enables a determination of the energy scale in a broader energy range as well as the DC-offset and non-linearity of the instrument. This is an improvement from the conventional method that only utilizes a mono-energetic peak from the conversion electrons. A detailed description of the procedure is provided, from constructing the model functions to determining the instrument response. Results of the method, as successfully applied to a space-borne instrument, are provided to demonstrate the method.