  The main task of an energy calibration is to find a relation between
pulse-height values and the corresponding energies. Doing this for each
pulse-height channel individually requires an elaborated input spectrum with an
excellent counting statistics and a sophisticated data analysis. This work
presents an easy to handle energy calibration process which can operate
reliably on calibration measurements with low counting statistics. The method
uses a parameter based model for the energy calibration and concludes on the
optimal parameters of the model by finding the best correlation between the
measured pulse-height spectrum and multiple synthetic pulse-height spectra
which are constructed with different sets of calibration parameters. A
CdTe-based semiconductor detector and the line emissions of an 241 Am source
were used to test the performance of the correlation method in terms of
systematic calibration errors for different counting statistics. Up to energies
of 60 keV systematic errors were measured to be less than 0.1 keV. Energy
calibration via correlation can be applied to any kind of calibration spectra
and shows a robust behavior at low counting statistics. It enables a fast and
accurate calibration that can be used to monitor the spectroscopic properties
of a detector system in near realtime.
