Use of discrete Fourier transform to sum spectra in measurements with long counting times

When measuring nuclear spectra for long counting times, it is usual to split the acquisition in a set of spectra of shorter duration that are later added after correcting by drift during the measurements. We describe a method to determine the shifting correction by using the properties of the Discrete Fourier Transform (DFT). The method does not require assuming a particular spectral shape and the implementation is essentially independent of the kind of spectra being analyzed. The drift correction is defined for an integer number of channels. We present the results of the application to alpha-particle spectroscopy of long-lived nuclides.