Digital pulse timing with semiconductor gamma-ray detectors using a wavelet transform technique

Obtaining precise timing information from semiconductor gamma-ray detectors is of great interest for a variety of applications such as high-resolution positron emission tomography. However, pulse timing with these detectors through the common constant-fraction discrimination (CFD) method is strongly affected by the time-walk error that results from the inherent variations in the shape of the detectors' pulses. This paper reports on the use of the wavelet transform for minimizing the time-walk error in digital CFD pulse timing with semiconductor gamma-ray detectors. The details of the method are described, and the experimental results with a 1 mm thick CdTe detector are shown. It is demonstrated that, by using the Haar wavelet transform of the digitized preamplifier pulses, the original tailed time spectrum of the detector with a time resolution of 8.22 ± 0.12 ns at full-width at half-maximum (FWHM) in the energy range of 300-550 keV improves to a symmetric time spectrum with a time resolution of 3.39 ± 0.02 ns (FWHM).