Spectroscopic technique for optimal P-Z setting in gamma-ray detection

A spectroscopic technique for optimally setting the Pole-Zero (P-Z) compensation in a digital spectrometer has been implemented, which has substantially improved the resolution of the measurements at high count rates. Before ADC conversion the signal undergoes an analog preprocessing, consisting of Pole-Zero compensation and simple three-pole shaping, which is the proper antialiasing-filter shape in this context. A subsequent suitable digital filter optimizes the overall weight function and introduces digital baseline restoration. It is well known that an imperfect P-Z setting causes pulse-tail pileup which is seen as an additional noise and may impact significantly on the final resolution of the measurements, particularly at high count rates. We introduce a spectroscopic technique which permits a second-order tuning of the P-Z compensation. Such a fine-tuning degree, which definitely could not be attained by oscilloscope observation, yields a substantial improvement in the performance of the system. Namely, at a count rate of 20kcounts/s the second-order tuning (1% adjustment) yields a 30% narrowing of the width of the 1.33MeV 60Co line.