Instrumental correction of counting losses in nuclear pulse spectroscopy

Abstract

The virtual pulse generator (VPG) method of counting loss correction [1–3] is the first truly quantitative instrumental correction procedure taking into account both dead-time and pileup losses of a spectroscopy system over its full operative range of counting rates without the need for fast signal detection channels [4–6] or ambiguous post-processing of data [7,8], or the necessity to process artificial test pulses in addition to the detector signals [9]. Consequently, the VPG method is not limited in test frequency thus enabling the on-line generation of loss correction factors of sufficient statistical accuracy within extremely short periods of time. By adding weighting factors to the channels addressed by the analog-to-digital converter during the course of the measurement (instead of one as in conventional pulse height analysis) real-time correction of counting losses is made possible with millisecond time of response. Increased statistical accuracy may be achieved when using the VPG principle for loss-dependent prolonging of the measuring time similar to the live-time clock method. Both real-time and live-time modes of operation are provided for in a commercially available VPG correction module [10]. After a description of the set-up procedure of the module in connection with a likewise commercial semi-Gaussian shaping amplifier the performance of the VPG correction is exemplified to a level of 0.2% with the aid of repetitive two-source measurements in both the real-time and the live-time mode of operation.