NUCLEAR SPECTROSCOPY PULSE-HEIGHT ANALYSIS BASED ON DIGITAL SIGNAL-PROCESSING TECHNIQUES

A digital approach to pulse height analysis is presented. It consists of entire pulse digitization, using a flash analog-to-digital converte r (ADC), being its height estimated by a floating point digital signal processor (DSP) as one parameter of a model best fitting to the pulse samples. The differential nonlinearity (DNL) is reduced by simultaneo usly adding to the pulse, prior to its digitization, two analog signal s provided by a digital-to-analog converter (DAC). One of them is a sm all amplitude dither signal used to eliminate a bias introduced by the fitting algorithm. The other, with large amplitude, corrects the ADC nonlinearities by a method similar to the well known Gatti's sliding s cale [1]. The simulations carried out showed that, using a 12-bit flas h ADC, a 14-bit DAC and a dedicated floating point DSP performing a po lynomial fitting to the samples around the pulse peak, it is actually possible to process about 10000 events per second, with a constant hei ght pulse dispersion of only 4 on 8192 channels and a very good differ ential linearity. A prototype system based on the Texas Instruments fl oating point DSP TMS320C31 and built following the presented methodolo gy has already been tested and performed as expected.