A fast-stretcher for an easy acquisition of the fast component of BaF 2 detectors signals

A gate-free fast-stretcher circuit has been developed for an easy acquisition of the fast and slow components of the signals produced by BaF 2 scintillators, in order to discriminate the types of incident particles. In experiments where many detectors are used, these measurements are normally performed providing the signal to two QDC's (Charge to Digital Converter) and using logical signals of different widths as gates. One gating signal is short to integrate the fast part of the signal only; the other is much longer to integrate the whole signal. Such a measurement technique has many inconveniences. One of the most critical is that the analog signals fed into the QDC must be delayed through long and cumbersome transmission lines to synchronize them with the QDC gate signals, which degrades the quality of the fast component. We have developed a new circuit structure that addresses these issues. The circuit uses no delay line. It simply builds two slow Gaussian signals: the first, called "Fast", is obtained after stretching the fast signal component, and is proportional to its amplitude; the second, called "Slow", is proportional to the energy of the entire signal. These outputs are easily acquired with a standard peak ADC with no gate-timing problem. An excellent Fast-Slow separation has been obtained even with small input signals of only a few millivolts.