Investigations for the use of the fast digitizers with [formula omitted] detectors for radiative capture measurements at GELINA

Abstract

The relatively long dead time in conventional data acquisition systems that provide simultaneously the pulse height and the time information for the detected events hinders cross-section measurements with high count rates. This is the case for capture cross-section measurements at the time-of-flight facility GELINA using high radioactive samples or thick samples of materials having strong resonances. Either the high average count rate (e.g. due to the radioactivity of the sample) or the high instantaneous count rate for strong resonances results in a large dead time correction. One solution to reduce the impact of the dead time is the use of a data acquisition system based on fast digitizers. The performances of two commercial digitizers (CAEN N172B and Acqiris DC282), coupled to a C 6 D 6 scintillator, have been tested in terms of pulse height linearity and resolution, dead time and time resolution. The signal processing was done on-line obtaining simultaneously the pulse height and time information for each detected event. With both digitizers a comparable pulse height linearity and resolution has been obtained as with a conventional system. The total dead time of both digital systems is at least a factor 5 shorter than the one for the conventional system. The main difference in performance between the two digitizers is the time resolution. For a relatively large scintillator, a time resolution of about 2 ns has been achieved with the DC282 module and the conventional system while the time resolution was limited to 15 ns with the CAEN N1728B module. For most nuclei a 15 ns time resolution is sufficient to perform resonance shape analysis. Therefore, the CAEN N1728B module can be used for the majority of capture cross-section measurements at GELINA. However, for nuclei with low level density, for which the resolved resonance region extends to the keV-region, a better time resolution is required and the Acqiris DC282 module has to be used.