Design and implementation of real time digital pulse processor for nuclear instrumentation

Digital pulse processing for nuclear applications related to measurement of radiation energy has found great advantages over traditional analog pulse processing due to the fast sampling facility. A distortion in energy spectrum and degradation in timing resolution is obtained when pulse pile-up occurred as it degrades the Signal-to-Noise Ratio (SNR) of nuclear data. Piled-up pulses are commonly removed in most traditional methods if they are detected, but in this case, getting a clean spectrum becomes a problem especially for high count rate radiations as most of the detected radiation pulses are piled-up. Also the correct estimation of radiation source activity is another problem as it related to the number of radiation pulses that the detector produces. Nuclear instrumentation also in case of measurement of neutron energies in different neutron experiments is affected by the predominant gamma background. The counting statistics in such experiments is low, and the gamma background degrades the acquired data. In the presence of gamma ray background, it is necessary to apply pulse processing technique to distinguish neutron pulses from gamma pulses. Accordingly, the discrimination between neutron and gamma pulses is a very vital process for nuclear physics applications. The discriminator is based on the fact that the detector output pulses have different decaying tails for neutron and gamma rays. A longer tail is expected for a neutron pulse than for a gamma pulse. Each acquired pulse is passed through a chain of signal processing algorithms that compares the total energy with the pulse amplitude to differentiate neutron and gamma pulses. This thesis proposes two different approaches for the recovery of pile-up problem to enhance both the system resolution and count rate. The proposed approaches consist of two sages; detection and recovery. The pile-up detection stage of the two approaches is performed using the same procedures while the recovery stage is performed using two different methods. The first method named as the extrapolation based method and it based on extrapolating the first pulse of the piled-up pulses after point of intersection by fitting the pre-amplifier data output. The extrapolated pulse is then used to recover (extract) the piled-up pulse to estimate its parameters. The second method of pile-up recovery stage is called reference based method and it based on using a reference pulse which is a normalized radiation even. The first pulse is then extracted in this method by multiplying the stored reference pulse by the peak of the first pulse.