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Designing a System for Pulse Pile-Up Processing in Gamma Ray Spectroscopy Based on Digital Method

Hojjat, Saeed | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56371 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Hosseini, Abolfazl
  7. Abstract:
  8. In Radiation Detection Systems applied in Spectroscopy and Imaging, if the rate of particle incidence with detector is high, the output pulses being stacked up on each other will be expected, which is known as “Pulse Pile-up”. Pulse pile-up might result in a serious disorder of energy and timing data expected from the pulses. In recent decades and after successful implementation of pile-up rejection methods on analog circuits, considering development and progression in the field of digital, different algorithms based on pileup correction methods have been developed to obtain all spectrum information, whether energy, rise time and recorded pulses. Such methods can be compared in different aspects, such as efficiency factor in pulse pileup correction, resulting resolution of the algorithm, sensitivity to variation of pulse shapes, sensitivity to lowering the sampling rate, etc. but, the subject of implementation possibility, is a new question for which less attention has been paid. The present research pertains design and systemic implementation as Real Time for processing the piled-up pulses in Gamma radiation spectroscopy under digital method. In spite of the various researches in this approach with the target of improvement in performance of detection systems, the matter of pulse pileup in high count rates is already a challenging subject.In this thesis, at first, all methods of confrontation with pulse pileup are presented, classified and compared, and then, in order to have the best confrontation with pulse pileup condition in high count rates, it was decided to use pulse pileup lowering method in the first step, and after that, pileup correction to find the amplitude of the piled-up pulse. In next step, between methods of lowering pulse pile-up method, trapezoidal filter was chosen among other filters because of its better performance and for the correction of the piled-up pulses, the concept of the method of template matching was benefited to present an algorithm of high efficiency, with the ability to implement in the form of real-time on modules of digital signals processing. Through the steps of this method, all blocks required to design a digital spectroscopy system have been identified, and their algorithms, considering the target of the final system, which was having the improvement on resolution of digital spectroscopy systems in high count rates, were coded and implemented. System output in both, the hardware and software sides, indicated high efficiency of the designed system in correction of pulse pileup.In the third part, by the use of the times of stochastic events from uniform probability density function, and stochastic domains from Gaussian Probability Distribution Function, simulated pulses with the standard deviation of 0.05 which shows natural resolution of detectors, around specified average, were generated in low, middle and high-count rates. Results indicate that by applying the described pileup correction algorithm on high count rates, lowers the resolution from 0.112 to 0.054 and for the middle count rates, lowers the resolution from 0.079 to 0.052. Quantity of photo peak percentage in high count rate state, has been changed from 0.112 (for not having the pileup) to 0.911 (after applying the pileup correction algorithm)
  9. Keywords:
  10. Scintillation Detector ; Digital Signal Processing ; Hardware Implementation ; Pulse Pileup Correction ; Gamma Ray Spectrometry ; Digital Method

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