Evaluation of pulse shape discrimination performance of scintillation materials and PSD methods by using statistical models
Introduction
Optimization of electronic components and pulse processing features for neutron-photon pulse shape discrimination (PSD) at low energies (<500 keV neutron energy) by using “trial-and-error” methods is a time consuming and difficult task. The experimental evaluation of scintillation properties of materials and the comparison of PSD methods are affected by many factors, such as the light coupling and equipment adjustment, and conflicting conclusions can be obtained. For example, Sabbah, et al. [1]mentioned two methods (zero-crossing and charge comparison), and they concluded that charge comparison is better than the zero-crossing method. Ranucci [2]evaluated PSD properties of scintillators with statistical analysis, and his results show that the charge comparison method offers superior PSD performance relative to the zero crossing approach. However, Wolski and Moszynski [3]experimentally show that the zero-crossing technique is superior to the charge comparison at low energies. In order to eliminate human and equipment errors, statistical models for calculation of intrinsic PSD performance characteristics of scintillators and of PSD methods are necessary, especially at low energies where the number of photoelectrons is small and statistical fluctuations are a dominant factor. Other advantages for using models to evaluate scintillation materials, to compare methods, and to optimize PSD parameters include time-savings and cost.
Present statistical models for the zero crossing and charge comparison methods are based on Ranucci's work [2], but they are extended by including transit time spread and electronic noise. The models are tested with characterization data for early NE213, trans-stilbene and Borexino scintillators, and results show that the transit time spread and electronic noise are important for determining PSD performance. The models are used for estimation of PSD low-energy limitation of three scintillators, for comparison of PSD methods, and for PSD parameter optimization.
Section snippets
Description of the models
Statistical models that include scintillation decay time, transit time spread, and electronic noise of the equipment are developed and programmed for zero-crossing and for charge comparison methods. Assumptions for the models are as follows:
- 1.
The light output of scintillators is proportional to energy deposition, and ambient conditions such as temperature are negligible. Photoelectrons produced from an energy deposition event are assumed to be Gaussian distributed in time when more than 30
Results and discussions
Computer codes are written to implement the previous statistical models under different conditions, such as scintillation materials, CFD values, time windows and transit time spread of PMTs. The slow component of the distribution is selected for computation because its photon and neutron peak locations are in the same order as in the rise-time distribution of the zero-crossing method, where the photon peak is on the left side of the neutron peak. This arrangement makes comparison more
Conclusions
Two statistical models, which simulate photoelectron pulse processing for the zero crossing and charge comparison PSD methods, are developed for evaluation of the PSD properties of scintillators and PSD methods. Transit time spread and electronic noise contributions are included in the models so that they represent real detection systems and can be used to predict the PSD performance of a given scintillation detector and associated electronics. Calculations shows that these two factors
Acknowledgements
The authors would like to acknowledge discussions and comments of Dr. N. Hill, Dr. P. Groer, Dr. L.W. Townsend, Dr. J. T. Mihalczo, Dr. D. J. Downing, and Dr. H. L. Dodds, and to thank Mr. G. L. Graves and Mr. R. J. Bailey for technical assistance.
References (5)
- et al.
Nucl. Instr. and Meth.
(1968) Nucl. Instr. and Meth. A
(1995)
Cited by (12)
Principal Component Analysis for pulse-shape discrimination of scintillation radiation detectors
2016, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentA comparison of digital zero-crossing and charge-comparison methods for neutron/γ-ray discrimination with liquid scintillation detectors
2015, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentCitation Excerpt :The common methods of exploiting this property in scintillation detectors are the analog Charge-Comparison (CC) method which is based on the integrations of pulses over two different time intervals [2,3] and the analog Zero-Crossing (ZC) method [4,5] in which a zero-crossing time bears the pulse-shape information. A number of intercomparisons show that there are applications in which either may be preferable [6,7,8]. In recent years, there has been a strong interest in using digital techniques for n/γ discrimination applications and various digital algorithms, including the digital versions of the CC and the ZC methods have been used for this purpose [9,10].
Optimization of integration limit in the charge comparison method based on signal shape function
2014, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentCharacterization of a tunable quasi-monoenergetic neutron beam from deuteron breakup
2007, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and AtomsCitation Excerpt :The Stilbene detector is sensitive to both photons and neutrons. However, neutrons deposit energy in the detector through proton recoil rather than direct interaction with electrons [9]. Therefore, neutrons can be discriminated from photons by their longer pulse shape.
Identification of shielded neutron sources with the liquid scintillator BC-501A using a digital pulse shape discrimination method
2007, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentCitation Excerpt :This difference in the intensity of slow neutron and γ-ray components serves as a basis for PSD methods used to identify and characterize pulses. Several analog methods for PSD have been developed and studied in the past; examples are charge-comparison and rise-time methods [6,11,12]. Two main trends in the improvement of the PSD properties of liquid scintillators for applications in high count-rate fields have been pursued.
Recent developments in neutron detection
2000, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment