Digital Charge Comparison Method Research Articles

Measuring and unfolding fast neutron spectra using solution-grown trans-stilbene scintillation detector

We propose an overall procedure for measuring and unfolding fast neutron spectra using a trans-stilbene scintillation detector. Detector characterization was described, including the information on energy calibration, detector resolution, and nonproportionality response. The digital charge comparison method was used for the investigation of neutron-gamma Pulse Shape Discrimination (PSD). A pair of values of 600 ns pulse width and 24 ns delay time was found as the optimized conditions for PSD. A fitting technique was introduced to increase the trans-stilbene Proton Response Function (PRF) by 28% based on comparison of the simulated and experimental electron-equivalent distributions by the Cf-252 source. The detector response matrix was constructed by Monte-Carlo simulation and the spectrum unfolding was implemented using the iterative Bayesian method. The unfolding of simulated and measured spectra of Cf-252 and AmBe neutron sources indicates reliable, stable and no-bias results. The unfolding technique was also validated by the measured cosmic-ray induced neutron flux. Our approach is promising for fast neutron detection and spectroscopy.

A comparison of four different digital algorithms for pulse-shape discrimination in fast scintillators

A comparison of four algorithms for the digital discrimination of neutrons and γ ‐ rays in organic scintillation detectors is described. The mixed fields from four different isotopic neutron sources have been investigated with a fast digital processing system. This system has been used to digitise the raw sampled data for each individual pulse collected for each of the mixed radiation fields. The discrimination methods considered are the digital Charge Comparison Method, Pulse Gradient Analysis, Neutron– γ Model Analysis and Simplified Digital Charge Collection. The ratio of the number of γ ‐ ray counts to the number of neutron counts, often referred to as the R-factor, has been calculated for each mixed radiation field. These provide a basis for reference where future R-factor analysis of isotopic sources is to be carried out for the purposes of calibrating discrimination systems or when estimating the γ ‐ ray rejection effectiveness of neutron detector systems based on fast liquid scintillators. The efficacy of each of these methods has been assessed in terms of the figure-of-merit (based on the separation of the event distributions). The SDCC technique is observed to provide the best discrimination performance in this research.

High efficiency large volume multiparametric neutron detector

Monitoring neutron emission with efficient detectors is the most straightforward way to study physics problems such as fission of heavy nuclei, where neutrons are preferentially emitted because of the Coulomb barrier, and the ( α , n ) reactions. A large volume (more than 5 l) neutron detector has been realized by organic liquid scintillator: the detector shows a very good performance for high efficiency measurements at low and very low neutron rate in the 0.03 – 10 MeV energy range. γ – n discrimination has been jointly performed by standard pulse shape discrimination and the digital charge comparison method, the results obtained by the two techniques are presented and discussed. A very good γ – n discrimination down to 100 kee with good efficiency has been achieved.

Study of neutron response and n–γ discrimination by charge comparison method for small liquid scintillation detector

The study of the neutron response and n–γ discrimination for small 18×26×8 mm 3 liquid scintillator BC501A (Bicron) detector was carried out by digital charge comparison method. Three ranges of neutron energies were used: uniform distribution from 0.95–1.23 MeV, continuous spectra of AmBe source and monoenergetic 16.2 MeV neutrons. The obtained results are compared with those of cylindrical liquid scintillation detector (40 mm diameter, 60 mm length) at the same energies of neutrons. A dramatic fall of the neutron response function at 400 keV ee for small detector at 16.2 MeV neutron energy was measured. For 0.95–1.23 MeV neutron energy range such fall takes place at 260 keV ee. The greater slope of neutron locus at 0.95–1.23 MeV neutron energy compared to 16.2 MeV for both detectors is explained by longer tail of pulse from proton recoils within 0.1–1.23 MeV energy range.

Investigation of some scintillation properties of YAG:Ce crystals

A light output expressed in the photoelectron (phe) number, a relative light yield for α-particles and light pulse shapes for γ-rays and α-particles excitation of the YAG:Ce crystals with different Ce doping between 0.012 and 1.08 mol% were studied. The highest light output of 1420 ± 70 phe/MeV was measured for the sample doped with 0.21 ± 0.03 mol% Ce, while the fastest pulse was observed for the sample doped with 1.08 ± 0.08 mol% Ce showing, however, lower light yield by 10%. The relative light yield for α-particles of 0.21 ± 0.03 as compared to γ-rays was approximately the same for all the samples studied. In conclusion, the YAG:Ce crystal doped with about 1 mol% of Ce is the most appropriate for different applications. For this crystal the α-γ discrimination by digital charge comparison method was studied. A clear separation was observed with the YAG crystal coupled to the XP2020Q photomultiplier for 5.49 MeV α-particles from 241Am source and 6.04 MeV as well as 8.77 MeV from ThC source. However, this separation was inferior compared to that known for CsI(Tl).

Comparison of n-γ discrimination by zero-crossing and digital charge comparison methods

A comparative study of the n-γ discrimination done by the digital charge comparison and zero-crossing methods was carried out for a 130 mm in diameter and 130 mm high BC501A liquid scintillator coupled to a 130 mm diameter XP4512B photomultiplier. The high quality of the tested detector was reflected in a photoelectron yield of 2300 ± 100 phe/MeV and excellent n-γ discrimination properties with energy discrimination thresholds corresponding to very low neutron (or electron) energies. The superiority of the Z C method was demonstrated for the n-γ discrimination method alone, as well as, for the simultaneous separation by the pulse shape discrimination and the time-of-flight methods down to about 30 keV recoil electron energy. The digital charge comparison method fails for a large dynamic range of energy and its separation is weakly improved by time-of-flight method for low energies.

Study of n-γ discrimination with NE213 and BC501A liquid scintillators of different size

A comparative study of n-γ discrimination by the digital charge comparison method was carried out for NE213 and BC501A scintillators of different size coupled to a 130 mm diameter XP4512B photomultiplier. Particularly, the scintillators of diameter 50 mm × 50 mm size are compared with those of 4 l volume (160 mm in diameter and 200 mm in depth). The figure of merit, M, of 3.81 measured with the diameter 50 mm × 50 mm BC501A scintillator at 1 MeV energy lost by recoil electrons, is much better than M of 2.05 as observed with the 4 l volume cell. This is the effect of the reduced photoelectron yield by about 50% determined for the 4 l volume scintillator. Moreover, the slowing down of the light pulse and multiscattering of neutrons have a further influence on the lowering of the M factor. The study of the M factor versus the initial delay and width of the gate set at the slow component showed that the early light of the slow component represented often by the intermediate component with the decay time constant of about 30 ns is of great importance for the n-γ discrimination. Particularly, for the 4 l volume cells it is sufficient to limit the width of the gate at the slow component to about 300 ns. The comparison of the NE213 and BC501A scintillators showed that the BC501A scintillator exhibits a larger light yield evidently observed for the 4 l volume cell and thus giving a better n-γ discrimination.

A low background, large solid angle neutron detector for spectroscopy and dosimetry application

A 4π neutron detector has been realized using liquid and plastic scintillators: the detector shows a very good performance for high efficiency, low background measurements of low and very low neutron rate in the 0.05–5 MeV energy range. Gamma-neutron discrimination has been performed by pulse shape analysis and by a digital charge comparison method. The pulse shape analysis does not allow a n-γ discrimination down to 600 kee (keV electron equivalent energy) with a reasonable efficiency, but we measured a very good n-γ discrimination down to 100 kee with the digital charge comparison method.

Identification of different reaction channels of high energy neutrons in liquid scintillators by the pulse shape discrimination method

A study of the n-γ discrimination with NE213 and BC501A liquid scintillators, carried out with 40 and 56 MeV neutron beams, reflects different reaction channels involved in the detection process of high energy neutrons. Up to seven different reaction channels were identified in the pulse shape discrimination spectrum measured by a digital charge comparison method. The analysis of the energy spectra of the secondary particles allowed the cross sections for different reaction channels to be estimated as well. This is shown for the important 12C(n, d) reaction and the non-negligible contribution of the 12C(n, t) reaction to the total efficiency of the NE 213 liquid scintillator for neutrons.

Study of n-γ discrimination by digital charge comparison method for a large volume liquid scintillator

The study of the n-γ discrimination for a large 4 I volume BC501A liquid scintillator coupled to a 130 mm diameter XP4512B photomultiplier was carried out by digital charge comparison method. A very good n-γ discrimination down to 100 keV of recoil electron energy was achieved. The measured relative intensity of the charge integrated at the slow component of the scintillation pulse and the photoelectron yield of the tested counter allow the factor of merit of the n-γ discrimination spectra to be calculated and to be compared with those measured experimentally. This shows that the main limitation of the n-γ discrimination is associated with the statistical fluctuation of the photoelectron number at the slow component. A serious effect of the distortion in the cable used to send the photomultiplier pulse to the electronics for the n-γ discrimination was studied. This suggests that the length of RG58 cable should be limited to about 40 m to preserve a high quality n-γ discrimination.