NE213 Scintillator Research Articles

Unfolding of mono-energy neutron spectra using artificial neural network based on LMBP training algorithm

In this work, neutron spectra are unfolded using artificial neural networks (ANNs). The neutron response of the NE213 scintillator detector, characterized by the pulse height distribution, is calculated to obtain the necessary data for unfolding the energy spectrum. This is achieved using both analytical response functions and response functions generated by the MCNPX-PHOTRACK code. In this query, the Levenberg-Marquardt method (LMM), which has a high computational speed in the learning method, is used to train the network. The performance of the ANN for unfolding the neutron energy spectrum of the NE213 scintillation detector was evaluated by comparing its results to the established Gravel method. The ANN method consistently produced spectra with a single peak closely matching the incident energy, while the Gravel method showed additional peaks and distortions. Quantitative analysis revealed a lower relative energy peak difference (indicating higher accuracy) for the ANN method compared to Gravel, particularly when noise was introduced into the data. These results suggest that ANNs offer a more robust and accurate approach for neutron spectrum unfolding.

Light-yield response of liquid scintillators using 2–6 MeV tagged neutrons

Knowledge of the neutron light-yield response is crucial to the understanding of scintillator-based neutron detectors. In this work, neutrons from 2–6MeV have been used to study the scintillation light-yield response of the liquid scintillators NE 213A, EJ 305, EJ 331 and EJ 321P using event-by-event waveform digitization. Energy calibration was performed using a GEANT4 model to locate the edge positions of the Compton distributions produced by gamma-ray sources. The simulated light yield for neutrons from a PuBe source was compared to measured recoil proton distributions, where neutron energy was selected by time-of-flight. This resulted in an energy-dependent Birks parameterization to characterize the non-linear response to the lower energy neutrons. The NE 213A and EJ 305 results agree very well with existing data and are reproduced nicely by the simulation. New results for EJ 331 and EJ 321P, where the simulation also reproduces the data well, are presented.

Measurements of the neutron spectra from the p+Be neutron generator of the NPI CAS

The Nuclear Physics Institute of the Czech Academy of Sciences (NPI CAS) operates several neutron sources, including a generator of a continuous spectrum of neutrons up to 33 MeV. Accelerated protons from the U-120M cyclotron are directed to an 8 mm thick beryllium target to produce the neutrons.In this work, the neutron spectrum at distances of 3–8 m was directly measured with NE213 and stilbene scintillator detectors in the forward, diagonal and perpendicular directions. At a distance of 50 cm from the Be target, the neutron spectrum was validated with a gold activation detector. From previous work, the neutron spectra at close distances were characterized for use in high-intensity irradiation. Both the newly measured spectra at large distances and the previously measured spectrum were simulated using the Monte Carlo code, MCNP6.2, with ENDF7PROT and JENDL-4.0/HE nuclear data libraries. The comparison of the simulated and experimentally measured spectra revealed several limitations of both libraries.

Technique for the measurement of intrinsic pulse-shape discrimination for organic scintillators using tagged neutrons

Fast-neutron/gamma-ray pulse-shape discrimination has been performed for the organic liquid scintillators NE 213A and EJ 305 using a time-of-flight based neutron-tagging technique and waveform digitization on an event-by-event basis. Gamma-ray sources and a Geant4-based simulation were used to calibrate the scintillation-light yield. The difference in pulse shape for the neutron and gamma-ray events was analyzed by integrating selected portions of the digitized waveform to produce a figure-of-merit for neutron/gamma-ray separation. This figure-of-merit has been mapped as a function of detector threshold and also of neutron energy determined from time-of-flight. It shows clearly that the well-established pulse-shape discrimination capabilities of NE 213A are superior to those of EJ 305. The extra information provided by the neutron-tagging technique has resulted in a far more detailed assessment of the pulse-shape-discrimination capabilities of these organic scintillators.

Technique for the measurement of intrinsic pulse-shape discrimination for organic scintillators using tagged neutrons

Fast-neutron/gamma-ray pulse-shape discrimination has been performed for the organic liquid scintillators NE 213A and EJ 305 using a time-of-flight based neutron-tagging technique and waveform digitization on an event-by-event basis. Gamma-ray sources and a Geant4-based simulation were used to calibrate the scintillation-light yield. The difference in pulse shape for the neutron and gamma-ray events was analysed by integrating selected portions of the digitized waveform to produce a figure-of-merit for neutron/gamma-ray separation. This figure-of-merit has been mapped as a function of detector threshold and also of neutron energy determined from time-of-flight. It shows clearly that the well-established pulse-shape discrimination capabilities of NE 213A are superior to those of EJ 305. The extra information provided by the neutron-tagging technique has resulted in a far more detailed assessment of the pulse-shape discrimination capabilities of these organic scintillators.

Measurements of gamma and neutron flux spectra in iron-water configurations

Abstract Neutron and gamma spectra were measured behind and inside of modules consisting of variable iron and water slabs which were installed in radial beams of the zero-power training and research reactors AKR of the Technical University Dresden and ZLFR of the University of Applied Sciences Zittau/Görlitz. The applied NE-213 scintillation spectrometer allowed the measurement of gamma and neutron fluence spectra in the energy regions 0.3–10 MeV for photons and 1.0–20 MeV for neutrons. Measurements with thermoluminescence dosemeters (TLD) between slabs supplied additional information about the space distribution of energy integrated fluxes. The paper describes the experiments and presents some important results of the measurements. They will be compared with the results of transport calculations made by means of MCNP and TRAMO in another paper.

Forward modeling of pile-up events in liquid scintillator detectors for neutron emission spectroscopy.

When using liquid scintillator detectors to measure the neutron emission spectrum from fusion plasmas, the problem of pile-up distortion can be significant. Because of the large neutron rates encountered in many fusion experiments, some pile-up distortion can remain even after applying traditional pile-up elimination methods, which alters the shape of the measured light-yield spectrum and influences the spectroscopic analysis. Particularly, pile-up events appear as a high-energy tail in the measured light-yield spectrum, which obfuscates the contribution that supra-thermal ions make to the energy spectrum. It is important to understand the behavior of such "fast ions" in fusion plasmas, and it is hence desirable to be able to measure their contribution to the neutron spectrum as accurately as possible. This paper presents a technique for incorporating distortion from undetected pile-up events into the analysis of the light-yield spectrum, hence compensating for pile-up distortion. The spectral contribution from undetected pile-up events is determined using Monte Carlo methods and is included in the spectroscopic study as a pile-up component. The method is applied to data from an NE213 scintillator detector at JET and validated by comparing with results from the time-of-flight spectrometer TOFOR, which is not susceptible to pile-up distortion. Based on the results, we conclude that the suggested analysis method helps counteract the problem of pile-up effects and improves the possibilities for extracting accurate fast-ion information from the light-yield spectrum.

Value-Assigned Pulse Shape Discrimination for Neutron Detectors

Using the waveforms from a digital electronic system, an offline analysis technique on pulse shape discrimination (PSD) has been developed to improve the neutron-gamma separation in a bar-shaped NE-213 scintillator that couples to a photomultiplier tube (PMT) at each end. The new improved method, called the ``valued-assigned PSD'' (VPSD), assigns a normalized fitting residual to every waveform as the PSD value. This procedure then facilitates the incorporation of longitudinal position dependence of the scintillator, which further enhances the PSD capability of the detector system. In this paper, we use radiation emitted from an AmBe neutron source to demonstrate that the resulting neutron-gamma identification has been much improved when compared to the traditional technique that uses the geometric mean of light outputs from both PMTs. The new method has also been modified and applied to a recent experiment at the National Superconducting Cyclotron Laboratory (NSCL) that uses an analog electronic system.

Energy spectra of neutrons penetrating concrete and steel shielding blocks from 24 GeV/c protons incident on thick copper target

In this study, experimental measurements were performed on the spectra of neutrons which penetrate concrete and steel of various thicknesses values when a proton beam of 24 GeV/c was incident on a copper target at the CHARM facility in the East Hall of the CERN Proton Synchrotron (PS) The thicknesses of concrete and steel ranged up to 360 cm and 80 cm, respectively. To measure the neutron spectra, an NE213 scintillator was positioned on the top roof of the shielding structure as the neutron detector. The light output distributions of the detector were converted into the neutron energy spectra using the unfolding method with a calculated response matrix after removing the γ-ray and charged particle events by pulse-shape discrimination and veto counter signals, respectively. The neutron spectra were in agreement with the results obtained using the Monte Carlo simulation code, PHITS, within a factor of 1.4 except for the case of steel 80 cm. The attenuation profiles for concrete and steel were consistent with previous foil activation results within the respective uncertainties.

Analytical modeling of the neutron response function of the NE213 organic liquid scintillator in the energy range of 0.2 MeV to 148 MeV

Determination of the neutron response function is essential for measuring the energy of neutrons emitted from natural and artificial neutron sources and nuclear reactions. This paper presents the calculation procedure of generating a neutron analytical response function for NE213 scintillation detectors in the energy range of 0.2–148 MeV. To obtain the analytical response function, the available neutron experimental response functions were grouped according to their behavior in different energy ranges. Different analytical functions were fitted to the experimental data of the detector response function for each neutron energy range. The function which best fits the experimental data was selected. Then a computer program was written for calculating the parameters of the analytical function by using the fitting functions and their parameters for each desired energy, and generating the analytical response functions. A comparison of the results shows that the analytical response functions are much faster and more consistent with the experimental response functions than the generated response functions of stand-alone codes and general-purpose Monte Carlo codes.

The effect of the aging of liquid organic scintillators used for gamma-neutron separation

Since the beginning of using liquid scintillators for gamma-neutron separation, there have been many articles dealing with long-term degradation especially due to oxygen presented during scintillator encapsulation. The effect of aging of liquid organic scintillators namely EJ301, EJ309 (both Eljen Technology), and new custom-made cocktails based on 1-Phenyl-3-(2,4,6-trimethylphenyl)-2-pyrazoline and 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene fluors were investigated for more than half a year. The research was focused on the Compton edge shifting of gamma particles since the position is proportional to the light yield of the selected scintillator. Furthermore, the gamma-neutron separation was observed and quantified using FOM (Figure Of Merit) for samples prepared and filled under normal and nitrogen atmosphere during the mentioned period. All stated parameters of liquid scintillator NE213 manufactured by Nuclear Enterprises Limited opened more than three decades ago were measured and used for comparison.

A comparison on three neutron-gamma discrimination methods used with NE213, UGLLT and UGAB scintillators

Liquid organic scintillators are widely used in radiation measurements. NE213 (or its equivalent, BC-501A) in neutron-gamma discrimination (NGD) and two new scintillators, UGLLT and UGAB, in alpha-beta discrimination are two common examples. In this paper, the NGD capabilities of these three scintillators were studied and their figure-of-merits (FoMs) were measured for comparison. The three different NGD methods used in this study were zero-cross method (ZCM), charge integration method (CIM) and filtered charge integration method (FCIM), where ZCM was analog and the two other methods were digital. A 1.1 μCi point 22Na gamma ray source and 100 mCi cylindrical 241Am–Be neutron source (3.5 cm diameter by 5 cm length) were used for the energy calibration and the NGD, respectively. The FoM values for NE213, UGLLT and UGAB at 100 keVee discrimination bias (i.e., the preset threshold voltage, generally expressed in keVee unit, upon which the generated pulse-heights are recorded) using ZCM, CIM and FCIM methods were (1.060±0.037, 1.430±0.040, 1.70±0.054), (0.910±0.029, 1.270±0.018, 1.460±0.027) and (0.890±0.027, 1.200±0.020, 1.460±0.026), respectively. Although UGAB scintillator exhibits the least discrimination quality, one can choose an appropriate neutron-gamma discrimination method to improve its FoM. The low-temperature flammability, toxicity and high-evaporation properties of NE213 scintillator may motivate some researchers to use UGLLT and UGAB scintillators as alternatives to NE213, however, by selecting the most efficient discrimination method.

Initial operation results of NE213 scintillation detector for time-resolved measurements on triton burnup in KSTAR.

In time-resolved measurement for triton burnup in Korea Superconducting Tokamak Advanced Research (KSTAR) deuterium plasmas, an NE213 liquid scintillation detector was installed and operated during the 2017 KSTAR campaign. The detector is composed of an NE213 scintillator (50 mm in diameter and 10 mm in thickness) and a photomultiplier tube (PMT). The PMT anode signal was processed under a data acquisition system which contains a field programmable gate array circuit and pulse processing software that is capable of discriminating gamma-ray and neutron pulse signals. In order to determine an appropriate threshold level for the 14 MeV neutron signal resulting from triton burnup, the NE213 scintillation detector was calibrated by using d-d and d-t neutron generators at the National Fusion Research Institute and Intense 14 MeV Neutron Source Facility, OKTAVIAN, Osaka University, Japan. The detector was installed on KSTAR with a 10 mm thick soft-iron stray magnetic field shield and a radiation shield which consists of 100 mm thick lead blocks and 200 mm thick borated polyethylene blocks. A discrimination range for d-t neutron was determined based on test results from neutron generators and KSTAR. Data points selected from the discrimination range were consistent with the classical triton confinement characteristics. In conclusion, under condition of an input counting rate of 1.9 × 105 counts per second (CPS), the detector is able to measure triton burnup signals up to 500 CPS for various plasma parameters.

Reproduction of neutron fluence by unfolding method with an NE213 scintillator

The reproduction of neutron fluence derived by the unfolding method was confirmed by simulating an experiment at Cern High energy AcceleRator Mixed field facility (CHARM). Fluences on an NE213 scintillator located at positions surrounded with shields were calculated using PHITS. A neutron light output spectrum and response matrix were calculated according to the calculated fluence. Furthermore, response matrices with simple distributions of neutron incident position and direction on the scintillator were also prepared because a response matrix with guessed distributions is used in measurements. In spite of using response matrices with different distributions, the unfolded fluence agreed with each other, unless the distribution was focused on a position. The agreement of the fluences enables us to measure the fluence at various positions even though the distributions are experimentally unknown. Finally, experimental fluences were obtained under the same conditions, and were compared with the simulation results.

Neutron energy spectrum measurement using an NE213 scintillator at CHARM

To establish a methodology for neutron spectrum measurement at the CERN High energy AcceleRator Mixed field facility (CHARM), neutron spectra were measured using an NE213 scintillator on top of the CHARM roof shielding where is the CERN Shielding Benchmark Facility (CSBF). The spectra were derived as fluences into the scintillator by the unfolding method using an iterative Bayesian algorithm. The methodology was verified based on the agreement of two spectra measured for different positions and directions of incident neutrons by changing the detector orientation. Since the spectra on the roof-top were obtained within a reasonable beam-time, this methodology is suitable for measuring the spectrum when there is less shielding material. Thus, experimental data for neutron transition can be obtained as a function of shielding thickness using this facility.

Generation of the neutron response function of an NE213 scintillator for fusion applications

In this work we present a method to evaluate the neutron response function of an NE213 liquid scintillator. This method is particularly useful when the proton light yield function of the detector has not been measured, since it is based on a proton light yield function taken from literature, MCNPX simulations, measurements of gamma-rays from a calibration source and measurements of neutrons from fusion experiments with ohmic plasmas. The inclusion of the latter improves the description of the proton light yield function in the energy range of interest (around 2.46 MeV).We apply this method to an NE213 detector installed at JET, inside the radiation shielding of the magnetic proton recoil (MPRu) spectrometer, and present the results from the calibration along with some examples of application of the response function to perform neutron emission spectroscopy (NES) of fusion plasmas.We also investigate how the choice of the proton light yield function affects the NES analysis, finding that the result does not change significantly. This points to the fact that the method for the evaluation of the neutron response function is robust and gives reliable results.

Copper benchmark experiment for the testing of JEFF-3.2 nuclear data for fusion applications

A neutronics benchmark experiment on a pure Copper block (dimensions 60 × 70 × 70 cm3 ) aimed at testing and validating the recent nuclear data libraries for fusion applications was performed in the frame of the European Fusion Program at the 14 MeV ENEA Frascati Neutron Generator (FNG). Reaction rates, neutron flux spectra and doses were measured using different experimental techniques (e.g. activation foils techniques, NE213 scintillator and thermoluminescent detectors). This paper first summarizes the analyses of the experiment carried-out using the MCNP5 Monte Carlo code and the European JEFF-3.2 library. Large discrepancies between calculation (C) and experiment (E) were found for the reaction rates both in the high and low neutron energy range. The analysis was complemented by sensitivity/uncertainty analyses (S/U) using the deterministic and Monte Carlo SUSD3D and MCSEN codes, respectively. The S/U analyses enabled to identify the cross sections and energy ranges which are mostly affecting the calculated responses. The largest discrepancy among the C/E values was observed for the thermal (capture) reactions indicating severe deficiencies in the 63,65 Cu capture and elastic cross sections at lower rather than at high energy. Deterministic and MC codes produced similar results. The 14 MeV copper experiment and its analysis thus calls for a revision of the JEFF-3.2 copper cross section and covariance data evaluation. A new analysis of the experiment was performed with the MCNP5 code using the revised JEFF-3.3-T2 library released by NEA and a new, not yet distributed, revised JEFF-3.2 Cu evaluation produced by KIT. A noticeable improvement of the C/E results was obtained with both new libraries.

Digital method comparision for discrimination of neutrons and gamma-rays with scintillation detector

The interference of gamma in neutron spectra reduces the accuracy of measurement results, especially when using the scintillation detector. The digital method can be used to identify either neutron or gamma pulses. In order to select the algorithm for NE213 scintillation detector, the Matlab Simulink tool was used to simulate neutron counting system. The results show that the figure of merits (FOM) of:rise-time discrimination method (RTD), pulsed gradient analysis (PGA) method, charge comparison method (CCM), and correlation pattern method (CPM) are 1.09, 0.66, 2.21 and 1.97, respectively.

Digital neutron–gamma discrimination with scintillators: An innovative approach

In this paper, a digital neutron–gamma discrimination (DNGD) method with an NE213 scintillator has been proposed in which the anode pulse is divided into two different pulses, one representing the amplitude and the other characterizes the DNGD. Then the two pulses are summed up after travelling through delay and mixer circuits to form an input pulse for sampling in analog–to–digital converter (ADC). The discrimination tests have been performed with an 8–bit digital storage oscilloscope (DSO) as ADC and 241Am–Be neutron source, whereas the Fourier method has been used to derive the discrimination characteristic. The results confirm the fast performance and efficiency of proposed method.

Fast neutron and gamma-ray spectra measurements with a NE-213 spectrometer in the FNG Copper Benchmark Experiment

A neutronics benchmark experiment on a pure Copper assembly was performed at the Frascati Neutron Generator. The work aimed at testing of recent nuclear data libraries. This paper focuses on the measurement of fast neutron and gamma-ray flux spectra in the Copper assembly under DT neutron irradiation in two selected positions with a spectrometer based on the organic liquid scintillator NE-213. The measurement results were compared with Monte Carlo radiation transport calculations using MCNP and nuclear data from the JEFF-3.1.1 library. Calculations have been done with Cu data from JEFF-3.1.1, JEFF-3.2, FENDL-3 and ENDF/B-7.0. Discrepancies appear in the intermediate neutron energy range between experiment and calculation. Large discrepancies were observed in the gamma-ray spectra calculated with JEFF-3.2.