Boron Loaded Plastic Scintillator Research Articles

Neutron Response of the EJ-254 Boron-Loaded Plastic Scintillator

Organic scintillators doped with capture agents provide a detectable signal for neutrons over a broad energy range. This work characterizes the fast and slow neutron response of EJ-254, an organic plastic scintillator with 5% natural boron loading by weight. For fast neutrons, the primary mechanism for light generation in organic scintillators is n-p elastic scattering. To study the fast neutron response, the proton light yield of EJ-254 was measured at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a broad-spectrum neutron source and a double time-of-flight technique, the EJ-254 proton light yield was obtained over the energy range of approximately 270 keV to 4.5 MeV and determined to be in agreement with other plastic scintillators comprised of the same polymer base. To isolate the slow neutron response, an AmBe source with polyethylene moderator was made incident on the EJ-254 scintillator surrounded by an array of EJ-309 observation detectors. Events in the EJ-254 target coincident with the signature 477.6 keV $\gamma$ ray (resulting from deexcitation of the residual $^{7}$Li nucleus following boron neutron capture) were identified. Pulse shape discrimination was used to evaluate the temporal differences in the response of EJ-254 scintillation signals arising from $\gamma$-ray and fast/slow neutron interactions. Clear separation between $\gamma$-ray and fast neutrons signals was not achieved and the neutron capture feature was observed to overlap both the $\gamma$-ray and fast neutron bands. Taking into account the electron light nonproportionality, the neutron-capture light yield in EJ-254 was determined to be 89.4$\pm$1.1 keVee.

The OLVE-HERO Calorimeter Prototype Beam Test at CERN SPS

A project of the OLVE-HERO space detector for measurement of the cosmic rays in the range 1012–1016 eV is proposed. It will include a large ionization-neutron 3D calorimeter with a high granularity and geometric factor of ~16 m2 sr. The main OLVE-HERO detector is expected to be an image calorimeter with boron loaded plastic scintillator and a tungsten absorber. Such a calorimeter allows to measure an additional neutron signal that should improve the detector energy resolution and also the rejection power between electromagnetic and nuclear components of cosmic rays. Improvement by factor 30–50 is expected. The OLVE-HERO detector prototype was designed and tested at SPS CERN beam during Pb ion run in 2018. Test results and the corresponding Monte-Carlo simulation are presented.

Tests of the OLVE-HERO Calorimeter Prototype at Heavy-Ion Beams at SPS CERN

A project of the OLVE-HERO space detector for measurement of the cosmic rays in the range 1012–1016 eV is proposed. It will include a large ionization-neutron 3D calorimeter with a high granularity and geometric factor of ∼16 m2 sr. The main OLVE-HERO detector is expected to be an image calorimeter with boron loaded plastic scintillator and a tungsten absorber. Such a calorimeter allows to measure an additional neutron signal that should improve the detector energy resolution and also the rejection power between electromagnetic and nuclear components of cosmic rays. Improvement by factor 30–50 is expected. The OLVE-HERO detector prototype was designed and tested at SPS CERN beam during Pb ion run in 2018. Test results and the corresponding Monte-Carlo simulation are presented.

Identifying thermal neutrons, fast neutrons, and gamma rays by using a scintillator-based time-of-flight method

Abstract An experiment based on a boron-loaded plastic scintillator as a neutron-sensitive media and a fast digital readout was implemented by means of time-of-flight method to distinguish γ -rays and fast neutrons as well as to thermal neutrons. The time-of-flight (TOF) method was used for separating fast neutrons and γ -rays directly. The thermal neutrons were indirectly identified by the characteristic (478 keV) γ -rays from the 10 B ( n , α ) reactions and the corresponding thermal neutron fluxes were extracted by fitting the energy spectrum measured by the boron-loaded plastic scintillator in this work.

The OLVE-HERO Calorimeter Prototype Tests at Heavy Ion Beams of CERN SPS

A project of the OLVE-HERO space detector is proposed for CR measurement in the range of 1012–1016 eV and will include a large ionization-neutron 3D calorimeter with a high granularity and geometric factor of ~16 m2 sr. The main OLVE-HERO detector is expecte to be image calorimeter of a boron loaded plastic scintillator with a tungsten absorber. Such a calorimeter allows to measure an additional neutron signal which will improve the energy resolution of the detector. More importantly, the rejection power between electromagnetic and nuclear CR components will be increased by factor 30–50 in the whole energy range. The boron loaded scintillator detector prototype was designed and tested at the H8 beam test area at CERN SPS during Pb ion run in 2016 and Xe ion run in 2017. The results of the beam tests and the corresponding Monte-Carlo simulation are presented.

Simulation of Gamma-Ray and Neutron Spectrometers for Microsatellite Missions

Microsatellites have recently opened windows of frequent and low cost missions for planetary exploration. The performance of gamma-ray and neutron spectrometers on future microsatellite missions is simulated to assess the possibility of observation of hydrogen and major elements, given their concentration on the observation target. The measured elemental abundance will provide important geological constraints, and some of them may serve as space resources. Four different types of target bodies with various hydrogen concentrations in the range of 0 - 20,000 ppm are assumed as target compositions; Earth’s core, C-type, S-type and Martian meteorites. Gamma-ray and neutron emission rates show unique footprints that are related to the different elemental compositions. The starting point is the solid angle subtended between observation target and spectrometers that allow estimating the gamma-ray and neutron count rates emitted by the celestial bodies. In this work, three types of gamma-ray detectors; high-purity germanium (HPGe), CeBr3 and LaBr3(Ce), a neutron spectrometer combining a lithium glass scintillator with a boron loaded plastic scintillator and a dual mode spectrometer Cs2LiYCl6(Ce) (CLYC) are simulated, focusing on their observation backgrounds as a model case for microsatellite based measurements. The background count level of both gamma-ray (except for the LaBr3 detector) and neutron count rates was negligible under these particular conditions. The gamma-ray detectors were compared by the figure of merit, which was determined by their efficiency and energy resolution. It was found that each detector has unique advantages. The HPGe detector has the highest figure of merit due to its excellent energy resolution, whereas the CLYC detector is low in weight and power consumption due to its dual sensitivity to gamma-ray and neutron. The CeBr3 detector is an intermediate choice. The neutron count rates are calculated separately in three energy ranges, i.e. , thermal ( 500 keV), as a function of the hydrogen concentration in the 0 - 20,000 ppm range. The thermal and epithermal neutron count rates are found to decrease with hydrogen concentration, while the fast neutron count rate increases with the target average atomic mass. The optimal detector should be decided by the mission restraints on mass, power consumption, and heat thermal design.

Boron-loaded plastic scintillator with neutron-γ pulse shape discrimination capability

Development of the plastic scintillator with neutron sensitivity from thermal to multi-MeV and pulse shape discrimination (PSD) has been demonstrated. Incorporation of 10B-containing compounds into the plastic scintillator with PSD capability leads to detector improvement in regard to neutron detection efficiency while preserving the discrimination between neutrons and γ-rays. Effects of boron loading on scintillation and pulse shape discrimination properties are discussed. A PSD figure-of-merit value of 1.4±0.03 has been achieved for events in a thermal neutron energy domain, 50–100keVee, for PSD plastic loaded with 5wt.% of m-carborane.

Fast neutron detection with 6Li-loaded liquid scintillator

We report on the development of a fast neutron detector using a liquid scintillator doped with enriched 6Li. The lithium was introduced in the form of an aqueous LiCl micro-emulsion with a di-isopropylnaphthalene-based liquid scintillator. A 6Li concentration of 0.15% by weight was obtained. A 125 mL glass cell was filled with the scintillator and irradiated with fission-source neutrons. Fast neutrons may produce recoil protons in the scintillator, and those neutrons that thermalize within the detector volume can be captured on the 6Li. The energy of the neutron may be determined by the light output from recoiling protons, and the capture of the delayed thermal neutron reduces background events. In this paper, we discuss the development of this 6Li-loaded liquid scintillator, demonstrate the operation of it in a detector, and compare its efficiency and capture lifetime with Monte Carlo simulations. Data from a boron-loaded plastic scintillator were acquired for comparison. We also present a pulse-shape discrimination method for differentiating between electronic and nuclear recoil events based on the Matusita distance between a normalized observed waveform and nuclear and electronic recoil template waveforms. The details of the measurements are discussed along with specifics of the data analysis and its comparison with the Monte Carlo simulation.

Data acquisition for the Combined Ion and Neutron Spectrometer (CINS)

The CINS (Combined Ion and Neutron Spectrometer) consists of three detector systems: a boron-loaded plastic scintillator for medium energy neutrons, a silicon detector system for high-energy neutrons, and a charged particle stack containing both silicon detectors and scintillators. A readout system built for the charged particle stack is described here. The stack must be able to detect particles over a wide range of charge and energy. It contains 7 detectors, including 4 silicon detectors that each have two output paths. The readout must have a large usable dynamic range and must be able to handle the relatively high event rates that occur when the stack is placed in an accelerator beam. The data acquisition system detects events (that is, compares incoming signals to user-supplied trigger definitions), proceeds to capture waveform data from the preamplifiers, and saves the data to a hard drive. Although only used with the charged particle stack to date, the system can also be used with the other elements of CINS.

Characteristics of Boron-Loaded Plastic Scintillators for Neutron Measurements

In this paper, we report investigations of the detector characteristics for boron-loaded plastic scintillators for neutron measurements. The detectors were tested with fast neutrons emitted from fission decays of a 5-µCi 252 Cf source and with slow neutrons provided by the MC50 cyclotron at the Korea Institute of Radiological and Medical Science. The energy spectrum of the fast neutrons was obtained by applying a time-of-flight method to the coincident measurement of neutrons and gamma rays emitted from fission decays. The detectors were also tested to perform a pulse-timing analysis for fast neutrons, slow neutrons, and gammas to understand the scope of the discrimination for gamma rays when the detector is applied to practical measurements.

Development of real-time thermal neutron monitor using boron-loaded plastic scintillator with optical fiber for boron neutron capture therapy

A new thermal neutron monitor for boron neutron capture therapy was developed in this study. We called this monitor equipped boron-loaded plastic scintillator that uses optical fiber for signal transmission as an [scintillator with optical fiber] SOF detector. A water phantom experiment was performed to verify how the SOF detector compared with conventional method of measuring thermal neutron fluence. Measurements with a single SOF detector yielded indistinguishable signals for thermal neutrons and gamma rays. To account for the gamma ray contribution in the signal recorded by the SOF detector, a paired SOF detector system was employed. This was composed of an SOF detector with boron-loaded scintillator and an SOF detector with a boron-free scintillator. The difference between the recorded counts of these paired SOF detectors was used as the measure of the gamma ray contribution in the measured neutron fluence. The paired SOF detectors were ascertained to be effective in measuring thermal neutron flux in the range above 10 6 (n/cm 2/s). Clinical trials using paired SOF to measure thermal neutron flux during therapy confirmed that paired SOF detectors were effective as a real-time thermal neutron flux monitor.

Study of a new boron loaded plastic scintillator (revised)

Neutron detection research using plastic scintillators has recently led to instrument development for several applications and particularly for nuclear material characterization. In particular, plastic scintillators exhibit a fast time response and a high efficiency for fast neutrons spectrometry. The use of boron loaded plastic scintillators has been also proposed in order to reduce dead time for fission neutron coincidence counting. We report here on the study of a new and low-cost boron loaded plastic scintillator. Further, a simulation study was performed, including light production and transport in this kind of scintillator. Its characteristics have been measured in terms of light response, photon and neutron induced signals. An experiment has been carried out using the ion beam of a Van de Graaff accelerator at Saclay so as to determine the Birks parameters of the scintillators. These parameters were obtained for proton (between 1-2 MeV) and alpha particles (between 3.1 MeV and 5.4 MeV). The correlation between the experimental data and the simulation predictions has been studied for the neutron response of these scintillators. In addition, performances of this scintillator are compared with those of commercially available boron loaded plastic scintillator (BC454 from Bicron, Newbury, OH).

Study of a new boron loaded plastic scintillator

Neutron detection research using plastic scintillators has recently led to instrument development for several applications and particularly for nuclear material characterization. In particular, plastic scintillators exhibit a fast time response and a high efficiency for fast neutrons spectrometry. The use of boron loaded plastic scintillators has been also proposed in order to reduce dead time for fission neutron coincidence counting. We report on the study of a new and low-cost boron loaded plastic scintillator. Further, a simulation study was performed, including light production and transport in this kind of scintillator. Its characteristics have been measured in terms of light response, photon and neutron induced signals. An experiment has been carried out using the ion beam of a Van de Graaff accelerator at Saclay so as to determine the Birks parameters of the scintillators. These parameters were obtained for proton (between 1-2 MeV) and alpha particles (between 3.1 MeV and 5.4 MeV). The correlation between the experimental data and the simulation predictions has been studied for the neutron response of these scintillators. In addition, the performance of this scintillator are compared with those of a commercially available boron loaded plastic scintillator (BC454 from Bicron, Newbury, OH).

Discrimination methods between neutron and gamma rays for boron loaded plastic scintillators

Boron loaded plastic scintillators exhibit interesting properties for neutron detection in nuclear waste management and especially in investigating the amount of fissile materials when enclosed in waste containers. Combining a high thermal neutron efficiency and a low mean neutron lifetime, they are suitable in neutron multiplicity counting. However, due to their high sensitivity to gamma rays, pulse shape discrimination methods need to be developed in order to optimize the passive neutron assay measurement. From the knowledge of their physical properties, it is possible to separate the three kinds of particles that have interacted in the boron loaded plastic scintillator (gamma, fast neutron and thermal neutron). For this purpose, we have developed and compared the two well known discrimination methods (zero crossing and charge comparison) applied for the first time to boron loaded plastic scintillator. The setup for the zero crossing discrimination method and the charge comparison methods is thoroughly explained, and the results on those boron loaded plastic scintillators are discussed.

Development of Current Mode Time-of-Flight Technique for Measurement of Thermal Neutron Spectrum

A current mode time-of-flight (CTOF) technique was developed as a new technique to measure the high intensity spectra of the thermal neutron produced by the spallation neutron source driven by a few shots. The CTOF technique was developed and tested at KENS by measuring thermal neutrons produced in the water moderator. As a neutron detector, enriched 6Li and 7Li glass scintillators were employed, which were coupled with some different type of photomultiplier tubes. The peak of Maxwell distribution due to the thermal neutron was observed in the TOF spectrum. It is recognized that the time resolution of this technique was well enough to measure the thermal neutrons. For the validation of the CTOF technique, the spectrum was compared with that by a conventional pulse counting TOF technique using boron loaded plastic scintillator. As a result, it is found that the result obtained by current mode technique shows in good agreement with that obtained by the pulse counting technique. It is concluded that the current mode TOF can be applied to the measurement of the neutron spectrum.

Design of a fast neutron coincidence counter

Monte Carlo simulations were carried out to simulate the response of a boron-loaded plastic scintillator array. These detectors offer potential advantages compared to moderated 3He systems because of their fast response and high efficiency. Tallies were made of neutron capture probability as a function of time and the results were coupled to assay variance estimates to evaluate detector performance. Orders-of-magnitude reductions in count time relative to a 50% efficient thermal counter are possible, in principle, for high (α,n) samples.

Warhead counting using neutron scintillators: detector development, testing, and demonstration

The authors describe the development of a fast-neutron detector based on a boron-loaded plastic scintillator used previously for space applications. The detector rejects gammas and scattered low-energy neutrons, and its segmentation allows narrow fan-shaped collimation within +or-20 degrees horizontally and +or-50 degrees vertically. Testing includes distinguishing between mockups with either two or three warheads and locating the ten warheads on a silo-based Peacekeeper missile. For warhead-counting applications, the results presented indicate that collimated proton-recoil scintillations can, at least in some circumstances, provide the position resolution needed to resolve individual warheads without revealing intrusive information about their design. >

Analysis of mean lifetime for capture of neutrons in boron-loaded plastic scintillators

The commercial availability of boron-loaded organic scintillators has led to the development of neutron detectors that operate as “electronically” black, totally absorbing spectrometers. The key to the enhanced spectroscopy is the delayed capture of nearly thermalized neutrons by 10B that can occur within a few microseconds after the energy pulse from prompt proton recoils. Accurate information regarding the mean lifetime is important for correct setting of the timing logic of the detection system to obtain good neutron detection efficiency with a low chance coincidence rate. In this paper we present an analysis of the mean lifetime for neutron capture for the boron-loaded plastic BC454. Measurements of the capture time constant obtained with a 7.62 cm diameter, 10.16 cm long detector are compared with values computed with the time-dependent Monte Carlo neutron transport code MCNP. Additional analyses using MCNP examine the dependence of the mean lifetime on the boron concentration, the detector's dimensions and the incident neutron energy.