Organic Plastic Scintillators Research Articles

A plastic scintillation muon veto for sub-Kelvin temperatures

Rare-event search experiments located on-surface, such as short-baseline reactor neutrino experiments, are often limited by muon-induced background events. Highly efficient muon vetos are essential to reduce the detector background and to reach the sensitivity goals. We demonstrate the feasibility of deploying organic plastic scintillators at sub-Kelvin temperatures. For the NUCLEUS experiment, we developed a cryogenic muon veto equipped with wavelength shifting fibers and a silicon photo multiplier operating inside a dilution refrigerator. The achievable compactness of cryostat-internal integration is a key factor in keeping the muon rate to a minimum while maximizing coverage. The thermal and light output properties of a plastic scintillation detector were examined. We report first data on the thermal conductivity and heat capacity of the polystyrene-based scintillator UPS-923A over a wide range of temperatures extending below one Kelvin. The light output was measured down to 0.8 K and observed to increase by a factor of 1.61 ± 0.05 compared to 300 K. The development of an organic plastic scintillation muon veto operating in sub-Kelvin temperature environments opens new perspectives for rare-event searches with cryogenic detectors at sites lacking substantial overburden.

Magnetic field influence on the light yield from fiber-coupled BCF-60 plastic scintillators of relevance for output factor dosimetry in MR-linacs

Organic plastic scintillators are of interest for ionizing radiation dosimetry in megavoltage photon beams because plastic scintillators have a mass density very similar to that of water. This leads to insignificant perturbation of the electron fluence at the point of measurement in a water phantom. This feature is a benefit for dosimetry in strong magnetic fields (e.g., 1.5 T) as found in linacs with magnetic resonance imaging. The objective of this work was to quantify if the light yield per dose for the scintillating fiber BCF-60 material from Saint-Gobain Ceramics and Plastics Inc. is constant regardless of the magnetic flux density. This question is of importance for establishing traceable measurement in MR linacs using this detector type. Experiments were carried out using an accelerator combined with an electromagnet (max 0.7 T). Scintillator probes were read out using chromatic stem-removal techniques based on two optical channels or full spectral information. Reference dosimetry was carried out with PTW31010 and PTW31021 ionization chambers. TOPAS/GEANT4 was used for modelling. The light yield per dose for the BCF-60 was found to be strongly influenced by the magnitude of the magnetic field from about 1 mT to 0.7 T. The light yield per dose increased (1.3 ± 0.2)% (k = 1) from 1 mT to 10 mT and it increased (4.5 ± 0.9)% (k = 1) from 0 T to 0.7 T. Previous studies of the influence of magnetic fields on medical scintillator dosimetry have been unable to clearly identify if observed changes in scintillator response with magnetic field strength were related to changes in dose, stem signal removal, or scintillator light yield. In the current study of BCF-60, we see a clear change in light yield with magnetic field, and none of the other effects.

Methods for Improving the Radiation Hardness of Detectors Based on Organic Plastic Scintillators

Methods for Improving the Radiation Hardness of Detectors Based on Organic Plastic Scintillators

A simulation study on spatial and time resolution for a cost-effective positron emission particle tracking system

This work is the second part of a simulation study investigating the processing of densely packed and moving granular assemblies by positron emission particle tracking (PEPT). Since medical positron emission tomography (PET) scanners commonly used for PEPT are very expensive, a PET-like detector system based on cost-effective organic plastic scintillator bars is being developed and tested for its capabilities. In this context, the spatial resolution of a resting positron source, a source moving on a freely designed model path, and a particle motion given by a discrete element method (DEM) simulation is studied using Monte Carlo simulations and the software toolkit Geant4. This not only extended the simulation and reconstruction to a moving source but also significantly improved the spatial resolution compared to previous work by adding oversampling and iteration to the reconstruction algorithm. Furthermore, in the case of a source following a trajectory developed from DEM simulations, a very good resolution of about 1 mm in all three directions and an average 3D deviation between simulated and reconstructed events of 2.3 mm could be determined. Thus, the resolution for realistic particle motion within the generic grate system (which is the test rig for further experimental studies) is well below the smallest particle size. The simulation of the dependence of the reconstruction accuracy on tracer particle location revealed a nearly constant efficiency within the entire detector system, which demonstrates that boundary effects can be neglected.

Accumulated dose implications from systematic dose-rate transients in gated treatments with Viewray MRIdian accelerators

The combination of magnetic resonance (MR) imaging and linear accelerators (linacs) into MR-Linacs enables continuous MR imaging and advanced gated treatments of patients. Previously, a dose-rate transient (∼8% reduced dose rate during the initial 0.5 s of each beam) was identified for a Viewray MRIdian MR-Linac (Klavsen et al 2022 Radiation Measurement 106759). Here, the dose-rate transient is studied in more detail at four linacs of the same type at different hospitals. The implications of dose-rate transients were examined for gated treatments. The dose-rate transients were investigated using dose-per pulse measurements with organic plastic scintillators in three experiments: (i) A gated treatment with the scintillator placed in a moving target in a dynamic phantom, (ii) a gated treatment with the same dynamic conditions but with the scintillator placed in a stationary target, and (iii) measurements in a water-equivalent material to examine beam quality deviations at a dose-per-pulse basis. Gated treatments (i) compared with non-gated treatments with a static target in the same setup showed a broadening of accumulated dose profiles due to motion (dose smearing). The linac with the largest dose-rate transient had a reduced accumulated dose of up to (3.1 ± 0.65) % in the center of the PTV due to the combined dose smearing and dose-rate transient effect. Dose-rate transients were found to vary between different machines. Two MR-Linacs showed initial dose-rate transients that could not be identified from conventional linearity tests. The source of the transients includes an initial change in photon fluence rate and an initial change in x-ray beam quality. For gated treatments, this caused a reduction of more than 1% dose delivered at the central part of the beam for the studied, cyclic-motion treatment plan. Quality assurance of this effect should be considered when gated treatment with the Viewray MRIdian is implemented clinically.

184 Automated HDR QA Tests Using an Organic Plastic Scintillator with Opencv

184 Automated HDR QA Tests Using an Organic Plastic Scintillator with Opencv

TOPS fast timing plastic scintillators: Time and light output performances

Organic plastic scintillators are largely exploited for fast timing detectors thanks to their short scintillation time with respect to inorganic crystals. Plastic scintillators are cheap to produce, light and easy to manipulate (any standard mechanical workshop can handle the cutting, polishing, etc.). Nowadays, fastest plastic scintillators available on the market are EJ-232 (Eljen Technology) and BC-422 (Saint Gobain) with a rise time of 350ps, a decay time of 1.6ns and a pulse width of 1.3ns. Foreseen the performance improvement of timing detectors based on plastic scintillators, the development of faster scintillators can give a crucial contribution. TOPS is a project focused on the development of a new class of organic scintillators producing several liquid and solid samples. Comparing the light output and the timing properties of the samples exploiting minimum ionising particles, a selection of the highly performing TOPS scintillators has been investigated and characterised. The performance achieved with TOPS samples are extremely promising: a time resolution improvement from 10 up to 35% with respect to the EJ-232 has been demonstrated. In addition, an increase of light output has been obtained for all samples with a consequent potential improvement in energy resolution measurements of a factor up to 35%.

A simulation study for a cost-effective PET-like detector system intended to track particles in granular assemblies

Since many industrial applications rely on the processing of densely packed and moving granular material, obtaining bulk internal information on the particle movement inside the reactors is of great importance. Such information can be delivered by Positron Emission Particle Tracking (PEPT). By marking pellets with a positron-emitting radioisotope, the position of these tracer particles can be determined via the time-of-flight differences of the emitted gamma-ray pairs. The current paper proposes a PET-like detector system based on cost-effective organic plastic scintillators instead of the more common but expensive inorganic scintillators. This system is currently under construction and was tested for its resolution and efficiency in this simulation study. Using Monte Carlo simulations and the software toolkit Geant4, three different geometries (an empty glass box, a generic grate system, and a cubic box of 1 m3 completely filled with pellets) were investigated, leading to a spatial resolution in the millimeter range and an efficiency, defined as the ratio of reconstructed decay locations to simulated decays, of 2.7%, 1.4%, and 0.3%.

X-Ray and Fast Neutron Radiographic Performance of an Ir-Bi-Plastic Array

Organic plastic scintillators offer the potential for exciting improvements in particle interaction efficiency, light yield (LY), and pulse shape discrimination (PSD). An area of particular application for select plastics exists in portable dual-particle imaging (DPI) systems supporting nuclear safety, security, and safeguards missions. One promising material, an Ir-Bi-Plastic, is experimentally evaluated within separate 370 kVp X-ray and 14.1 MeV neutron fields in the form of a pixelated array, which was fabricated by Lawrence Livermore National Laboratory (LLNL). Ir-Bi-Plastics pair high bismuth loadings with iridium-complex fluorophores to provide high intrinsic efficiencies for both photoelectric absorption and fast neutron detection, as well as improved LYs from the triplet-harvesting capabilities of the iridium-complex. These attributes make Ir-Bi-Plastics ideal candidates for DPI applications. Radiographic performance results for the Ir-Bi-Plastic array are compared against similar evaluations of smaller arrays made from EJ-200 and EJ-256, both industry standard materials. Measurements were recorded by pressure-coupling the three arrays to a commercial a-Si digital radiographic panel, and ASTM standard test methods and practices were utilized to calculate the modulation transfer function (MTF) and limits of spatial resolution for all three arrays. The results suggest the Ir-Bi-Plastic array, despite its larger pixel pitch, provides significantly improved performance over equivalent arrays made from either EJ-200 or EJ-256 for all X-ray and fast neutron environments practical for portable DPI.

Development of an Organic Plastic Scintillator-based Muon Veto Operating at Sub-Kelvin Temperatures for the NUCLEUS Experiment

The NUCLEUS experiment aims at measuring the coherent elastic scattering of nuclear reactor antineutrinos off nuclei using cryogenic calorimeters. Operating at an overburden of 3 m.w.e., muon-induced backgrounds are expected to be dominant. It is therefore essential to develop an efficient muon veto, with a detection efficiency of more than 99 %. This will be realized in NUCLEUS through a compact cube assembly of plastic scintillator panels. In order to prevent a large unshielded area where the cryostat intersects the shielding arrangement without unnecessarily increasing the induced detector dead time, a novel concept has been investigated, featuring a plastic scintillator-based active muon veto operating inside the NUCLEUS cryostat at sub-Kelvin temperatures. The verification of the key physical aspects of this cryogenic muon veto detector led to the first reported measurements of organic plastic scintillators at sub-Kelvin temperatures. The functionality of the principal scintillation process of organic plastic scintillators at these temperatures has been confirmed. On the basis of these findings, a disk-shape plastic scintillator equipped with wavelength shifting fibers and a silicon photomultiplier to guide and detect the scintillation light has been developed. The NUCLEUS cryogenic muon veto will be the first of its kind to be operated at sub-Kelvin temperatures.

Temperature-Dependent Properties of BC-412 Polyvinyl Toluene Scintillator

Polyvinyl toluene (PVT), with additives, is a widely used organic plastic scintillator that is robust and inexpensive for large-volume gamma-ray detectors. Even though PVT-based scintillators have been used for decades in many applications, some of their basic optical properties have not been fully explored. Measurements of the attenuation length, index of refraction, and scintillation light output of a specific commercial PVT-based scintillator (Saint-Gobain BC-412) as a function of temperature are presented. These properties are important to the performance of systems using PVT-based scintillators in environments subject to wide temperature variations and are being used to better model the performance of such applications.

Optimization of fast neutron and X-ray pulse shape discrimination (PSD) using an EJ276G scintillator in high radiation mixed conditions

Organic crystalline, liquid, and plastic scintillators with low Z-number materials are commonly used in fast neutron detectors. Pulse shape discrimination (PSD) is used to distinguish neutrons from X-rays because these detectors are affected by X-rays due to Compton scattering during fast neutron measurement. PSD was performed with a 1 × 1 × 3 cm3 EJ276G plastic scintillator, SiPM, and DAQ (10-bit resolution, 400 MHz) using the charge comparison method, which compares the total charge (Q body) and the delayed charge (Q tail) from the peak. Most studies have been conducted under laboratory conditions, such as with 252Cf or 241Am-Be sources. This study will perform PSD in a 15 MeV electron accelerator with a total flux of 6.72 × 1014 #/sec and an X-ray-to-neutron ratio of up to 4071:1. The PSD was optimized before the measurement in high flux conditions because it was difficult to perform PSD due to the pile-up effect in these conditions. Optimization focused on the figure of merit (FoM), which is an index of PSD performance. To distinguish neutrons from X-rays under these conditions, lead shielding is necessary to reduce the X-ray-to-neutron ratio. We performed Monte Carlo N-Particle Transport Code (MCNP6) simulations to determine the optimal shielding thickness. Fast neutrons interact with lead due to its high density, which results in small neutron energy loss and direction changes by scattering. This effect can affect other pixels as noise. We plan to evaluate the neutron images under high X-ray flux conditions by comparing the images of the MCNP6 simulation results and the measurement results.

Design and calibration of an optically segmented single volume scatter camera for neutron imaging

The Optically Segmented Single Volume Scatter Camera (OS-SVSC) aims to image neutron sources for non-proliferation applications using the kinematic reconstruction of elastic double-scatter events. Our prototype system consists of 64 EJ-204 organic plastic scintillator bars, each measuring 5mm × 5mm × 200mm and individually wrapped in Teflon tape. The scintillator array is optically coupled to two silicon photomultiplier ArrayJ-60035 64P-PCB arrays, each comprised of 64 individual 6x6mm J-Series sensors arranged in an 8 × 8 array.We report on the design details, including component selections, mechanical design and assembly, and the electronics system. The described design leveraged existing off-the-shelf solutions to support the rapid development of a phase 1 prototype. Several valuable lessons were learned from component and system testing, including those related to the detector's mechanical structure and electrical crosstalk that we conclude originates in the commercial photodetector arrays and the associated custom breakout cards.We detail our calibration efforts, beginning with calibrations for the electronics, based on the IRS3D application-specific integrated circuits, and their associated timing resolutions, ranging from 3090ps. With electronics calibrations applied, energy and position calibrations were performed for a set of edge bars using 22Na and 90Sr, respectively, reporting an average resolution of 12.07±0.03mm for energy depositions between 900keVee and 1000keVee. We further demonstrate a position calibration method for the internal bars of the matrix using cosmic-ray muons as an alternative to emission sources that cannot easily access these bars, with an average measured resolution of 14.86+-0.29mm for depositions between 900keVee and 1000keVee. The coincident time resolution reported between pairs of bars measured up to 400ps from muon acquisitions. Energy and position calibration values measured with muons are consistent with those obtained using particle emission sources.

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.

Simulated X-Ray Radiographic Performance of a Bismuth-Loaded PVT Array

Recent material advancements in organic plastic scintillators enable marked increases in material detection efficiency, light yield, and pulse shape discrimination properties. These advances may resolve significant capability gaps for low-cost, portable, and durable dual-particle imaging (DPI) systems for nuclear safety, security, and safeguard purposes. One such material, a 21% bismuth-loaded polyvinyl toluene (BiPVT), is computationally evaluated as a small, pixelated radiographic array using Monte Carlo N-Particle (MCNP) and Zemax OpticStudio, and it is compared to identical evaluations of EJ-200 and EJ-256 arrays. MCNP software enables estimates of particle interaction and energy deposition, while OpticStudio computes optical light transport within each material. Computational estimates of spatial resolution and relative light collection at 370 kVp are found to agree with experimental results for both EJ-200 and EJ-256 arrays, thereby validating predictions of the same for the BiPVT array. As such, for equivalent exposures at 370 kVp, a BiPVT array may provide $\sim 20\times $ the light collection expected from EJ-200 and $\sim 10\times $ that expected from EJ-256. Similar comparisons of estimated light collection are also computed at 150 and 270 kVp, and these results suggest that BiPVT will provide significantly improved performance over EJ-200 and EJ-256 across all energies practical for portable X-ray radiography.

NICE - Neutron Induced Charged particle Emission

A new detector setup (NICE-detector) based on an organic plastic scintillator is presented. It will be used during experiments measuring neutron-induced reactions with a charged particle in the exit channel. The proposed design was tested at the Goethe University Frankfurt. One of the test cases was the capture cross-section of 209Bi at different astrophysically important energies, including thermal capture cross-section and resonance integral. This research presents the performance of the detector setup, as well as preliminary results for the calculated cross-sections. The preliminary results demonstrate that the newly developed NICE-detector can be used to determine capture cross-sections with sufficient accuracy, and might be adopted in the future as an alternative for charged particle measurements in different nuclear and astrophysical applications.

Electric charge estimation using a SensL SiPM

The Silicon Photomultipliers (SiPMs) are commonly used in the construction of radiation detectors such as those used in high energy experiments and its applications where an excellent time resolution is required for triggering. In most of this cases, the trigger systems electric charge information is discarded due to limitations in data acquisition. In this work we propose a method, using a simple radiation detector based on an organic plastic scintillator 2×2×0.3 cm3 size, to estimate the electric charge obtained from the acquisition of the fast output signal of a SensL SiPM model C-60035-4P-EVB. Our results suggest a linear relation between the reconstructed electric charge from the fast output of the SiPM used with respect to the one reconstructed with its standard signal output. Using our electric charge reconstruction method, we compared the sensitivity of two plastic scintillators, BC404 and BC422Q, under the presence of 90Sr, 137Cs, 60Co and 22Na radiation sources.

Neutron/gamma pulse discrimination analysis of GS10 lithium glass and EJ-204 plastic scintillators

Two radiation sensitive scintillators known for their dual sensitivity to neutron and gamma-ray fields are investigated for their pulse discrimination abilities; a lithium glass GS10 inorganic scintillator and a fast organic plastic scintillator EJ-204. Each of these scintillators are optically coupled with an 8 × 8-silicon photomultiplier array to act as a photodetector. Pulse height analysis, the charge comparison method and pulse gradient analysis have all been applied here on neutron and gamma-ray events generated by a Cf-252 source. The three discrimination methods were evaluated based on the figure of merit of the probability density plots generated. Within a GS10 crystal, it has been deduced that pulse height analysis and pulse gradient analysis possess greater abilities to discriminate between the two radiation fields compared to the charge comparison method with both showing a figure of merit of over one. The charge comparison method indicated a lower discrimination ability with a figure of merit around 0.3. When the EJ-204 detector was used, it was deduced that only pulse height analysis exhibits discrimination abilities with a figure of merit around 0.6, while the other two discrimination methods presented no distinction between the two radiation fields.

Real‐Time Optical Response of Polysiloxane/Quantum Dot Nanocomposites under 2 MeV Proton Irradiation: Luminescence Enhancement of Polysiloxane Emission through Quantum Dot Sensitization

The growing interest toward the development of high‐Z–sensitized organic scintillators is related with the potential possibility to merge the advantages of organic materials with those of inorganics. In fact, organic plastic scintillators offer large‐area applications and fast response at a low cost, yet their performances for high‐energy photons and charged particles are limited by the poor stopping power related with low‐Z materials. The real‐time optical investigation in terms of steady‐state luminescence spectra of polysiloxane/quantum dot (QD) nanocomposite samples under 2 MeV proton irradiation is presented. Results show an increase in the light yield of the polysiloxane samples embedding QDs up to 8% in comparison with the undoped polymer, paving the way for high‐Z sensitization through QDs in polysiloxane‐based active radiation detection systems.

Evaluation of the ionization quenching effect in an organic plastic scintillator using kV x-rays and a modified Birks model with explicit account of secondary electrons

Organic plastic scintillators are attractive for several applications in medical dosimetry due to their high degree of water equivalence and their minimal perturbation of the radiation field. There is, however, a non-proportionality between the produced scintillation light and the absorbed energy for electrons below about 125 keV. This ionization quenching can be described by Birks formalism. In this work, a modified version of Birks formalism was developed. The model explicitly accounts for the light yield from secondary electrons and the model therefore can take advantage of the detailed electron spectra computed by Monte-Carlo techniques. The use of the model is demonstrated by comparison of modelling results and scintillator measurements of air kerma in a series of well-characterized, low energy x-rays beams with generating potentials from 60 kV to 300 kV (mean photon energies from 38 to 158 keV). The new model predicted the scintillator light production in good agreement with the experimental data. The model enables improved evaluations of the influence of quenching losses in MV photon beam dosimetry and other medical applications.