Plastic Scintillator Material Research Articles

Wavelength-shifter coated polystyrene as an easy-to-build and low-cost plastic scintillator detector

We studied the light yield of a pure polystyrene slide coated with wavelength-shifter molecules, coupled to a photomultiplier, using β - particles from a 90Sr source, as a possible easy-to-build, low-cost plastic scintillator detector. Comparison measurements were performed with an uncoated polystyrene slide as well as with uncoated and coated PMMA slides, the latter which can only produce Cherenkov light when being traversed by charged particles. The results with the single (double) coated polystyrene slides show about 4.9 (6.3) times higher detected photon yield compared to the uncoated slide. For comparison, the light yield of a polystyrene-based extruded plastic scintillator material doped with PTP and POPOP was measured as well. The absolute detected light yield motivates future studies for developing easy-to-build, low-cost polystyrene-based plastic scintillator detectors.

Investigation of a new approach for 36Cl determination in solid samples using plastic scintillators

This work reports a new approach for the determination of 36Cl in radioactive waste samples from nuclear decommissioning, wherein novel plastic scintillator (PS) materials were used for the concentration of 36Cl prior to the detection with scintillation counting. Different plastic scintillator (PS) materials were tested for their selective absorption and detection of 36Cl activity in solid samples. PS microspheres (PSm), cross-linked PSm (CPSm) and PS resin have been investigated. PS resin was identified as the most suitable material for 36Cl analysis. Pyrolysis and subsequent trapping of the volatile elements in a bubbler was used. The trapping solution was finally loaded onto a cartridge of the PS resin. Scintillation counting and ion chromatography were used to determine the activity concentration and the chemical recovery, respectively.

Lead-doped scintillator dosimeters for detection of ultrahigh dose-rate x-rays

Objective. Lead-doped scintillator dosimeters may be well suited for the dosimetry of FLASH-capable x-ray radiotherapy beams. Our study explores the dose rate dependence and temporal resolution of scintillators that makes them promising in the accurate detection of ultrahigh dose-rate (UHDR) x-rays. Approach. We investigated the response of scintillators with four material compositions to UHDR x-rays produced by a conventional x-ray tube. Scintillator output was measured using the HYPERSCINT-RP100 dosimetry research platform. Measurements were acquired at high frame rates (400 fps) which allowed for accurate dose measurements of sub-second radiation exposures from 1 to 100 ms. Dose-rate dependence was assessed by scaling tube current of the x-ray tube. Scintillator measurements were validated against Monte Carlo simulations of the probe geometries and UHDR x-ray system. Calibration factors converting dose-to-medium to dose-to-water were obtained from simulation data of plastic and lead-doped scintillator materials. Main Results. The results of this work suggest that lead-doped scintillators were dose-rate independent for UHDR x-rays from 1.1 to 40.1 Gy s−1 and capable of measuring conventional radiotherapy dose-rates (0.1 Gy s−1) at extended distance from the x-ray focal spot. Dose-to-water measured with a 5% lead-doped scintillator detector agreed with simulations within 0.6%. Significance. Lead-doped scintillators may be a valuable tool for the accurate real-time dosimetry of FLASH-capable UHDR x-ray beams.

Desarrollo de Técnicas de Muongrafía para Estudios Densitométricos de Objetos de Importancia Estratégica

La muongrafía es una técnica de prospección no destructiva que permite la determinación de la estructura interna de grandes estructuras tanto naturales como artificiales, por ejemplo volcanes. Esto es posible al construir una imagen con base en la absorción diferencial del flujo direccional de muones atmosféricos producto de la interacción de rayos cósmicos con la atmósfera. Este trabajo doctoral es desarrollado con el propósito principal de aportar en el avance de la muongrafía como técnica de prospección en Geofísica. El trabajo se compone de dos lineas de trabajo, una experimental y una teórica. La experimental se basa en el desarrollo de un prototipo de detector de astropartículas con base en centelladores plásticos y fotomultiplicadores, para esto se usa una electrónica de adquisición desarrollada para el proyecto AMIGA en el Observatorio Pierre Auger y materiales centelladores de plástico. La segunda linea de trabajo trata del estudio del detector y las estructuras de investigación a través de simulaciones computacionales y modelos teóricos. Durante los dos primeros años se completaron los créditos de cursos solicitados por el doctorado, Ademas se trabajó en el estudio de la respuesta de la electrónica, los pulsos, técnicas de análisis de datos y el acople de fotomultiplicadores con los centelladores. Gracias a esto se avanzo en el desarrollo del prototipo y se investigo la posibilidad de incrementar la resolución espacial a través de la detección sincrónica usando electrónicas conectadas al mismo centellador. Actualmente iniciamos el trabajo en los modelos computacionales, estamos estudiando e investigando con respecto a los candidatos a objetos de estudio, destacando el volcán Copahue, volcán Peteroa y la posibilidad de realizar mediciones bajo tierra.

Time Resolution Simulation Measurement for the Configuration Plastic Scintillator Material+SiPM and its Application to Medical Physics

The Silicon Photomultipliers (SiPMs) have been used more frequently in the last years compared to Photomultiplier Tubes (PMT), due to its low cost, lower bias operation voltage and its smaller size, which can be up to 1×1 mm2. In this work, it is shown the time resolution simulation results for two scintillating materials: BC404 and BC422 (20×20×3 mm3 of size)+ SiPM (3×3 mm2 of size). The studies of this configuration can replace the PMT and crystals, commonly used in a Positron Emission Tomography (PET). The time resolution can be improved to be able to make the greatest data collection, to use an isotope with less life time and thus perform less damage to the patient by radiation.

Use of poly(ethylene naphthalate) as a self-vetoing structural material

The discovery of scintillation in the blue regime from poly(ethylene naphthalate) (PEN), a commonly used high-performance industrial polyester plastic, has sparked the interest of the physics community as a new type of plastic scintillator material. This observation in addition to its good mechanical and radiopurity properties makes PEN an attractive candidate as an active structure scintillator for low-background physics experiments. This paper reports on investigations of its potential in terms of production tests of custom made tiles and various scintillation light output measurements. These investigations substantiate the high potential of usage of PEN in low-background experiments.

Advanced Multilayer Composite Heavy-Oxide Scintillator Detectors for High-Efficiency Fast Neutron Detection

We have developed and evaluated a new approach to fast neutron and neutron–gamma detection based on large-area multilayer composite heterogeneous detection media consisting of dispersed granules of small-crystalline scintillators contained in a transparent organic (plastic) matrix. Layers of the composite material are alternated with layers of transparent plastic scintillator material serving as light guides. The resulting detection medium—designated as ZEBRA—serves both as an active neutron converter and a detection scintillator which is designed to detect both neutrons and gamma quanta. The composite layers of the ZEBRA detector consist of small heavy-oxide scintillators in the form of granules of crystalline ZWO, BGO, GSO(Ce), and other materials. We have produced and tested the ZEBRA detector of sizes $100 \mathrm{mm} \times 100 \mathrm{mm} \times 41 \mathrm{mm}$ , and determined that they have very high efficiency of fast neutron detection (up to 49% or greater), comparable to that which can be achieved by large sized heavy-oxide single crystals of about $\varnothing 40 \times 80 \mathrm{cm}^3$ volume. We have also studied the sensitivity variation of fast neutron detection by using different types of multilayer ZEBRA detectors of 100-cm2 surface area and 41-mm thickness (with a detector weight of about 1 kg) and found it to be comparable to the sensitivity of a 3He-detector representing a total cross section of about 2000 cm2 (with a weight of detector, including its plastic moderator, of about 120 kg). The measured count rate in response to a fast neutron source of 252Cf at 2 m for the ZEBRA-GSO(Ce) detector of size $100 \mathrm{mm} \times100 \mathrm{mm} \times41 \mathrm{mm}$ was 2.84 Hz/ng of 252Cf isotope, and this count rate can be doubled by increasing the detector height (and area) up to $200 \mathrm{mm} \times100 \mathrm{mm}$ . In summary, the ZEBRA detectors represent a new type of high efficiency and low-cost large-area solid-state neutron detector that can be used for stationary neutron/gamma portals. They may represent an interesting alternative to expensive, bulky gas counters based on 3He or 10Bneutron detection technologies.

Identification of Particles of Ionizing Radiation by the Analysis of Fluorescence Pulse Form of the Thin Pen Film Scintillator

Polyethylene 2.6-naphthalate (PEN) is a promising plastic scintillator material. In this paper, a thin PEN film was used for detection, identification, and energy spectrum measurements of various ionizing radiation particles. A thin PEN film was used to separate $\alpha $ (5.49 MeV) and $\beta $ (up to 2.2 MeV) particles coming from 238Pu and 90Sr + 90Y sources, respectively, as well as for the neutron (up to 14 MeV) and gamma separation from the isotopic PuBe neutron source. Acquired photomultiplier pulses were analyzed by the long tail method based on the delayed fluorescence intensity dependence on the mass and charge of particles absorbed. For determination of the separation quality, the figure of merit (FOM), based on the ratio of short and long tails, was used. It was found that depending on the FOM values of neutron/gamma and $\alpha /\beta $ separation, the thin PEN film is suitable for the ionizing radiation particle separation.

Advanced Multilayer Composite Heavy-Oxide Scintillator Detectors for High Efficiency Fast Neutron Detection

We have developed and evaluated a new approach to fast neutron and neutron-gamma detection based on large-area multilayer composite heterogeneous detection media consisting of dispersed granules of small-crystalline scintillators contained in a transparent organic (plastic) matrix. Layers of the composite material are alternated with layers of transparent plastic scintillator material serving as light guides. The resulting detection medium – designated as ZEBRA – serves as both an active neutron converter and a detection scintillator which is designed to detect both neutrons and gamma-quanta. The composite layers of the ZEBRA detector consist of small heavy-oxide scintillators in the form of granules of crystalline BGO, GSO, ZWO, PWO and other materials. We have produced and tested the ZEBRA detector of sizes 100x100x41 mm and greater, and determined that they have very high efficiency of fast neutron detection (up to 49% or greater), comparable to that which can be achieved by large sized heavy-oxide single crystals of about Ø40x80 cm3 volume. We have also studied the sensitivity variation to fast neutron detection by using different types of multilayer ZEBRA detectors of 100 cm2 surface area and 41 mm thickness (with a detector weight of about 1 kg) and found it to be comparable to the sensitivity of a 3He-detector representing a total cross-section of about 2000 cm2 (with a weight of detector, including its plastic moderator, of about 120 kg). The measured count rate in response to a fast neutron source of 252Cf at 2 m for the ZEBRA-GSO detector of size 100x100x41 mm3 was 2.84 cps/ng, and this count rate can be doubled by increasing the detector height (and area) up to 200x100 mm2. In summary, the ZEBRA detectors represent a new type of high efficiency and low cost solid-state neutron detector that can be used for stationary neutron/gamma portals. They may represent an interesting alternative to expensive, bulky gas counters based on 3He or 10B neutron detection technologies.

Synthesis and characterisation of scintillating microspheres made of polystyrene/polycarbonate for 222Rn measurements

Several studies have demonstrated that polycarbonate-based polymers have good capacities for the absorption of 222Rn. Meanwhile, polystyrene polymers are reported to be the most appropriate for developing plastic scintillator materials for the detection of radioactivity. The objective of this work was to develop plastic scintillators in the form of microspheres (PSm) composed of polystyrene and polycarbonate that could be used to measure 222Rn and improve this performance thanks to the combination of characteristics of both polymers. Our results show that PSm of polystyrene and polycarbonate can be made via the evaporation/extraction method, despite the two polymers not being miscible. From the point of view of the radioactive measurements, we observed that the addition of polycarbonate causes quenching, although it does not significantly affect the detection efficiency for alpha and high-energy beta emitters. From the point of view of 222Rn absorption, we observed that synthesis of the PSm through the evaporation/extraction method changes the 222Rn absorption of the raw material. This result demonstrates that the method of production of the polymer and the resulting physical characteristics are a key parameter for its final 222Rn absorption properties.

Experimental tests of the new plastic scintillator with pulse shape discrimination capabilities EJ-299-33

We have studied the prototype of a new plastic scintillator material (EJ-299-33) engineered for gamma-neutron discrimination. Energy and time resolutions as well as pulse shape discrimination capability have been compared with those of standard plastic and liquid scintillators. EJ-299-33 characteristics are somewhat poorer compared to standard scintillators. However, results obtained with the new plastic material suggest its possible use in basic research (time-of-flight measurements) as well as in Homeland Security applications (neutron/gamma monitoring device).

Memory effect, resolution, and efficiency measurements of an Al2O3 coated plastic scintillator used for radioxenon detection

A cylindrical plastic scintillator cell, used for radioxenon monitoring within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty, has been coated with 425nm Al2O3 using low temperature Atomic Layer Deposition, and its performance has been evaluated. The motivation is to reduce the memory effect caused by radioxenon diffusing into the plastic scintillator material during measurements, resulting in an elevated detection limit. Measurements with the coated detector show both energy resolution and efficiency comparable to uncoated detectors, and a memory effect reduction of a factor of 1000. Provided that the quality of the detector is maintained for a longer period of time, Al2O3 coatings are believed to be a viable solution to the memory effect problem in question.

Response and noise characteristics of small-sized inorganic and organic scintillation detectors measured with vacuum and solid-state photodetectors

Response and noise properties of scintillation detectors were investigated using a 137Cs radioactive source. The experimental setup consisted of a scintillator, photodetector, amplifier, and spectrometric analog-to-digital converter. Small-sized, cubic crystals were manufactured of stilbene, p-terphenyl and thallium-doped cesium iodide, as well as of a plastic scintillator material based on polystyrene. Vacuum and solid-state photomultipliers and a silicon PIN photodiode were used as photodetectors. The energy equivalent noise was determined for all used photodetectors. The response of various scintillators when using vacuum and semiconductor photomultipliers was found to be closely similar.

Investigations of surface coatings to reduce memory effect in plastic scintillator detectors used for radioxenon detection

In this work Al2O3 and SiO2 coatings are tested as Xe diffusion barriers on plastic scintillator substrates. The motivation is improved beta–gamma coincidence detection systems, used to measure atmospheric radioxenon within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty. One major drawback with the current setup of these systems is that the radioxenon tends to diffuse into the plastic scintillator material responsible for the beta detection, resulting in an unwanted memory effect. Here, coatings with thicknesses between 20 and 900 nm have been deposited onto plastic scintillators, and investigated using two different experimental techniques. The results show that all tested coatings reduce the Xe diffusion into the plastic. The reduction is observed to increase with coating thickness for both coating materials. The 425 nm Al2O3 coating is the most successful one, presenting a diffusion reduction of a factor 100, compared to uncoated plastic. In terms of memory effect reduction this coating is thus a viable solution to the problem in question.

MO-A-203-01: Scintillation Dosimetry: From Plastics to Liquids and from Photons/Electrons to Protons

Development of plastic scintillation detector systems for dosimetry has been evolving for more than a decade. Scintillation materials (plastic, scintillating fibers and liquid) have many properties that make them ideal for dosimetry including water equivalence and energy independence for MV photons, linearity with dose, dose rate independence, and high spatial resolution. Therefore, these detectors do not require the usual conversion and/or correction factors used for other commonly used detectors to convert the dosimeter reading to absorbed dose. This evolution started with point detectors and has led to matrix arrays to respond to the ever-increasing complexity of radiotherapy treatment fields such as IMRT. Small fields, high dose gradients and other challenging conditions could soon require the development of commercial scintillation detectors. The liquid scintillators also show promise for use in proton therapy. While offering excellent treatment conformity, proton therapy is also posing new challenges in terms of treatment verification and quality assurance. This is especially true with intensity modulated proton therapy (IMPT) with scanned proton beams where a single treatment may use several thousands proton spots. We will show how liquid scintillators can be used to quickly and accurately verify such complex treatments and to measure parameters such as the range, the position and the intensity of individual proton beams. This lecture will provide an overview of the dosimetric characteristics and properties of plastic scintillation detectors when exposed to high-energy photon, electron as well as proton beams. We will discuss all forms of scintillation detector materials: plastic scintillators, plastic scintillating fibers and liquid scintillators. We will present few applications for plastic scintillation detectors in clinical radiotherapy: stereotactic radiosurgery, quality assurance and in vivo dosimetry applications. Finally, we will describe how liquid scintillators can be used for routine verification of proton treatments. Learning Objectives: 1. Review the underlying physics of scintillation materials. 2. Review the properties of plastic scintillation materials used in radiation dosimetry. 3. Understand the principles of this method and recent innovations in scintillation dosimetry. 4. Identify potential applications that could benefit from scintillation detectors.

Modeling scintillator and WLS fiber signals for fast Monte Carlo simulations

In this work we present a fast, robust and flexible procedure to simulate electronic signals of scintillator units: plastic scintillator material embedded with a wavelength shifter optical fiber coupled to a photo-multiplier tube which, in turn, is plugged to a front-end electronic board. The simple rationale behind the simulation chain allows to adapt the procedure to a broad range of detectors based on that kind of units. We show that, in order to produce realistic results, the simulation parameters can be properly calibrated against laboratory measurements and used thereafter as input of the simulations. Simulated signals of atmospheric background cosmic ray muons are presented and their main features analyzed and validated using actual measured data. Conversely, for any given practical application, the present simulation scheme can be used to find an adequate combination of photo-multiplier tube and optical fiber at the prototyping stage.

On possible role of neutrons in appearance of delayed muons in MUON-T setup at the Tien Shan high-altitude station

The MUON-T setup operated at the Tien Shan high-altitude station of the Lebedev Physical Institute (3340 m above sea level) at a soil depth of ∼10 m (∼20 m m.w.e.). Muons with delay times of 30–150 ns with respect to the extensive air shower front were observed at this setup. Calculations showed that delay times of relativistic muons, taking into account their deviations in the geomagnetic field, do not exceed ∼30 ns. To elucidate the possible role of neutrons in the appearance of delayed events due to the n-p reaction in the plastic scintillator material, the problem of neutron transport in a medium with a density of 2 g/cm3 and a humidity of 10% was solved by the Monte Carlo method. Calculations for a point source of neutrons with energies of 5, 10, and 20 MeV (such neutrons can be generated, in particular, in cascades in soil from hadrons of the shower core) showed that the neutron flux decreases more than by a factor of 104 at a distance of 2.8 m of soil from the source. Neither neutron crosses the boundary of 3m at the total statistics of 3 · 105 events. Since the MUON-T setup is at a depth of 10 m, it is clear that neutrons from the atmosphere and soil upper layer are absorbed, scattered, and do not reach the detector. Thus, the formation of delayed muons in the MUON-T setup cannot be explained by these neutrons.

Energy Resolution of Plastic Scintillation Detector for Beta Rays

Many experiments on neutrinoless double beta decays have been proposed recently for determining the effective mass of neutrinos. Some of them use a plastic scintillator for measuring the beta-ray energy. Achieving a high energy resolution is critical for neutrinoless double beta decay experiments (e.g., MOON and superNEMO). The motivation of this study is to investigate the energy resolution of a plastic scintillation detector in terms of ldquocomponentsrdquo in the MeV-electron region. It is known that the total energy resolution of a plastic scintillation detector for a monoenergetic spectrum consists of two components: statistical and intrinsic energy resolution. In this paper, these two components were investigated for electrons. Experiments on protons were also performed for the purpose of comparison. Three additional experiments were performed to determine (1) the uniformity of the plastic scintillator materials by scanning a 2.8-MeV proton microbeam, (2) the energy spread of electrons and protons, and (3) the effect of the electron-beam size on the set-up. These additional experiments were performed to ensure that these factors did not affect measurements of the two above-mentioned components.

TH‐B‐350‐01: Scintillation Dosimetry: Review, New Innovations and Applications

Interest in the development of plastic scintillation detector systems for dosimetry has been evolving for more than a decade. Plastic scintillation materials have many properties that make them ideal for dosimetry including water equivalence and energy independence for MV photons, linearity with dose, dose rate independence, and high spatial resolution. Therefore, these detectors do not require the usual conversion and/or correction factors used for other commonly used detectors to convert the dosimeter reading to absorbed dose. The only disadvantage of plastic scintillation detectors is the spurious effect arising from Cerenkov radiation produced in the optical fiber that guides the scintillation light, which has been solved. This evolution started with point detectors and is leading to matrix arrays to respond to the ever‐increasing complexity of radiotherapy treatment fields such as IMRT. Small fields, high dose gradients and other challenging conditions could soon require the development of commercial scintillation detectors. Moreover by using a photodetector with a large sensitive area (e.g. a CCD camera), arrays of several hundreds of scintillation detectors could be made to simplify long and arduous quality assurance tests.This lecture will provide an overview of the dosimetric characteristics and properties of plastic scintillation detectors when exposed to high‐energy photon, electron as well as proton beams. We will discuss both forms of plastic‐based scintillation detectors: plastic scintillators and plastic scintillating fibers. Finally, we will present few applications for plastic scintillation detectors in clinical radiotherapy: stereotactic radiosurgery, quality assurance and in vivo dosimetry applications.Educational Objectives:1. Review the underlying physics of scintillation materials.2. Review the properties of plastic scintillation materials used in radiation dosimetry.3. Understand the principles of this method and recent innovations in scintillation dosimetry.4. Identify applications that could benefit from scintillation detectors.

The use of energy information in plastic scintillator material

Plastic scintillator material is often used for gamma-ray detection in many applications due to its relatively good sensitivity and cost-effectiveness compared to other detection materials. However, due to the dominant Compton scattering interaction mechanism, full energy peaks are not observed in plastic scintillator spectra and isotopic identification is impossible. Typically plastic scintillator detectors are solely gross count detectors. In some safeguards and security applications, such as radiation portal monitors for vehicle screening, naturally-occurring radioactive material (NORM) often triggers radiation alarms and results in innocent or nuisance alarms. The limited energy information from plastic scintillator material can be used to discriminate the NORM from targeted materials and reduce the nuisance alarm rate. An overview of the utilization of the energy information from plastic scintillator material will be presented, with emphasis on the detection capabilities and potential limitations for safeguards and security applications.