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Plastic scintillator produced by the substitution of epoxy resins for the commonly used polystyrene is easy to cast, stable at room temperature, and has the desirable properties of a thermoset or cross-linked system. Such scintillators can be immersed directly in strong solvents, an advantage in many chemical and biological experiments.
Compact neutron imagers using double-scatter kinematic reconstruction are being designed for localization and characterization of special nuclear material. These neutron imaging systems rely on scintillators with a rapid prompt temporal response as the detection medium. As n-p elastic scattering is the primary mechanism for light generation by fast neutron interactions in organic scintillators, proton light yield data are needed for accurate assessment of scintillator performance. The proton light yield of a series of commercial fast plastic organic scintillators—EJ-200, EJ-204, and EJ-208—was measured via a double time-of-flight technique at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a tunable deuteron breakup neutron source, target scintillators housed in a dual photomultiplier tube configuration, and an array of pulse-shape- discriminating observation scintillators, the fast plastic scintillator light yield was measured over a broad and continuous energy range down to proton recoil energies of approximately 50 keV. Furthermore, this work provides key input to event reconstruction algorithms required for utilization of these materials in emerging neutron imaging modalities.
Scintillating plastics resistant to crazing and fogging, methods of making and using the same are disclosed. The scintillating plastics include: one or more primary polymers present in an amount ranging from about 40 wt % to about 95 wt %; one or more secondary polymers present in an amount ranging from about 1 wt % to about 60 wt %; and one or more fluors present in an amount ranging from about 0.1 wt % to about 50 wt %. Methods of making such plastics include: creating a homogenous mixture of precursor materials including primary polymer, secondary polymer, and fluor in the amounts set forth above; and polymerizing the homogenous mixture. Methods of using such plastics include: exposing the scintillating plastic to one or more extreme environmental conditions for a predetermined amount of time without generating crazing or fogging within the scintillating plastic. Various additional features and specific embodiments of these inventive concepts are also disclosed.
To provide efficient and reproducible response to nuclear radiation, scintillating plastics should be prepared as materials of high optical transparency and homogeneity that should remain intact during the lifetime of their operation. A problem with traditionally used polyvinyltoluene (PVT) or polystyrene (PS) plastic scintillators arises from their exposure to repeated large temperature swings that cause surface and volume defects, resulting in decreased sensitivity of the detection properties. We find that the problem can be avoided by composition modifications that enable preparation of plastics with properties that are resistant to the continuous variations in environmental conditions. This paper describes improvements in physical properties that can be achieved by the addition of crosslinkers (such as divinylbenzene, DVB) and oxygen-containing compounds or copolymers (e.g. polymethylamethacrylate, PMMA) to the traditional PVT or PS polymer matrices. Results of characterization show that the new materials can be prepared with the scintillation performance equal to that of commercial plastic scintillators, such as EJ-200.
Scintillating plastic optical fibers have increasingly been used as radiation detectors in nuclear and high energy physics research since they were first made in 1965. It is proposed to make fibers which are at least a factor of 2 brighter and thereby improve detection efficiency, spatial resolution and energy resolution. When radiation strikes existing plastic scintillator only the singlet excited states rather than the triplet excited states are used to produce scintillation light. This means only 25% of the deposited energy is available to produce scintillation light. Utilization of phosphorescent molecules should therefore drastically improve the light output. This process has been called “triplet harvesting” and has been successfully demonstrated in improving the light output of “Organic Light Emitting Diodes, OLEDs”. The objective of this proposal is to produce a bright scintillating fiber using triplet harvesting and a light output time constant of a few nanoseconds. In addition, an increase in the light containment will be achieved by using a new low refractive index cladding material. In Phase 1, polystyrene plastic material will be used. Organo-metallic phosphorescent and conventional dyes will be dissolved in the plastic to demonstrate both the desired brightness and fast decay time. Photophysical properties will be measured. Scintillating fiber will be made. Commercial benefits of this new material include providing improved detection of rare events such as the HIGGS BOSON at the billion dollar high energy facilities. and monitoring stored radioactive material. The new material will also play an important role in making improved imaging detection facilities for protecting civilians and facilities against CBRN-E threats. In addition, the resolution will be improved for medical brachytherapy. The results of selected organic dyes dissolved in a polystyrene matrix performing as scintillating samples are presented. The proposed organo-metallic phosphorescent dyes were not used due to lengthy synthesis times and cost. Rather, an attempt was made to harvest triplet energy from polystyrene using appropriately wavelength-matched dyes. Samples studied include films and blocks. Fibers were not manufactured as a suitable set of dyes was not determined.
Plastic scintillators are widely used as radiation detection media in homeland security and nuclear physics applications. Their attributes include low cost, scalability to large detector volumes, and additive compounding to enable additional material and detection features, such as pulse shape discrimination (PSD), gamma-ray spectroscopy, aging resistance, and coincidence timing. However, traditional chemically cured plastic scintillators (CCS) require long reaction times, and hazardous wet chemical procedures performed by specially trained personnel, and can leave residual monomer, resulting in deleterious optical and material properties. Here, we synthesize melt blended scintillators (MBSs) in 2.5 days using easily accessible solid-state compounding of commercially-available poly(styrene) with 30–60 wt% fluorene-based compound “P2” to create monolithic detectors with < 100 ppm residual monomer, in several form factors. Further, the best scintillation performance was recorded for 60 wt% P2 in Styron 665, including gamma-ray light yield 139% of EJ- 200 commercial scintillator and PSD figure of merit (FOM) value of 2.65 at 478 keVee, approaching P2 organic glass scintillator (OGS). The capability of MBS to generate fog-resistant scintillators and poly(methyl methacrylate) (PMMA)-based scintillators for use in challenging environments is also demonstrated.
A plastic scintillator includes a polymeric matrix comprising a primary fluorophore capable of forming an amorphous glass in its pure form. The primary fluorophore is also capable of generating luminescence in the presence of ionizing radiation and includes: a central species including silicon; a luminescent organic group bonded to the central species or to an optional organic linker group, the luminescent organic group including fluorene or an analog thereof; and the optional organic linker group, if present, is bonded to the central species and the luminescent organic group.
A plastic scintillator includes a polymeric matrix comprising a primary fluorophore capable of forming an amorphous glass in its pure form. The primary fluorophore is also capable of generating luminescence in the presence of ionizing radiation and includes: a central species including silicon; a luminescent organic group bonded to the central species or to an optional organic linker group, the luminescent organic group including fluorene or an analog thereof; and the optional organic linker group, if present, is bonded to the central species and the luminescent organic group.
A plastic scintillator performance for an in-situ measurement system was analyzed using both simulation and experimental methods. The measurement results of four major pure beta-emitting radionuclides - namely H-3. C-14, P-32 and Sr-90/Y-90 - were compared with those from a Monte Carlo N-particle (MCNP) code simulation. Good agreement between the simulation and experimental results was observed for P-32 and Sr-90/Y-90. However, due to the short range of their beta particles in water, the efficiency for both H-3 and C-14 was rather low, and these radionuclides could not be detected. The optimal thickness for the plastic scintillator was identified, as was its suggested diameter. The effect of water depth on system performance was also considered. (authors)
New organic–plastic scintillation compositions have demonstrated pulse-shape discrimination (PSD) of neutrons and gamma rays. We present cross-correlation measurements of 252 Cf and mixed uranium–plutonium oxide (MOX) with the EJ-299-33 plastic scintillator. For comparison, equivalent measurements were performed with an EJ-309 liquid scintillator. Offline, digital PSD was applied to each detector. These measurements show that EJ-299-33 sacrifices a factor of 5 in neutron–neutron efficiency relative to EJ-309, but could still utilize the difference in neutron–neutron efficiency and neutron single-to-double ratio to distinguish 252 Cf from MOX. These measurements were modeled with MCNPX-PoliMi, and MPPost was used to convert the detailed collision history into simulated cross-correlation distributions. MCNPX-PoliMi predicted the measured 252 Cf cross-correlation distribution for EJ-309 to within 10%. Greater photon uncertainty in the MOX sample led to larger discrepancy in the simulated MOX cross-correlation distribution. In conclusion, the modeled EJ-299-33 plastic also gives reasonable agreement with measured cross-correlation distributions, although the MCNPX-PoliMi model appears to under-predict the neutron detection efficiency.
The apparent ion temperature and neutron-reaction history are important characteristics of a fusion plasma. Extracting these quantities from a measured neutron-time-of-flight signal requires accurate knowledge of the instrument response function (IRF). This paper describes a novel method for obtaining the IRF directly for single DT neutron interactions by utilizing n-alpha coincidence. The t(d,α)n nuclear reaction was produced at Sandia National Laboratories’ Ion Beam Laboratory using a 300 keV Cockcroft-Walton generator to accelerate a 2.5 μA beam of 175 keV D + ions into a stationary ErT 2 target. The average neutron IRF was calculated by taking a time-corrected average of individual neutron events within an EJ-228 plastic scintillator. The scintillator was coupled to two independent photo-multiplier tubes operated in the current mode: a Hamamatsu 5946 mod-5 and a Photek PMT240. Finally, the experimental setup and results will be discussed.
A plastic scintillator includes an anti-fog additive or comonomer. The plastic scintillator is formulated to resist the development of hydrothermally-induced aging defects (e.g. discoloration and “fogging”) while maintaining scintillation light output and other desirable physical properties.
Scintillation detectors (SD) based on organic plastic scintillators and optical fibers are basic detectors at all modern accelerators and in astrophysics and neutrino physics experiments. In recent years, interest in SD has significantly increased due to the upcoming major upgrade of the LHC and the construction of new accelerators NICA, FAIR, FCC, etc. At the same time, requirements on the stability and reliability of SD operation under new conditions have become stricter, and their fulfillment largely depends on radiation hardness of scintillators, optical fibers, and photodetectors. The review presents the results of the radiation hardness investigations of various scintillators, optical fibers (scintillating, as well as wavelength-shifting and clear), and optical glues used to increase light collection from scintillators by fibers. The influence of various factors (dose, dose rate, type of radiation, scintillator materials, and fluors) on light output, light collection, and transmittance of the irradiated materials and their recovery is considered. Aging of scintillators caused by environmental effects (temperature, humidity) irrespective of radiation is also briefly considered.
Studies have revealed that plastic scintillators such as polyvinyl toluene and polystyrene can undergo environmentally related material damage (“fogging”) that adversely affects detection performance under certain conditions and histories. A significant decrease in sensitivity has been seen in some gamma-ray detectors as they age as a result of this damage. Performance degradation due to such damage is characterized by a signal change from the detector, which shifts to lower energy, and ultimately a reduction in the ability to detect gamma radiation. This degradation is due to the permeation of water into the plastic, which can then cause temporary fogging and permanent damage to the material. As an example, a 1-mm thick barrier of high-density polyethylene with an area of 1 m 2 would allow 5 g per year of water transmission at 100% relative humidity. Thus, significant amounts of water can penetrate plastics over time and provide the potential for damage to the plastic. Such damage to plastic scintillator can cause problems for radiation detection applications in uncontrolled environments. Mitigation approaches that have been proposed to prevent damage to plastic scintillator include encapsulation of the plastic scintillator to prevent water intrusion that leads to damage during cold cycles. It is concluded that an encapsulation material with a moisture vapor transmission rate on the order of 10 -4 g∙m -2 ∙d -1 or better is needed for protecting large pieces of plastic scintillator from fogging over years of use. This article presents information on testing of bare and encapsulated plastic scintillator samples and on diagnostic approaches to measure the nature and progression of the fogging condition. It is shown that several encapsulation approaches fail to prevent water intrusion, while a couple methods can successfully encapsulate plastic and prevent water from penetrating the plastic and producing fogging.
Purpose: The doping of plastic scintillators with high-Z elements changes the radiation interaction cross section of the medium and therefore changes the intrinsic response of the detector. The selection of doped plastic scintillators available commercially is limited. This research aims to develop a novel methodology for the mechanical doping of plastic scintillating materials. The ultimate goal of this project is to use doped scintillators of varying intrinsic behavior to unfold the LET (energy) spectrum of any radiation beam. Methods: Commercially available BC408 plastic scintillator was obtained and crushed into uniform powder (using ball mill). Two separate materials were tested for light output signal: uncrushed scintillator and scintillating powder bound by glue. Commercially available U301 UV-hardening glue was used. Scintillation response was measured by creating a thin housing of black acrylic that allowed light from each scintillator to be guided to an optical fiber via a taper. The optical fiber was connected to a PMT; signal was measured using an electrometer. Tests were conducted to determine if crushing+bonding distorted linearity and energy dependence of detector response. Linearity was tested for by irradiating (uncrushed and crushed+glued) for varying durations ensuring signal scaled accordingly; this was done using 300kV x-rays and 6MeV electrons. The effect on energy dependence was examined by obtaining a signal ratio (100kV vs. 300kV; 6MeV vs. 18MeV) for both uncrushed and crushed+glued scintillating material. Results: Crushing and binding with U301 glue did not have an effect on linearity. Energy dependence was changed by 20.3%; crushing+bonding decreased the sensitivity at low energy radiation. Conclusion: This work indicates that crushing and binding of plastic scintillating material does not change the linearity of its response to radiation but does have an effect on the energy dependence. Future work involves addition of high-Z dopants (W, Mo, Pb) and characterization of the detector response.
Lithium-loaded organic plastic scintillators combine sensitivity to γ rays with the ability to detect both fast and slow neutrons, making them valuable for applications in nuclear security and in basic nuclear and particle physics. The goal of this work is to characterize the neutron response of two custom lithium-loaded organic plastic scintillators developed at Lawrence Livermore National Laboratory. Both are ternary polystyrene-based formulations containing 1.5 wt.% 6 Li salts of isobutyric acid, but they differ in their primary and secondary dye compositions: one uses m-terphenyl as the primary fluor and with Exalite 404 as the wavelength shifter, whereas the other uses 2,5-diphenyloxazole (PPO) and 9,10-diphenyl-anthracene, respectively. The temporal response of the scintillators was measured via time-correlated single photon counting for γ-ray and neutron events. The proton light yield was measured using the double time-of-flight technique from 1.3 to 15 MeV at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. For the slow neutron response, an AmBe source moderated with polyethylene was used, and the light output from the 6 Li(n,α)t reaction was characterized. Differences in ionization quenching and temporal response were observed between the two materials with the PPO-containing scintillator exhibiting higher ionization quenching. These results provide performance benchmarks that can guide the design and optimization of future lithium-loaded plastic scintillators for use in basic science and applications.
Fogging in plastic scintillators is a degradation mechanism that reduces light collection efficiency. In an effort to reduce maintenance costs, multiple groups have attempted to understand and prevent this problem by changing plastic compositions and system level designs. New formulations have been produced that are promising with respect to fogging resistance. In this paper, we study a variety of new compositions by subjecting them to an accelerated aging experiment with varying temperature and humidity profiles. Compositions are analyzed for their resistance to degradation after saturation periods, with those containing polymethyl methacrylate and divinyl benzene being the most promising. Pulse height spectra revealed that after environmental aging, many of the samples suffered a reduction in light yield to different degrees, a result that could be due to heating of the samples and may be prevented by further production optimization.
The Nuclear and Energy Research Institute - IPEN, offers post-graduate programs, namely: Nuclear Technology - Applications (TNA), Nuclear Technology - Materials (TNM), Nuclear Technology - Reactors (TNR). The Institute programs mission is to form expert technicians, physicists and engineers with a strong knowledge in their discipline to work in the nuclear area. The course: 'Theoretical Fundamentals and Practices of the Instrumentation used in Nuclear Data Acquisition' covers the use of laboratory nuclear instrumentation and the accomplishment of experiments to obtain nuclear parameters. One of these experimental exercises is object of this work: 'Study of influence of plastic scintillators to detect Beta particles and Gamma radiation by means of spectral analysis of {sup 90}Sr, {sup 90}Y and {sup 137}Cs sources'. The use of scintillators plastic for the detection has the advantage of low cost, high mechanical strength, is not hygroscopic and can be manufactured in large volumes. This work aims to present the analysis of relative efficiency of detection of plastic scintillators of various thicknesses for beta particles and gamma radiation by the spectrum of {sup 137}Cs and {sup 90}Sr. Due to lack of resolution of the detectors plastic scintillators we worked with relative efficiency. The evaluation was done by reading deposited energy, using the software MAESTRO, for each detector thickness. For beta particles was observed an ideal thickness around 3 mm and the better photon efficiency was observed with increasing the thickness of the detector. The present experiment does not intend to establish a new technique for this subject: it solely aims student's practical exercises in nuclear properties of elements and detectors being part of the nuclear experimental course. (authors)