Plastic Scintillation Microspheres Research Articles

The Future of Health Physics: Trends, Challenges, and Innovation.

This paper offers a comprehensive exploration of the future trajectory of health physics, examining influential factors in external and internal dimensions. External factors include an in-depth analysis of low-dose (10-100 mSv) measurement challenges and priorities, highlighting the transformative potential of biomarkers in solving radiation susceptibility following low-dose exposures. Cutting-edge technologies are at the forefront, with insights into emerging radiation detection tools like plastic scintillators with triple discrimination capabilities and sensors based on plastic scintillation microspheres (PSm) for estimating α and β emitting radionuclides in environmental samples. Remote detection systems using drones, robot dogs, and quantum sensors boasting heightened sensitivity and precision also are discussed. Integrating artificial intelligence (AI) and data analytics emerges as a pivotal element, promising to redefine health physics by minimizing radiation exposure risks. The exploration includes innovative materials for radiation shielding, advancements in virtual reality applications, preparation for radiological protection during armed conflicts, and the ever-evolving landscape of decommissioning health physics. Examining health effects from non-ionizing radiation and analyzing broader contextual factors such as regulatory shifts, geopolitics, and socioeconomic influences adds depth to understanding the external forces leading to the future of health physics. Internally, the paper focuses on the transformative dynamics of health physics education and training, encompassing expanded educational horizons, innovative delivery methods, targeted student outreach strategies, and insights into navigating health physics careers amid a dynamically evolving job market. The discussion unfolds further, focusing on new risk communication strategies, the collaborative potential of interdisciplinary approaches, and the significance of health physics summer schools and consortia for transformative educational paradigms. The objective of this paper is not only to unravel the multifaceted factors shaping the future of health physics but also to foster dialogue and collaboration for the unpredictable yet exciting journey ahead.

Suspension polymerization method for preparing plastic scintillation microspheres

Suspension polymerization method for preparing plastic scintillation microspheres

Development of an equipment for real-time continuous monitoring of alpha and beta radioactivity in river water

Different regulations require the monitoring of radioactivity in the environment (e.g., 2013/51/Euratom, Real Decreto 314/2016) to protect the environment and the population from abnormal radioactivity presence caused by natural reasons or discharges or accidents in nuclear installations. Nowadays, the monitoring of α- and β-emitting radionuclides is performed discontinuously in laboratories due to the difficulties in applying classical techniques to continuous measurements. This limits the number of samples that can be measured per day, produces high costs per analysis, and introduces a significant delay between the moment of contamination and when it is detected. Plastic scintillation microspheres (PSm) represent a new possibility for continuous measurements because water samples can flow through a bed of PSm connected to a pair of photomultipliers (PMTs), allowing continuous monitoring of the activity. This idea is the basis of the Waterrad detector, which can monitor radioactivity at environmental levels in river water. This paper describes the optimization of a detection cell containing PSm, a detection chamber as well as active and passive shielding. In its final set-up, the Waterrad detector presents a background signal of 0.23 (1) cps and detection efficiencies of 1.86(7)·10−5 cps·L·Bq−1 for 3H, 7.4(8)·10−3 cps·L·Bq−1 for 90Sr/90Y and 5.5(5)·10−3 cps·L·Bq−1 for 241Am. The detection limits in the optimum window for a counting time of 5 h were 490 Bq/L for 3H, 2.3 Bq/L for 90Sr/90Y and 3.0 Bq/L for 241Am. These values indicate that Waterrad can be used as an alarm detector for monitoring radioactivity in water at activity levels similar to those of environmental samples, making it suitable for water or waste surveillance involving a high frequency of measurements.

PSresin for the analysis of alpha-emitting radionuclides: Comparison of diphosphonic acid-based extractants

The analysis of radionuclides is complex, with high economic and time costs. For this reason, there is a need to develop new methods and strategies to reduce these costs. One important group in the analysis of radionuclides is the actinides, which are the main constituents assessed in the total gross alpha together with radium and radon test used to measure radioactivity in drinking water. Moreover, in nuclear dismantling processes, the possible spread of the released radionuclides has to be controlled, which is measured by many techniques, depending on the radionuclides, through scintillation. This work presents a new method to analyse actinides using plastic scintillation resins (PSresins) packed in a solid-phase extraction cartridge. The proposed method combines chemical separation and sample measurement into a single step, reducing the effort, time and reagents required for analysis as well as decreasing the amount of waste generated. The PSresins compared in this study contained three selective extractants based on methylenediphosphonic acid with different radicals, which has a high affinity for tri-, tetra-, and hexavalent actinides in dilute acids. These extractants were immobilised on plastic scintillation microspheres at a ratio of 1/1:6, producing a retention and detection efficiency of 100% for 241Am, 230Th, Uranium and 238Pu. The retention and detection efficiency were 20% and 100%, respectively, for 210Po and low for 226Ra.

Plastic scintillators and related analytical procedures for radionuclide analysis

This article is a general overview of the potential capacities of plastic scintillators in radionuclide activity determination. Plastic scintillation (PS) behaves as liquid scintillation does, but with some differences related to the solid state of plastic scintillators. These differences are the base of some drawbacks and some advantages, related to the use of PS. This article describes how these capacities are affected by PS composition, sample preparation, scintillation mechanisms and quenching calibration procedures. It also describes the capabilities for alpha and beta emitter determination and discrimination through the use of PS microspheres and PS resins and their application to different types of samples and radionuclide determination.

Analysis of 210Pb in water samples with plastic scintillation resins

210Pb is a radioactive lead isotope present in the environment as member of the 238U decay chain. Since it is a relatively long-lived radionuclide (T1/2 = 22.2 years), its analysis is of interest in radiation protection and the geochronology of sediments and artwork. Here, we present a method for analysing 210Pb using plastic scintillation resins (PSresins) packaged in solid-phase extraction columns (SPE cartridge). The advantages of this method are its selectivity, the low limit of detection, as well as reductions in the amount of time and reagents required for analysis and the quantity of waste generated. The PSresins used in this study were composed of a selective extractant (4′,4″(5″)-Di-tert-butyldicyclohexano-18-crown-6 in 1-octanol) covering the surface of plastic scintillation microspheres. Once the amount of extractant (1:1/4) and medium of separation (2 M HNO3) were optimised, PSresins in SPE cartridges were calibrated with a standard solution of 210Pb. 210Pb could be fully separated from its daughters, 210Bi and 210Po, with a recovery value of 91(3)% and detection efficiency of 44(3)%. Three spiked water samples (one underground and two river water samples) were analysed in triplicates with deviations lower than 10%, demonstrating the validity of the PS resin method for 210Pb analysis.

Robustness of plastic scintillation microspheres in the continuous measurement of different river waters

Plastic scintillation microspheres (PSm) represent one of the most promising options for monitoring alpha and beta radioactivity in river water. For that reason, a study of the stability of PSm packed into a cell against the continuous flow of river water with different degrees of turbidity was performed over a period of 100h. The results showed that the volume of the cell became stable after 15h of pumping and continued to be stable throughout the 100h of the experiment. During this period of time, the detection efficiency of the PSm, in terms of efficiency*volume, presented mean values of 0.75(3)% for 3H and 272(11)% for 90Sr/90Y. No dependence on flow time or river water type was observed. The background was also constant for 100h and for the different water types, although 222Rn should be removed from the water beforehand to prevent its accumulation in the PSm. Since PSm did not present any degradation throughout the whole experiment, PSm can undoubtedly be used for monitoring radioactivity with low reagent consumption, low waste generation and low maintenance costs.

Influence of preparation parameters on the synthesis of plastic scintillation microspheres and evaluation of sample preparation

Plastic scintillation microspheres (PSm) are solid dispersions of fluorescent solutes encapsulated in a polymeric matrix; they are used to measure β and α decay of radionuclides. Since organic solvent evaporation/extraction methods have been successfully employed to produce PSm, this work evaluates the influence of different parameters (i.e., polystyrene (PS) and polyvinyl alcohol (PVA) concentrations, temperature, stirring speed and the organic/aqueous phase ratio) on the final size of the PSm; and the relationship between this final size and the radiometric capacities of the PSm in relation to emitters of both beta (3H, 14C and 90Sr/90Y) and alpha (241Am) radiation.The results show that when the concentration of PVA is increased, the size of the PSm decreases; meanwhile, an important decrease in particle size is also achieved when the PS concentration is decreased. For almost all the parameters evaluated, the resultant PSm were smoothed and spherical. However, when temperature was increased, the particle size increased and the PSm eventually became amorphous and porous. The observed decrease in particle size correlated with an increase in radiation detection efficiency and a movement in the positioning of the spectra at lower energy values.We also evaluated the reproducibility of the vial preparation for 3H measurements and confirmed that small variations in the quantity of PSm and preparation of different vials by different experimenters did not influence the radiometric capacities.

Pilot Study of the Application of Plastic Scintillation Microspheres to Rn-222 Detection and Measurement

This work demonstrates that when plastic scintillation microspheres (PSms) synthesized from polystyrene are exposed to $^{222}{\rm Rn}$ in air or water, they concentrate $^{222}{\rm Rn}$ in their volume. A theoretical model, based on the solution of the diffusion equation is developed, in order to describe the $^{222}{\rm Rn}$ sorption and desorption processes in PSms. A macroscopic quantity termed “sampling efficiency” is used to quantify the absorption properties of the PSms. The sampling efficiency is estimated by exposure of PSms to $^{222}{\rm Rn}$ in air and water. Estimates of the counting efficiency for measurement of the exposed PSms by commercial scintillation counters are presented. The results show that polystyrene PSms are simultaneously good samplers and detectors of $^{222}{\rm Rn}$ . These properties indicate that sensitive approaches for the measurement of $^{222}{\rm Rn}$ based on absorption and scintillation counting of PSms can be developed.

Measurement of 222Rn by absorption in plastic scintillators and alpha/beta pulse shape discrimination

This work demonstrates that common plastic scintillators like BC-400, EJ-200 and SCSF-81 absorb radon and their scintillation pulse decay times are different for alpha- and beta-particles. This allows the application of pulse shape analysis for separation of the pulses of alpha- and beta-particles emitted by the absorbed radon and its progeny. It is shown that after pulse shape discrimination of beta-particles’ pulses, the energy resolution of BC-400 and EJ-200 alpha spectra is sufficient to separate the peaks of 222Rn, 218Po and 214Po and allows 222Rn measurements that are unaffected by the presence of thoron (220Rn) in the environment. The alpha energy resolution of SCSF-81 in the experiments degrades due to imperfect collection of the light emitted inside the scintillating fibers. The experiments with plastic scintillation microspheres (PSM) confirm previous findings of other researchers that PSM have alpha-/beta-discrimination properties and show suitability for radon measurements. The diffusion length of radon in BC-400 and EJ-200 is determined. The pilot experiments show that the plastic scintillators are suitable for radon-in-soil-gas measurements. Overall, the results of this work suggest that it is possible to develop a new type of radon measurement instruments which employ absorption in plastic scintillators, pulse-shape discrimination and analysis of the alpha spectra. Such instruments can be very compact and can perform continuous, real-time radon measurements and thoron detection. They can find applications in various fields from radiation protection to earth sciences.

Production of polystyrene-based scintillation microspheres for the measurement of radioactivity by spray-drying

The use of plastic scintillation microspheres (PSm) is an innovative technique for measuring the radioactivity of beta-emitting radionuclides. PSm can be produced via different methods; none of which has been assayed at the industrial scale. In the present paper, we evaluate the production of PSm by spray-drying on an industrial scale. Our results indicate that fluorescent solutes were indeed encapsulated within polystyrene producing spherical particles of 10 μm in diameter. Detection efficiencies for the measurement of 3H and 14C were 3–5 % and 60–75 %, respectively. These efficiencies are comparable to those of PSm produced via other methods.

Polystyrene based sub-micron scintillating particles produced by supercritical anti-solvent precipitation

Plastic scintillation microspheres (PSm) are a novel material employed in the measurement of radioactivity (α and β emitters). This work is focused on the formation of plastic scintillation particles through the precipitation and encapsulation of two fluorescent solutes (2,5-diphenyloxazol (PPO) and 1,4-Bis(5-phenyloxazol-2-yl) benzene (POPOP)) and an aromatic solvent 2,6-diisopropyl-naphthalene (DIN), which acts as an enhancer for α and β emitters discrimination, into a polymeric matrix of polystyrene (PS) by Supercritical Anti-Solvent process (SAS) using ethyl acetate (EtAc) for dissolving the PS and supercritical CO2 as antisolvent. Different process parameters were varied; solute concentration in the organic solution (W, wt%), injection velocity of the organic solution (u, ms−1), molar ratio of the organic solvent regarding to CO2 (XEA) and injection capillary tube diameter (μm). In the different experimental conditions tested, SAS coprecipitation was successfully achieved resulting in yields higher than 90% and very low quantities of residual solvent (600–1200ppm). The different polystyrene based particles obtained were nearly spherical sub-micron particles (ranged between 150 and 400nm) and also agglomerates of a few micrometers were observed in most of the studied conditions. Radiometric capacities of particles were evaluated through measuring different beta and alpha emitting radionuclide. The coprecipitates showed scintillation behavior when fluorescent solutes were added, therefore confirming their encapsulation.

Application of the CIEMAT–NIST method to plastic scintillation microspheres

An adaptation of the MICELLE2 code was used to apply the CIEMAT–NIST tracing method to the activity calculation for radioactive solutions of pure beta emitters of different energies using plastic scintillation microspheres (PSm) and 3H as a tracing radionuclide. Particle quenching, very important in measurements with PSm, was computed with PENELOPE using geometries formed by a heterogeneous mixture of polystyrene microspheres and water. The results obtained with PENELOPE were adapted to be included in MICELLE2, which is capable of including the energy losses due to particle quenching in the computation of the detection efficiency. The activity calculation of 63Ni, 14C, 36Cl and 90Sr/90Y solutions was performed with deviations of 8.8%, 1.9%, 1.4% and 2.1%, respectively. Of the different parameters evaluated, those with the greatest impact on the activity calculation are, in order of importance, the energy of the radionuclide, the degree of quenching of the sample and the packing fraction of the geometry used in the computation.

Synthesis of plastic scintillation microspheres: Alpha/beta discrimination

Plastic scintillation microspheres (PSm) have been developed as an alternative for liquid scintillation cocktails due to their ability to avoid the mixed waste, besides other strengths in which the possibility for alpha/beta discrimination is included. The aim of this work was to evaluate the capability of PSm containing two combinations of fluorescence solutes (PPO/POPOP and pT/Bis-MSB) and variable amounts of a second organic solvent (naphthalene) to enhance the alpha/beta discrimination. Two commercial detectors with different Pulse Shape Discrimination performances (Quantulus and Triathler) were used to evaluate the alpha/beta discrimination. An optimal discrimination of alpha/beta particles was reached, with very low misclassification values (2% for beta particles and 0.5% for alpha particles), when PSm containing PPO/POPOP and between 0.6 and 2.0g of naphthalene were evaluated using Triathler and the appropriate programme for data processing.

Alpha/beta indices determination in drinking water using plastic scintillation and evaporation to dryness

Alpha/beta indices are screening parameters that provide a quick approach to the determination of the radioactivity levels of water samples. These indices have commonly been determined by methods involving measurement by proportional counter or liquid scintillation (LS) techniques. However, both of these types of techniques present some limitations. Plastic scintillation (PS) is an alternative technique that does not generate mixed wastes and also provides a solid surface onto which the sample can be evaporated. The objective of this study is to evaluate a new procedure for the determination of alpha/beta indices using PS microspheres and evaporation to dryness. For this purpose, the capabilities of this technique were first compared with those of LS and PS in solution. Various parameters were then optimised: the diameter of the microspheres, the discrimination values and the evaporation system. Next, the calibration procedure was established, and finally, the procedure was validated with the analysis of spiked water samples. The results show that this technique can be applied for alpha/beta indices determination with a simple procedure, high detection efficiency and acceptable uncertainties.

Systematic study of particle quenching in organic scintillators

Among the different factors that affect measurements by organic scintillators, the majority of attention has been focused on those related to the scintillator (i.e., ionization, chemical, color and optical quenching), and less attention has been paid to the loss of energy before the particle (i.e., alpha or beta) arrives at the scintillator (i.e., particle quenching). This study evaluates the effect of particle quenching in different scintillation methods (i.e., using two plastic scintillation microspheres (PSm1 and PSm2), liquid scintillator and gel scintillator) by measuring solutions that contain increasing concentrations of NaCl, BaCl2 and glycerin. The results show the importance of particle quenching in PSm measurements because detection efficiency decreases with increasing concentrations of the quenching component, although the spectrum position and external standard parameter remain constant. The results have shown evidence of particle quenching, although at a lower magnitude, in the liquid scintillation or gel scintillation measurements. Moreover, the use of two PSm with different diameters and salty compound that alters the equilibrium of the liquid and gel emulsions also exemplified the importance of the transmission of optical photons through different scintillation media (i.e., optical quenching). Improvement and deterioration of the optical conditions on the scintillation media is manifested as a movement of the spectrum to higher and lower energies, respectively. The results obtained with PSm were confirmed by Monte Carlo simulation.

Synthesis of plastic scintillation microspheres: Evaluation of scintillators

The use of plastic scintillation microspheres (PSm) appear to be an alternative to liquid scintillation for the quantification of alpha and beta emitters because it does not generate mixed wastes after the measurement (organic and radioactive). In addition to routine radionuclide determinations, PSm can be used for further applications, e.g. for usage in a continuous monitoring equipment, for measurements of samples with a high salt concentration and for an extractive scintillation support which permits the separation, pre-concentration and measurement of the radionuclides without additional steps of elution and sample preparation. However, only a few manufacturers provide PSm, and the low number of regular suppliers reduces its availability and restricts the compositions and sizes available.In this article, a synthesis method based on the extraction/evaporation methodology has been developed and successfully used for the synthesis of plastic scintillation microspheres. Seven different compositions of plastic scintillation microspheres have been synthesised; PSm1 with polystyrene, PSm2 with 2,5-Diphenyloxazol(PPO), PSm3 with p-terphenyl (pT), PSm4 with PPO and 1,4-bis(5-phenyloxazol-2-yl) (POPOP), PSm5 pT and (1,4-bis [2-methylstyryl] benzene) (Bis-MSB), PSm6 with PPO, POPOP and naphthalene and PSm7 with pT, Bis-MSB and naphthalene.The synthesised plastic scintillation microspheres have been characterised in terms of their morphology, detection capabilities and alpha/beta separation capacity. The microspheres had a median diameter of approximately 130μm. Maximum detection efficiency values were obtained for the PSm4 composition as follows 1.18% for 3H, 51.2% for 14C, 180.6% for 90Sr/90Y and 76.7% for 241Am. Values of the SQP(E) parameter were approximately 790 for PSm4 and PSm5. These values show that the synthesised PSm exhibit good scintillation properties and that the spectra are at channel numbers higher than in commercial PSm. Finally, the addition of naphthalene modifies the shape of the pulses produced by alpha and beta particles leading to better alpha/beta separation.

Determination of oil reservoir radiotracer (S14CN−) in a single step using a plastic scintillator extractive resin

The analysis of radiotracers is important in the study of oil reservoir dynamics. One of the most widely used radiotracer is S14CN−. Prior to activity measurements by Liquid Scintillation (LS), routine determinations require the pretreatment steps of purification and concentration of the samples using anion exchange columns. The final elution media produces samples with high salt concentration that may lead to problems with phase separation during the LS measurement. Plastic Scintillation (PS) is an alternative technique that provides a solid surface that can be used as a platform for the immobilisation of selective extractants to obtain a PS resin. The proposed procedure unifies chemical separation and sample measurement preparation in a single step, serving to reduce the number of reagents needed and manpower required for the analysis while also avoiding mixed waste production by LS.The objective of this study is to develop a PS resin for the determination of 14C-labelled thiocyanate radiotracer in water samples.For this purpose, the immobilisation procedure was optimised, including optimisation of the proportion of PS microspheres:extractant and the use of a control blank to monitor the PS resin immobilisation process. The breakthrough volume was studied and the detection and quantification limits for 100mL of sample were determined to be 0.08BqL−1 and 0.31BqL−1, respectively. The established procedure was applied to active samples from oil reservoirs and errors lower than 5% in the sample determinations were obtained.

Application of a free parameter model to plastic scintillation samples

In liquid scintillation (LS) counting, the CIEMAT/NIST efficiency tracing method and the triple-to-double coincidence ratio (TDCR) method have proved their worth for reliable activity measurements of a number of radionuclides. In this paper, an extended approach to apply a free-parameter model to samples containing a mixture of solid plastic scintillation microspheres and radioactive aqueous solutions is presented.Several beta-emitting radionuclides were measured in a TDCR system at PTB. For the application of the free parameter model, the energy loss in the aqueous phase must be taken into account, since this portion of the particle energy does not contribute to the creation of scintillation light. The energy deposit in the aqueous phase is determined by means of Monte Carlo calculations applying the PENELOPE software package. To this end, great efforts were made to model the geometry of the samples. Finally, a new geometry parameter was defined, which was determined by means of a tracer radionuclide with known activity. This makes the analysis of experimental TDCR data of other radionuclides possible. The deviations between the determined activity concentrations and reference values were found to be lower than 3%.The outcome of this research work is also important for a better understanding of liquid scintillation counting. In particular the influence of (inverse) micelles, i.e. the aqueous spaces embedded in the organic scintillation cocktail, can be investigated. The new approach makes clear that it is important to take the energy loss in the aqueous phase into account. In particular for radionuclides emitting low-energy electrons (e.g. M-Auger electrons from 125I), this effect can be very important.

A novel method for the detection of receptors and membrane proteins by scintillation proximity radioassay

A rapid and convenient binding assay for receptors and membrane proteins has been developed. It is based on the binding of 125I-labeled ligands to membrane proteins adsorbed to polyvinyltoluene plastic scintillation microspheres. Membranes or isolated membrane proteins adsorb to the beads upon mixing, and addition of 125I-labeled ligand induces photon emission which is proportional to the amount of added receptor or membrane protein. The interaction of acetylcholine receptor with 125I-labeled α-bungarotoxin and antigens with 125I-labeled antibodies or protein A were used as models to test the system. As little as 1 ng of acetylcholine receptor is detected by the assay and a linear relationship with receptor concentration is observed up to 50 ng of receptor per 250 μl reaction medium. The effects of detergents, salts, soluble proteins, and neutral membranes were studied. Inclusion of bovine serum albumin up to 1 mg/ml, sodium chloride up to 0.5 m, and membranes up to 10 μg/ml cause little or no effect on the assay. Detergents at 10-fold below their critical micelle concentrations had little or no effect on the assay. The pharmacological effects of agonists such as acetylcholine were conveniently studied by following the displacement of the 125I-labeled ligand. Similarly, the amount of toxin in crude snake venom can be assayed by measuring competition with the labeled toxin. Only a few seconds are required to perform each binding assay.