Plastic scintillators for positron emission tomography obtained by the bulk polymerization method

This paper describes three methods regarding the production of plastic scintillators. One method appears to be suitable for the manufacturing of plastic scintillator, revealing properties which fulfill the requirements of novel positron emission tomography scanners based on plastic scintillators. The key parameters of the manufacturing process are determined and discussed.Comment: 7 pages, 4 figure

A pilot study of the novel J-PET plastic scintillator with 2-(4-styrylphenyl)benzoxazole as a wavelength shifter

For the first time a molecule of 2-(4-styrylphenyl)benzoxazole containing benzoxazole and stilbene groups is applied as a scintillator dopant acting as a wavelength shifter. In this article a light yield of the plastic scintillator, prepared from styrene doped with 2 wt% of 2,5-diphenylbenzoxazole and 0.03 wt% of 2-(4-styrylphenyl)benzoxazole, is determined to be as large as 60% $\pm$ 2% of the anthracene light output. There is a potential to improve this value in the future by the optimization of the additives concentrations

PALS investigations of free volumes thermal expansion of J-PET plastic scintillator synthesized in polystyrene matrix

The polystyrene dopped with 2,5-diphenyloxazole as a primary fluor and 2-(4-styrylphenyl)benzoxazole as a wavelength shifter, prepared as a plastic scintillator was investigated using positronium probe in wide range of temperatures from 123 to 423 K. Three structural transitions at 260 K, 283 K and 370 K were found in the material. In the o-Ps intensity dependence on temperature, the significant hysteresis is observed. Heated to 370 K, the material exhibits the o-Ps intensity variations in time.Comment: in Nukleonika 201

Fast emitting nanocomposites for high-resolution ToF-PET imaging based on multicomponent scintillators

Time-of-Flight Positron Emission Tomography is a medical imaging technique, based on the detection of two back-to-back {\gamma}-photons generated from radiotracers injected in the body. Its limit is the ability of employed scintillation detectors to discriminate in time the arrival of {\gamma}-pairs, i.e. the coincidence time resolution (CTR). A CTR < 50 ps that would enable fast imaging with ultralow radiotracer dose. Monolithic materials do not have simultaneously the required high light output and fast emission characteristics, thus the concept of scintillating heterostructure is proposed, where the device is made of a dense scintillator coupled to a fast-emitting light material. Here we present a composite polymeric scintillator, whose density has been increased upon addition of hafnium oxide nanoparticles. This enhanced by +300% its scintillation yield, surpassing commercial plastic scintillators. The nanocomposite is coupled to bismuth germanate oxide (BGO) realizing a multilayer scintillator. We observed the energy sharing between its components, which activate the nanocomposite fast emission enabling a net CTR improvement of 25% with respect to monolithic BGO. These results demonstrate that a controlled loading with dense nanomaterials is an excellent strategy to enhance the performance of polymeric scintillators for their use in advanced radiation detection and imaging technologies

Ultrafast hybrid nanocomposite scintillators: A review

In recent years, demand for scintillation detectors with high time resolution (better than 100 ps) has emerged in high-energy physics and medical imaging applications. In particular, time of flight positron emission tomography (TOF-PET) can greatly benefit from increasing time resolution of scintillators, which leads to the increase of signal-to-noise ratio, decrease of patient dose, and achievement of the superior spatial resolution of PET images. Currently, extensive research of various types of materials is carried out to achieve the best time resolution. In this review, the recent progress of various approaches is summarized and scintillation compounds with the best temporal characteristics are first reviewed. The review presents the physical processes causing fast luminescence in inorganic and organic materials. Special attention is paid to nanocomposites which belong to a new perspective class of scintillating materials, consisting of a plastic matrix, inorganic nanocrystalline fillers, and organic or inorganic luminescence activators and shifters. The main features and functions of all parts of existing and prospective nanocomposite scintillators are also discussed. A number of currently created and investigated nanocomposite materials with various compounds and structures are reviewed. © 2021 Elsevier B.V.Eesti Teadusagentuur, ETAg: PRG111, PRG629; European Regional Development Fund, ERDF: 2014-2020.4.01.15–0011, TK141Authors thank Minobrnauki project FEUZ-2020-0059 and Estonian Research Council (grants PRG629 and PRG111 ) for financial support. Authors are also grateful for partial support from the European Regional Development Fund (DoRA Pluss program) and the ERDF funding in Estonia granted to the Center of Excellence TK141 “ Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics ” (project No. 2014-2020.4.01.15–0011 )

Ce or Pr-doped type III KGd(PO3)4 crystalline materials. Growth and characterization as scintillators

Els materials escintil·ladors són àmpliament utilitzats com a detectors en els sistemes de detecció de diverses aplicacions, com la imatge mèdica, la física d’alta energia, l’astrofísica i en proves no destructives (seguretat aeroportuària, control industrial, etc.). Hi ha diversos requisits importants per avaluar favorablement el rendiment d’un escintil·lador. Donat que no existeix el escintil·lador ideal, s’estan dedicant molts esforços a buscar nous escintil·ladors inorgànics amb millors propietats que els dels escintil·ladors existents. En aquesta tesi, es creixen monocristalls amb alta qualitat cristal·lina de KGd(PO3)4 tipus III dopats amb Ce3+ i Pr3+, i també nanocristalls de Pr:KGd(PO3)4 tipus III per posteriorment caracteritzar-los estructuralment i òpticament com a possibles nous materials escintil·ladors. Aquests monocristalls es creixen a partir de solucions d’alta temperatura mitjançant la tècnica Top Seeded Solution Growth-Slow Cooling (TSSG-SC) i els nanocristalls es sintetitzen mitjançant el mètode de Pechini. La caracterització estructural inclou la morfologia cristal·lina, estabilitat i expansió tèrmiques, distribució de mida de les partícules, entre altres. S’estudia amb detall l’espectroscòpia de les transicions 4f–5d, sobre les quals es basa el mecanisme d’escintil·lació. Inclou mesures d'absorció òptica, mesures de luminescència i del temps de decaiguda d’aquesta excitant amb llum de sincrotró en el rang espectral des de l'ultraviolat de buit fins l'ultraviolat (VUV-UV), mesures de radioluminescència excitant amb raigs X, entre altres. A més, es proporcionen les dades espectroscòpiques bàsiques dels monocristalls de Pr:KGd(PO3)4 tipus III per aplicacions làser en la gamma de longitud d'ona visible basades en les transicions electròniques 4f-4f. També, es determina la regió de cristal·lització primària del KYP4O12 tipus B i del KY(PO3)4 tipus IV en el sistema ternari K2O–Y2O3–P2O5, ja que són candidats interessants per actuar com a matriu per ions lantànids actius en aplicacions de centelleig.Los materiales centelleadores son ampliamente utilizados como detectores en los sistemas de detección de diversas aplicaciones, como la imagen médica, la física de alta energía, la astrofísica y en pruebas no destructivas (seguridad aeroportuaria, control industrial, etc.). Hay varios requisitos importantes para evaluar favorablemente el rendimiento de un centelleador. Dado que no existe el centelleador ideal, se están dedicando muchos esfuerzos para buscar nuevos centelleadores inorgánicos con mejores propiedades que los de los centelleadores existentes. En esta tesis, se crecen monocristales con alta calidad cristalina de KGd(PO3)4 tipo III dopados con Ce3+ y Pr3+, y también nanocristales de Pr:KGd(PO3)4 tipo III para posteriormente caracterizarlos estructuralmente y ópticamente como posibles nuevos materiales centelleadores. Estos monocristales se crecen a partir de soluciones de alta temperatura mediante la técnica Top Seeded Solution Growth-Slow Cooling (TSSG-SC) y los nanocristales se sintetizan mediante el método de Pechini. La caracterización estructural incluye la morfología cristalina, estabilidad y expansión térmicas, distribución de tamaño de las partículas, entre otros. Se estudia con detalle la espectroscopia de las transiciones 4f-5d, sobre las que se basa el mecanismo de centelleo. Incluye medidas de absorción óptica, medidas de luminiscencia y del tiempo de decaída de ésta excitando con luz de sincrotrón en el rango espectral desde el ultravioleta de vacío hasta el ultravioleta (VUV-UV), medidas de radioluminiscencia excitando con rayos X, entre otros. Además, se proporcionan los datos espectroscópicos básicos de los monocristales de Pr:KGd(PO3)4 tipo III para aplicaciones láser en la gama de longitud de onda visible basadas en las transiciones electrónicas 4f-4f. También, se determina la región de cristalización primaria de KYP4O12 tipo B y de KY(PO3)4 tipo IV en el sistema ternario K2O-Y2O3-P2O5, ya que son candidatos interesantes para actuar como matriz para iones lantánidos activos en aplicaciones de centelleo.Scintillators materials are widely used as detectors in the detection systems of a variety of applications, such as medical imaging, high energy physics, astrophysics and non-destructive testing (airport security, industrial control, etc.). There are several important requirements to evaluate favourably the performance of a scintillator. Since the ideal scintillator does not exist, many efforts are dedicated to find new inorganic scintillators with better properties than those of the existing scintillators. Here, Ce3+- and Pr3+-doped type III KGd(PO3)4 bulk single crystals with high crystalline quality and type III Pr:KGd(PO3)4 nanocrystals are grown and structurally and optically characterized as possible new scintillator materials. These bulk single crystals are grown from high temperature solutions by the Top Seeded Solution Growth-Slow Cooling (TSSG-SC) technique, while the nanocrystals are synthesized by the Pechini method. The structural characterization includes the crystal morphology, thermal stability, thermal expansion, particle size distribution, among others. The spectroscopy of the 4f–5d transitions, on which the scintillation mechanism is based, is studied in detail. The spectroscopic characterization includes optical absorption measurements, luminescence and decay time measurements under synchrotron vacuum ultraviolet-ultraviolet (VUV-UV) excitation, radioluminescence measurements after synchrotron X-ray irradiation, among others. In addition, the basic spectroscopic data of the type III Pr:KGd(PO3)4 crystal for lasing applications in the visible wavelength range based on the 4f–4f electronic transitions is provided. Moreover, the primary crystallization region of type B KYP4O12 and type IV KY(PO3)4 in the K2O–Y2O3–P2O5 ternary system is determined, since these are interesting candidates as hosts for active lanthanide ions in scintillation applications

pH SENSING AND IMAGING WITH NANOPARTICLES AND IMPLANTABLE FILMS

pH is a very important parameter in biological systems. Monitoring pH in situ may provide useful information for studying pH regulated cellular events, diagnosing diseases and assessing treatment efficacy. Various strategies have been introduced for developing pH sensors. However, it is still challenging to monitor pH in biological systems with high specificity, especially through thick tissue. In this dissertation, we describe three types of pH sensors which are used to noninvasively monitor pH in living cells, monitor and map bacterial growth caused pH variation through thick tissue with minimal autofluorescence background. In Chapter 2, a pH nanosensor with high specificity and sensitivity is developed based on surface-enhanced Raman scattering by encapsulating 4-mercaptobezonic acid functionalized silver nanoparticles in a proton permeable silica shell. The performance of silica protected nanosensor against aggregation and biomolecular interference is investigated. The nanosensors are introduced to report intracellular pH in living macrophages. In Chapter 3, a pH sensor film is designed for monitoring pH variation on a surface through thick tissue in real time. The pH sensor film is composed of a film of upconverting nanoparticles which functions as a local light source and a thin layer of pH indicator which modulates the luminescence in a pH dependent way. Upconverting nanoparticles are excited by near infrared laser (980 nm) which allows high tissue penetration depth and avoids autofluorescence from tissue. The pH sensor film is applied to monitor bacterial growth caused pH decrease at the interface of sensor film and trypic soy agar in real time through 6 mm porcine tissue. In Chapter 4, a pH sensor film with the ability to image pH variation through thick tissue with high spatial resolution is designed utilizing X-ray radioluminescent particles as a local light source. pH calibration curves are generated by taking the ratio of peak intensity at 620 nm over that at 700 nm. By creating a localized reference region on the sensor film, the tissue effect on the ratio of the two peaks is adjusted. The pH sensor film is used to monitor bacterial growth and study antibiotic effect with millimeter of spatial resolution which is primarily determined by the width of the X-ray beam. Both upconverting luminescence and X-ray radioluminesce based pH sensors have the potential to revolutionize the ability to diagnose and assess treatment for implanted medical devices associated bacterial infection