Radiation detectors including scintillator compositions and methods for radiation detection and discrimination therewith

Abstract

Radiation detectors which employ scintillator compositions that emit photons when exposed to ionizing radiation or particles suitable for the detection of nuclear threats, medical imaging, high-energy physics, and other usages. Methods for radiation detection and discrimination with the radiation detectors are also described.

Description

RADIATION DETECTORS INCLUDING SCINTILLATOR COMPOSITIONS AND METHODS FOR RADIATION DETECTION AND DISCRIMINATION THEREWITHFIELD OF THE INVENTION

[0001] The present invention relates to radiation detectors which employ scintillator compositions that emit photons when exposed to ionizing radiation or particles suitable for the detection of nuclear threats, medical imaging, high-energy physics, nuclear power plant control, environmental control, homeland security and other usages. For some of these applications, it is vital to distinguish neutrons and charged particles from y-rays. This is achievable by pulse shape discrimination (PSD), a time-gated technique, which exploits that the scintillation kinetics can depend on the nature of the incident radiation. As described herein, sensitive and rapid PSD is possible with the scintillator compositions that include a solid polymer matrix and liquid nanodomains in which an active material, such as an organic dye, capable of triplet-triplet annihilation (TTA) is dissolved. The liquid nature of the nanodomains renders TTA highly efficient so that delayed fluorescence can occur at low energy density. The scintillator compositions allow discriminating a particles, y-rays, x-rays, and neutrons with a time response that is better than that of commercial scintillators. The liquid nanodomains can facilitate energy transfer processes that are otherwise difficult to realize in solid polymers, and this allows embodiments that contain an auxiliary triplet sensitizer. This approach further increases the scintillator composition’s sensitivity towards a particles and neutrons and other high-energy processes where localized interactions are involved.BACKGROUND OF THE INVENTION

[0002] Ionizing radiation and particles of natural or anthropogenic origin, including X-rays, y- rays, neutrons, a-particles, p-particles, can pose significant risks to human health and the environment1, and therefore sensors that allow their detection are highly relevant2 3. Scintillation counters represent one of the most frequently employed devices to detect and / or measure such radiation. Scintillation counters contain a scintillating material or scintillation composition, i.e., the scintillator, which emits photons when exposed to radiation, and a photodetector, such as a photodiode, a charge-coupled device camera, or a photomultiplier tube, that captures the photons emitted by the scintillating material. The photodetector converts the photons emitted by the scintillator into an electronic signal, whichcan optionally be further processed by electronic components that can be part of or external to the scintillation counter.

[0003] The scintillator is a luminescent material that produces low-energy photons, typically light in the visible or ultraviolet range of the electromagnetic spectrum when exposed to high- energy radiation. Scintillation is observed in different material classes, including inorganic and organic crystals, liquids, polymers, gases, and organic and inorganic glasses. In some cases, the scintillator consists of multiple components, for example, a polymer matrix that is doped with scintillating molecules or a solution that contains scintillating molecules. Auxiliary components, such as wavelength-shifting compounds that convert the light produced by the scintillating molecules into light having a lower wavelength, can also be used. Preferably, the scintillation material has a high conversion yield, i.e. , it efficiently converts the incident radiation into photons, is transparent for the light that it emits, has an emission spectrum that is matched to the spectral sensitivity of the photodetector, and exhibits high stability.

[0004] Scintillators are widely used to provide protection against radiological and nuclear threats4’7, as well as in other applications that range from medical dosimetry8to high-energy experiments9. Some scintillating counters allow discrimination between the type of incident high-energy radiation by means of pulse shape discrimination (PSD) techniques. PSD techniques involve a time-resolved analysis of the signals produced by the scintillation counterwhich enables the distinction between fast and slow components of the scintillation signal (FIG. 5)10, i.e., prompt and delayed emission, whose relative intensity and lifetime depend on the type of the incident radiation. PSD allows, for example, estimating the power generated in nuclear reactors or distinguishing radioactive threat materials, for example Uranium-235 and Plutonium-230, from non-threatening materials.

[0005] Thus far, PSD detection has been mostly realized with organic conjugated dyes, whose electronic structure enables triplet-triplet annihilation (TTA, FIG. 1 b)11. The excitation of such molecules upon recombination of free charges produced by the ionizing radiations generates both excited singlet (Sn*) and triplet (Tn*) states. Prompt photons result on a timescale of nanoseconds from the radiative transition of excited singlets S back to the ground state So, i.e., fluorescence. The Tn* excitons relax through ultrafast internal conversion to the Ti* level, from which the transition to Sois spin-forbidden. If two Ti* molecules collide, the two triplets may annihilate, which causes the promotion of one molecule to the S state, whose relaxation causes the emission of an additional photon11’12. Because the underlying processes involve energy migration and bimolecular interactions13,this emission is delayed by up to a few milliseconds and can therefore be distinguished from prompt luminescence by PSD techniques (FIG. 1 c).

[0006] Since TTA is a bimolecular process, its rate kTTAand yield <pTTAdepend on the density of triplets that are available for annihilation and on their diffusivity14. Consequently, this mechanism can be used to discriminate high-energy photons (X-rays or y- rays), which interact only weakly with the matrix in which the dye molecules are embedded and produce only fast prompt fluorescence, from high-energy particles, a particles, [3 electrons, and neutrons, which release their energy in localized volumes (FIGS. 6a-6b and Table 1 below) and thereby generate triplets in a concentration that is sufficiently high to cause delayed fluorescence by TTA15. Commercial PSD counters exploit either liquid scintillators, i.e., solutions of TTA-active dyes in organic solvents, or polymer-based scintillators, which consist of a host polymer that is doped with the scintillating dye (FIG. 1 d)10. In liquid scintillators, translational molecular motions are fast, and this enables excited molecules to collide and annihilate. However, due to aggregation effects the dye concentration and therewith the achievable light output are limited16’17. Another critical disadvantage of liquid scintillators is that liquid radioactive waste is difficult to manage. These problems are in part mitigated by solid polymer scintillators, which are also more convenient for device integration and are mechanically robust. However, realizing efficient TTA in solid polymers is challenging. The required bimolecular processes can be achieved by incorporating the scintillating dye in high concentration, but miscibility problems plague this approach. To solve this problem, one can kinetically trap molecular mixtures of polymers and TTA-capable dyes with dye concentrations of as high as 30 wt.%18. The average intermolecular distance between the dye molecules in such materials is on the nanometer scale, and this enables triplet diffusion by Dexter energy-transfer mediated hopping and TTA between adjacent triplets14. However, the slow diffusivity of triplet excitons in such solids limits the TTA efficiency with respect to liquids and leads to long emission delays. This limits the sensitivity of PSD detection and the ability to monitor rare events, such as weakly interacting massive particles for dark matter sensing19, or high-rate phenomena (»100 kHz) due to pile up-of the harvested scintillation photons20.SUMMARY OF THE INVENTION

[0007] In view of the above, the art still needs scintillator compositions, and radiation detectors including the same, in order to detect and distinguish between different types of radiation such as a particles, 0 particles, y-rays, x-rays, and neutrons. The problems notedabove, including the need for more sensitive and faster radiation detectors, and others, are solved by the radiation detectors of the invention which include a nanostructured multiphase polymeric scintillator composition capable of exhibiting a PSD response, as well as methods for detecting and / or discriminating between different types of radiation.

[0008] The present invention discloses radiation detectors including nanostructured polymer scintillator compositions which provide sensitive and fast PSD detection that was unexpectedly achieved by modifying a design concept that was originally developed for low- power TTA-based photon upconversion21 22(FIGS. 1 a-d). The nanostructured polymer scintillator compositions of the invention include a solid polymer matrix that provides structural stability, and liquid nanodomains that contain a TTA-active material such as a dye, and optionally a triplet sensitizer, so that delayed fluorescence can occur even at ultralow energy densities. In preferred embodiments of the invention, the nanostructured polymer scintillator compositions are highly transparent at the wavelength of the emitted light. The examples set forth herein document the PSD response of suitable materials by means of photoluminescence and scintillation spectroscopy experiments and demonstrate that it is possible to discriminate between a particles, y-rays, x-rays, and neutrons using the radiation detectors of the invention. Moreover, it was discovered and shown that the scintillation efficiency and sensitivity towards y-rays, a particles and neutrons is significantly increased by the incorporation of the triplet sensitizer1423.

[0009] Accordingly, in one aspect, a radiation detector capable of detecting at least one type of ionizing radiation from the list of a particles, 0 particles y rays, X-rays, and neutrons is disclosed, comprising: at least a scintillator composition and a photodetector; wherein said scintillator composition is a phase-separated material that comprises at least one solid phase that comprises by majority, a polymer, and at least one liquid phase, wherein said at least one liquid phase contains at least a photoluminescent compound capable of triplet-triplet annihilation (TTA); and wherein said photodetector is capable of converting photons produced by the scintillator composition into an electrical signal.

[0010] In a further aspect, the detector allows for pulse shape discrimination of the one or more of a particles, 0 particles, y rays, x-rays, and neutrons.

[0011] In yet another aspect, the detector allows discriminating between at least two types of the ionizing radiation from the list of a particles, 0 particles, y rays, x-rays, and neutrons.

[0012] In an additional aspect, the at least one liquid phase additionally contains at least one triplet sensitizer that is capable of being electronically excited by said ionizing radiation and transferring at least a fraction of the energy of its excited states to said compound capable of TTA.

[0013] In another aspect, the scintillator composition is substantially transparent to light emitted by said at least one photoluminescent compound, except for the optical absorbances caused by said at least one photoluminescent compound capable of TTA and said at least one triplet sensitizer when present; wherein the scintillator composition displays, after correction for absorbances caused by said at least one photoluminescent compound capable of TTA and said at least one triplet sensitizer when present, a transmission of at least 50%, more preferably above 70%, and most preferably above 80%, measured over a pathlength of 1 cm at normal incidence at any wavelength between 420 and 680 nm with a single-beam or double-beam spectrophotometer.

[0014] In a further aspect, the scintillator composition absorbs at least a portion of the ionizing radiation incident thereon.

[0015] In yet a further aspect, the at least one photoluminescent compound capable of TTA is one or more of anthracene; an anthracene derivative such as 9,10-diphenylanthracene (DPA) and 9,10-bis(phenylethynyl)anthracene (BIPEA); perylene; a perylene derivative such as 2,5,8, 11 -tetra-tert-butyl perylene (TBPe); pyrene; a pyrene derivative such as 2,7- di-tert-butyl pyrene and 3,8-di-tert-butyl pyrene; naphthalene; a naphthalene derivative such as 1 ,4-bis((triisopropylsilyl)ethynyl)naphthalene (1 ,4-TIPS-Nph) or bis((triisopropylsilyl)ethynyl)naphthalene (1 ,5-TIPS-Nph); 2,5-diphenyloxazole (PPO); other oxazole derivatives; rubrene (5,6,11 ,12-tetraphenylnapthacene); a rubrene derivative such as rubrene that is modified with tert-butyl or 2,5-di-tert-butylphenyl groups; and BODIPY- derivative.

[0016] In a further aspect, the at least one triplet sensitizer is one or more of a metallo- porphyrin, such as palladium octaethyl porphyrin (PdOEP), platinum octaethyl porphyrin (PtOEP), palladium^ I) 1 ,4,8,11 ,15,18,22,25-octa-n-butoxyphthalocyanine [PdPc(OBu)8], platinum(ll) 1 ,4,8,11 ,15,18,22, 25-octa-n-butoxyphthalocyanine [PtPc(OBu)8], palladium^ I) meso-tetraphenyl-tetrabenzoporphyrin (PdTPTBP) and platinum(ll) meso-tetraphenyl- tetrabenzoporphyrin (PtTPTBP); a ruthenium complex such as [Ru(4,4'-dimethyl-2,2'-dipyridyl)3]2+and Ru(bpy)32+; an iridium complex such as tris[2-phenylpyridinato- C2, N]iridium(l II); and a luminescent compound that comprises one or more of the following atoms Ir, Pt, Pd, Re, Os, Ru, I, Br.

[0017] Still further, said liquid phase comprises one or more of 1 -tert-butyl-3,5- dimethylbenzene (BMB), another, optionally aliphatic hydrocarbon residue-containing (poly- )aromatic compound such as 1 ,1 -bis(3,4-dimethylphenyl)ethane, 1 -phenyldodecane, 2,7- diisopropylnaphthalene, o-terphenyl, and 1 ,2-diphenylethane; a liquid aliphatic hydrocarbon compound such as 1 -octadecene; a liquid ester such as butyl benzoate, ethyl benzoate, hexyl benzoate, dibutyl phtalate, bis(2-ethylhexyl) terephthalate, 1 ,4-bis((2- ethylhexyl)oxy)benzene) and bis(2-ethylhexyl) sebacate; ether; a halogenated liquid aromatic optionally containing an aliphatic residues (such as 1 ,2,4-trichlorobenzene) and other high-boiling (>200°C) nonpolar solvent.

[0018] In another aspect, said scintillator composition includes a plasticizer, preferably one or more of a polyol such as ethylene glycol, diethylene glycol, triethylene glycol, triethylene glycol monomethylether, and tetraethylene glycol monomethylether; wherein said scintillator composition includes also at least one auxiliary absorber for the ionizing radiation that is one or more of a particles, y rays, x-rays, and neutrons, according to the aspects above.

[0019] In still another aspect, the scintillator composition includes a surfactant, preferably one or more of a cationic surfactant (such as a cetyltrimethylammonium bromide (CTAB) or cetyltrimethylammonium chloride (CTAC)), an anionic surfactant (such as a sodium stearate), an alkyl benzene sulfonate (such as sodium dodecylbenzenesulfonate), and a nonionic surfactant (such as a polyoxyethylene glycol alkyl ether and a polyoxyethylene glycol octylphenol ether, and poly(ethylene glycol)-block-poly(propylene glycol)-block- poly(ethylene glycol) (PEG-PPG-PEG)).

[0020] In a further aspect, said polymer is derived from one or more of a polar acrylate (such as 2-hydroxyethyl acrylate) a methacrylate (such as a 2-hydroxyethyl methacrylate and a dimethylaminoethyl methacrylate), an acrylamide or a methacrylamide, an acrylic acid or a methacrylic acid and their salts (such as an acrylic acid or a methacrylic acid), a vinylpyridine (such as a 4-vinyl pyridine), an oxazoline, a non-polar acrylate (such as a butyl acrylate or a methyl acrylate), a methacrylate (such as a methyl methacrylate), an acrylamide (such as N-octadecylacrylamide), a methacrylamide, a styrene, a polyurethane, an epoxy resin, a vinyl ester and a polyester.

[0021] In still a further aspect, the at least one triplet sensitizer is present and is palladium octaethyl porphyrin (PdOEP), and wherein the at least one photoluminescent compound capable of TTA is DPA.

[0022] In yet another aspect, the at least one liquid phase forms domains with average dimensions of less than 200 nm, and preferably less than 100 nm.

[0023] In another aspect, the photodetector comprises a photodiode, a charged-coupled device camera, a photomultiplier, a microchannel plate detector or any other detector or combination of detectors that converts photons produced by the scintillator composition into an electrical signal, and wherein the electrical signal is processed by an analog device or digital device also present in the photodetector to produce PSD measurements.

[0024] In still a further aspect, the photodetector further includes a light guide or a refractive index matching material that directs photons produced by the scintillator composition to the photodetector.

[0025] In a further aspect, said scintillator composition is encapsulated in a high-reflectivity non-scintillating shell (such as aluminum or other metal sheets, reflective (multilayer) polymer films) or in a custom-designed holder (such as a non-scintillating holder made of metal or non-scintillating plastic, which inner parts are covered by the high-reflectivity material) to mechanically couple the scintillator and the photodetector and then maximizing the harvesting of the scintillation emission by the photodetector.

[0026] In a further aspect, a method for detecting at least type of ionizing radiation that is one or more of a particles, 0 particles, y rays, x-rays, and neutrons, and / or discriminating between different types of the ionizing radiation is disclosed, comprising the steps of: obtaining a scintillator composition comprising: a phase-separated material that comprises at least one solid phase that comprises by majority, a polymer, and at least one liquid phase, wherein said at least one liquid phase contains at least a photoluminescent compound capable of triplet-triplet annihilation (TTA) and optionally at least one triplet sensitizer that is capable of being electronically excited by said ionizing radiation and transferring at least a fraction of the energy of its excited states to said compound capable of TTA, operatively coupling the scintillator composition to a photodetector to obtain a radiation detector; exposing the radiation detector to an environmental location; anddetermining if photons are produced by the scintillator composition with the photodetector, wherein the production of the photons indicates the ionizing radiation is present and is one or more of the a particles, y rays, x-rays, and neutrons.

[0027] In yet another aspect, the radiation detector is configured according to any of the above aspects.

[0028] In yet another aspect, the method further including the steps of: converting the photons produced by the scintillator composition with the photodetector into an electrical signal, analyzing the electrical signal produced with the photodetector with an analog device or digital devices, and determining if the ionizing radiation is one or more the a particles, y rays, x-rays, and neutrons.

[0029] In another aspect, the photodetector includes one or more of a photodiode, a charged-coupled device camera, a photomultiplier, a micro channel plate detector, or any other detector or combination of detectors and further including the step of converting the photons into an electrical signal utilizing the photodetector.

[0030] In still a further aspect, the method further includes a step of processing the electrical signal with an analog device or digital device to produce PSD measurements that are used to determine the type of ionizing radiation.

[0031] In a further aspect, a method for discriminating between different types of ionizing radiation that is one or more of a particles, a particles, y rays, x-rays, and neutrons is disclosed, comprising the steps of: obtaining the radiation detector; exposing the detector to ionizing radiation comprising one or more of a particles, y rays, x-rays, and neutrons; analyzing photons produced by the scintillator composition with the photodetector; and determining if the radiation is one or more the a particles, a particles, y rays, x-rays, and neutrons.

[0032] In a further aspect, analyzing the photons produced by the scintillator composition includes the step of converting photons produced by the scintillator composition into an electrical signal using the photodetector.

[0033] In a further aspect, the method further includes the step of processing the electrical signal with an analog device or digital device to produce the PSD measurements that are used to determine the type of radiation.

[0034] Still further, a method is disclosed comprising the step of: using a scintillator composition comprising a phase-separated material that comprises at least one solid phase that comprises by majority, a polymer, and at least one liquid phase, to discriminate between ionizing radiation that is one or more of a particles, y rays, x-rays, and neutrons.

[0035] In yet another aspect, the method utilizes pulse shape discrimination. For the avoidance of doubt, it is understood that while various embodiments or aspects of the invention are described individually, it should be clear that two or more embodiments or aspects can, and often times are present in a single device according to the present invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will be better understood and other features and advantages will become apparent by reading the detailed description of the invention, taken together with the drawings, wherein:

[0037] FIGS. 1 a-d are schematics of the operating principle in nanostructured multiphase polymeric scintillators, wherein:

[0038] FIG 1 a is a sketch of the scintillation mechanism in polymeric materials, wherein ionized diffusing charges recombine on the lower singlet and triplet levels of a conjugated chromophore embedded in a polymer host, causing fluorescence-based emission form singlets and the population of triplets;

[0039] FIG. 1 b is a schematic of the triplet-triplet annihilation (TTA) process that leads to delayed fluorescence;

[0040] FIG. 1 c illustrates the pulse shape discrimination technique (PSD) employed to distinguish high-energy photons (X-rays, y-rays), which cause prompt emission, and particles (a, |3, neutrons), which promote TTA-based, delayed emission, wherein and particles (a, |3, neutrons), which promote TTA-based, delayed emission. The analysis of the scintillation pulse time decays allows discriminating the type of incident radiation and in some cases the energy it releases;

[0041] FIG. 1d shows a nanostructured polymeric scintillator, the solid matrix host liquid nanodroplets containing a TTA dye and a triplet sensitizer dye; a and [3 particles as well as neutrons trigger delayed, X-rays and y-rays prompt emission;

[0042] FIGS. 2a-g illustrate structural and optical properties of the nanostructured polymer scintillators and reference materials, wherein:

[0043] FIGS. 2a and 2b are photographs of the polymer scintillators under illumination with ambient (a) and UV (b) light; left to right: nanostructured polymer containing DPA and PdOEP (referred to as DPA:PdOEP), nanostructured polymer containing DPA only (DPA), and the non-structured reference material containing DPA only (DPA*);

[0044] FIG. 2c is a graph showing steady-state photoluminescence (PL) spectra of the polymer scintillators and a nanostructured reference polymer containing PdOEP only (PdOEP) under excitation at 340 and 535 nm;

[0045] FIG. 2d is a graph showing Radioluminescence (RL) spectra of the polymer scintillators under steady-state excitation with soft X-rays;

[0046] FIG. 2e is a graph showing fluorescence decay of the polymer scintillators recorded at 420 nm under pulsed excitation at 340 nm, wherein solid lines represent single exponential decay functions fitted to the data;

[0047] FIG. 2f is a graph showing scintillation intensity decay recorded at 420 nm under pulsed X-ray excitation, wherein solid lines represent single exponential decay functions fitted to the data;

[0048] FIG. 2g shows transmission spectra of the DPA:PdOEP nanostructured plastic scintillator (dashed line) and the dye-free reference nanostructured polymer (solid line), optical path length = 10 mm for both samples.

[0049] FIGS. 3a-e illustrate scintillation and pulse shape discrimination (PSD) of nanostructured polymer scintillators exposed to y-rays and a particles, wherein:

[0050] FIG. 3a is a graph showing scintillation and pulse shape discrimination (PSD) of nanostructured polymer scintillators exposed to y-rays and a particles - PSD histograms of DPA*, DPA, and DPA:PdOEP scintillators under y-ray exposure;

[0051] FIG. 3b is a graph with averaged prompt scintillation pulse decay of these scintillators under y-ray exposure, recorded with PSD values of 0.35 (DPA*) and 0.40 (DPA, DPA:PdOEP);

[0052] FIG. 3c is a graph showing averaged prompt scintillation pulse decays of DPA and DPA:PdOEP scintillators under simultaneous exposure to y-rays and a particles recorded with a PSD value of 0.40, wherein solid lines represent single exponential decay functions fitted to the data;

[0053] FIG. 3d shows PSD histograms of DPA and DPA:PdOEP scintillators under simultaneous exposure to y-rays and a particles, y-rays and a particles had energies of 662 keV and 5.5 MeV, respectively;

[0054] FIG. 3e is a graph showing averaged prompt scintillation pulse decays of DPA and DPA:PdOEP scintillators under simultaneous exposure to y-rays and a particles recorded with a PSD value of 0.55, wherein the inset shows the decoupled delayed emission component generated by triplet-triplet annihilation (TTA), and wherein solid lines represent multi-exponential decay functions fitted to the data;

[0055] FIGS. 4a-e illustrate pulsed shape discrimination (PSD) and scintillation of the nanostructured polymer scintillators exposed to y-rays and neutrons, wherein:

[0056] FIG. 4a is a graph showing the scintillation pulse height spectra of the DPA and DPA:PdOEP nanostructured polymer scintillators exposed to y-rays and neutrons.

[0057] FIG. 4b shows PSD histograms of DPA and DPA:PdOEP scintillators under simultaneous exposure to y-rays and neutrons;

[0058] FIGS. 4c and 4d are graphs showing averaged prompt scintillation pulse decays of DPA and DPA:PdOEP scintillators, solid lines in FIG. 4c represent single exponential decay functions fitted to the data (fast emission generated by y-rays interaction at PSD = 0.4), wherein solid lines in FIG. 4d represent multi-exponential decay functions fitted to the data (emission generated by neutron interaction at PSD = 0.55), the neutrons had an energy of 2.5 MeV; and

[0059] FIG. 4e is a graph showing decoupled delayed emission component generated by triplet-triplet annihilation (TTA) at PSD = 0.55, wherein solid lines represent multiexponential decay functions fitted to the data;

[0060] FIG. 5 illustrates principles of the pulse shape discrimination (PSD) technique, wherein each scintillation event was analyzed off-line by calculating the area under a gate as long as the waveform, namely the long gate (t|Ong), which is proportional to the total amount of scintillation light produced, wherein the area of each waveform was used to populate the histogram representing the recorded energy spectrum (x-axis in the PSD plotsin the main text), and where a shorter gate (tShort) was used to calculate the area that enables the pulse shape discrimination, and wherein the PSD plot was populated by using the parameter y-axis of the PSD plots;

[0061] FIGS. 6a-c illustrate simulated ionizing radiations penetration, wherein:

[0062] FIG. 6a shows 5.5 MeV alpha particles in nanostructured polymeric scintillators using the SRIM code40,

[0063] FIG. 6b shows 2.5 MeV protons in nanostructured polymeric scintillators using the SRIM code40;

[0064] FIG. 6c shows 0.7 MeV carbon ions in nanostructured polymeric scintillators using the SRIM code40;

[0065] FIG. 7 illustrates structural and optical properties of nanostructured polymers for sensitized-TTA, wherein time-domain NMR FID of the nanophase-separated polymer containing two dyes (DPA:PdOEP) or the annihilator alone (DPA) in comparison with the system fabricated with the annihilator but without the solvent (DPA*), acquired with MSE refocusing block at 303 K, wherein the initial fast Gaussian relaxation characterizes the rigid phase while the slower exponential relaxation associated with the mobile phase, wherein DPA and DPA:PdOEP lines are practically superimposed indicating that the presence of the triplet sensitizer PdOEP does not affect the material structure, wherein without the solvent the sample present a rigid fraction as high as 59%, wherein the mobile phase in this case is given by the presence of the plasticizer, necessary to the formation of the nanodroplets in the complete sample, that works as plasticizer, and wherein upon addition of the solvent, the rigid fraction is reduced to 53% (-6%) in both samples (the presence of the PdOEP has no effects) in agreement with the predicted decrease due to addition of the liquid BuBz (- 7%) calculated considering the synthesis parameters and reagents composition;

[0066] FIG. 8 is a graph illustrating a Hahn echo experiment on all samples at 303 K, wherein the pure matrix DPA* sample is well fitted by a monomodal single component exponential decay with short T2, wherein the nanophase separated polymer systems, a component with the same decay is present consisting of more than 80% of the sample, but a second component is clearly present that can be associated to a population of protons of high mobility, possibly associated to nanodroplets since it has a distinctly slower decay;

[0067] FIGS. 9a and 9b illustrate rigid fraction of the material estimated as a function of the temperature by time-domain NMR FID of the nanophase-separated on the polymercontaining two dyes (DPA:PdOEP) in comparison with the system fabricated with the annihilator but without the solvent (DPA*), acquired with MSE refocusing block, wherein in both cases, by decreasing the temperature the rigid fraction increases as expected, growing above 95% in the solvent free system, wherein on the other hand, in presence of the solvent nanodroplets it still has a mobile phase of about 11 % ascribed to the liquid BuBz (melting point is at 180 K), and wherein considering the relative proton % of each component, the % of 1 H signal associated with the BuBz alone is 10%, in perfect agreement with the obtained results;

[0068] FIG. 10 is a graph illustrating differential scanning calorimetry (DSC) curves of DPA- containing nanostructured scintillating polymers with (DPA) and without solvent BuBz (DPA*), wherein DSC measurements were performed by using a Mettler-Toledo DSC-1 equipped with a Huber TC100 cooling regulation system and were conducted as reported in ref. 22, wherein all measurements consisted of three cycles of heating (-40 to 120°C) and cooling (120 to -40°C) and were carried out with a rate of 20°C min’1, wherein all measurements were repeated four times per sample, wherein the second and third heating were equivalent, wherein both systems' glass transition temperatures (Tg) fall between 50- 55°C, and wherein no other transitions were observed in the measured temperature range;

[0069] FIGS. 11 a-c illustrate triplet-triplet annihilation (TTA) in nanostructured polymers, wherein:

[0070] FIG. 11a illustrates photophysics of sensitized green-to-blue photon upconversion based on TTA under optical excitation, wherein the energy diagram shows the processes leading to sensitized TTA in materials containing palladium (II) octaethylporphyrin (PdOEP) as triplet sensitizer and 9,10-diphenylanthracene (DPA) as emitter / annihilator, and wherein GS: ground state; S1 , T1 : first singlet and triplet excited state; ISC: intersystem crossing; TTET: triplet-triplet energy transfer.

[0071] FIG. 11 b illustrates normalized UV-Vis absorption (solid lines) and PL emission (dashed lines) spectra of nanostructured polymers containing DPA (1.5x10-2 M) or PdOEP (1 .9x10-5 M), wherein the spectra were acquired with excitation at 350 nm (DPA) or 543 nm (PdOEP);

[0072] FIG. 11 c shows digital pictures of a nanostructured polymer containing PdOEP (1 .9x10-5 M) and DPA (1 .5x10-2 M) that was optically excited with a laser at 543 nm under ambient light conditions and in the dark;

[0073] FIGS. 12a-f illustrate TTA properties of the PdOEP:DPA pair in solution and the nanostructured polymer, wherein:

[0074] FIGS. 12a and 12b are graphs illustrating photoluminescence (PL) spectra of FIG. 12a a BuBz solution and FIG. 12b the nanostructured polymer as function of the excitation intensity at 532 nm (CW excitation);

[0075] FIGS. 12c and 12d are graphs illustrating upconverted emission intensity decays recorded at 430 nm for FIG. 12c the solution and FIG. 12d the nanostructured polymer under modulated excitation at 532 nm as a function of excitation intensity (from 2 mW cm’2to 400 mW cm’2);

[0076] FIG. 12e is a graph illustrating TTA rate kTTA as function of the density of triplets generated in solution and the nanostructured polymer at different excitation intensities;

[0077] FIG. 12f is a graph illustrating TTA yield 07-7-^ as function of the density of triplets generated in solution and the nanostructured polymer, wherein the 0*7-7- ! values equal kTTAl (kTTA+kT), where kT= 844 Hz is the spontaneous DPA triplet decay rate, wherein the effect of the confinement of the dyes in the liquid nanodomains results in an almost constant value of kTTAand a high TTA efficiency, independent of the excitation intensity, due to the high collisional probability of DPA triplets in the nanodroplets, wherein the experiments were carried out with a solution and a nanostructured polymer that contain DPA and PdOEP in concentrations of 1.5x1 O’2M and 1.9x1 O’5M, respectively, and wherein in the nanostructured polymer, the dyes concentrate in the liquid nanodroplets, for which the concentrations are estimated to be 1.0x10’1M DPA and 1.3x1 O’4M PdOEP;

[0078] FIG. 13 is a graph illustrating averaged scintillation pulse decay of DPA and DPA: PdOEP scintillators and the DPA* reference under y-ray and a particle exposure at PSD = 0.90;

[0079] FIG. 14 depicts one embodiment of a radiation detector capable of detecting at least one type of ionizing radiation from a source of ionizing radiation or particles; and

[0080] FIG. 15 illustrates chemical structures of the DPA:PdOEP nanostructured plastic scintillator components including 1 ) methacrylic acid, 2) 2-hydroxyethyl methacrylate, 3) triethylene glycol, 4) triethylene glycol dimethacrylate, 5) 2-mecaptoethanol, 6) hydrogen peroxide, 7) dimethylthiomethane, 8) butyl benzoate, 9) cetyltrimethylammonium chloride, 10) palladium (II) octaethylporphyrin, 11 ) 9,10-diphenylanthracene. For reference samples, 10) palladium (II) octaethylporphyrin was omitted in the preparation of DPA referencesamples, and 8) butyl benzoate and 10) palladium (II) octaethylporphyrin were omitted in the preparation of DPA* reference samples.

[0081] FIG. 16 is a graph showing Radioluminescence (RL) spectra of the polymer scintillators under steady-state excitation with soft X-ray using a triplet harvester resonant (PdOEP) or not resonant (PdTPBP) with the triplet energy (700 nm) of the TTA species DPA. The PdOEP works as triplet sensitizer for DPA, while PdTPBP work as energy loss channel reducing the DAP blue scintillation intensity. For reference the graph report the RL spectra of polymer scintillators PdOEP and PdTPBP alone.DETAILED DESCRIPTION OF THE INVENTION

[0082] Disclosed herein are radiation detectors including scintillator compositions and methods for radiation detection and discrimination utilizing the radiation detectors. The radiation detectors are capable of detecting at least one type of ionizing radiation, for example one or more of a particles, y-rays, x-rays, and neutrons. At a base level, the radiation detector includes at least a scintillator composition and a photodetector, see FIG. 14.

[0083] Scintillator Composition

[0084] The scintillator composition is a phase-separated material that comprises at least one solid phase and at least one liquid phase. In preferred embodiments of the invention, the scintillator composition is highly transparent at the wavelength of the emitted light.

[0085] Solid Phase

[0086] The at least one solid phase comprises, by majority, a polymer, herein defined as a polymer or copolymer, the term “majority” indicating 50 wt.% or more of the at least one solid phase. The solid phase may contain other components such as stabilizers, plasticizers, and compounds that modify the refractive index. In one embodiment, the polymer or copolymer comprises, or is formed from monomers including hydrophilic units. Monomers useful for the purpose typically comprise two or more functional groups, and are capable of undergoing a polymerization reaction. It is should be understood that the liquid phase does not need to be encapsulated prior to being used to fabricate the scintillator composition. In one embodiment, the components forming the liquid phase are combined with the other components used to form the phase-separated materials and the resulting liquid curable composition can be cured to form the phase-separated material that includes the at least one solid phase and the at least one liquid phase. Suitable phase-separated materials are disclosed for example in U.S. Pub. 2019 / 0169495, herein fully incorporated by reference.The properties of the scintillator compositions can be specifically tailored by varying the concentrations of the components, as well as the individual species or types of components perse. For example, minimizing the size of the domains and matching the refractive indices of the solid phase and liquid phase help to minimize scattering affects and thus maximize the transmission. The refractive index can be matched via the specific components used to form the phases and / or the use of refractive index modifying compounds in at least one of the two phases.

[0087] The at least one solid phase of the scintillator composition provides mechanical stability and retains or houses the at least one liquid phase. Various monomers can be utilized that, upon polymerization or curing, form the solid phase.

[0088] Examples of suitable hydrophilic monomers that can be polymerized by free radical processes to create a hydrophilic solid phase include, but are not limited to, polar acrylates (such as 2-hydroxyethyl acrylate) or methacrylates (such as 2-hydroxyethyl methacrylate and dimethylaminoethyl methacrylate), acrylamides or methacrylamides, acrylic acids or methacrylic acids and their salts (such as acrylic acid or methacrylic acid), vinylpyridines (such as 4-vinyl pyridine), oxazolines and combinations thereof. Multifunctional cross-linkers such as tetraethylene glycol diacrylate or triethylene glycol dimethacrylate can be added to create cross-linked materials. Those skilled in the art will appreciate that if materials are made in which the polarity of the solid and liquid phase are reversed, hydrophobic monomers are used. Examples include non-polar acrylates (such as butyl acrylate or methyl acrylate) or methacrylates (such as methyl methacrylate), acrylamides or methacrylamides (such as N-octadecylacrylamide), and styrenes. In the case of curing by free radical polymerization, the curable composition normally contains an initiator or initiator system. Suitable initiators are those known in the art of free radical polymerization and include, but are not limited to, thermal initiators such as 2,2'-azobisisobutyronitrile and other azo initiators or benzoyl peroxide and other peroxides or hydroperoxides, as well as photoinitiators such as alpha- hydroxyalkylphenones or benzophenone / amine systems. In preferred embodiments redox initiators are used, such as the pair benzoyl peroxide and N, N-dimethylaniline or mixtures of H2O2, 2-mercaptoethanol and cetyltrimethylammonium bromide (CTAB) or chloride (CTAC) as a halogen source.

[0089] As an alternative or addition to monomers that can be polymerized by free radical polymerization, the curable composition of the present invention can comprise monomer systems that can be polymerized by step growth polymerization, such as diisocyanate / diolmixtures, or epoxy resin and other thermoset resin formulations such as vinylesters and polyesters.

[0090] Other materials that can be included as matrix forming material are compounds that influence the phase separation, act as a plasticizer, and / or modify the refractive index such as ethylene glycol and other polyols, water, oligo and polyethers such as oligo and poly(ethylene oxide) and oligo and poly(tetrahydrofuran).

[0091] The curable composition utilized to form the scintillator compositions according to the invention includes generally up to about 99 wt.% monomers, preferably up to about 90 wt.% monomers, and most preferably up to about 75 wt.% monomers based on the total weight, i.e. 100 wt.% of the material forming composition. Normally, the fraction of the monomers in the curable composition is at least 1 wt.%, in preferred embodiments more than 30 wt.%, more preferably more than 50 wt.% and in most preferred embodiments more than 70 wt.%. In one embodiment, the liquid curable composition includes 30 to 90 wt.% of the monomer or monomers. Various additional materials can be present that help controlling the morphology, i.e., the phase separation and size and shape of the resulting domains. In some embodiments, multifunctional monomers are utilized which allow or facilitate cross-linking of the matrix polymer.

[0092] Other components that can be present in the curable composition are stabilizers, plasticizers, and compounds that modify the refractive index.

[0093] Liquid Phase

[0094] The curable composition utilized to form the scintillator compositions according to the invention also includes the components forming the liquid phase.

[0095] The at least one liquid phase serves to dissolve or disperse the at least one photoluminescent compound capable of TTA. In embodiments where the solid phase is a hydrophilic, the liquid phase is preferably hydrophobic. The hydrophobicity is provided by utilizing a hydrophobic liquid component, such as a nonpolar organic solvent or an oil. Examples of suitable liquid components or oils include, but are not limited to, nonpolar high- boiling low-vapor pressure liquids formed by small-molecule compounds such as 1 -tert- butyl-3,5-dimethylbenzene (BMB) and other, optionally aliphatic hydrocarbon residues- containing (poly-)aromatic compounds such as 1 ,1 -bis(3,4-dimethylphenyl)ethane, 1 - phenyldodecane, 2,7-diisopropylnaphthalene, o-terphenyl, and 1 ,2-diphenylethane; liquid aliphatic hydrocarbon compounds such as 1 -octadecene; liquid esters such as butyl benzoate, ethyl benzoate, hexyl benzoate, dibutyl phtalate, bis(2-ethylhexyl) terephthalate,1 ,4-bis((2-ethylhexyl)oxy)benzene) and bis(2-ethylhexyl) sebacate; or ethers, halogenated liquid aromatics optionally containing aliphatic residues (such as 1 ,2,4-trichlorobenzene) and other high-boiling (>200° C) nonpolar solvents. In some embodiments, the hydrophobic liquid phase may contain only a minor solvent fraction or no solvent at all, for example if a liquid compound capable of TTA is used, such as a liquid anthracene or perylene derivative. In other embodiments, the hydrophobic liquid phase can also be formed by hydrophobic oligomers or polymers, which may display a higher viscosity or even elastic behavior. Examples include, but are not limited to optionally cross-linked poly(budadiene), poly(dimethylsiloxane), and poly(butyl acrylate). The at least one liquid phase can, of course, also be formed by mixtures of various compounds, including, but not limited to, the above. Finally, these examples should also provide a guideline for the choice of a hydrophilic liquid phase, should the polarity be switched and a hydrophobic solid phase be used.

[0096] The curable composition utilized to form the scintillator compositions according to the invention include generally up to about 70 wt.% components forming the liquid phase, preferably up to about 40 wt.% components forming the liquid phase, and most preferably up to about 30 wt.% components forming the liquid phase. In certain embodiments, components forming the liquid phase make up less than 20 wt.% based on the total weight, i.e. 100% of the material forming composition. Normally, the fraction of the components forming the liquid phase in the curable composition is at least 1 wt.%, in preferred embodiments more than 2 wt.% and in most preferred embodiments more than 5 wt.%.

[0097] As described herein, the at least one liquid phase contains at least one photoluminescent compound capable of TTA. Examples of suitable photoluminescent compounds include, but are not limited to, anthracene and anthracene derivatives such as 9,10-diphenylanthracene (DPA) and 9,10-bis(phenylethynyl)anthracene (BIPEA); perylene or perylene derivatives such as 2,5,8, 11 -tetra-tert-butyl perylene (TBPe); pyrene or pyrene derivatives such as 2,7-di-tert-butyl pyrene and 3,8-di-tert-butyl pyrene; naphthalene and naphthalene derivatives such as 1 ,4-bis((triisopropylsilyl)ethynyl)naphthalene (1 ,4-TIPS- Nph) or bis((triisopropylsilyl)ethynyl)naphthalene (1 ,5-TIPS-Nph); 2,5-diphenyloxazole (PPO) and other oxazoles; rubrene (5,6,11 ,12-tetraphenylnapthacene) and rubrene derivatives such as rubrene that is modified with tert-butyl or 2,5-di-tert-butylphenyl groups; or BODIPY-derivatives. Those skilled in the art will appreciate that many other organic molecules capable of TTA can be used in embodiments of the present invention. The at least one photoluminescent compound is present in a concentration that ranges generallyfrom about 0.01 wt.% to about 0.05 wt.%, desirably from about 0.05 wt.% to about 0.5 wt.% and preferably from about 0.5 wt.% to about 5 wt.% based on the total weight of the liquid phase. Those skilled in the art will appreciate that the specific structure of the at least one photoluminescent compound can be modified to maximize its solubility in a solvent that is used to form the liquid phase. If the at least one photoluminescent compound is a liquid, for example a liquid anthracene or perylene derivative, the concentration of the at least one photoluminescent compound can be higher than about 5 wt.% and can reach 100 wt.%.

[0098] In some embodiments of the invention, the at least one liquid phase contains at least one triplet sensitizer that is capable of being excited by ionizing radiation thereby forming triplet excited states when the scintillator composition according to the present invention is exposed to high-energy radiation and can transfer at least a fraction of the energy of its excited states to the compound capable of TTA. We surprisingly found that that compounds that are capable of serving as sensitizers for optical upconversion, disclosed for example in U.S. Pub. 2019 / 0169495, herein fully incorporated by reference, can also serve as sensitizers for high energy radiation. Examples of suitable sensitizers include, but are not limited to, metallo-porphyrins, such as palladium octaethyl porphyrin (PdOEP), platinum octaethyl porphyrin (PtOEP), palladium(ll) 1 ,4,8,11 ,15,18,22, 25-octa-n- butoxyphthalocyanine [PdPc(OBu)8], platinum(ll) 1 ,4,8,11 ,15,18,22, 25-octa-n- butoxyphthalocyanine [PtPc(OBu)8], palladium^ I) meso-tetraphenyl-tetrabenzoporphyrin (PdTPTBP) and platinum(ll) meso-tetraphenyl-tetrabenzoporphyrin (PtTPTBP); ruthenium complexes such as [Ru(4,4'-dimethyl-2,2'-dipyridyl)3]2+and Ru(bpy)32+; iridium complexes such as tris[2-phenylpyridinato-C2, N]iridium(l II) or a luminescent compound that comprises one or more of the following atoms Ir, Pt, Pd, Re, Os, Ru, I, Br. Examples of metal-free sensitizer are also known, for example compounds that exhibit thermally activated delayed fluorescence (TADF) such as 4CzPN and 4CzlPN. The at least one triplet sensitizer, when present, is at concentration that ranges generally from about 0.001 wt.% to about 0.005 wt.%, desirably from about 0.005 wt.% to about 0.05 wt.% and preferably from about 0.05 wt.% to about 0.55 wt.% based on the total weight of the liquid phase.

[0099] In preferred embodiments of the present invention, an amphiphilic component, preferably a surfactant is utilized. Various surfactants that aid in forming nanostructures and stabilize the phased-separated morphology are preferably incorporated into the scintillatorforming composition. Examples of suitable surfactants include, but are not limited to, cationic surfactants such as cetyltrimethylammonium bromide (CTAB) or cetyltrimethylammoniumchloride (CTAC), anionic surfactants such as sodium stearate and alkyl benzene sulfonates, such as sodium dodecylbenzenesulfonate, and nonionic surfactants such as polyoxyethylene glycol alkyl ethers and polyoxyethylene glycol octylphenol ethers, and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG- PEG). The amphiphilic component or surfactant can be utilized in the curable composition in a concentration of generally less than about 30 wt.%, preferably in a concentration of less than about 20 wt.% and in certain embodiments in a concentration of about 15 wt.% or less based on the total weight of the composition. Generally, the curable composition could contain no surfactant or amphiphilic at all, but preferably the content in the curable composition is at least 0.5 wt.%, and more preferably more than about 2 wt.%.

[0100] Further Radiation Detector Components

[0101] The radiation detector according to the present invention includes at least the scintillator composition and a photodetector capable of converting photons produced by the scintillator composition into an electrical signal. The photodetector in various embodiments may comprise a photodiode, a charge-coupled device camera, a photomultiplier, a microchannel plate detector or any other detector or combination of detectors that can convert photons produced by the scintillator composition into an electrical signal. In preferred embodiments the detector produces a signal that allows PSD analysis. The electrical signal is optionally further processed by electronic components that may form part of the radiation counter or are used in connection with the radiation counter. These may include a CPU, processor, and / or controller, or the like, and are utilized in various embodiments to control each of the applicable components of the radiation detector and provide useful output to a user of the device. Analog devices or digital devices can be used to analyze the electrical signal produced by the photodetector in preferred embodiments.

[0102] In preferred embodiments, the photodetector further includes a light guide or a refractive-index matching material that guides the photons produced by the scintillator composition to the photodetector.

[0103] In a preferred embodiment, the scintillator composition is encapsulated in a high reflectivity non-scintillating shell, such as, but not limited to, aluminum or other metal sheets, reflective (multilayer) polymer films, etc., or in a custom-designed holder, such as but not limited to, a non-scintillating holder made of metal or non-scintillating plastic, wherein inner parts are covered by the high-reflectivity material to mechanically couple the scintillator andthe photodetector which maximizes harvest of the scintillating emission by the photodetector.

[0104] The components of the radiation detector are preferably arranged within a suitable housing, in some embodiments, that can be deployed by the end user at a desired location as necessary to detect and / or discriminate between different types of ionizing radiation, for example that is one or more of a particles, y-rays, x-rays, and neutrons.

[0105] FIG. 14 depicts one embodiment of a radiation detector capable of detecting at least one type of ionizing radiation from a source 100. The radiation detector is composed of a scintillator composition 101 and a photodetector 104. Optionally the scintillator composition101 is connected to photodetector 104 through a light guide or refractive index matching material 103 and optionally contained in a high-reflectivity shell or custom-designed holder102 to physically and optically couple the scintillator composition 101 with photodector 104, which act also as a light harvester for the scintillation photons not emitted toward the photodetector 104. The signals, such as electronic pulses, generated by the photosensitive devices are analyzed by, for example, using a processor 105. The results of the analysis of the signals, which can provide an indication of the presence of radiation, can be provided. In an embodiment, the results are displayed by a visual display or device 106. Operators can then be informed when radiation is detected. Specific embodiments relate to the detection of gamma rays and neutrons, such as fast and / or thermal neutrons.

[0106] Examples

[0107] The at least one photoluminescent compound capable of TTA utilized here as a model system is 9,10-diphenylanthracene (DPA), a blue-light emitting scintillating fluorophore with a photoluminescence quantum efficiency (PLQY) of 0.9624and a scintillation light yield (LY) of 20,000 ph MeV’1as a single crystal2025. DPA triplets have an energy of 1.77 eV and can be efficiently sensitized by the phosphorescent palladium octaethyl porphyrin (PdOEP)26(FIG. 7). Adapting a previously reported procedure,22we prepared scintillating materials that consist of a cross-linked polymer matrix formed by the polymerization of methacrylic acid, 2-hydroxyethyl methacrylate, and triethylene glycol dimethacrylate and contain ~10 wt.% of the solvent butylbenzoate in the form of nanodroplets. The examples of scintillating materials also contain a plasticizer and a surfactant that promotes the formation of the nanodroplets (Methods). Materials were investigated in which the nanodroplets were doped with only the fluorophore (DPA, concentration in the nanodroplets = 1 x10’1M), only the sensitizer (PdOEP, concentration inthe nanodroplets = 1.3X10’4M, this reference material is outside of the invention), or both these components (DPA:PdOEP, concentration in the nanodroplets = 1 x10’1M : 1.3x1 O’4M, average concentration in the total volume = 1.5X10’2M: 1.9X10’5M). We also omitted the solvent and incorporated the fluorophore in the matrix without providing a high mobility environment (DPA*, average concentration in the total volume = 1.5x1 O’2M, this reference material is outside of the invention). Optical absorption measurements confirm the inclusion of conjugated chromophores (FIG. 11 ). FIG. 2a shows that the DPA-containing scintillating materials are highly transparent and fluoresce strongly upon excitation with UV light. Timedomain NMR experiments confirm the coexistence of both mobile and rigid phases at room temperature in the solvent-free DPA* sample, due to the presence of the plasticizers (Methods, FIG. 7). Notably, a higher mobility phase is clearly present in samples containing the solvent-containing nanodroplets27’28. Upon studying the systems in greater detail with the Hahn Echo sequence (FIG. 8), we can observe a relaxation time associated to the intrinsic mobile phase in the DPA* sample is around 0.5 ms, a value compatible with the presence of a slightly plasticized polymer matrix. In contrast, the relaxation time of the samples containing solvent BuBz is clearly bimodal, with a second component showing a large relaxation time over 15 ms, in perfect agreement with the typical mobility of viscous or confined liquids. Spin diffusion experiments performed on the DPA:PdOEP sample put the average diameter of the liquid domains, which are assumed to be spherical, at « 15 nm29. A conclusive proof of the existence of a strongly segregated liquid phase is provided by low temperature experiments. Upon cooling down to 230 K, only the nanodroplets containing polymers still show indeed the mobile phase fraction due to presence of the solvent (FIGS. 9a-b).

[0108] The emission characteristics of the different materials were investigated by means of steady-state and time-resolved photoluminescence and scintillation spectroscopy. FIG. 2c shows the photoluminescence spectra of the scintillators under excitation at 340 nm. All DPA-containing materials exclusively show the characteristic fluorescence of DPA with an emission maximum at 430 nm. By contrast, the PdOEP reference sample phosphoresces with maximum at 660 nm (FIG. 2c). Upon excitation at 532 nm, the DPA:PdOEP containing material shows weak residual sensitizer emission (FIGS. 12a-f), which demonstrates efficient triplet energy transfer from PdOEP to DPA9. Under pulsed excitation, the fluorescence intensity in the solvent-free DPA* sample decays according to a single exponential function with a characteristic decay time of ~10 ns (FIG. 2e, and Table 1 below).This lifetime is slightly longer than in organic solvents24, which reflects that embedding this emitter in a more rigid host limits the vibration-mediated intramolecular non-radiative internal conversion. The emission decay in the nanostructured polymers containing DPA or DPA:PdOEP also follows a single exponential function, but the lifetime is reduced to 8 ns in both materials; this reflects that in the nanostructured scintillating materials, the DPA predominantly or exclusively resides in the liquid phase and that the presence of the sensitizer does not affect its emission characteristics in a major way, e.g., through back- transfer effects24.

[0109] Table 1. The maximum density of triplet excitons generated in the investigated scintillators was estimated by considering an energy deposition volume of conical shape, whose height and base radius were determined by numerical simulation of the interaction between the different ionizing radiation employed and the polymeric materials (FIGS. 6a and 6b). The number of triplets per droplet was calculated for spherical droplets with a diameter of 25 nm that constitute 15% of the samples’ total volume.

[0110] The scintillation behavior of the different materials was first probed by radioluminescence emission spectroscopy under continuous irradiation with soft X-rays (FIG. 2d and Methods). The emission spectrum of the PdOEP-doped reference sample shows two weak emission bands with maxima at 320 and 660 nm that are ascribed to butyl benzoate and PdOEP, respectively. These bands are absent in the scintillation spectrum of DPA:PdOEP, demonstrating complete energy transfer from the solvent and sensitizer to the emitting dyes. The sample exclusively emits blue light with a LY of 750±50 ph MeV’1and the emission spectrum shows exclusively DPA photoluminescence. The radioluminescence intensity of the DPA: PdOEP scintillator is slightly higher than that of the nanostructured material containing only DPA (LY = 675±45 ph MeV’1), which reflects a benefit ofsensitization. Both nanostructured polymers show a clearly higher emission intensity than the solvent-free DPA* reference (LY = 250±60 ph MeV’1), which highlights that the solvent droplets may play a crucial role in the conversion of the energy of ionized free charges into emissive states by reducing non-radiative losses during the energy transfer towards the conjugated dyes3031. FIG. 2f, which shows the decay of scintillation light pulses at 430 nm generated by 14.5 keV pulsed X-ray excitation (Methods), reveals that the different materials investigated also display dissimilar scintillation kinetics. The emission intensity in solvent- free DPA* decays according to a single exponential function with a lifetime (~10 ns) that mirrors the photoluminescence decay. On the other hand, both nanostructured polymers show a scintillation lifetime that is longer than the corresponding fluorescence, with characteristic decay times of 14.1 and 12.5 ns for the DPA and DPA:PdOEP containing materials, respectively. Considering that the DPA PLQY is close to unity and competitive intramolecular dissipation mechanisms are absent, we speculate that this effect is possibly related to a local polarization of the solvent around the excited dyes during the scintillation process, and a concomitant change of the oscillator strength of the radiative S - Sotransition of DPA, as recently observed for other blue-light-emitting scintillating dyes13’31 32. Nevertheless, the increase of the emission lifetime is small, with no consequences on the prompt response of the material and on the TTA process.

[0111] FIG. 2g shows transmission spectra of the DPA:PdOEP nanostructured plastic scintillator (dashed line) and the dye-free reference nanostructured polymer (black solid line), optical path length = 10 mm for both samples.

[0112] After confirming that the nanostructured DPA-PdOEP containing material displays TTA-driven optical upconversion and that the nanoconfinement optimizes the TTA rate and yield (FIGS. 12a-f, and Table 3 below), we tested the PSD response of the scintillating materials using137Cs emitting 0.662 MeV y-rays and241Am emitting 5.5 MeV a particles as radiation sources. FIG. 3a shows the PSD histograms recorded with the three scintillating materials under y-ray exposure (Methods). The x-axis is a relative indication of the energy absorbed by the scintillator, which is proportional to the number of photons produced. On the y-axis, the PSD value is calculated as the relative weight of the slow scintillation component with respect to the emission produced in the selected time window (Methods, FIG. 5)17; therefore, its value varies from 0, for only fast emission, to 1 , for only slow emission. Finally, the z-axis shows the relative intensity of the scintillation at any PSD value between 0 and 1. This time-gated analysis of the scintillation pulse allows distinguishingprompt and delayed scintillation events and thus discriminating the type of incident radiation that produces the luminescence.

[0113] Besides a very fast spurious signal due to the instrumental response, all histograms in FIG. 3a show a clear single signal with a PSD value of 0.35 for DPA* and 0.40 for DPA and DPA:PdOEP. Notably, the signal intensity increases by one order of magnitude in the order solvent-free DPA* (outside of the invention) < nanostructured DPA < nanostructured DPA:PdOEP, in line with the above-discussed scintillation efficiency of the three materials for high energy photons. The corresponding recorded average scintillation pulse decay traces (FIG. 3b) confirm that in all cases the scintillation is due to prompt emission, with characteristic lifetime of 9.9 ns, 10.6 ns, and 9.1 ns for DPA* DPA, and DPA:PdOEP, respectively. Considering the instrument time resolution of ±2 ns, these values agree with the fluorescence and X-ray scintillation lifetimes discussed above (FIGS. 2d, f). In contrast to the other two materials, the scintillation pulse decay trace of DPA:PdOEP also displays a weak slow component (< 2% of total signal) that is clearly evident in the time regime above 50 ns. We ascribe this slow emission to sensitized emission, i.e. , a sequence of processes that includes the formation of PdOEP triplets even under weakly ionizing y-rays, energy transfer to DPA, and subsequent TTA.

[0114] A more complex behavior is observed when the nanostructured scintillators are simultaneously exposed to a-particles and y-rays. FIG. 3e shows the PSD histograms for the DPA and DPA: PdOEP samples. In both cases an extremely slow scintillation on the microsecond time scale at PSD = 0.9 is observed, likely due to emission from the plasticized matrix that enable some very slow TTA for the small fraction of segregated and aggregated DPA molecules, even in absence of the solvent (FIGS. 7-9a-b). At PSD = 0.4, the prompt emission generated by y-rays is seen (FIG. 3c), and a third process with a PSD = 0.55 is observed that is associated with the a-particles. The latter signal is enhanced by approximately one order of magnitude in the presence of the triplet sensitizer. The analysis of the decay kinetics of the corresponding averaged light pulse waveforms, which all display a multi-exponential decay behavior (FIG. 3d, and Table 2 below) reveals a fast emission component with a lifetime that matches the one of light pulses generated by y-rays (See Table 3 below). This prompt fluorescence is generated by direct recombination of diffusing free charges on the DPA molecules during the scintillation process. The slower emission component is ascribed to the TTA process. The initial (i.e., at time zero) relative contributionof the slow component in the DPA:PdOEP scintillator (20%) is twice as high as the one observed in the nanostructured polymer containing only DPA (10%). Considering that the statistical probability to generate a DPA singlet upon TTA is a constant value,33this results indicates that number of triplets generated in the DPA:PdOEP scintillator is approximately four times higher than in the material containing DPA only. This estimation is further supported by a detailed analysis of the delayed emission kinetics. The inset of FIG. 3d shows the decay of the delayed emission intensity over time. Considering that the natural lifetime of the DPA triplets is on the millisecond time scale,24one can assume that the TTA emission lifetimeTTA, defined as the time when the intensity is reduced to a value 1 / e, directly mirrors the average initial TTA annihilator rate kTTA= (rrr)-1. The decay plots (FIG. 3d) show that the delayed emission in the DPA:PdOEP scintillator decays faster than in the DPA scintillator, in agreement with the larger initial population of DPA triplets that set their collision probability and kTTA. Thus, the kTTAvalue, which is proportional to the triplet density [T], determined for the DPA:PdOEP scintillator (3.8X107HZ) is twice as high as observed for the DPA-only material (1 .8X107Hz). This extremely high kTTAmirrors the double positive effect of the nano-confinement of the dyes. First, the simultaneous presence of multiple triplets in any solvent droplets (Table 1 ) enables a confined TTA with unitary yield. Second the TTA efficiency for PSD analysis the prompt emission LY are further enhanced by efficient sensitization, thanks to the crucial advantage of the nanostructured scintillator platform that it is possible to incorporate and intimately mix with annihilators an auxiliary and efficient triplet sensitizer as the metallated porphyrin. This approach is impossible to realize in traditional plastic scintillators at the concentrations employed here without segregation of the different dyes.

[0115] Table 2. Fit parameters for the PL and scintillation emission intensity decay curves.

[0116] Table 3. Summary of the analysis of TTA kinetics for the PdOEP (2x1 O’5M) and DPA (1.5x1 O’2M) pair in solution vs. the nanostructured polymer (FIG. 8) under modulated optical excitation at 532 nm. The triplet density generated in the system was calculated considering the sample absorbance at the excitation wavelength and an energy transfer yield of 100% between the photo-excited PdOEP and the DPA triplets.

[0117] The PSD capability of the new scintillating polymers was further tested with a 2.5 MeV neutron source (Methods)34. Since nuclear reactions always produce a combination of neutrons and y-rays, the ability to discriminate these species is crucial3435. Plastic scintillators are ideal detectors for fast neutrons, because their preferential punctual interaction with hydrogen and carbon atoms produces charged ions, which through interactions with the surrounding matter are eventually translated into scintillation pulses.10Considering the initial neutron energy and the presence of charged particles as secondary medium interacting with the nanostructured material, one can expect that the response of the present scintillators to neutrons and a-particles is similar. FIG. 4a shows the standard pulse height spectra of the nanostructured DPA and DPA:PdOEP scintillators. The histograms integrals are proportional to the number of detected scintillation photons, and therefore to the LY of the scintillator at the given radiation energy. Also in this case, the LY of the DPA:PdOEP scintillator is twice that one of the DPA-only material, confirming again the beneficial effect of the triplet sensitizer species.

[0118] FIG. 4b shows PSD histograms of the nanostructured scintillators containing DPA or DPA:PdOEP upon simultaneous exposure to neutrons and y-rays. It is worth noting that in both cases the intensity of the PSD = 0.9 emission is almost negligible, thus demonstrating a better yield of the useful scintillation mechanisms when neutrons are involved with respect to the a particles. Indeed, in both materials the signals associated with y-rays at PSD = 0.4, generated by discriminating the prompt emission on the nanosecond time scale (FIG. 4c), and the delayed emission generated by neutrons at PSD = 0.55 can be identified. However, the data show that the signals are more intense and better resolved when the scintillator contains PdOEP, approximately by one order of magnitude, thus allowing a better PSD discrimination (FIG. 4b, right panel). In agreement with the results discussed for a-particles and y-rays, this emission consists in fast and slow components (FIG. 4d), with a doubled delayed component intensity (46% of the total emission) in the DPA:PdOEP sample vs. DPA (22% of the total emission). The analysis of the time-resolved data results a kTTAof 3.5x107Hz and 1 .8x107Hz for DPA:PdOEP and DPA scintillators (FIG. 4e), again in agreement with results discussed above (FIG. 3d) and with the energy of the detected particles. Considering the lower probability of neutron-carbon interaction in the materials and the lower LY of the scintillation process generated by charged carbon ions37, we ascribe the detected signal to the interaction of high energy protons generated by scattering with incident neutrons.Notably, the scintillation signal in the nanostructured DPA:PdOEP scintillator is completely exhausted within ~400 ns, thus allowing PSD analysis for event of rates as high as 1 MHz. This means that the time response of the new scintillator is better than that of the commercial BC-501 liquid scintillator and other plastic scintillators in which alternative triplet harvesting strategies are exploited.37

[0119] The data in FIG. 16 demonstrate the role of the triplet sensitizer when added in the polymer scintillator. As a model case, in the liquid case we used DPA as the TTA / emitter species. The annihilating triplet energy was at 700 nm. We therefore added two different phosphorescent systems to be evaluated as triplet sensitizers. First the PdOEP, which phosphorescence emission at 645 nm (dotted line) is resonant with the DPA triplet and can experiment exothermic energy transfer to sensitize the DPA triplet population during scintillation population and therefore promoting the production of the blue emission (dash dot line). Second, the PdTPBP, which low energy emission at 800 nm (solid line) is not resonant with the DPA triplet energy. This does not allow energy transfer to sensitizer the DPA triplet and, conversely, the PdTPBP acts as energy dissipation channel by reducing the intensity of the blue scintillation.

[0120] Discussion of Results

[0121] In summary, the examples demonstrate sensitized delayed scintillation in nanostructured multiphase polymeric scintillator compositions. While our discovery that the nanostructured materials according to the present invention display attractive scintillation characteristics was serendipitious, these advantageous properties can be rationally explained in a manner that can guide the development of additional embodiment. The scintillator compositions according to the invention consist of a rigid transparent polymeric host that contains liquid nanodroplets in which TTA-active photoluminescent compounds are dissolved. The radiation-dependent activation of the TTA process leads to delayed emission, thus enabling the detection and discrimination of ionizing radiations and particles by time-resolved pulsed shape discrimination.

[0122] The scintillation and pulse shape discrimination properties of the example materials have been studied under different operating conditions. The sensitized scintillator composition shows a three times enhanced scintillation efficiency with respect to the reference sample DPA* (outside of the invention) under high energy photons, thus demonstrating the importance of the liquid phase for a better conversion of the released radiation energy into luminescent emissive states. Thanks to the confinement innanodroplets, also the yield and rate of the TTA process enhanced with respect to the reference sample DPA* (outside of the invention), showing a three-to-four times enhanced scintillation efficiency for a / y nl irradiation. The material proved to be effective to provide a / y and n / y discrimination for events in the MHz counting rate range. Notably, the sensitivity and discrimination ability of the sensitized scintillator compositions are significantly better than the non-sensitized counterpart. Considering the structure of the sensitizer molecule and its properties, the data presented here demonstrate that the improved scintillation capability of the sensitizer-containing scintillation materials is due to the sensitizer’s ability to capture some of the incident energy that cannot be harnessed by the TTA-active photoluminescent compound, and the efficient transfer of the triplets thus generated to the TTA-active compound, giving rise to an enhanced localized release and conversion of the radiation energy.

[0123] The results show that especially the sensitized TTA scintillator compositions of the invention represent a radical technological advance in the scintillation detection field. We emphasize that the inventive material platform has an unprecedented compositional versatility in comparison to alternative plastic scintillator designs, in particular with respect to the choice of the photoluminescent compound and optionally at least one triplet sensitizer that can be embedded. The efficient TTA that is promoted by this design is impossible to achieve in conventional bulk amorphous plastic scintillators. Consequently, this easy-to- handle material platform produces high-tech ultrasensitive radiation detectors that enable the efficient and fast radiation discrimination and detection of rare, low-energetic events.

[0124] Methods

[0125] Preparation of the nanostructured polymer scintillator compositions and reference material. All chemicals were purchased from Frontier Scientific, Inc, Sigma-Aldrich, ABCR or Tokyo Chemical Industry Co. Ltd. (TCI) and were used as received without further purification. The nanostructured polymer scintillator compositions and the nanostructured reference material were prepared by adapting previously reported methods16under ambient conditions without prior deoxygenation of the single components or their mixtures. The polymer matrix components cetyltrimethylammonium chloride (250 mg), methacrylic acid (665 mg), triethylene glycol (750 mg), triethylene glycol dimethacrylate (175 mg), and 2- hydroxyethyl methacrylate (2.66 g) were mixed in a 20 mL glass vial equipped with a stir bar. To prepare the nanostructured scintillator compositions containing only DPA, 9,10- diphenylanthracene (DPA, 25 mg) and butyl benzoate (500 mg) were added. The mixturewas heated in an oil bath to 80°C and stirred for 30 min. The vial was then removed from the oil bath and an aqueous hydrogen peroxide solution (30%, 10 mg) and 2- mercaptoethanol (10 mg) were sequentially added. The mixture was briefly shaken and kept for 2 min before dimethylthiomethane (27 mg) was added and the vial was briefly shaken again. The mixture was filtered through a 0.2 pm PTFE-filter and filled into a glass cuvette (external dimensions = 12.5x12.5x45 mm, optical path length and internal width = 10 mm) that was closed with a stopper. The clear mixture was left to react at room temperature overnight and a hard and transparent glassy material was obtained, which was then released from the glass cuvette for further use. To prepare the nanostructured scintillator compositions containing DPA and PdOEP, the same process was applied, but instead of neat butylbenzoate, a solution of DPA (25 mg) and PdOEP (0.062 mg) in butyl benzoate (500 mg) was added. The nanostructured reference material containing only PdOEP (outside of the invention) was made by the same process, but the DPA was omitted and only a solution of PdOEP (0.062 mg) in butyl benzoate (500 mg) was added. Assuming a density of 1 g em’3for the final materials, the dye concentration in the final materials is 1 .9x1 O’5M PdOEP and / or 1 .5x1 O’2M DPA, respectively. Assuming that the dyes exclusively reside in the liquid nanodroplets, which represent 15% of the materials, the dye concentration in the nanodroplets is 1.3x1 O’4M PdOEP and / or 1.0x10’1M DPA.

[0126] Preparation of solvent-free reference material (DPA*) outside of the invention. A scintillating reference material that was based on DPA and the solid polymer matrix only was prepared by using the above protocol, but omitting the butyl benzoate and reducing the amount of DPA to 22.5 mg, in order to keep the overall emitter concentration, i.e. the same as for the nanostructured scintillators.

[0127] Structural characterization of plastic scintillators and reference materials. Time domain1H-NMR measurements were performed on a 0.5 T Broker Minispec mq20 instrument with proton Larmor frequency of 19.9 MHz, equipped with a static probe and a BVT3000 heater temperature control unit working with nitrogen gas. The temperature was calibrated using an external thermometer with an accuracy of 1 K. The precision is 0.1 K and the temperature is stable within that range during the measurement. The samples were left around ten minutes in the magnet to ensure thermal equilibration before starting the experiments; for variable temperature measurements, the same 10 min isotherm was applied before each point. FIDs for rigid phase determination were acquired after a pulsed mixed magic sandwich echo (MSE) was performed on each sample with 128 scans. Domainsize calculations were performed on FIDs collected after a MSE refocused Goldman-Shen sequence, using the initial rate approximation for the sink (rigid) region. T2relaxation time was measured with standard Hahn Echo sequence. The receiver dead time was set to 12.7 ps, and phase switching time to 2.2 ps while the 90° pulse length was set to 2.10 ps.

[0128] Chemical Structures. FIG. 15. illustrates chemical structures of the DPA:PdOEP nanostructured plastic scintillator components including 1 ) methacrylic acid, 2) 2- hydroxyethyl methacrylate, 3) triethylene glycol, 4) triethylene glycol dimethacrylate, 5) 2- mecaptoethanol, 6) hydrogen peroxide, 7) dimethylthiomethane, 8) butyl benzoate, 9) cetyltrimethylammonium chloride, 10) palladium (II) octaethylporphyrin, 11 ) 9,10- diphenylanthracene. For reference samples, 10) palladium (II) octaethylporphyrin was omitted in preparation of DPA reference samples, and 8) butyl benzoate and 10) palladium (II) octaethylporphyrin were omitted in preparation of DPA* reference samples.

[0129] Photoluminescence studies. Time-resolved photoluminescence experiments in the nanosecond time scale were performed by using a pulsed laser LED at 340 nm (3.65 eV, EP-LED 340 Edinburgh Instruments, pulse width 120 ps) as excitation source and an FLS1000 Edinburgh setup in Time-Correlated Single Photon Counting (TCSPC) for acquisition. Quartz Suprasil cuvettes with an optical path length of 1 cm were used for all experiments involving dye solutions. The solid samples were all excited at 340 nm to avoid any excitation of the polymer matrix.

[0130] Radioluminescence (RL) studies. Steady-state RL measurements were carried out at room temperature using a homemade apparatus featuring, as a detection system, a liquid nitrogen-cooled, back-illuminated, and UV-enhanced charge coupled device (Jobin-Yvon Symphony II) combined with a monochromator (Jobin-Yvon Triax 180) equipped with a 100 lines / mm grating. All spectra are corrected for the spectral response of the detection system. RL excitation was obtained by unfiltered X-ray irradiation through a Be window, using a Philips 2274 X-ray tube with tungsten target operated at 20 kV. At this operating voltage, a continuous X-ray spectrum is produced by a Bremsstrahlung mechanism superimposed to the L and M transition lines of tungsten, due to the impact of electrons generated through thermionic effect and accelerated onto a tungsten target. The dose rate was 0.2 Gy / s, evaluated by comparison with a calibrated 90Sr-90Y beta radioactive source and using optically stimulated luminescence emission from quartz crystalline powder (100 - 200 pm grains).

[0131] Soft X-ray scintillation studies. The scintillation emission rate was studied in time- correlated single photon counting (TCSPC mode under pulsed X-ray excitation. For this purpose, a Hamamatsu N5084 X-ray tube was used. The X-ray energy spectrum is a bremsstrahlung continuous spectrum extending up to 40 keV (as the operating voltage is 40 kV) with an additional pronounced peak around 9 keV due to Tungsten L-characteristic X- ray photons. As photodetector, a hybrid photomultiplier tube (HPM 100-07 from Becker&Hickl) optimized for TCSPC measurement was used. The samples were measured in reflection positioning.39The global instrumental time response function is 120 ps FWHM, which enables a maximum temporal resolution of ~50 ps.

[0132] Scintillation and PSD measurements. The scintillation light, comprising photons, was converted into an electrical signal by using a Hamamatsu model R9420-100-10 photomultiplier tube (PMT)). The scintillator compositions were wrapped with Teflon® tape in order to form a light guide and to direct the light toward the PMT surface through multiple reflections. The electric signal was then fed into a CAEN DT5730 digitizer, sampling every 2 ns with 14 bit resolution, recording all waveforms higher than a selectable threshold. Each event was analyzed off-line by calculating the area (T|Ong) under a gate as long as the waveform, which is proportional to the total scintillation light produced. The area of each waveform was then used to populate the histogram representing the recorded energy spectrum. A shorter gate was used to calculate the area (TShort)> enabling pulse shape discrimination (PSD) measurements. The PSD plot was populated by using the parameter PSD=(Tiong-TShorty'Ciong for the y-axis and the T|Ongfor the x-axis.

[0133] -Ray and a particle detection and discrimination. The measurements were performed at the nuclear measurement laboratory at the Institute for Plasma Science and Technology (CNR-IST) in Milano. The detectors, made by the scintillation material coupled to the PMT, were exposed to a137Cs y-ray source (E = 662 keV) or a241Am (E = 5.5 MeV), respectively. The y-source was placed in front of the detector, emitting y-rays isotropically. The a particle source, instead, was attached to the scintillator surface in order to decrease the a particle straggling. A hole in the Teflon® tape allowed the particles to reach the scintillator.

[0134] / Veufron and y-ray detection and discrimination. 2.5 MeV neutron detection experiments have been performed at the Frascati Neutron Generator (FNG-ENEA). Here neutrons are produced via deuterium-deuterium nuclear reactions occurring between a deuterium beam accelerated up to 300 kV and a deuterated-titanium target. The energy ofthe emitted neutrons is related to the emission angle and in case of 90°, it is peaked at 2.5 MeV. For this experiment, the detectors were placed at an angle of 90 degrees with respect to the incoming deuterium. 2.5 MeV neutrons mainly interact in the scintillator material via elastic scattering with hydrogen and carbon nuclei producing a recoiled proton or carbon nucleus, respectively. When elastic scattering reactions occur, the neutron can transfer part of its kinetic energy to the recoil nucleus, according with the emission angle and the mass of the recoiled nucleus. The amount of energy transferred to the recoil nucleus is defined by4 ■ A the equation ER=1)2~ cos26 ■ Enwhere A is the mass of the target nucleus, e is the scattering angle of the recoil nucleus in the laboratory coordinate system, Enand ERare the incoming neutron energy and the recoil nucleus kinetic energy in the laboratory system, respectively39. When the scattering angle is 90°, the transferred energy to the reoil nucleus is zero, while when a head-on collision occurs, the transferred energy reaches its maximum4 ■ AER\MAX = ( + 1)2 ' En. Since there are no preferred scattered angles and all the angles are allowed, the energy distribution of the recoil nuclei results in a continuum from zero to the maximum value. For the hydrogen nuclei, the maximum transferred energy is equal to the energy of the neutron EH\MAX= En= 2.5 MeV , while for the carbon nuclei is EC\MAX = 0.284 - En= 0.71 MeV.

[0135] For the avoidance of doubt, the compositions, devices and methods of the present invention encompass all possible combinations of the components, including various ranges of said components, disclosed herein. It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description of a product comprising certain components also discloses a product consisting of these components. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps.In accordance with the patent statutes, the best mode and preferred embodiment have been set forth; the scope of the invention is not limited thereto, but rather by the scope of the attached claims.References1 Reisz, J. A. et al. Effects of ionizing radiation on biological molecules — mechanisms of damage and emerging methods of detection. Antioxidants & Redox Signaling 21, 260-292 (2014).2 Dujardin, C. et al. Needs, trends, and advances in inorganic scintillators. IEEE Transactions on Nuclear Science 65, 1977-1997 (2018).3 Lecoq, P. Development of new scintillators for medical applications. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 809, 130-139 (2016).4 Orfano, M. et al. Efficient radioactive gas detection by scintillating porous metal-organic frameworks. Nature Photonics 17, 672-678, doi: 10.1038 / s41566-023-01211-2 (2023).5 Schoeppner, M. & Glaser, A. Present and future potential of krypton-85 for the detection of clandestine reprocessing plants for treaty verification. Journal of environmental radioactivity 162, 300-309 (2016).6 Danagoulian, A. et al. Prompt neutrons from photofission and its use in homeland security applications. IEEE International Conference on Technologies for Homeland Security (HST). 379-384 (2010)7 Han, J. etal. Pulse characteristics of CLYC and piled-up neutron-gamma discrimination using a convolutional neural network. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1028, 166328 (2022).8 Ferrer, C., Huertas, C., Garcia, D. & Saez, M. Dosimetric characterization of a novel commercial plastic scintillation detector with an MR-Linac. Medical Physics 50, 2525-2539 (2023).9 Pozzi, S. A., Bourne, M. M. & Clarke, S. D. Pulse shape discrimination in the plastic scintillator EJ-299-33. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 723, 19-23 (2013).10 Bertrand, G. H., Hamel, M., Normand, S. & Sguerra, F. Pulse shape discrimination between (fast or thermal) neutrons and gamma rays with plastic scintillators: State of the art. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment lf>, 114-128 (2015).11 Birks, J. B. Photophysics of aromatic molecules, 372-394 (Wiley-Interscience, 1970).12 Ronchi, A. & Monguzzi, A. Sensitized triplet-triplet annihilation based photon upconversion in full organic and hybrid multicomponent systems. Chemical Physics Reviews 3 (2022).13 Pope, M. & Swenberg, C. E. Electronic processes in organic crystals and polymers, 138 - 139 (Oxford University Press, 1999).14 Ronchi, A. & Monguzzi, A. Sensitized triplet-triplet annihilation based photon upconversion in full organic and hybrid multicomponent systems. Chemical Physics Reviews 3, 041301 (2022).15 Knoll, G. F. Radiation detection and measurement, 29-57 (John Wiley & Sons, 2010).16 Brooks, F. D. A scintillation counter with neutron and gamma-ray discriminators. Nuclear Instruments and Methods 4, 151-163 (1959).17 Hamel, M. Plastic Scintillators, 35-89 (Springer, 2021).18 Lee, S. H., Lott, J. R., Simon, Y. C. & Weder, C. Melt-processed polymer glasses for low- power upconversion via sensitized triplet-triplet annihilation. Journal of Materials Chemistry C l, 5142-5148 (2013).19 Gelmini, G. B . Light weakly interacting massive particles. Reports on Progress in Physics 80, 082201 (2017).van Loef, E. V., Glodo, J., Shirwadkar, U., Zaitseva, N. & Shah, K. S. Solution growth and scintillation properties of novel organic neutron detectors. Nuclear Instruments and Methods in Physics Research Section A 652, 424-426 (2011).Vadrucci, R. et al. Nanodroplet-containing polymers for efficient low-power light upconversion. Advanced Materials 29, 1702992 (2017).Saenz, F. et al. Nanostructured Polymers Enable Stable and Efficient Low-Power Photon Upconversion. Advanced Functional Materials 31, 2004495 (2021).Meroni, D., Monguzzi, A. & Meinardi, F. Photon upconversion in multicomponent systems: Role of back energy transfer. The Journal of Chemical Physics 153, 114302 (2020).Montalti, M., Credi, A., Prodi, L. & Gandolfi, M. T. Handbook of photochemistry . (CRC press, 2006).Ogawa, T., Yamaki, T. & Sato, T. Analysis of scintillation light intensity by microscopic radiation transport calculation and Forster quenching model. PLoS One 13, e0202011 (2018). Khnayzer, R. S. et al. Upconversion-powered photoelectrochemistry. Chemical Communications 48, 209-211 (2012).Maus, A., Hertlein, C. & Saalwachter, K. A Robust Proton NMR Method to Investigate Hard / Soft Ratios, Crystallinity, and Component Mobility in Polymers. Macromolecular Chemistry and Physics, 207, 1150-1158 (2006).Bonetti, S. et al. Core@shell Poly(n-butylacrylate)@polystyrene Nanoparticles: Baroplastic Force-Responsiveness in Presence of Strong Phase Separation. Macromolecular Rapid Communications 37, 584-589 (2016).Mauri, M., Thomann, Y., Schneider, H. & Saalwachter, K. Spin-diffusion nmr at low field for the study of multiphase solids. Solid State Nuclear Magnetic Resonance 34, 125-141 (2008).Lombardi, P., Ortica, F., Ranucci, G. & Romani, A. Decay time and pulse shape discrimination of liquid scintillators based on novel solvents. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 701, 133-144 (2013).Zheng, Z. et al. Preparation and performance study of a novel liquid scintillator with mixed solvent as the matrix. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 850, 12-17 (2017).Baruah, M. et al. Solvent and pH dependent fluorescent properties of a dimethylaminostyryl borondipyrromethene dye in solution. The Journal of Physical Chemistry A 110, 5998-6009 (2006).Monguzzi, A., Mezyk, J., Scotognella, F., Tubino, R. & Meinardi, F. Upconversion-induced fluorescence in multicomponent systems: Steady-state excitation power threshold. Physical Review B 78, 195112 (2008).Martone, M., Angelone, M. & Pillon, M. The 14 MeV Frascati neutron generator. Journal of Nuclear Materials 212-215, 1661-1664 (1994).Frangville, C. et al. Nanoparti cles-loaded plastic scintillators for fast / thermal neutrons / gamma discrimination: Simulation and results. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 942, 162370 (2019).Wang, Q. et al. Achieving efficient neutron and gamma discrimination in a highly stable '’Li- Loaded Cs3Cu2l5 perovskite scintillator. The Journal of Physical Chemistry Letters 13, 9066- 9071 (2022).Laplace, T. A. etal. Simultaneous measurement of organic scintillator response to carbon and proton recoils. Physical Review C 104, 014609 (2021).Feng, P. L. et al. Spectral- and Pulse-Shape Discrimination in Triplet-Harvesting Plastic Scintillators. IEEE Transactions on Nuclear Science 59, 3312-3319 (2012). Knoll, G.F. Radiation Detection and Measurement, 217 (Wiley, Hoboken, 2010) J.F. Ziegler et al., Nuclear Instruments and Methods in Physics Research B, 268, 1818-1823 (2010)

Claims

WHAT IS CLAIMED IS:1 . A radiation detector capable of detecting at least one type of ionizing radiation from the list of a particles, 0 particles y rays, X-rays, and neutrons, comprising: at least a scintillator composition and a photodetector; wherein said scintillator composition is a phase-separated material that comprises at least one solid phase that comprises by majority, a polymer, and at least one liquid phase, wherein said at least one liquid phase contains at least a photoluminescent compound capable of triplet-triplet annihilation (TTA); and wherein said photodetector is capable of converting photons produced by the scintillator composition into an electrical signal.

2. The detector according to claim 1 , wherein the detector allows for pulse shape discrimination of the one or more of a particles, 0 particles, y rays, x-rays, and neutrons.

3. The detector according to any of claims 1 -2, wherein the detector allows discriminating between at least two types of the ionizing radiation from the list of a particles, 0 particles, y rays, x-rays, and neutrons.

4. The detector according to any of claims 1-3, wherein said at least one liquid phase additionally contains at least one triplet sensitizer that is capable of being electronically excited by said ionizing radiation and transferring at least a fraction of the energy of its excited states to said compound capable of TTA.

5. The detector according to any of claims 1-4, wherein the scintillator composition is substantially transparent to light emitted by said at least one photoluminescent compound, except for the optical absorbances caused by said at least one photoluminescent compound capable of TTA and said at least one triplet sensitizer when present; wherein the scintillator composition displays, after correction for absorbances caused by said at least one photoluminescent compound capable of TTA and said at least one triplet sensitizer when present, a transmission of at least 50%, more preferably above 70%, and most preferablyabove 80%, measured over a pathlength of 1 cm at normal incidence at any wavelength between 420 and 680 nm.

6. The detector according to any of claims 1 -5, wherein the scintillator composition absorbs at least a portion of the ionizing radiation incident thereon.

7. The detector according to any of claims 1 -6, wherein the at least one photoluminescent compound capable of TTA is one or more of anthracene; an anthracene derivative such as 9,10-diphenylanthracene (DPA) and 9,10-bis(phenylethynyl)anthracene (BIPEA); perylene; a perylene derivative such as 2,5,8, 11 -tetra-tert-butyl perylene (TBPe); pyrene; a pyrene derivative such as 2,7-di-tert-butyl pyrene and 3,8-di-tert-butyl pyrene; naphthalene; a naphthalene derivative such as 1 ,4-bis((triisopropylsilyl)ethynyl)naphthalene (1 ,4-TIPS-Nph) or bis((triisopropylsilyl)ethynyl)naphthalene (1 ,5-TIPS-Nph); 2,5- diphenyloxazole (PPO); other oxazole derivatives; rubrene (5,6,11 ,12- tetraphenylnapthacene); a rubrene derivative such as rubrene that is modified with tert-butyl or 2,5-di-tert-butylphenyl groups; and BODIPY-derivative.

8. The detector according to claim 4, wherein the at least one triplet sensitizer is one or more of a metallo-porphyrin, such as palladium octaethyl porphyrin (PdOEP), platinum octaethyl porphyrin (PtOEP), palladium(ll) 1 ,4,8,11 ,15,18,22, 25-octa-n- butoxyphthalocyanine [PdPc(OBu)8], platinum(ll) 1 ,4,8,11 ,15,18,22, 25-octa-n- butoxyphthalocyanine [PtPc(OBu)8], palladium^ I) meso-tetraphenyl-tetrabenzoporphyrin (PdTPTBP) and platinum(ll) meso-tetraphenyl-tetrabenzoporphyrin (PtTPTBP); a ruthenium complex such as [Ru(4,4'-dimethyl-2,2'-dipyridyl)3]2+and Ru(bpy)32+; an iridium complex such as tris[2-phenylpyridinato-C2, N]iridium(lll); and a luminescent compound that comprises one or more of the following atoms Ir, Pt, Pd, Re, Os, Ru, I, Br.

9. The detector according to any of claims 1 -8, wherein said liquid phase comprises one or more of 1 -tert-butyl-3,5-dimethylbenzene (BMB), another, optionally aliphatic hydrocarbon residue-containing (poly-)aromatic compound such as 1 ,1 -bis(3,4- dimethylphenyl)ethane, 1 -phenyldodecane, 2,7-diisopropylnaphthalene, o-terphenyl, and 1 ,2-diphenylethane; a liquid aliphatic hydrocarbon compound such as 1 -octadecene; a liquid ester such as butyl benzoate, ethyl benzoate, hexyl benzoate, dibutyl phtalate, bis(2-ethylhexyl) terephthalate, 1 ,4-bis((2-ethylhexyl)oxy)benzene) and bis(2-ethylhexyl) sebacate; ether; a halogenated liquid aromatic optionally containing an aliphatic residues (such as 1 ,2,4-trichlorobenzene) and other high-boiling (>200° C) nonpolar solvent.

10. The detector according to any of claims 1 -9, wherein said scintillator composition includes a plasticizer, preferably one or more of a polyol such as ethylene glycol, diethylene glycol, triethylene glycol, triethylene glycol monomethylether, and tetraethylene glycol monomethylether; wherein said scintillator composition includes also at least one auxiliary absorber for the ionizing radiation that is one or more of a particles, y rays, x-rays, and neutrons,11. The detector according to any of claims 1 -10, wherein the scintillator composition includes a surfactant, preferably one or more of a cationic surfactant (such as a cetyltrimethylammonium bromide (CTAB) or cetyltrimethylammonium chloride (CTAC)), an anionic surfactant (such as a sodium stearate), an alkyl benzene sulfonate (such as sodium dodecylbenzenesulfonate), and a nonionic surfactant (such as a polyoxyethylene glycol alkyl ether and a polyoxyethylene glycol octylphenol ether, and poly(ethylene glycol)-block- poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG)).

12. The detector according to any of claims 1-11 , wherein said polymer is derived from one or more of a polar acrylate (such as 2-hydroxyethyl acrylate) a methacrylate (such as a 2-hydroxyethyl methacrylate and a dimethylaminoethyl methacrylate), an acrylamide or a methacrylamide, an acrylic acid or a methacrylic acid and their salts (such as an acrylic acid or a methacrylic acid), a vi ny Ipyridine (such as a 4-vinyl pyridine), an oxazoline, a non-polar acrylate (such as a butyl acrylate or a methyl acrylate), a methacrylate (such as a methyl methacrylate), an acrylamide (such as N-octadecylacrylamide), a methacrylamide, a styrene, a polyurethane, an epoxy resin, a vinyl ester and a polyester.

13. The detector according to any of claims 1 -12, wherein the at least one triplet sensitizer is present and is palladium octaethyl porphyrin (PdOEP), and wherein the at least one photoluminescent compound capable of TTA is DPA.

14. The detector according to any of claims 1 -13, wherein the at least one liquid phase forms domains with average dimensions of less than 200 nm, and preferably less than 100 nm.

15. The detector according to any of claims 1 -14, wherein the photodetector comprises a photodiode, a charged-coupled device camera, a photomultiplier, a microchannel plate detector or any other detector or combination of detectors that converts photons produced by the scintillator composition into an electrical signal, and wherein the electrical signal is processed by an analog device or digital device also present in the photodetector to produce PSD measurements.

16. The detector according to any of claims 1 -15, wherein the photodetector further includes a light guide or a refractive index matching material that directs photons produced by the scintillator composition to the photodetector.

17. The detector according to any of claims 1 -15, wherein said scintillator composition is encapsulated in a high-reflectivity non-scintillating shell (such as aluminum or other metal sheets, reflective (multilayer) polymer films) or in a custom-designed holder (such as a nonscintillating holder made of metal or non-scintillating plastic, which inner parts are covered by the high-reflectivity material) to mechanically couple the scintillator and the photodetector and then maximizing the harvesting of the scintillation emission by the photodetector.

18. A method for detecting at least one type of ionizing radiation from the list of a particles, 0 particles, y rays, x-rays, and neutrons, and / or discriminating between different types of the ionizing radiation, comprising the steps of: obtaining a scintillator composition comprising: a phase-separated material that comprises at least one solid phase that comprises by majority, a polymer, and at least one liquid phase, wherein said at least one liquid phase contains at least a photoluminescent compound capable of triplet-triplet annihilation (TTA) and optionally at least one triplet sensitizer that is capable of being electronically excited by said ionizing radiation and transferring at least a fraction of the energy of its excited states to said compound capable of TTA,operatively coupling the scintillator composition to a photodetector to obtain a radiation detector; exposing the radiation detector to an environmental location; and determining if photons are produced by the scintillator composition with the photodetector, wherein the production of the photons indicates the ionizing radiation is present and is one or more of the a particles, y rays, x-rays, and neutrons.

19. The method according to claim 18, wherein the radiation detector is configured according to any of claims 1 -17.

20. The method according to any of claims 18-19, further including the steps of: converting the photons produced by the scintillator composition with the photodetector into an electrical signal, analyzing the electrical signal produced with the photodetector with an analog device or digital devices, and determining if the ionizing radiation is one or more the a particles, y rays, x-rays, and neutrons.

21. The method according to any of claims 18-20, wherein the photodetector includes one or more of a photodiode, a charged-coupled device camera, a photomultiplier, a micro channel plate detector, or any other detector or combination of detectors and further including the step of converting the photons into an electrical signal utilizing the photodetector.

22. The method according to claim 21 , further including a step of processing the electrical signal with an analog device or digital device to produce PSD measurements that are used to determine the type of ionizing radiation.

23. A method for discriminating between different types of ionizing radiation that is one or more of a particles, 0 particles, y rays, x-rays, and neutrons, comprising the steps of: obtaining the radiation detector according to any of claims 1-17;exposing the detector to ionizing radiation comprising one or more of a particles, y rays, x-rays, and neutrons; analyzing photons produced by the scintillator composition with the photodetector; and determining if the radiation is one or more the a particles, 0 particles, y rays, x-rays, and neutrons.

24. The method according to claim 23, wherein analyzing the photons produced by the scintillator composition includes the step of converting photons produced by the scintillator composition into an electrical signal using the photodetector.

25. The method according to claim 24, further including the step of processing the electrical signal with an analog device or digital device to produce the PSD measurements that are used to determine the type of radiation.

26. A method comprising the step of: using a scintillator composition comprising a phase-separated material that comprises at least one solid phase that comprises by majority, a polymer, and at least one liquid phase, to discriminate between ionizing radiation that is one or more of a particles, y rays, x-rays, and neutrons.

27. The method according to claim 26, wherein the method utilizes pulse shape discrimination.

Images