WO2015118533A1

WO2015118533A1 - Methods for fabricating 3-dimentional scintillators

Info

Publication number: WO2015118533A1
Application number: PCT/IL2015/050127
Authority: WO
Inventors: Guy RON; Shlomo Magdassi; Ido COOPERSTEIN; Michael Layani; Yonatan MISHNAYOT
Original assignee: Yissum Research Development Co of Hebrew University of Jerusalem
Current assignee: Yissum Research Development Co of Hebrew University of Jerusalem
Priority date: 2014-02-04
Filing date: 2015-02-04
Publication date: 2015-08-13
Anticipated expiration: 2016-08-04

Abstract

The methods of the invention permit design modalities which are currently unavailable in the printing of scintillating materials and objects, significantly reducing difficulties associated with manufacture of scintillating materials, decrease development time and associated costs.

Description

METHODS FOR FABRICATING 3-DIMENTIONAL SCINTILLATORS

FIELD OF THE INVENTION

The invention generally contemplates methods for fabricating three-dimensional scintillating materials and objects and uses thereof.

BACKGROUND

Scintillating materials, which emit light when a charged particle traverses through the material, are commonly used in many applications requiring particle detection, from particle and nuclear physics experiments, through medial applications, and homeland security applications and in the detection of sensitive and suspicious materials. These scintillators are manufactured either by casting resins into pre-formed molds, or by machining (subtractive manufacturing) of large, extruded, scintillator blocks. Both of these techniques suffer from the inability to provide precise, small scale geometries, as well as from the relatively high cost and long lead-time.

Scintillators are typically made by either casting of a resin and a hardener combination, or by extrusion of a molten scintillator [1]. These cast or extruded scintillator bars are then machined to the required geometry using standard machining techniques.

PUBLICATIONS

[1] Scintillator manufacture at Fermilab, Mellott, K. and Bross, A. and Pla- Dalmau, A., AIP Conference Proceedings, 450, 106-112 (1998).

SUMMARY OF THE INVENTION

The invention disclosed herein, provides methods and techniques for three- dimensional printing of scintillating materials. The methods of the invention may be carried out employing commercial 3D-printing materials, as base materials, to which selective and specific functional materials may be added to optimize the scintillation and optical properties of the printed materials; thus forming "Functional Scintillators" tailored for a specific application, as detection of radiation sources such as neutron, or gamma-ray radiations. As known in the art, use of organic scintillators such as anthracene, stilbene and naphthalene has been determined ineffective or difficult as such materials cannot be easily machined, nor can they be grown in large sizes. Therefore, such materials, despite their unique properties, have not been often used.

Similarly, fluors such as p-terphenyl, 2-(4-Biphenylyl)-5-phenyl- 1,3,4- oxadiazole (PBD), 2-(4-tert-Butylphenyl)-5-(4-phenylphenyl)-l,3,4-oxadiazole (butyl PBD), 2,5-diphenyloxazole (PPO) and wavelength shifter such as 5-Phenyl-2-[4-(5- phenyl-l,3-oxazol-2-yl)phenyl]-l,3-oxazole (POPOP) could not be typically used where UV-mediated polymerization reactions were involved due to their competitive light absorption.

Additionally, all current techniques suffer from the inability to produce specific fine geometries, have long production times (up to 2 weeks in the case of cast scintillators), of careful machining and polishing (machined scintillators). In contrast, printed scintillators, as herein described, offer simple design and manufacture, require no or little polishing, are potentially significantly, and most importantly, allow the production of geometries that cannot be manufactured in any other techniques, paving the way for new applications.

All current techniques used in scintillator manufacture rely of subtractive manufacturing (i.e., the machining of scintillator blocks to the required shape), or on casting in a specially designed mold (it should be noted that due to the shrinking experienced by cast scintillators during the curing phase (up to 25% by volume for some scintillators) the production of precise geometries by casting is almost impossible and usually not undertaken.

In this implementation, the ability to incorporate different compounds into the polymer matrix is of great importance, since it may be used to introduce dopants that exhibit a strong neutron absorption cross section (for example ⁶Li and ¹⁰B), which allow printing of scintillators with increased efficiency for the detection of fissionable materials.

The invention overcomes the above hurdles by providing a printing method for directly manufacture scintillator designs that cannot be achieved using standard approaches (e.g., hollow, gas filled scintillators, or scintillator designs with features which are too small to be machined). The 3D printing of the invention allows integrating in the scintillator material, during the printing process, additives and dopants with a desired activity, ranging from wavelength shifting, dopants with enhanced reactivity to various radiation types and nanoparticles.

The methods of the invention permit design modalities which are currently unavailable in the printing of such materials and objects, thereby significantly reducing difficulties associated with manufacture of such scintillating materials, decrease development time and associated costs.

Generally, the invention provides an ink formulation suitable for printing or otherwise forming the 3D-scintilators of the invention. The ink formulation typically comprises a scintillator, a material which absorbs a radiation, such as gamma-ray or X- ray, and emits an electromagnetic wave with a wavelength of visible light or near visible light, a primary phosphor, e.g., an organic phosphor for absorbing energy from the scintillator material, and optionally a further phosphor, which too may be an organic phosphor to shift the wavelength of the photons received from the primary phosphor to photons which more closely match that detected by a photo multiplier.

In certain embodiments of the invention, the ink formulation comprises a polymerizable pre -polymer material, monomers or oligomers, which acts as a matrix for the scintillator material or as the scintillator material itself, and one or more phosphor materials such as 2,5-diphenyloxazole (PPO) which emits at 360-380 nm, 1,3,5- triphenyl-2-pyrazoline (TPP) which emits at 410 nm and l,4-bis(4-methyl-5- phenyloxazol-2-yl)benzene dimethyl (POPOP) which emits at 427 nm. In ink formulations of the invention, one of the phosphor materials may be used as the primary phosphor, e.g., PPO, to accept energy from the scintillator material, e.g., an aromatic material, and a further or secondary scintillator, also known as a wavelength shifter, such as POPOP, to shift the wavelength of the photons, as explained herein.

To affect polymerization of the polymerizable pre-polymer, the ink formulation may further comprise a photoinitiator.

Thus, in an aspect of the invention, there is provided a (bottom up) process for fabricating a three-dimensional scintillator material, the process comprising:

(1) forming a pattern, e.g., by printing, onto a surface region a scintillator formulation comprising at least one pre-polymer e.g., monomers polymerizable into a desired polymer and at least one photoinitiator,

(2) affecting polymerization of said at least one pre-polymer forming said pattern, e.g., by UV irradiation; (3) forming a further pattern on the polymerized pattern by, e.g., printing the same or a different ink formulation comprising the same or different at least one pre- polymer and same or different at least one photoinitiator,

(4) affecting polymerization of said further pattern, e.g., by UV irradiation; and

(5) repeating steps (3)-(4) one or more times to afford a three dimensional structure,

wherein the scintillator formulation comprises:

1. a pre -polymer polymerizable to adapt scintillation properties, or

2. a combination of a pre-polymer polymerizable into a polymer not having scintillation properties and a scintillating material, or

3. a combination of a pre-polymer polymerizable into a polymer having scintillation properties and a scintillating material.

Surprisingly, polymerization of the pre-polymer material, by e.g., UV irradiation, in the presence of the scintillator material(s) was not affected by the presence of the scintillator materials as was expected. Without wishing to be bound by theory, it would seem that the reason for the efficient polymerization and construction of the 3D-scintillator is the step-wise construction and the selection of the materials, as detailed herein.

As recited above, the scintillator formulation comprises at least one pre-polymer e.g., monomers, polymerizable into a desired polymer, e.g., an aromatic polymer (polymer containing aromatic rings), at least one photoinitiator and one or more phosphors.

In some embodiments, the phosphors are selected amongst primary and secondary phosphors, wherein the primary phosphor e.g., an organic phosphor, is capable of absorbing energy from the scintillator material, and wherein the secondary phosphor, which may be an organic phosphor as well is selected as a wavelength shifter capable of shifting the wavelength of the photons received from the primary phosphor to photons which match that detected by a photo multiplier.

As used herein, the term " cintillator" or any lingual variation thereof, refers to a material which has the ability to emit light when excited by ionizing radiation and/or incoming charged particle, or which has the ability to shift the wavelength of the light. The materials which are used for fabricating the 3D-scintilator may be selected amongst plastic scintillators, organic scintillators, inorganic scintillators, ceramic scintillators, liquid scintillators, base scintillators and glass scintillators, in which wavelength shifting dopants as well as other functional additives may be embedded.

The polymerizable pre-polymers are typically said to adapt scintillation properties, namely become scintillator materials, as defined herein, or to adapt no scintillation properties once polymerized. Thus, the expression "adapt scintillation properties" refers to a polymer formed from pre-polymers, e.g., monomers and/or oligomers, and which presents scintillator characteristics (has the ability to emit light when excited by ionizing radiation and/or incoming charged particle, or which has the ability to shift the wavelength of the light) when formed, irrespective of the scintillating properties of the pre-polymers. Similarly, a polymer said "not to adapt scintillation properties" is one which is incapable of emiting light when excited by ionizing radiation and/or incoming charged particle, or which has the ability to shift the wavelength of the light.

For the purposes of the invention, the scintillator material may be comprised of a single scintillation material or may be in the form of a composition comprising a carrier, which by itself does not exhibit scintillation, and at least one agent which renders the composition scintillating, or the carrier itself has a scintillation property or combinations thereof. Thus, any of the scintillator materials recited herein, may be used by themselves or in combination with at least a carrier or any one or more additive, as further disclosed herein below.

Scintillators, whether alone or in combination with a carrier, may be selected from: (a) polyethylene naphthalate, polyvinyl naphthalene, polymethylmethacrylate (PMMA), polyvinyl xylene (PVX), polymethyl styrenes, 2,4-dimethyl styrene, 2,4,5- trimethyl styrene, polyvinyl diphenyl, ethoxylated trimethylolpropanetriacrylate (ethoxylated TMPTA), ethoxylated bisphenol A diacrylate, polyvinyl tetrahydronaphthalene ;

(b) aromatic hydrocarbons such as anthracene (CMHJO), stilbene (C₁4H₁2), naphthalene (CioH₈), polyvinyltoluene (PVT);

(c) organometallic compounds such as triphenylbismuth;

(d) alkali metal halides such as Nal(Tl) (sodium iodide doped with thallium);

(e) inorganic alkali halides such as CsI(Na), Csl(pure), CsF, KI(T1), Lil(Eu); (f) non-alkali materials such as BaF₂, CaF₂(Eu), ZnS(Ag), CaW0₄, CdW0₄, YAG(Ce) (Y₃Al₅0₁₂(Ce)), GSO, LSO;

(g) inorganic scintillators such as LaCl₃(Ce), LaBr₃(Ce);

(h) glass scintillators based on cerium-activated lithium or boron silicates;

(i) polyphenyl hydrocarbons such as oxazole and oxadiazole aryls, n-terphenyl (PPP), 2,5-diphenyloxazole (PPO), l,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), 2- phenyl-5 -(4-biphenylyl) - 1 , 3 ,4-oxadiazole (PB D) , 1,3,3 -Trimethyl- 1 -phenylindan (TMPI) and 2-(4'-tert-butylphenyl)-5-(4"-biphenylyl)-l,3,4-oxadiazole (B-PBD);

(j) tungstate and gadolinium based materials such as radmium tungstate or terbium-doped gadolinium oxysulphide (Gd₂(¾S), cadmium tungstate (CdWC>4 or CWO), terbium activated gadolinium and calcium tungstate (CaWO/_t);

(k) ceramic scintillators such as (Y,Gd)2(¾:Eu,Pr; Gd₂(¾S:Pr,Ce,F; and Gd₃Ga₅0₁₂:Cr,Ce;

(1) zinc sulfide based materials;

(m) p-terphenyl (C₁₈H₁₄), PBD (C₂oH₁₄N₂0), butyl PBD (C24H22N2O), PPO (C₁₅H„NO), and POPOP (C₂4H₁₆N₂0).

In some embodiments, the scintillator formulation comprises primary and secondary phosphors, each independently being selected from polyphenyl hydrocarbons. In some embodiments, the polyphenyl hydrocarbons are selected from s oxazole and oxadiazole aryls, n-terphenyl (PPP), 2,5-diphenyloxazole (PPO), l,4-di-(5- phenyl-2-oxazolyl)-benzene (POPOP), 2-phenyl-5-(4-biphenylyl)-l,3,4-oxadiazole (PBD), 1,3,3-Trimethyl-l-phenylindan (TMPI) and 2-(4'-tert-butylphenyl)-5-(4"- biphenylyl)-l,3,4-oxadiazole (B-PBD).

In some embodiments, the primary and secondary phosphors are selected from PPO and POPOP.

In some embodiments, the primary and secondary phosphors are TMPI.

In some embodiments, the scintillator formulation comprises a resin material of an aromatic polymer (a polymer containing at least one aromatic or aryl group), such polymers may be selected from polyethylene naphthalate, polyvinyl xylene (PVX), polymethyl styrenes, 2,4-dimethyl styrene, 2,4,5-trimethyl styrene, polyvinyl diphenyl, polyvinyl naphthalene, ethoxylated bisphenol A diacrylate, bisphenol A, polyvinyl tetrahydronaphthalene. In some embodiments, the resin material is of bisphenol A acrylate, e.g., ethoxylated bisphenol A diacrylate or dimethylacrylate.

In some embodiments, the phosphor materials are selected from aromatic hydrocarbons such as anthracene (C₁4H₁₀), stilbene (C₁4H₁2), naphthalene (CioHg) and polyvinyltoluene (PVT).

In some embodiments, the phosphor materials are selected from polyphenyl hydrocarbons such as oxazole and oxadiazole aryls, n-terphenyl (PPP), 2,5- diphenyloxazole (PPO), l ,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), 2-phenyl-5-(4- biphenylyl)-l ,3,4-oxadiazole (PBD), 1 ,3,3-Trimethyl-l-phenylindan (TMPI) and 2-(4'- tert-butylphenyl)-5-(4"-biphenylyl)-l ,3,4-oxadiazole (B-PBD).

In some embodiments, the phosphor materials are selected from TMPI, p- terphenyl, PBD, butyl PBD, PPO and POPOP.

In some embodiments, the scintillator formulation for forming a 3D-scintillator according to the invention is selected from

(a) PPO, POPOP, TPO and ethoxylated bisphenol A diacrylate or dimethylacrylate ;

(b) PPO, POPOP, naphtalene, ethoxylated TMPTA and TPO;

(c) PPO, POPOP, naphtalene, TPO and ethoxylated TMPTA;

(d) TMPI, naphthalene, TPO and ethoxylated TMPTA;

(e) TMPI, naphtalene, ethoxylated TMPTA and TPO

(f) TMPI, TPO and ethoxylated bisphenol A diacrylate or dimethylacrylate.

In some embodiments, the scintillators are made of a resin material and a hardener or crosslinker, or polystyrene based materials. Where a pre -polymer material is used as a carrier to the scintillator, or where the scintillator is composed of a pre- polymer material such as monomers and/or oligomers, the polymerization of the monomers and/or oligomers may be initiated by the use of at least one polymerization initiator which may be comprised and patterned with the scintillating material and optionally the carrier. In some embodiments, the initiator is a photoinitiator such as 2,4,6-Trimethylbenzoyl-diphenyl-phosphineoxide (TPO).

The scintillator materials fabricated according to the invention may be used in a variety of applications, and thus in order to render the materials suitable for various applications, the materials may be doped or treated with suitable wavelength shifting materials and functional scintillators. The amount of the materials, as dopants, which may be introduced, varies based on the final intended application, inter alia, on the type of material, the type of dopant material, the effect to be achieved, the strength of the effect, the end application, presence or absence of other materials and others.

In some embodiments, the concentration of material in the scintillator material is at most 10% w/w. In some embodiments, the concentration of the material is at least 0.5%. In some embodiments, the concentration of the material is between at least 0.5% and 10%. In some embodiments, the concentration of the material is between at least 0.5% and 20%. In some embodiments, the concentration of the material is between at least 0.5% and 30%. In some embodiments, the concentration of the material is between at least 0.5% and 40%. In some embodiments, the concentration of the material is between at least 0.5% and 50%. In some embodiments, the concentration of the material is between at least 0.5% and 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1%. In some embodiments, the concentration of the material is between at least 0.5% and 1%.

In some embodiments, the wavelength shifter are selected amongst optically active materials, e.g., nano- or micro-particles which are active at any wavelength ranging from the near UV through the visible wavelengths and up to the near IR spectrum. Such may be selected from charged particles (which traverse the scintillator and excite the material, thereby causing the material to emit light upon recombination, organic or inorganic materials or in combination thereof.

In some embodiment, the scintillator material is the carrier itself. The carrier may comprise of a pre-polymer material (monomers and oligomers) which contains functional groups that emit light when excited by ionizing radiation and/or incoming charged particle. The carrier can contain also other dopants.

In some embodiments, the dopants are semiconductor materials capable of shifting wavelength from short wavelengths to longer wavelengths. In some embodiments, the materials are selected amongst core/shell semiconductor nanocrystals such as CdSe/ZnSe, CdSe/CdS, CdSe/ZnS and InP/ZnS.

In some embodiments, oxides having absorbance in UV and IR may be used. Such oxides may be selected from Si(¾, Ti0₂, ZnO and AI2O3.

For achieving plasmonic effects, metallic nanoparticles such as Ag, Au, Al, Fe, Cu, and others may be utilized, each based on its characteristic absorbance (e.g., Au - 550 nm, Al - 700-800 nm, Ag - 400 nm). In some embodiments nanoparticles may be embedded in the scintillator using chemical binding. The nanoparticles may be embedded by forming covalent or hydrogen bonds with the material or by physical interactions within the material matrix. In such cases, the nanoparticles may be pre -coated with relevant surface ligands and linkers which assist their association with the scintillator material.

The "nanoparticles" which may be embedded in the scintillator material may be any type of nanoparticle, of a material or shape known in the art. The nanoparticles typically have at least one dimension, such as length, width, height, and diameter, below 1,000 nm. In some embodiments, the nanoparticles have at least one dimension which is less than about 100 nm. In some embodiments, the nanoparticles have at least one dimension which is between about 10 nm and 300 nm.

The nanoparticles employed in accordance with the invention may have any shape and symmetry, and may display branched or net structures. Without being limited thereto, the nanoparticles may be symmetrical or unsymmetrical, may be elongated having rod-like shape, round (spherical), elliptical, pyramidal, disk-like, branch, network or have any irregular shape. It should be emphasized that for the purposes of products and application according to the invention, the term "particle" by no means suggests any one particular pre-defined shape.

The nanoparticles may be of a single material or a combination of at least one material(s). The material may be a metal, a metal oxide, a metal alloy, an insulator, a semiconductor material or any combination thereof. The nanoparticles are optically active at any wavelength ranging from the UV through the visible wavelengths and up to the near IR spectrum.

The nanoparticles may be defined by having a plurality of material regions which are defined by continuous segments of differing chemical compositions. The regions may be confined by a region of a different material, e.g., a metallic region confined by a different metal/metal alloy regions, or may be at a terminal region defining the ends of the nanoparticles.

The nanoparticle may similarly have the form of a continuous surface of one material, having thereon spaced apart regions (islands) of at least one other, e.g., metal/metal alloy material. For certain applications, the nanoparticles may preferably be selected amongst non-spherical nanoparticles, e.g., nanorods, having at least one elongated region and one or more end regions of the same or different material.

The nanoparticles may also be selected based on their optical or electronic properties. For example, in some embodiments, the nanoparticles may be selected to have an absorption onset in the visible, the visible and the near infrared range or even at deeper infrared then 3μ (micron), or to have the ability to (also or only) absorb in the UV range.

Without wishing to be bound by theory, different nanoparticle materials have different band gap energies and hence different optical properties and therefore may be employed in a variety of different applications. Thus, the nanoparticles may, for example, be selected to actively transform the wavelength or to change one or more optical property associated with a product of the invention. For example, the presence of silicon particles in a product of the invention allows light absorption at the UV and emission at the blue-green, to thereby increase protection from UV irradiation and to enhance efficiency.

In some embodiments, the nanoparticles are quantum dots (QD).

In some embodiments, heavy metals such as europium and terbium are embedded in the scintillator material.

The dopants used in a scintillator material according to the invention may be selected to provide an enhancement of a specific feature of the scintillators response.

"Functional Scintillators" as described herein are scintillators that are tailored to provide an enhancement of a specific feature of the scintillators response. Such scintillating materials may be doped with, e.g., ¹⁰B. Boron is known to have an unusually large cross section for the (η,α) reaction for the efficient detection of neutrons emitted from fissionable materials. ¹⁰B in powder form may be easily mixed into the base resin, together with the required scintillation dopants, to allow for printing of such scintillators. Also contemplated for neutron detection are ⁶Li-based materials.

Another possible doping strategy for creation of functional scintillators is doping with a high Z (atomic charge) material. Such doping enhances the photon interaction cross sections [PDG] making the scintillator an efficient γ detector. Such detectors are useful for example for Prompt Gamma-Ray Neutron Activation Analysis (PGNAA), a technique widely used for in-situ elemental analysis of bulk samples in several scientific disciplines including environmental, industrial, and health sciences, allowing to measure concentrations of carbon, nitrogen, and oxygen in bulk materials.

In some embodiments, the formulation for forming a scintillator according to the invention may be utilized in three-dimensional printing, which comprises:

(a) forming a pattern of a scintillator formulation, as defined, on a surface region of a substrate;

(b) forming a further pattern on top of the pattern formed on said surface, said further pattern may or may not be of the same shape and size, and may or may not have the same counter as the pattern formed on the surface region; the formulation forming this pattern may or may not be the same as the formulation forming the pattern on the surface;

(c) optionally forming one or more patterns on a previously formed pattern, wherein each of said one or more patterns may or may not be of the same shape and size, and may or may not have the same contour as a previous pattern, to obtain a three- dimensional pattern.

In some embodiments, process step (c) is repeated several times to obtain a three-dimensional pattern or object which may be detached from the substrate on which it has been prepared and utilized in a process of scintillation. In some embodiments, the patterning steps are repeated more than twice. In other embodiments, the patterning steps are repeated between 2 and several thousand times. In other embodiments, the patterning steps are repeated between 2 and several hundred times. In other embodiments, the patterning steps are repeated between 2 and 50,000 times. In other embodiments, the patterning steps are repeated between 2 and 50,000 times.

In other embodiments, the patterning steps are repeated between 2 and 40,000 times. In other embodiments, the patterning steps are repeated between 2 and 30,000 times. In other embodiments, the patterning steps are repeated between 2 and 20,000 times. In other embodiments, the patterning steps are repeated between 2 and 10,000 times. In other embodiments, the patterning steps are repeated between 2 and 5,000 times. In other embodiments, the patterning steps are repeated between 2 and 4,000 times. In other embodiments, the patterning steps are repeated between 2 and 3,000 times. In other embodiments, the patterning steps are repeated between 2 and 2,000 times. In other embodiments, the patterning steps are repeated between 2 and 1,000 times. In other embodiments, the patterning steps are repeated between 2 and 900 times. In other embodiments, the patterning steps are repeated between 2 and 800 times. In other embodiments, the patterning steps are repeated between 2 and 700 times. In other embodiments, the patterning steps are repeated between 2 and 600 times. In other embodiments, the patterning steps are repeated between 2 and 500 times. In other embodiments, the patterning steps are repeated between 2 and 400 times. In other embodiments, the patterning steps are repeated between 2 and 300 times. In other embodiments, the patterning steps are repeated between 2 and 200 times. In other embodiments, the patterning steps are repeated between 2 and 100 times. In other embodiments, the patterning steps are repeated between 2 and 90 times. In other embodiments, the patterning steps are repeated between 2 and 80 times. In other embodiments, the patterning steps are repeated between 2 and 70 times. In other embodiments, the patterning steps are repeated between 2 and 60 times. In other embodiments, the patterning steps are repeated between 2 and 50 times. In other embodiments, the patterning steps are repeated between 2 and 40 times. In other embodiments, the patterning steps are repeated between 2 and 30 times. In other embodiments, the patterning steps are repeated between 2 and 20 times. In other embodiments, the patterning steps are repeated between 2 and 10 times.

In other embodiments, the patterning steps are repeated between 10 and 90 times. In other embodiments, the patterning steps are repeated between 20 and 90 times. In other embodiments, the patterning steps are repeated between 30 and 90 times. In other embodiments, the patterning steps are repeated between 40 and 90 times. In other embodiments, the patterning steps are repeated between 50 and 90 times. In other embodiments, the patterning steps are repeated between 60 and 90 times. In other embodiments, the patterning steps are repeated between 70 and 90 times. In other embodiments, the patterning steps are repeated between 80 and 90 times.

In some embodiments, where the pattern or 3D-object to be fabricated by a method of the invention requires localization of a scintillator material or certain distribution of one or more scintillators in a pattern or object, the process of the invention may comprise a step of forming a pattern of a carrier material or of a first formulation of a scintillator material, followed by forming a further or subsequent pattern thereof with a scintillator material or a different scintillator material. Thus, the process of the invention may comprise the following:

(a) forming a first pattern of a carrier material on a surface region of a substrate; (b) forming a further pattern on top of said first pattern, said further pattern being formed of a scintillator formulation; and

(c) repeating steps (a) and (b); or repeating step (a); or repeating step (b) one or more times to obtain a three-dimensional pattern.

In some further embodiments, the process comprising:

(a) forming a first pattern of a scintillating material on a surface region of a substrate;

(b) forming a further pattern on top of said first pattern, said further pattern being of a further or different scintillating material; and

This process allows the manufacture of multilayered patterns or objects. For other purposes, the methods of the invention permit manufacture of arrays of scintillator materials, wherein each array being composed of a plurality of scintillators, each scintillator may be selected, independently to have a structural or functional parameter selected from size, shape, composition, scintillator material, scintillation capacity, and others.

In some embodiments, the process further comprises a step of treating the pattern or object fabricated under conditions selected from aqueous or organic washing, UV radiation, thermal treatment, polymerization, photopolymerization, laser sintering and others as may be known in the art.

The 3D-pattern or object may be fabricated by any printing process known in the art. Such printing technologies may include, ink-jet printing, digital light processing (DLP) and Fused Deposition Modeling (FDM via extrusion), and 3D powder printing. In some embodiments, the printing is achieved by ink-jet printing. As used herein, the term "ink-jet printing" refers to a non-impact method for producing a pattern by the deposition of ink droplets in a pixel-by-pixel manner onto the substrate. The ink-jet technology may be any ink-jet technology known in the art, including thermal ink-jet printing, piezoelectric ink-jet printing and continuous ink-jet printing.

In some embodiments, the printing method is FDM, wherein 3D printing is performed by the extrusion of a plastic filament through a thin nozzle, and constructing the pattern geometry layer by layer. The technique relies on printing using pre-existing plastic and/or any scintillator material, doped or un-doped, in fiber form or in any other geometry, as a printing medium.

Photopolymerization (PP) approaches using UV light may be utilized to selectively polymerize a liquid, either inside a resin bath, or in a printed or sprayed layer, similar to the method used in inkjet printers.

3D Powder printing relates to placing a layer of powder material onto which a liquid binder is printed. Thus, the scintillator can be made by printing a binder on powder of the scintillator material, thus forming a 3D scintillator. In some embodiments, the printed binder itself contains the scintillation formulation.

In another aspect, there is provided a three-dimensional scintillator material prepared according to a method of the invention.

Also contemplated are three-dimensional scintillating materials in a form selected from hollow structures, net-like structures, wires, cone-like structures, cylindrical structures, porous structures, branched structures, gas filled structures, and scintillator designs with features with are too small to be machined or produced by methods of the art.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 shows the absorption (solid) and emission (dashed) spectra for both PPO (black) and POPOP (gray), note the overlap of the PPO emission with the POPOP absorption.

Figs. 2A-2B provide: Fig. 2A- a typical spectrum of a reference sample (EJ-204, sample 8 in Table 1), and one of the printed samples of the invention. Fig. 2B- The printed sample achieved -30% efficiency as compared to a commercial scintillator material, proving the viability of the technique of the invention.

Fig. 3 shows a printed design according to the invention; note the mesh and the threaded top of the cylinder, which are almost impossible to create in a scintillator using standard production techniques. Fig. 4 demonstrates the efficiency measured for the different samples listed in Table I, compared to a commercial scintillator (EJ-204, sample 8 in Table 1).

DETAILED DESCRIPTION OF THE INVENTION

Scintillating materials are commonly used in charged particle detectors as detector elements due to their ease of manufacture, relatively low cost, and good timing resolution. The most common type of scintillator is the plastic scintillator, in which wavelength shifting dopants are embedded in a polystyrene matrix. A charged particle, traversing the polystyrene base excited some of the polymer molecules, causing them to emit UV light upon recombination. Typically, 2,5-diphenyloxazole (PPO) is used as a first step to down-convert the UV light to longer wavelength, peaking at 350nm. Due to the short absorption length of the polymer base in the UV range, a second wavelength shifting dopant, typically l,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), with an emission wavelength peak at 410 nm is used to further shift the emitted light to the visible range, while keeping the wavelength short enough to be effectively detected by the detection element (usually a photocathode).

The invention describes several technologies including laser sintering, Fused Deposition Modeling (FDM via extrusion), 3D powder printing and photopolymerization (PP). FDM 3D printing may be performed by the extrusion of a plastic filament through a thin nozzle, constructing geometry layer by layer.

Furthermore, PP approaches use UV light to selectively polymerize a liquid, either inside a resin bath, or in a sprayed and/or patterned layer, similar to the method used in inkjet printers is herein described.

The invention discloses both FDM and PP printing to allow direct printing of scintillator materials. FDM allows printing unclad scintillating fibers as the filament for the printing, while in the PP approach the doping of the base resin used in the printing with various wavelength shifting compounds.

The doped sample has shown significant florescence under UV exposure, indicating that the dopant may be incorporated into the polymer matrix. Additionally, the doped sample has shown increased response to a radioactive source (i.e. scintillation).

The invention further provides a method for the manufacture of scintillator materials in the form of plastic filaments In order to test the applicability of additive manufacturing techniques to the manufacture of scintillators, the inventors have designed a formulation, which is UV- polymerizable, e.g., based on acrylic monomers, doped with different fractions of scintillating and wavelength shifting materials.

Ink preparation

The scintillator materials may be printed from ink formulations comprising, for example:

(g) 1.5% PPO, 0.08% POPOP, 0.5% TPO, 97.92% ethoxylated (30) bisphenol A diacrylate;

(h) 1.5% PPO, 0.08% POPOP, 15% naphtalene, ethoxylated (15) TMPTA, 0.5% TPO;

(i) 1% PPO, 0.05% POPOP, 3% naphtalene, 4.8% TPO, 91.15 ethoxylated (15) TMPTA.

Curable formulations were composed of 99.5 wt. % SR9035 (Sartomer, Arkema) as the monomer and 0.5 wt. % Lucirin TPO (BASF) as the photoinitiator.

The formulations were generally stirred (in some embodiments for a period of 30 min in a water bath at 60°C) until all components were added. The formulations were treated with the scintillator components: PPO, POPOP and naphthalene, at various concentrations (see Table I).

In some cases, the final formulations were further stirred for 1 h in a water bath at 60°C.

Sample Layer Naphtalene PPO POPOP Efficiency Comments

Number Thickness Content Content Content (%)

(um) (%) (%) (%)

1 127 - 1 0.05 0.6 -

2 127 3 1 0.05 1.2 -

3 127 3 1 0.05 1.5 - 4 25 3 1 0.05 2.4 -

5 25 15 1.5 0.08 28 -

6 127 15 1.5 0.08 27 -

7 - - - - 0 Clear

8 - - - - 100 EJ-204

Table I- formulations prepared according to the invention in comparison to available formulations.

The formulations were printed into a pattern and polymerized into the required shape (a cylinder 6.3mm in height and 20mm diameter) using an Asiga Pico Plus 39 printer (Asiga, Australia). Two different layer thicknesses were tested, 25 μπι and 127 μπι, in order to test the effect of the interface between printed layers on the light collection efficiency. The printed output was compared to reference samples of clear PMMA (plexiglas) and EJ-204 scintillator (Eljen Ltd.) of the same dimensions.

All samples were tested in a light tight box using both background cosmic radiation and a 15.1 KBq 90Sr source. The samples were matched to a photomultiplier (Hamamatsu R647) operated at 1 kV, through a 100 mm Perspex light guide. Light output was readout from the PMT using a CAEN charge integrating digitizer (VI 720) and histograms were recorded to a PC. A typical histogram from the EJ-204 sample is shown in Fig. 2A. The efficiency is demonstrated in comparison to a commercial product in Fig. 2B.

In addition, several prints were made of scintillators with more complex geometries, in order to demonstrate that such geometries may be printed using he formulated materials. Since these geometries were almost impossible to machine, a comparison to a standard sample was not performed. In particular, geometry relevant for the Frozen Spin Active Target at the Crystal Ball detector at MAMI5 was printed, consisting of a thin walled, hollow cylinder, capped with a mesh to allow for the flow of super-fluid helium, and including external grooves for coupling to wavelength shifting fibers.

Fig. 3 shows a printed design according to the invention; note the mesh and the threaded top of the cylinder, which are almost impossible to create in a scintillator using standard production techniques. FDM Printing of Scintillators

Methods of the invention as herein described utilized the Fused Deposition Modeling techniques for scintillator printing by using exiting scintillator plastics, in fiber form, as a printing medium. The potential benefit of this technique is in that these fibers constructed from material, which is known to operate in the desired manner, the invention focuses on the ability to accurately print and utilize the available material.

The invention further describes the operating parameters (temperature, speed, etc.) changes required in the 3D printer that will allow for printing of these materials (since, for example, the softening/melting points of scintillators are widely different from those of ABS plastic). Further, using two different materials in the printing, where the second material is either an opaque plastic such as ABS (for segmentation of the final product) or a wavelength-shifting plastic (used as part of common detector configurations and typically glued in specially made grooves) is herein described. The FDM material filament can be made by solution casting or extrusion as known in the plastic industry compounding processes.

Photo-polymerization Printing - Scintillator Material Design

Under this printing technology, various dopants and concentrations may be used in order to optimize the scintillation and light collection properties of the resin used in PP printers. The use may involve various monomers and resins, provided by several companies, and dope them with varying concentrations of PPO and secondary wavelength shifters. As the photopolymers strongly absorb in the UV and short visible wavelength, care must be taken to shift as much of the available light into the visible range, where absorption is less of a problem. Suitable resin (monomers/oligomers/polymers-dopant combinations may be photopolymerized and each sample characterized for its optical and scintillation properties.

Quantum dots may also be used in order to tailor the emission wavelength to match both the optical properties of the polymer base and the quantum efficiency of typical detector, such as Photo Multplier Tubes.

The 3D fabrication can take place by various technologies in which exposure to radiation (UV, IR etc.) leads to localized polymerization. Among these are DLP, inkjet- UV and laser curing. Functional Scintillators

Scintillators doped with a ¹⁰B may be utilized in a variety of applications. Boron is known to have an unusually large cross section for the (η,α) reaction [Boron Cite], making it a good dopant. ¹⁰B in powder form may be easily mixed into the base resin, together with the required scintillation dopants, to allow for printing of such scintillators.

Another possible doping strategy for creation of functional scintillators is doping with a high Z (atomic charge) material. Such doping enhances the photon interaction cross sections [PDG] making the scintillator an efficient γ detector. Such detectors are useful for example for Prompt Gamma-Ray Neutron Activation Analysis (PGNAA), a technique widely used for in-situ elemental analysis of bulk samples in several scientific disciplines including environmental, industrial, and health sciences, allowing to measure concentrations of carbon, nitrogen, and oxygen in bulk materials. Such measurements are also performed in the detection of explosive compounds (nitrogen content) in many airports and docks.

Claims

CLAIMS:

1. A process for fabricating a three-dimensional scintillator material, the process comprising:

(1) on a surface region forming a pattern of a scintillator formulation, the formulation comprising at least one pre -polymer polymerizable into a polymer and at least one photoinitiator;

(2) affecting polymerization of said at least one pre -polymer forming said pattern;

(3) forming a further pattern on the polymerized pattern;

(4) affecting polymerization of said further pattern; and

wherein the scintillator formulation comprises:

1. a pre -polymer polymerizable to adapt scintillation properties, or

2. The process according to claim 1, wherein the scintillator formulation comprises at least one pre-polymer polymerizable into a desired polymer, at least one photoinitiator and one or more phosphor materials.

3. The process according to claim 2, wherein the phosphor materials are selected amongst primary and secondary phosphors.

4. The process according to claim 3, wherein the primary phosphor is selected amongst organic phosphors capable of absorbing energy from the scintillator material.

5. The process according to claim 3, wherein the secondary phosphor is selected amongst organic phosphors capable of shifting a wavelength of the photons received from the primary phosphor to a different wavelength.

6. The process according to claim 1 , wherein the scintillator material is selected to emit light when excited by ionizing radiation and/or incoming charged particle.

7. The process according to claim 6, wherein the scintillator material is selected amongst plastic scintillators, organic scintillators, inorganic scintillators, ceramic scintillators, liquid scintillators, base scintillators and glass scintillators.

8. The process according to claim 6, wherein the scintillator material is selected from:

(a) polyethylene naphthalate, polyvinyl naphthalene, polymethylmethacrylate (PMMA), polyvinyl xylene (PVX), polymethyl styrenes, 2,4-dimethyl styrene, 2,4,5- trimethyl styrene, polyvinyl diphenyl, ethoxylated trimethylolpropanetriacrylate (ethoxylated TMPTA), ethoxylated bisphenol A diacrylate, polyvinyl tetrahydronaphthalene ;

(b) aromatic hydrocarbons;

(c) organometallic compounds;

(d) alkali metal halides;

(e) inorganic alkali halides;

(f) non-alkali materials;

(g) inorganic scintillators;

(h) glass scintillators;

(i) polyphenyl hydrocarbons;

(j) tungstate and gadolinium based materials;

(k) ceramic scintillators;

(1) zinc sulfide based materials; and

9. The process according to claim 8, wherein the aromatic hydrocarbons are selected from anthracene, stilbene, naphthalene and polyvinyltoluene.

10. The process according to claim 8, wherein the organometallic compound is triphenylbismuth. ;

11. The process according to claim 8, wherein the alkali metal halide is sodium iodide or sodium iodide doped with thallium.

12. The process according to claim 8, wherein the inorganic alkali halides are selected from Csl, optionally doped with Na; Csl; CsF; KI optionally doped with Tl; and Lil optionally doped with Eu.

13. The process according to claim 8, wherein the non-alkali materials are selected from BaF2, CaF2 optionally doped with Eu, ZnS optionally doped with Ag, CaWO/_t, CdW0₄ and YAG optionally doped with Ce (Y₃Al₅0₁₂(Ce)).

14. The process according to claim 8, wherein the polyphenyl hydrocarbons are selected from oxazole, oxadiazole aryls, n-terphenyl (PPP), 2,5-diphenyloxazole (PPO), l,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), 2-phenyl-5-(4-biphenylyl)-l,3,4- oxadiazole (PBD), 1,3,3-Trimethyl-l-phenylindan (TMPI) and 2-(4'-tert-butylphenyl)- 5-(4"-biphenylyl)-l,3,4-oxadiazole (B-PBD).

15. The process according to claim 8, wherein the tungstate and gadolinium based materials are selected from radmium tungstate, terbium-doped gadolinium oxysulphide (Gd2(¾S), cadmium tungstate (CdWC>4 or CWO), terbium activated gadolinium and calcium tungstate (CaWO/_t).

16. The process according to claim 3, wherein each of the primary and secondary phosphors is selected from polyphenyl hydrocarbons.

17. The process according to claim 16, wherein the polyphenyl hydrocarbons are selected from s oxazole and oxadiazole aryls, n-terphenyl (PPP), 2,5-diphenyloxazole (PPO), l,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), 2-phenyl-5-(4-biphenylyl)- 1,3,4-oxadiazole (PBD), 1,3,3-Trimethyl-l-phenylindan (TMPI) and 2-(4'-tert- butylphenyl)-5-(4"-biphenylyl)-l,3,4-oxadiazole (B-PBD).

18. The process according to claim 8, wherein the primary and secondary phosphors are selected from PPO and POPOP.

19. The process according to claim 8, wherein the primary and secondary phosphors are TMPI.

20. The process according to claim 1, wherein the scintillator formulation comprises a pre -polymer of an aromatic polymer, such polymer being selected from polyethylene naphthalate, polyvinyl xylene (PVX), polymethyl styrenes, 2,4-dimethyl styrene, 2,4,5- trimethyl styrene, polyvinyl diphenyl, polyvinyl naphthalene, ethoxylated bisphenol A diacrylate, bisphenol A and polyvinyl tetrahydronaphthalene.

21. The process according to claim 20, wherein the polymer is derived from ethoxylated bisphenol A diacrylate or dimethylacrylate.

22. The process according to claim 3, wherein the phosphor materials are selected from aromatic hydrocarbons.

23. The process according to claim 22, wherein the aromatic hydrocarbons are selected from anthracene (C₁4H₁₀), stilbene (C₁4H₁2), naphthalene (CioHg) and polyvinyltoluene (PVT).

24. The process according to claim 3, wherein the phosphor materials are selected from polyphenyl hydrocarbons.

25. The process according to claim 24, wherein the polyphenyl hydrocarbons are selected from oxazole, oxadiazole aryls, n-terphenyl (PPP), 2,5-diphenyloxazole (PPO), l,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), 2-phenyl-5-(4-biphenylyl)-l,3,4- oxadiazole (PBD), 1,3,3-Trimethyl-l-phenylindan (TMPI) and 2-(4'-tert-butylphenyl)- 5-(4"-biphenylyl)-l,3,4-oxadiazole (B-PBD).

26. The process according to claim 25, wherein the phosphor materials are selected from TMPI, p-terphenyl, PBD, butyl PBD, PPO and POPOP.

27. The process according to claim 1, wherein the scintillator formulation is selected from:

(b) PPO, POPOP, naphtalene, ethoxylated TMPTA and TPO;

(c) PPO, POPOP, naphtalene, TPO and ethoxylated TMPTA;

(d) TMPI, naphthalene, TPO and ethoxylated TMPTA;

(e) TMPI, naphtalene, ethoxylated TMPTA and TPO; and

(f) TMPI, TPO and ethoxylated bisphenol A diacrylate or dimethylacrylate.

28. The process according to claim 1, wherein scintillator formulation comprises a pre -polymer material selected from monomers and oligomers, the polymerization there being achieved by an initiator.

29. The process according to claim 28, wherein the initiator is a photoinitiator.

30. The process according to claim 24, wherein the photoinitiator is 2,4,6- Trimethylbenzoyl-diphenyl-phosphineoxide (TPO) .

31. The process according to claim 1, wherein the concentration of each of the at least one photoinitiator and one or more phosphor materials is at most 10% w/w.

32. The process according to claim 2, wherein at least one of the phosphor materials is a wavelength shifter selected amongst optically active nano- or micro-particles.

33. The process according to claim 2, wherein at least one of the phosphor materials is a semiconductor material capable of shifting wavelength from short wavelengths to longer wavelengths.

34. The process according to claim 33, wherein the semiconductor material is selected amongst core/shell semiconductor nanocrystals.

35. The process according to claim 34, wherein the core/shell semiconductor material is selected from CdSe/ZnSe, CdSe/CdS, CdSe/ZnS and InP/ZnS.

36. The process according to claim 32, wherein the nanoparticles are quantum dots (QD).

37. The process according to claim 1, wherein the scintillator formulation is doped with ¹⁰B-based material or ⁶Li-based materials.

38. The process according to any one of the preceding claims, wherein the pattern formed in step (3) or any further patterning step is of the same shape and size as the pattern previously formed.

39. The process according to any one of claims 1 to 38, wherein the pattern formed in step (3) or any further patterning step is of a different shape and size as compared to the pattern previously formed.

40. The process according to any one of the preceding claims, wherein the pattern formed in step (3) or any further patterning step is of the same material composition as the pattern previously formed.

41. The process according to any one of claims 1 to 38, wherein the pattern formed in step (3) or any further patterning step is of a different material composition as compared to the pattern previously formed.

42. The process according to any one of the preceding claims, wherein the patterning steps are repeated between 2 and 50,000 times.

43. The process according to claim 1, further comprising the step of detaching the 3D object or pattern from the substrate on which it has been prepared.

44. The process according to claim 43, further comprising the step of treating the pattern or object fabricated prior to or after detachment from the substrate under conditions selected from aqueous or organic washing, UV radiation, thermal treatment, polymerization, photopolymerization and laser sintering.

45. The process according to any one of the preceding claims, wherein the 3D- pattern or object is fabricated by a printing process selected from ink-jet printing, digital light processing (DLP), Fused Deposition Modeling (FDM via extrusion), and 3D powder printing.

46. The process according to claim 45, wherein printing is achieved by ink-jet printing.

47. The process according to claim 45, wherein printing is achieved by FDM.

48. A three-dimensional scintillator material prepared according to the process of any one of claims 1 to 47.

49. A three-dimensional scintillating material in form selected from a hollow structure, a net-like structure, a wire, a cone-like structure, a cylindrical structure, a porous structure, a branched structure, a gas filled structure, and a scintillator design having one or more feature being of a micron or submicron size.