News Column

Patent Issued for Polymer Composite Based Thermal Neutron Detectors

August 20, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Penumadu, Dayakar (Knoxville, TN); Sen, Indraneel (Kolkata, IN); Uppal, Rohit (Knoxville, TN), filed on March 14, 2013, was published online on August 5, 2014.

The assignee for this patent, patent number 8796631, is University of Tennessee Research Foundation (Knoxville, TN).

Reporters obtained the following quote from the background information supplied by the inventors: "Scintillators are materials that can emit light upon absorbing radiation or energy from ionizing radiation. The research, defense, and industrial communities use scintillators as radiation detectors in a variety of applications, such as, but not limited to, imaging, nuclear power generation, detection of special nuclear materials, and homeland security.

"Detectors for the detection of neutrons in the presence of photons can use many different methods to discriminate signals that originate from either neutrons or photons. As an example, use of .sup.3He in a pressurized tube for neutron detection permits discrimination of neutrons from photons by pulse amplitude. These detectors fail to correctly discriminate neutrons from photons only about one per 50,000 events. There are a few other scintillation materials that have slightly different light output characteristics when the energy is deposited by a photon or by a charged particle. This permits pulse shape discrimination (PSD) with sophisticated electronics. Another approach is to employ detectors with a very small probability of interaction for photons and a relatively high probability of interaction for neutrons. Some detectors of this type can achieve essentially 100% discrimination if charged particles are directly detected.

"There is an ongoing need in the research, defense and industrial communities for scintillators that demonstrate improved capabilities in terms of light output, detection efficiency, high count rate capability, better time resolution of events, and, for neutron scintillators, fewer false counts due to gamma radiation. Especially in view of the imminent shortage of .sup.3He, there is a need for an inexpensive replacement technology for thermal neutron detection, particularly for replacement technologies that provide easy to make detectors that can have various geometries and/or sizes."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "In some embodiments, the presently disclosed subject matter provides a polymer composite comprising: a polymeric matrix material, wherein the matrix material comprises an organic polymer, copolymer or blend thereof, and wherein the matrix material comprises at least one polymer or copolymer comprising an aromatic moiety; a neutron capture agent distributed within the matrix material, optionally wherein the neutron capture agent comprises a .sup.6Li compound; and an organic or inorganic luminescent fluor distributed within the matrix material.

"In some embodiments, the matrix material comprises a polymer, copolymer or blend thereof comprising an aromatic moiety having a higher quantum yield than the quantum yield of phenyl. In some embodiments, the matrix material comprises at least one aromatic moiety selected from the group comprising naphthylene, anthracene, fluorene, terphenyl, phenanthrene, pyridine, furan, and thiophene.

"In some embodiments, the matrix material comprises a polymer or copolymer selected from the group comprising a polyester, a polyamide, a polyether, a polyimide, a polythioester, a polyarylvinyl, a vinylpolyether, a vinylpolyester, a vinylpolyamide, and a vinylpolythioester. In some embodiments, the matrix material comprises a polyester. In some embodiments, the polyester is selected from the group comprising polyethylene naphthalate (PEN), polytrimethylene naphthalate (PTN), poly(9H-fluorene-9,9-dimethanol malonate), poly(9H-fluorene-9,9-dimethanol terephthalate), and poly(4,4'-(9-fluorenylidene)-diphenol terephthalate).

"In some embodiments, the matrix material comprises a derivatized polyacrylic or polyalkylacrylic acid, wherein acid groups of the polyacrylic or polyalkylacrylic acid are derivatized to form ester, thioester or amide linked side chains, wherein the side chains comprise aromatic groups.

"In some embodiments, the neutron capture agent is non-hygroscopic. In some embodiments, the neutron capture agent comprises .sup.6LiF micro- or nanoparticles. In some embodiments, the micro- or nanoparticles are 3.2 microns or smaller. In some embodiments, the nanoparticles are about 200 nm or smaller, and/or in some embodiments, about 100 nm or smaller.

"In some embodiments, the organic or inorganic luminescent fluor is selected based on acceptor donor resonance and/or is selected from the group comprising 2,5-diphenyloxazole (PPO), 1,4-bis-(5-phenyloxazol-2-yl) (POPOP), anthracene, 9,9,9',9',9'',9''-hexakis(octyl)-2,7',2',7''-trifluorene, n-terphenyl, 2-biphenyl-5-phenyl-1,3-oxazole, 2-biphenyl-5(.alpha.-naphthyl)-1,3-oxazole, 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole, 2-(4'-tert-butylphenyl)-5-(4''-biphenylyl)-1,3,4-oxadiazole, n-bis-(o-methylstyryl)-benzene 1,4-di-(5-phenyl-2-oxazolyl)-benzene, conjugated polymeric and oligomeric dyes, metal organic framework dyes, quantum dots and two-photon absorber semiconductor fluors.

"In some embodiments, the composite has a ratio of matrix material to neutron capture agent of between about 3:1 by weight and about 1:2 by weight. In some embodiments, the composite comprises about 5% or less by weight of the organic or inorganic luminescent fluor. In some embodiments, the composite comprises .sup.6Li salicylate or .sup.6LiF as a neutron capture agent and poly(2-vinylnaphthalene) (P2VN) as a matrix material. In some embodiments, the composite comprises .sup.6LiF as a neutron capture agent and PEN as a matrix material.

"In some embodiments, the presently disclosed subject matter provides a film comprising a polymer composite comprising: a polymeric matrix material, wherein the matrix material comprises an organic polymer, copolymer or blend thereof, and wherein the matrix material comprises at least one polymer or copolymer comprising an aromatic moiety; a neutron capture agent distributed within the matrix material, wherein the neutron capture agent comprises a .sup.6Li compound; and an organic or inorganic luminescent fluor distributed within the matrix material.

"In some embodiments, the film has a thickness of about 500 microns or less. In some embodiments, the film has a thickness of about 220 microns or less. In some embodiments, the film has a thickness of about 50 microns or less. In some embodiments, the film is a biaxially or uniaxially stretched film. In some embodiments, the film is thermally annealed. In some embodiments, the thermal annealing is performed at a temperature between about 150.degree. C. and about 180.degree. C.

"In some embodiments, the matrix material comprises a polymer or copolymer selected from the group comprising a polyester, a polyamide, a polyether, a polyimide, a polythioester, a vinylpolyether, a vinylpolyester, a vinylpolyamide, and a vinylpolythioester. In some embodiments, the matrix material is a polyester. In some embodiments, the polyester is selected from the group comprising polyethylene naphthalate (PEN), polytrimethylene naphthalate (PTN), poly(9H-fluorene-9,9-dimethanol malonate), poly(9H-fluorene-9,9-dimethanol terephthalate), and poly(4,4'-(9-fluorenylidene)-diphenol terephthalate).

"In some embodiments, the neutron capture agent is non-hygroscopic. In some embodiments, the neutron capture agent comprises .sup.6LiF micro- or nanoparticles. In some embodiments, the matrix material comprises PEN, the neutron capture agent comprises .sup.6LiF micro- or nanoparticles and the film is a stretched and/or thermally annealed film.

"In some embodiments, the film comprises a polymer composite having a ratio of matrix material to neutron capture agent of between about 3:1 and about 1:5 by weight. In some embodiments, the film comprises a polymer composite comprising about 49.5% by weight PEN, about 49.5% by weight .sup.6LiF, and about 1% by weight 9,9,9',9',9'',9''-hexakis(octyl)-2,7',2',7''-trifluorene. In some embodiments, the film comprises a polymer composite comprising about 70% by weight PEN, about 25% by weight .sup.6LiF, and about 5% by weight PPO/POPOP.

"In some embodiments, the film has a neutron count rate per mg of .sup.6Li of between about 4 and about 12 counts per second (cps).

"In some embodiments, the film is prepared by: providing a mixture of the matrix material, a neutron capture agent, and a luminescent fluor; and hot pressing or extruding the mixture to form the film. In some embodiments, providing the mixture comprises preparing micro- or nanoparticles of .sup.6LiF; and mixing the micro- or nanoparticles with the matrix material and the luminescent fluor.

"In some embodiments, the presently disclosed subject matter provides an apparatus for detecting neutron radiation, wherein the apparatus comprises a photon detector and a polymer composite comprising: a polymeric matrix material, wherein the matrix material comprises an organic polymer, copolymer or blend thereof, and wherein the matrix material comprises at least one polymer or copolymer comprising an aromatic moiety; a neutron capture agent distributed within the matrix material, wherein the neutron capture agent comprises a .sup.6Li compound; and an organic or inorganic luminescent fluor distributed within the matrix material. In some embodiments, the polymer composite is in the form of a film having a thickness of about 500 microns or less.

"In some embodiments, the presently disclosed subject matter provides a method for detecting neutron radiation, wherein the method comprises: providing a polymer composite comprising a polymeric matrix material, wherein the matrix material comprises an organic polymer, copolymer or blend thereof, and wherein the matrix material comprises at least one polymer or copolymer comprising an aromatic moiety; a neutron capture agent distributed within the matrix material, wherein the neutron capture agent comprises a .sup.6Li compound; and an organic or inorganic luminescent fluor distributed within the matrix material; disposing the polymer composite in the path of a beam of radiation, wherein the matrix and the luminescent fluor of the polymer composite emits light when the composite absorbs said radiation; and detecting neutron radiation by detecting the light emitted by the composite, wherein the detecting discriminates between neutron and gamma radiation.

"In some embodiments, providing a polymer composite of claim 1 comprises providing a film of the polymer composite. In some embodiments, providing the film comprises providing a biaxially or uniaxially stretched and/or thermally annealed film.

"In some embodiments, the presently disclosed subject matter provides a method of making a film or molded coupon comprising a polymer composite comprising a polymeric matrix material, wherein the matrix material comprises an organic polymer, copolymer or blend thereof, and wherein the matrix material comprises at least one polymer or copolymer comprising an aromatic moiety; a neutron capture agent distributed within the matrix material, wherein the neutron capture agent comprises a .sup.6Li compound; and an organic or inorganic luminescent fluor distributed within the matrix material, wherein the method comprises: providing micro- or nanoparticles of the neutron capture agent; mixing the micro- or nanoparticles with the matrix material and the luminescent fluor to form a mixture; and pressing and heating the mixture to form the film or molded coupon.

"In some embodiments, the matrix material is powdered prior to mixing with the micro- or nanoparticles and the luminescent fluor. In some embodiments, the mixture is ground into a powder and the powder is sieved and/or blended to obtain a homogenous mixture. In some embodiments, the mixture is sieved through a 500 .mu.m or smaller sieve.

"In some embodiments, the neutron capture agent is .sup.6LiF micro- or nanoparticles that are 3.2 microns or smaller. In some embodiments, providing the neutron capture agent comprises titrating .sup.6Li enriched lithium hydroxide with hydrofluoric acid to provide precipitated .sup.6LiF particles, and collecting the precipitated particles. In some embodiments, the neutron capture agent is .sup.6LiF nanoparticles that are about 200 nm or about 100 nm or smaller. In some embodiments, the .sup.6LiF nanoparticles are provided by ball milling (e.g., cryo ball milling) larger particles.

"In some embodiments, pressing and heating the mixture comprises heating the mixture to a temperature of about 260.degree. C. to about 300.degree. C. In some embodiments, the method of making a film or molded coupon further comprises stretching the film. In some embodiments, the stretching is performed at a temperature of between about 120.degree. C. and about 150.degree. C. In some embodiments, the stretching is biaxial or uniaxial stretching. In some embodiments, the method further comprises thermally annealing the film. In some embodiments, the annealing is performed at a temperature between about 150.degree. C. and about 180.degree. C.

"In some embodiments, the presently disclosed subject matter provides a method of making a polymer composite comprising a polymeric matrix material, a neutron capture agent and an organic or inorganic luminescent fluor, wherein the method comprises solution casting a solution comprising the matrix material, the neutron capture agent, and the luminescent fluor. In some embodiments, the solution comprises tetrahydrofuran as a solvent.

"In some embodiments, the presently disclosed subject matter provides a fiber comprising a polymer composite comprising: a polymeric matrix material, wherein the matrix material comprises an organic polymer, copolymer or blend thereof, and wherein the matrix material comprises at least one polymer or copolymer comprising an aromatic moiety; a neutron capture agent distributed within the matrix material, wherein the neutron capture agent comprises a .sup.6Li compound; and an organic or inorganic luminescent fluor distributed within the matrix material.

"In some embodiments, the fiber is prepared by electrospinning, extrusion, meltblowing, and/or meltdrawing. In some embodiments, the fiber has an average diameter between about 200 nm and about 500 microns. In some embodiments, the fiber is prepared from a polymer composite comprising .sup.6Li salicylate or .sup.6LiF as the neutron capture agent and polystyrene (PS) or a blend of poly(2-vinylnapthalene) (P2VN) and polystyrene (PS) as the matrix material. In some embodiments, the presently disclosed subject matter provides a fiber mat comprising the fiber comprising the polymer composite.

"Accordingly, it is an object of the presently disclosed subject matter to provide polymer composites (including films, fibers and fiber mats thereof) and to fabricate detectors comprising the composites that efficiently detect thermal neutrons and that can discriminate neutron from gamma radiation.

"An object of the presently disclosed subject matter having been stated hereinabove, and which is achieved in whole or in part by the presently disclosed subject matter, other objects will become evident as the description proceeds hereinbelow."

For more information, see this patent: Penumadu, Dayakar; Sen, Indraneel; Uppal, Rohit. Polymer Composite Based Thermal Neutron Detectors. U.S. Patent Number 8796631, filed March 14, 2013, and published online on August 5, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8796631.PN.&OS=PN/8796631RS=PN/8796631

Keywords for this news article include: Fluorenes, Nanoparticle, Nanotechnology, Organic Chemicals, Emerging Technologies, Aromatic Polycyclic Hydrocarbons, University of Tennessee Research Foundation.

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Source: Journal of Engineering


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