PLASTIC SCINTILLATOR BASED ON AN ORGANIC POLYADDITION PRODUCT

Abstract

Provided are transparent molded bodies for use as a scintillator for measuring the type and intensity of ionizing and non-ionizing radiation, including an organic polymer and, if desired, at least one additive which, under the influence of at least one of ionizing and non-ionizing radiation, emits scintillation radiation in the range from UV to IR light, the aim is to improve optical and mechanical properties, robustness against environmental influences and the manufacturability. This was achieved in that the organic polymer at least in part contains a polyaddition product of polyfunctional isocyanates and one or more polyfunctional hardener components.

Claims

1. A transparent molded body for use as a plastic scintillator for measuring the type and intensity of at least one of ionizing and non-ionizing radiation, comprising an organic polymer which, under the influence of at least one of ionizing and non-ionizing radiation, emits scintillation radiation in the range from UV to IR light, wherein the organic polymer, at least in part, contains a polyaddition product of polyfunctional isocyanates with at least one of one or more polyfunctional hardener components and an additive.

2. The molded body as claimed in claim 1, wherein the body comprises; 10% by weight to 99.99% by weight of a polyaddition product of polyfunctional isocyanates with at least one of polyfunctional alcohols, phenols, amines, amino alcohols and aminophenols, 0.01% by weight to 90% by weight of other organic substances scintillating when irradiated with at least one of ionizing radiation n 0.01% by weight to 90% by weight of an additive which scintillates when irradiated with non-ionizing radiation, 0% by weight to 5% by weight of substances for stabilizing at least one of the polyaddition product and further auxiliaries.

3. The molded body as claimed in claim 1, wherein the additives which scintillate when irradiated with at least one of ionizing and non-ionizing radiation are at least partially covalently incorporated in or are bound to the polymer structure.

4. The molded body as claimed in claim 1, wherein diisocyanates are used as polyfunctional isocyanates, or diisocyanates having NCO groups on aliphatic carbon atoms.

5. The molded body as claimed in claim 1, wherein the di isocyanates having NCO groups on aliphatic carbon atoms with aromatic or aliphatic rings are used.

6. The molded body as claimed in claim 1, wherein diisocyanates used are selected from the group comprising isophorone diisocyanate, 1,3-bis(1-isocyanato-1-methylethylbenzene, hexamethylene diisocyanate, 4,4-methylenebis(cyclohexyl isocyanate) as at least one of trans-trans, cis-cis and cis-trans isomer, 1,3-bis(isocyanatomethyl)cyclohexane as at least one of trans-trans. cis-cis, cis-trans isomer and mixtures of these diisocyanates.

7. The molded body as claimed in claim 1, wherein the isocyanates used are the trimerization products of diisocyanates having NCO groups on at least one of aliphatic carbon atoms and reaction products thereof with a stoichiometric deficit of di- or at least one of trifunctional alcohols, amines and amino alcohols (prepolymers).

8. The molded body as claimed in claim 1, wherein the polyfunctional alcohols used are aliphatic or cycloaliphatic diols having 2 to 20 carbon atoms.

9. The molded body as claimed in claim 1, wherein the polyfunctional alcohols used are the reaction products of aromatic dihydroxy compounds with on average 1 to 20 mol of at least one of ethylene oxide and propylene oxide.

10. The molded body as claimed in claim 1, wherein the dihydroxy compound is selected from the group comprising bisphenol A ethoxylate, bis(hydroxyethyl) terephthalate and hydroquinone bis(2 hydroxy ethyl) ether and mixtures thereof.

11. The molded body as claimed in claim 1, wherein the polyfunctional amines used are at least one of diamines and triamines having primary or secondary amino groups.

12. The molded body as claimed in claim 1, wherein the polyfunctional amine used is at least one of an aliphatic diamine having 2 to 8 carbon atoms and bis(2-aminoethyl)amine.

13. The molded body as claimed in claim 1, wherein the stoichiometric ratio of the NCO groups to the sum of the OH groups and primary amino groups is between 0.9 and 1.1, especially between 0.95 and 1.05.

14. The molded body as claimed in claim 1, wherein the isocyanates are present at 0% by weight to 20% by weight, based on the isocyanates, these being present as trifunctional compounds.

15. The molded body as claimed in claim 1, wherein the modifiers present in the polymer chain are hydroxymethylation products of at least one of aromatic scintillators and lithium salts of polyhydroxycarboxylic acids.

16. The molded body as claimed in claim 1, wherein the additives, which scintillate on irradiation with at least one of ionizing and non-ionizing radiation, are polynuclear aromatic compound/s, preferably selected from the group comprising 9,10-diphenylanthracene, 2,5-diphenyloxazole (PPO), p-terphenyl; 1,4-bis(5-phenyloxazol-2-yl)benzene (POPOP); 1,4-bis(2-methylstyryl)benzene (bis-MSB); napthalene; biphenyl; 1,1,4,4-tetraphenylbutadiene; diphenylstilbene; 2-(1-naphthyl)-5-phenyloxazole (-NPO); 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD); 2,5-di(4-biphenyl)oxazole (BBO); 1,4-di(2-(5-p-tolyloxazolyl))benzene (TOPOT); 1,4-di(2-(4-methyl-5-phenyloxazolyl))benzene (BiMePOPOP); 2-(diethoxyphenyl)-5-phenyl-1,3,4-oxadiazole (DF); 2-phenyl-5-(4-biphenyl)-1,3-oxazole (BPO); 1,3,5-triphenyl-2-pyrazoline (3P-2); 1,2-di(4-biphenylol)ethylene (BBE); 1-(4-biphenylyl)-2--naphthylethylene (BNE); 2,5-bis(5-tert-butylbenzoxazol-2-yl)thiophene; 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole; trans,trans-1,4-diphenyl-1,3-butadiene.

17. The molded body as claimed in claim 1, wherein the primary or secondary scintillators are present in amounts from 0.01% by weight to 90% by weight or in amounts from 0.05% by weight to 5% by weight.

18. The molded body as claimed in claim 1, wherein the substance scintillating on irradiation with neutrons is lithium salts, or lithium carbonate, in amounts from 0.05% by weight to 5% by weight.

19. The molded body as claimed in claim 1, wherein free radical scavengers are present as stabilizer in amounts from 0.1% by weight to 5% by weight.

20. The molded body as claimed in claim 1, wherein an impact modifier is present as further auxiliary.

21. A process for producing a molded body as claimed in claim 1, wherein auxiliaries and additives are dissolved in the hardener component, the hardener component and isocyanate component are mixed, if required a curing catalyst is added and the mixture is allowed to react in a form of the desired geometry until hardening.

22. A radiation measuring device comprising a molded body as claimed in claim 1 as a scintillator.

Description

BRIEF DESCRIPTION

[0046] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0047] FIG. 1 shows a simplified schematic representation of the scintillation process; and

[0048] FIG. 2 shows the structure of such radiation measuring devices.

DETAILED DESCRIPTION

[0049] The simplified schematic representation of the scintillation process is shown in FIG. 1. This includes (1) non-ionizing radiation and (2) ionizing radiation. After excitation of atoms or molecules of the scintillating material (3), photons (4) are emitted.

[0050] Examples of scintillating and wavelength-shifting substances, to which embodiments of the invention is not restricted, are listed in the following table: [0051] Naphthalene [0052] Biphenyl [0053] TP p-terphenyl 1,1,4,4-tetraphenylbutadiene [0054] Diphenylstilbene [0055] PPO 2,5-diphenyloxazole [0056] -NPO 2-(1-naphthyl)-5-phenyloxazole [0057] PBD 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole [0058] BBO [2,5-di(4-biphenyl)oxazole] [0059] POPOP [1,4-bis(2-(5-phenyloxazolyl))benzene] [0060] TOPOT [1,4-di(2-(5-p-tolyloxazolyl))benzene [0061] BiMePOPOP 1,4-di(2-(4-methyl-5-phenyloxazolyl))benzene [0062] DF 2-(diethoxyphenyl)-5-phenyl-1,3,4-oxadiazole [0063] BPO 2-phenyl-5-(4-biphenyl)-1,3-oxazole [0064] 3P-2 1,3,5-triphenyl-2-pyrazoline [0065] BBE 1,2-di(4-biphenylol)ethylene [0066] BNE 1-(4-biphenylyl)-2-(-naphthylethylene) [0067] 2,5-bis(5-tert-butylbenzoxazol-2-yl)thiophene [0068] Bis-MSB 1,4-bis(2-methylstyryl)benzene [0069] 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole [0070] trans,trans-1,4-diphenyl-1,3-butadiene [0071] DAN 9,10-diphenylanthracene.

[0072] A person skilled in the art can easily determine experimentally the assignment of these substances to primary or secondary scintillators. Reference is made here to the monograph Kolanoski, Hermann; Wermes, Norbert: Particle Detectors: Principles and Applications Heidelberg: Springer Spektrum, 2016. -ISBN 978-3-662-45349-0.

[0073] The molded bodies according to embodiments of the invention can also comprise substances which are capable of a nuclear chemical reaction, for example with thermal neutrons or alpha particles. Suitable isotopes of, for example, lithium, gadolinium, boron or other elements are customary here. These substances are often used as salts of organic acids or in the case of boron as borates of amines. Preference is given here to using lithium salts, in particular lithium carbonate or lithium salts of organic acids in amounts of 0.05% by weight to 5% by weight, based on the molded body.

[0074] The molded body according to embodiments of the invention can furthermore comprise substances for stabilizing at least one of the polyaddition product and further auxiliaries. For instance, hydroxphenylbenzotriazole, antioxidants of the sterically hindered phenol type and the like can be used as stabilizers. Polyaddition catalysts can also be present. The molded bodies may also comprise impact modifiers (impact strength improvers). Suitable for this purpose are elastic polymers of similar compositions.

[0075] All of the additives mentioned originate from materials which do not substantially impair the light yield of the materials claimed. A reduction in the light yield due to the additives should, for example, not fall below 10%, preferably not below 60%, of the original values based on the molded body without the addition of these additives.

[0076] The composition of the molded bodies according to embodiments of the invention can be adapted to the requirements within a wide range of limits by a person skilled in the art. Suitable molded bodies can have the following composition (all percentages by weight relate to the molded body): [0077] 10% by weight to 99.99% by weight of a polyaddition product of polyfunctional isocyanates with at least one of polyfunctional alcohols and amines and amino alcohols, [0078] 0.01% by weight to 90% by weight of further organic substances (at least one of primary and secondary scintillators) scintillating when irradiated with at least one of ionizing radiation, and [0079] 0.01% by weight to 90% by weight of an additive which scintillates when irradiated with at least one of non-ionizing radiation, and [0080] 0% by weight to 5% by weight of substances for stabilizing at least one of the polyaddition product and further auxiliaries.

[0081] The contents by weight (% by weight) are based on the total weight of the molded body, the total weight content in % of all components making up or not exceeding 100% by weight.

[0082] Particularly preferred ranges are 70% by weight to 95% by weight, in particular 80% by weight to 90% by weight (based on the molded body) of the polyaddition product and 0.05% by weight to 30% by weight, preferably 0.5% by weight to 20% by weight and in particular 0.6% by weight to 5% by weight at least one of primary and secondary scintillators and, if desired, 0.05% by weight to 30% by weight, preferably 1% by weight to 5% by weight of an additive which scintillates when irradiated with non-ionizing radiation and, if desired, 0.1% by weight to 5% by weight of substances for stabilizing the at least one of polyaddition product and further auxiliaries.

[0083] According to a further preferred embodiment of the invention, the polyaddition products according to embodiments of the invention comprise at least one of the primary and secondary scintillators covalently bound to the polymer. In order to accomplish this, the scintillator molecules are converted, for example, to hydroxyalkyl compounds. Examples include 2,2-(naphthalene-2,7-diylbis(oxy))bis(ethan-1-ol) and 2,2-((9,10-diphenylanthracene-2,7-diyl)bis(oxy))bis(ethan-1-01).

[0084] According to a further embodiment of the invention, the scintillator molecules are converted to hydroxymethylene compounds on one or more aromatic rings, which are then used as hardener components.

[0085] According to a further embodiment of the invention, lithium is incorporated in the polymer matrix in the form of the salt of a hydroxycarboxylic acid, preferably a dihydroxycarboxylic acid.

[0086] According to a further preferred embodiment of the invention, at least one of the primary and secondary scintillators are both incorporated and mixed into the polymer.

[0087] Embodiments of the invention further relates to a process for producing a molded body. For this purpose, auxiliaries and additives are dissolved in the hardener component, the hardener component and the isocyanate component are mixed, and the mixture is allowed to react in a form of the desired geometry until it has fully hardened. Preferred embodiments are provided to accelerate the curing process by adding catalyst. The catalysts commonly used here in polyurethane synthesis are, for example, triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N,N-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol, diazabicyclo[2,2,2]octane and similar, organic metal compounds such as titanic acid esters, iron compounds such as iron (III) acetylacetonate, tin compounds, e.g. tin diacetate, tin dioctoate, tin dilaurate or the tin dialkyl salts of aliphatic carboxylic acids such as dibutyltin diacetate, dibutyltin dilaurate or the like.

[0088] A further preferred embodiment of the process provides for the hardener component to be made water-free by suitable measures, for example adding solid drying agents, in order to prevent bubbles from being formed by eliminated CO.sub.2.

[0089] It has also proven useful to harden the casting resin in molds having an inert surface, for example molds made of polytetrafluoroethylene.

[0090] The molded bodies according to embodiments of the invention are used in radiation measuring devices. The structure of such radiation measuring devices is shown in FIG. 2. Inside is (1) the plastic scintillator. In this, ionizing radiation is converted to light in the range of UV to IR radiation and is passed into the photosensor (2), which converts it into an electrical current, which the display device (3) indicates.

[0091] The plastic scintillators according to embodiments of the invention can be used in measuring devices which, on the one hand, measure ionizing and non-ionizing radiation within a very large energy range thereof and can be scaled very well in terms of their size and thus the detection sensitivity.

[0092] The plastic scintillators according to embodiments of the invention can be offered in standard sizes as rods, plates and cylinders. The requirements for sensitivity and energy range determine the size and type of the measuring systems, which range from hand-held devices with a single scintillator to extremely heavy measuring devices with thousands of scintillators.

[0093] The plastic scintillators according to embodiments of the invention can be used in measuring devices which are used for measurements at high radiation levels. [LAMBERT, J., et al. A plastic scintillation dosimeter for high dose rate brachytherapy. Physics in medicine and biology, 2006, 51st Vol., No. 21, p. 5505.]

[0094] Particles and electromagnetic radiation in the range from a few keV to TeV are detected in different applications. For instance, calorimeters with plastic scintillators are standard instruments on many particle accelerators. [CMS COLLABORATION, et al. CMS physics technical design report, volume II: physics performance. Journal of Physics G: Nuclear and Particle Physics, 2007, 34. Vol., No. 6, p. 995.]

[0095] The plastic scintillators according to embodiments of the invention can be used in measuring devices as are customary for measurements in astrophysics [Abdo, Aous A., et al. Measurement of the cosmic ray e++ e spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope. Physical Review Letters 102.18 (2009): 181101.]

[0096] Furthermore, the plastic scintillators according to embodiments of the invention can be used in measuring devices, as are common in portal monitors in the wide application field of homeland protection. [ELY, James H., et al. Discrimination of naturally occurring radioactive material in plastic scintillator material. In: Nuclear Science Symposium Conference Record, 2003 IEEE. IEEE, 2003. pp. 1453-1457].

[0097] Plastic scintillator-based measuring devices have a light-sensitive sensor that converts the scintillation radiation into electrical impulses for further processing, described for example in KNOLL, Glenn F. Radiation detection and measurement. John Wiley & Sons, 2010., p. 247.

[0098] Examples of preferred diisocyanate and a hardener component:

##STR00002##

EXAMPLE 1

[0099] Additives according to the table below were dissolved in 2 g of bisphenol A ethoxylate. After addition of 1 g of 1,3-bis(1-isocyanato-1-methylethyl)benzene, 0.5% by weight of dibutyltin dilaurate was added to the reaction mixture, whereby a transparent polyurethane was obtained after 1 to 5 hours.

TABLE-US-00001 PPO POPOP DAN p-Ter BMB Light [% by [% by [% by [% by [% by yield Sample weight] weight] weight] weight] weight] [pC] 1 A 0.5 0.02 40 2 A 1 0.02 43 3 A 2.5 0.2 43 4 A 5 1 46 5 A 5 0.2 45 6 A 10 0.2 47 7 A 30 0.5 44 1 B 1 0.02 34 1 C 5 30 1 D 1 25 1 E 0.2 1 25 1 F 1 0.02 42

EXAMPLE 2

[0100] The additives in % by weight were dissolved in 2 g of bisphenol A ethoxylate according to the table below. After addition of 0.9 g of isophorone diisocyanate (sample names: 1-IPDI and 2-IPDI) or 0.76 g of m-xylylene diisocyanate (sample names: 1-MX, 2 MX, 3 MX), 0.5% by weight of dibutyltin dilaurate was added to the reaction mixture, after which a transparent polyurethane was obtained.

TABLE-US-00002 PPO POPOP p-Ter Bis-MSB Light [% by [% by [% by [% by yield Sample weight] weight] weight] weight] [pC] 1 IPDI 5 28 2 IPDI 1 3 26 1 MX 3 0.02 42 2 MX 1 0.02 40 3 MX 1 0.05 36

[0101] Abbreviations: [0102] PPO 2,5-diphenyloxazole [0103] POPOP 1,4-bis(5-phenyl-2-oxazolyl)benzene [0104] p-Ter p-terphenyl [0105] DAN 9,10-diphenylanthracene [0106] Bis-MSB 1,4-bis(2-methylstyryl)benzene

[0107] Determination of the Light Yield: [0108] 1. A cylindrical plastic scintillator sample of 15 mm diameter and 10 mm length is connected to the end face of the photocathode of a photomultiplier tube (PMT) from Hamamatsu with optically transparent grease so that light quanta from the sample can illuminate the photocathode. [0109] 2. The sample is irradiated with gamma quanta at a distance of 50 mm by a Cs-137 emitter of 4 Ci intensity. [0110] 3. The current pulses thereby generated on the PMT anode are recorded with an oscilloscope from LeCroy, integrated and sorted according by height in a histogram, the gamma spectrum (PHA method, Pulse Height Analysis). [0111] 4. The position of the characteristic Compton edge in the gamma spectrum is proportional to the amount of light that the scintillator emits. [0112] 5. The position of the Compton edge is compared to that of a known scintillator sample and thus enables the calculation of the photons/MeV, the light output of the sample material.

[0113] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0114] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements. The mention of a unit or a module does not preclude the use of more than one unit or module.