CA1079516A - Scintillation counting compositions and elements - Google Patents

Abstract

Abstract of the Disclosure Scintillation counting compositions are described, comprising polymeric particles derived from a latex and loaded with at least one uniformly dispersed hydrophobic fluor so as to permit detection of low-energy radiation.
Scintillation counting elements comprising a sub-strate coated with a dried layer of the above-described scintillation counting compositions are also described.

Description

Background of the Invention Field of the Inventlon:
The present invention relates to scintil]ation counting and more particularly to novel high efficiency scintillation counting compositions useful in "dry" counting ~ elements.
S~ate of the Prior Art Scintillation counters are used for measuring the density or concentration of emissions ~rom radioactive sources, such as beta particles, gamma radiation, etc.
Such counters are well known in the art and the principles on which they operate are described, for example, in "Source Book on Atomic Energy" by Samuel Glasstone at pages 140 -142, and "Two Liquid Scintillation Neutron Detectors," by Muelhouse and Thomas, Nucleonics 11, 44 (1953). Briefly, these counters detect and quantify emissions from scintillator compositions which comprise a solvent (liquid or solid) which "captures" the incoming radiation to be detected and measured, a primary fluor which responds to the incoming, "captured" radiation by fluorescing at a specified wavelength, .~and if desired, a secondary fluor or wave shifter which responds to the emissions of the primary fluor by fluorescing at a specified second wavelength.
There are three types of scintillator compositions.
I'hese are: (1) solid scintillators comprising a crystal of a solid hydrocarbon material; (2) liquid scintillators which .
~; comprise one or more suitable solid scintillators dissolved ln a liquld so]venl;; and (3~ so-called solid solution scin-tillators which comprise a solid scintillator in a solid - polymeric solution. The compositions of this invention are most closely related to solid solution scintillators.
The most commonly used commercial solid solution scintillators comprise, e.g., a polystyrene block having , .
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fluors included therein. In use, samples are analyzed, for example, ~or ~-particle emission, by dissolving the sample in a suitable solvent, for example, toluene; applying the solvent solution of sample to the solid solution scintillator block; and scintillation counting, i.e., quantifying the fluorescent emissions from the block. Unfortunately, such scintillators can only be used with very strong radiation emitters such as 60Co, 137Cs and UV excitation, with certain very specific organic solvent sample systems of weak ~-emitters such as 14C, tritium or the like, or pure Y-emitters such as 125I or the like. The utility limitations of these systems are apparently due in large part to an inability to achieve the intimate contact between the emitter and the flu~or or scintillator. Such intimate contact is required if these short range radiations are to affect the fluor. Thus, the efficiency of such counting systems is reduced. As a .
point of reference, the counting efficiencies of such prior , art solid solution scintillators generally range below about 20% of theoretical maximum, apparently due to the lack of emitter-fluor intimacy. Llquid scintillator compositions on ._the other hand are capable of efficiencies above 35% and in ~
some cases 100% of theoretical, most probably due to the .
intimate emitter-fluor contact possible in a liquid medium.
Use of liquid scintillator compositions, however, involves ; a large number of handling problems well known to those skilled in the art.
The following patents further illustrate the l above-noted developments in scintillation counting compositions.
;~ U S. patent No. 3,010,908, issued November 28, l-30 -1961, discloses the use of dialkyl styrene polymers as the :: .
primary absorber in a solid solution scintillation counting composition. The maximum weight percent of fluors which can be carried as a solute in such a solvent system is disclosed to be about 5%.

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U. S. patents No. 2,985,593 and 3,356~616, disclose s~yrene-derived monomers polymerized or copolymerized with vinyl or methacrylate monomers to form the solvent ~or a solid solution scintillation counting composition. The fluors are carried as solutes, and the fluor concentrations do not ; exceed about 3 weight percent.
; U. S. patent No. 3,457,180, issued July 22, 1969, discloses as the solvent for a solid solution scintillator, copolymerized p-vinyltoluene and methyl methacrylate. The disclosed amount of fluor dissolved in such a solvent is less than 3 weight percent.
. U. S. patent No. 3,150,101, describes the formation of scintillating ion exchange beads by the suspension-polymerization of polyvinyltoluene or polystyrene crosslinked with divinylbenzene, the monomers containing the fluors dissolved in them. Such beads, by virtue of their large size, and therefore their small surface area per unit-of weight, do not have ~ high counting efficiencies for low-energy radiation.
; U. S. patent No. 3,513,102 discloses a fluorescent coating in which a fluor and a copolymer of an acrylate and styrene is dissolved in an organic solvent, and the solution is emulsified in an aqueous dispersion of a hydrophilic colloid. The copolymer is not derived from a latex, but is a solution polymer isolated, redissolved and blended by high-speed milling for dispersion in a gel binder.
U. S. patent No. 3,418,127, issued to A. G. Millikan December 24, 1968; describes a technique for increasing the efficiency of direct electron recording compositions by incorporating increased levels of fluor into solid polymer solutions. Specifically the fluor is dispersed in an aqueous . - . . . .
~- dlspersion of monomer and then the monomer is emulsion polymerized. According to the teachings of this reference, maximum fluor concentrations on the order of 12 - 15% (col.
` 4, line 15) are achievable. Such compositions are formed into coatings as part of a composite photographic element 3L~7951~

suitable for the detection and recording, for example, of x-rays and other high energy emissions. No suggestion is made to use the coated element as a scintillation counter for, in particular, low energy emissions such as ~-particles.
Other documents of interest are as follows:
Commonly owned Canadian Patent Application Serial No.
234,405, filed by T.J. Chen on August 28, 1975, entitled "Uniform, Efficient Distribution of Hydrophobic Materials Through Hydrophilic Colloid Layers, and Products Useful 10 Therefor," describes a novel technique for incorporating un-usually large concentrations of hydrophobic materials, for example, color ~orming couplers, into polymeric particles derived from a latex. Gelatin photographic elements are formed, for example, by a process which involves the steps of ; ta) forming an aqueous dispersion by lntermixing the hydrophobic material and an aqueous polymeric latex, optionally including gelatin in the dispersion;
~; (b) forming a wet layer by coating onto a suitable support the aqueous dispersion from step (a); and (c) thereafter removing a substantial proportlon of the water from the wet layer through which the hydro-phobic material is dispersed.
U.S. Patent No. 3,024,221, issued March 6~ 1962 dis-closes certain new sulfo esters of ~-methylene carboxylic acids.
~ No mention is made of the compounds being useful in scintillation ; counting compositons.
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~bjects Or the Invention It is an object of the invention to provide scintil-lation counting compositions capa~le of efficiently detecting low energy radioactive emissions, i,e., emissions having energy levels as low as about 0.01 Mev.
- It is a related object of the invention to provide such a composition in a form that can be coated onto a support and dried.
Another object of the invention is to provide a process of measuring such low energy emissions by the use of a non-liquid coating.
Other objects and advantages will become apparent upon reference to the following Summary and Detailed Description of the Invention.

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Summary o~ the Invention According to the present invention there are provided novel scintillation counting compositions, novel scintillation counting elements and processes for detecting - and quantitatively determining low-energy radioactivity in samples for analysis. More specifically, there is pro~ided a scintillation counting composition comprising loaded polymer particles derived from a latex, the particles being loaded with at least one hydrophobic fluor, the composition having a counting efficiency of at least about 23% when used as a subst~ntially dry layer coated with a maximum wet thick-ness of 30 ml/100 cm2 and tested with a water solution of tritium-labeled benzoic acid. The compositions can also be in the form of polymer latices which exhibit essentially no visible coagulation or settling when 250 ml of the latex ' containing about 12 to about 20 weight percent polymeric particles dispersed in an aqueous continuous phase is slowly stirred at 25C into 250 ml of acetone over a l minute period at a uniform rate, and the blend is thereafter allowed to stand at 25C for about 10 minutes. The CQmpositiOn is particularly useful in a "dry" form, i.e., as a coating on a support~ in which case a substantially non-quenching binder can be added for physical integrity.
The scintillator compositions of the instant invention contain ~luor concentrations apparently unattaina-ble in the prior art when in solid solution or "dry" form.
Such relatively high fluor concentrations provi~e scintil-lation counting compositions demonstrating counting effi-~. ciencies for low energy emissions of approximately the same ;~ 30 magnitude as those attainable with the liquid scintil-lator compositions of the prior art ~i.e.~ from about 23 to about 100%), thus permitting detection of sources emitting ; radiation at levels as low as about 0.01 Mev.

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Detailed Description of the Invention Although the following description is directed primarily to "dry" scintillator compositions, it is not so limited and applies to such scintillation compositions in whatever form found to be desirable.
The compositions o~ this invention concern a loadable late~, and specifically the polymeric particles derived from the latex, and at least one fluor distributed within these particles, -pre~erably in relatively high concentrations. Such a composition is particularly useful in the form of a "dried" residue, such as a coating on a support. In such "dried" ~orm, stabilizing binders can be added. As used herein "dry" or "dried" refers to that state in which most, out not necessarily all, water or other solvent has been removed by evaporation or otherwise. "Substantially dry"
refers to the removal of substantial amounts of water, and thus as used herein means ~he condition in which at least about 80% by weight of water has been removed.
The aforesaid Canadian Patent Application of Chen is directed generally to a process ~or manufacturing a latex 20 dispersion containing one or more hydrophobic materials uniformly ; dispersed therethrough. The application also describes a process ~ for manufacturing improved polymeric latex compositions which ; are useful in the manufacture of such layers; and the improved polymeric latex compositions and products that can be manu~actured thereby. The polymeric latex compositions or "loaded" latex ~: ....................................................................... ..
compositions described in the Chen application are polymeric latices in which the dispersed or discontinuous phase consists essentially of partlcles of a synthetic polymer, and one or more hydrophobic compounds distributed among the polymeric particles.
Distribution of the hydrophobic compounds is achieved by a process comprisin~ blending together a "loadabIe" latex and a solution of the hydrophobic compound~s~ dissolved in ~ater-miscible organic solvent(s~.

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As used herein "distributed among the polymeric particles"
means associated with the polymer particles bo~h on the sur~ace of the particles and in their interior.

Some of the products described in this application are supports coated with at least one layer in which such particles of "loaded" latex are distributed. The term "loadable polymeric latex" or "loadable polymer latex" is intended, as used herein, to include those latex compositions which:
(a) provide polymeric particles which are compatible with the water-miscible solvent (i.e., they do not coagulate or precipitate when the latex is gradually blended into the solution of hydrophobe in the water-miscible organic solvent); :~
(b) pre~erably are compatible with binder solutions ~` or dispersions, such as gelatin, in water (at 25C) containing as much as about 5 weight percent each of gelatin and latex "solids"; and (c) when dispersed in water have a discontinuous .~ phase which consists essentially of polymeric particles which will absorb or otherwise receive hydrophobic compounds forced out of solution in the water miscible solvent.
A "loaded" latex then is a loadable latex in which a hydro-phobe has been distributed according to the techniques i discussed herein.
~' ~he scintillation counting compositions of this invention can comprlse the latex formed in the manner described in the Chen application, except that the hydrophobe is the primary, and optionallyl the secondary fluor appropriate to scintillation counters, instead of those disclosed in Chen.
~

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~`7~5~6 Since the success~ul practice of the instant invention relies substantially on the preparation o~ materials and composi-tions as described in the above-noted Chen application, the salient features of that application will be described in greater detail.

The preferred polymeric latex compositions which form the basis for all aspects of this invention thus are manu~actured by a process which comprises the step of gradually blending an aqueous loadable polymer latex into a solution of the hydrophobic fluor(s) dissolved in water-miscible organic solvent(s). The order of addition is of importance to prevent the latex from coagulating and to keep the fluor(s) from accumulating outside the latex particles in excessive amounts.
As described in the Chen application, as the aqueous latex is gradually introduced into the water-miscible solvent solution of hydrophobe, i.e., the fluor~ the solution ; gradually becomes more hydrophilic or water-like in its character due to the incorporation of more and more water into the acetone solution. At some point (depending on the particular type and quantity of hydrophobe and the particular . type of water-miscible solvent that is used) the solution becomes so hydrophilic that the hydrophobe can no longer remain dissolved therein, and the hydrophobe begins to ;; change to an undissolved~ dispersed state. By this time, , there has been introduced into the solution a large number - of uniformly dispersed, loadable polymeric latex particles along with the water. These particles evidently swell at i least to some slight extent in the presence of the sol~ent, thereby becoming so receptive to the hydrophobic material -3~ that, when the hydrophobe is forced out of solution in some as yet unexplained manner~ the hydrophobic material is preferentially absorbed into or is otherwise associated with the loadable polymeric latex particles.

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Thus, the process described involves gradually increasing the hydrophilicity of a solution of a hydrophobe in a water-miscible solvent in the presence of uncoagulatedg undissolved, loadable polymeric latex particles to a point a~ which substantially no hydrophobe remains dissolved in the water-miscible solvent phase.
The increase in hydrophilicity is accomplished b~ adding water to the solution of hydrophobe in the water~miscible solvent, pre~erably in the form of an aqueous loa~able pol~neric latex.
One advantage of the above-described technique applied to this invention is that some of the thus-loaded latex compositions possess unique properties; for example~
the hydrophobic fluor thereof appears in some cases to be more effective and/or more available for reception of the low energy emissions in the desired manner. This may be due to ; the fact that the process makes it possible to incorporate considerably larger amounts of fluor into the scintillation counting composition~ i.e., into particles of the latex polymer, than was possible heretofore as evidenced by the relatively higher levels thereof which are incorporated. Scintillation counting compositions are produced which are particularly well suited to the measurement of low energy particles such as ~-emissions produced by radioactive materials wherein the energy of emission is as low as about 0.01 Mev, the typical lower energy levels of tritium.
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Water-Miscible Organic Solvents The preferred water-miscible organic solvents - are those which:
(a) can be dissolved in (i.e., are "miscible"
with) distilled water at 20C to the extenf of ~t least about 20 parts by volume of solvent in 80 parts by volume of water;
(b) have boiling points (at atmospheric pressure) above about 20C;

(c) do not detrimentally react chemically with the loadable polymer latexes which are useful in the practice of this invention;
(d) do not dissolve more than about 5 weight percent of such loadable polymer laf,ices at 20Cj and (e) act as solvents for the organic fluors described hereinafter at least to the extent of 0.02 weight percent at 20C for the secondary fluor and 1.0 weight percent for the primary fluor.
Examples o~ water-miscible solvents useful in the .. . ...
successful practice of the present invention include3 solely by way of example, tetrahydrofuran, ethanol, methanol, acetone and the like.
` Loadable Polymeric Latices Loadable polymer latices apparently include (but are not limited to) all of the polymeric latices having (i) a polymeric discontinuous phase ~particles) wh~ch consists ~ ~
essentially of polymer polymerized from at least two ethenic ~ ;
monomers, from about 0 to abouf, 10 weight percent of f,he -polymer preferably being made from monomer~containing a f' sulfonic acid or a sulfonate group, and (ii) an aqueous continuous phase; which polymeric latices do not coagulate or settle out when sub;ected to the following fest:

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Loadable Polymer Latex Test At 25C, slowly stir 250 ml of polymeric latex containing about 12 - 20 weight percent dispersed phase into an equal volume o~ acetone. The addition should take place over 1 minute at a steady, uniform rate, while the acetone is being stirred moderately. Discontinue the agitation and let the resulting blend stand at about 25C for 10 minutes.
At the end of that time observe the blend. "Loadable polymer latices" are those which exhibik essentially no visible coagulation or settling out under these test con-ditions.

Preferred Loadable Polymeric Latices Although any polymer which will meet the above "Loadable Polymer Test" is useful, polymer latices which are particularly useful in the successful practice of the present invention are those loadable latices wherein the dispersed phase comprises a polymer made of (a) from about 1 to about 99 weight percent of a styrene monomer having the formula ' ' . ' .

CHz=C-R1 -R4~ /R~
~ 20 ,n~
Rs t ~, '.

whcrein ~ is hydrogen or mcthyl; ~3, ~4 and R are hydrogen or lower alkyl of 1 to 4 carbon ;
atoms; R5 is hydrogen or with R constitutes the . . . , . . :.
atoms necessary to complete a fused benzene ring; ;

of which particularly useful examples are styrene, vinyltoluene,

2-vinylmesitylene and l-vin~lnaphthalene; and either or both of 12- ;

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:- ~ - - - . ~ ., (b) from about O to about 95 weight percent of units derived from one or more acrylic ester monomers having the structureO

R Rl H - C = C - C - O ~ R2 O
wherein R is hydrogen or alkyl containing l-5 carbon atoms, R is hydrogen or meth~l, and R2 is an aliphatic group containing l to 6 carbon atoms; methyl methacrylate, ethyl methacrylate~
butyl acrylate, n-butyl methacrylate being particularly use~ul examples; and (c) from about O to about lO weight percent o~
a hydrophilic ethenic monomer containing a s~lfonic acid group, or an ammonium or alkali metal salt thereo~, said ethenic monomer having a pre~erred molecular weight of at most about 300.
In addition, other monomers of the class (a), (b) or (c), can be ; added, where copolymerization is possible. Or alternatively, a monomer such as acrylamide can be added where additional hydro-philicity is required to absorb, for example, solutions having a high protein content.

. It should be noted that the ratios of monomers set out herein are based upon the relative proportions of various monomers as they are charged into the polymerization reactor in a conventional free radical polymerization process.
Products from such reactions may vary to some eXtent in the ratios derived from the charged monomers for various reasons , - which are well known to those skilled in the art of manufac-turing synthetic polymeric latices. While "loadable" polymer latices can be made from two, three, four or even more ' ~ ,'' . :.
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" ~795~6 dif~erent monomers, those which are preferred for use in the practice o~ this invention are generally comprised Or two to ~our di~ferent types of monomers, depending upon the particular properties desired in the final products o~ the invention.
As the manufacture of latices of this type is well-known, details o~ such procedures need not be described herein, except to point out that the preferred "loadable" polymer latices described above are general].y prepared via free radical initiated reactions of monomers dispersed in an 10 aqueous medium with one or more appropriate surfactants.
See, for example, U. S. patents 2,914~499; 3,033,833; 3~547,899 and Canadian patent 704,778.
Monomers which are still further preferred for use in the manufacture of loadable polymer latices are those wherein (i) the acrylic ester monomer is selected from the group consisting of methyl, ethyl, propyl and butyl acrylates and methacrylates, and (ii) the hydrophilic ethenic monomer, if used, - is selected from those having a sulfonic acid group (or _water soluble salt thereof) preferably attached to a terminal . ~

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arbon atom such as, for exarnple, those having the following structures:

Il , 3 (1) CH2 = CHC - N - ,C - CH2 ~ S03H*, . :
0 3 : ::
(2) CH2 = CH - C - 0 -CH2 - S03H*, ,0, :' .

(3) CH2 CH - C ~ 0 - (CH2)3 - S03H*, ~ ' .

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CH3 .
( ) H2 C - C - 0 - (CH2)4 - S03H*, O
- r 3 (5) H2 C - C" - 0 - (CH2)2 ~ S03H*, : o ': ' r 3 (6) H2 C - ~C, - 0 - (~H2)3 - S03~I*, ~: :
H `;
(7) CH2 = C - S03~I*, " ~ 3 H2 = CH - C - N ~ C - CH2 - S03H*, H H
CH H CH
.. 3 1 , 3 -.
(9) CH2 = C - ,C, - N - C, - CH2 - S03H , . - . 3 - - - - - ~ : .

ll , 3 ...
(10) CH2 = CH -~C - N - C - (CH2)2 - S03H*, where R

H R is H or CH .
: 3 .
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~*=in place of H can be an alkali metal cation, preferably Na or K, or ammonium ion.) The generic formula for the preferred subclass of hydrophilic ethenic monomers containing the sulfonic acid group is (A) CH2 = C - C - 0 - R7 - S03M
O ~ ~:
Rl (B) CH2 = C - C - NH - R - S03M
O ',:

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Certain variations within the formulas (A) and (B) may require increased amounts of binder when used as a coating as described hereinafter. i ` ' . . . :

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~ 15- :
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~ 795~6 where Rl is methyl or hydrogen; R7 is methylene, ethylene, 2~methylethylene, trimethylene, tetramethylene, or 2,2-dimethylethylene; and M is ammonium, hydrogen or alkali metal cation.
From the foregoing description it is evident that many combinations o~ monomers can be used in the manufacture of loadable synthetic polymeric latices in accordance with this invention. It must be pointed out, however, that many polymeric latices are not "loadable latices" as set out above. For this reason, it is recommended tllat~ before a given latex is assumed to be "loadable", the latex be tested via the procedure set out above under the heading "Loadable ~olymer Latex Test." The use of this test is also recommended as a control procedure because of the relatively low level of batch-to-batch reproducibility that sometimes occurs in the commercial manufacture of polymeric latices. A preferred method for manufacturing loadable latices is described below, preceding the Examples.
The dispersed polymeric particles thus comprising the discontinuous phase of the latex, formed in the manner described above, have an average diameter of from about 0.02 to about 0.2 microns. Thus, the latex can be considered a colloidal dispersion.

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Fluors Fluors useful in the successful practice of the present invention include any of the hydrocarbon rluors well-known in the scintillation counting art which are compatible with the loaded latex compositions described .
herein; i.e., are hydrophobic. As used in this application, a "hydrophobic fluor" is one which has substantially zero water solubility. Generally, suitable organic fluorescent `

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compounds may be selected, for example, from those described as "organic fluors" and "organic scin~illators" in Organic Scin~illation Detection, E. Schram and R. Lombaert, Elsvier Publishing Co., 1963. Materials of this type include as the primary fluor the following:
p-terphenyl (PTP), m-terphenyl, trans stilbene, phenanthrene, indene, anthracene, 9,10-diphenyl anthracene, 2-phenyl-5-(4-biphenyl) 1,3,4-oxidiazole, 2,5-diphenyloxazole (PPO)~ p,p'~
quaterphenyl, l,1,4,4-tetraphenyl-1,3-butadiene, naphthalene, 2,5-di-(4-biphenylyl)-oxazole; 2-(1-naphthyl)-5-phenyloxazoleg and 1,3,5-triaryl-2-pyrazolines including 1,3,5-triphenyl-2-pyrazoline, l,3-diphenyl-5-p-acetoamidophenyl 2-pyrazoline, 1~3-diphenyl-5-p-hydroxyphenyl-2-pyrazoline, 1,5-diphenyl-2-p-methoxyphenyl-2-pyrazoline, 1-phenyl-3,5-di p-methoxyphenyl-2-pyrazoline, 1,3-diphenyl-5-p-methoxyphenyl-2-pyrazoline, 1,3-diphenyl-5-p diphenyl-2-pyrazoline, and compatible mixtures of any of the preceding.

Useful wavelength shifters (i.e., secondary fluors) are conventional compounds including 1,1,4,4-tetraphenyl-1,3-butadiene, p~bis(o-methystyryl)benzene, 1,4-bis-2-(4-methyl-5-phenyloxyazolyl)benzene, 2,2'-p-phenylenebis(5-phenyloxazole) (POPOP), diphenyl stilbeneg and 1~3,5-triaryl-2-pyrazoline, the last being both a primary fluor and a wave shifter.

. ' . .
Preferred among these classes of materials are 2,5-diphenyloxazole (PPO) as the primary fluor and 2,2'-p-phenyl-enebis(5-~henyloxazole) (POPOP) as the secondary fluor or wave shifter. The concentration of fluor required to provide a : .
useful latex, coated element or solid scintillator composition -will, of course, vary depending upon the sensitivity of the particular fluor used as well as the type of particles to be measured with a particular fluor composition. Generally, however, the concentration of primary fluor will range from about 16.0 'to about 40.0 weight percent and the concentration ~7~5~;
~ secondary ~luor or wavelength shifter from about 0.001 toabout 0.2 weight percent, measured on a dry solids weight basis, in order to achieve userul results. Relatively higher concentration levels than those available in prior art solid scintillator compositions are obtainable using the technique of this invention. Specifically, the fluor can constitute at least as much as about 25~ of the weight of the dry solids content of the composition.
Process of Manufacture of the Latex . . .
With re~pect to the process o~ manu~acturing the compositlon~ and elements of the present invention, the order of addition of the loadable polymeric latex into the solutlon of fluor dissolved in water-miscible solvent is important. Reversing the order results in the coagulation and settling out of the latex or the accumulation of a large proportion of the fluor Gutside the latex particles in a much less desirable or less usefu]. form.
In the manufacture of the loaded latex composi~
tions of this invention, generally the relative volume of (a) loadable polymeric latex; and ~b) solution of fluor material(s) (in water-miscible solvent) which are intermixed in the required manner, are not believed critical. Thus, so long as some loadable latex particles are present in the solution during that interval of time in which the fluor ls forced out of solution (because of the increasing hydrophilicity of the solution, as described above), some loaded latex particles will be created. For example, one embodiment of the present generic process involves, stepwise, (a) the introduction of a quantity of loadable latex which is not sufficient to affect the hydro-philicity of the solution of fluor to the extent necessary to force the fluor out of solution; and (b) adding enough water to the resulting mixture ; to affect the desired transfer of fluor from the water-miscible solvent into the latex particles.
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In this way, loaded latex compositions containing relatively larger proportions of fluor per particle can be made using a relatively dilute solution of fluor. Thus, it can be seen that there is more than one technique whereby the necessary increase in the hydrophilicity of the solution of fluor (during the period in which the fluor becomes insoluble in such solution) can be obtained. For this reason, when the phrase "at least ; sufficient water to cause the fluor to become insoluble in the solution" (with ref`erence to the essential step of this pro-cess) is used herein, the "water" referred to in that phrase means not only water alone, but also the "aqueous" portion of a loadable aqueous polymeric latex as described hereinbefore, as well as water in the form of a solution of one or more dissolved salts and the like.
~owever, it is generally preferred that when the dispersed phase polymer "solids" of the loadable polymeric latex is above 10 weight percent, the relative amount of fluor solution that is blended with such latex should be between about 50 and about 200 parts by volume per 100 parts by volume of loadable polymeric latex; and still more preferably, about one part by volume of fluor solution per part by volume of `
loadable polymeric latex, particularly when the latex contains from about 12 to about 20 weight percent of polymeric particles.
The actual optimum amount of time necessary to carry out the gradual mixing of ~i) the latex and (ii) the fluor solution in accordance with the present processes will vary in any given instance, depending upon such factors as (a) the identity of the polymeric latex, fluor and water-miscible solvent;
(b) the relative concentrations of fluor and polymeric dispersed phase in the respective materials to be mixed, as well as;

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(c) the relative amounts o~ latex and ~luor solution.
However, it is ~enerally ~referred that the ~radual inter-mixing o~ loadable polymeric latex into the fluor solution take place over at least about 10 seconds, particularly in those instances in which the polymeric "solids" content o~
the loadable polymeric latex is above about 12 weight percent.
Too fast intermixing has been found to result in formation of a second solid phase in the system and/or coagulation or settling of the latex particles. Gradual intermixing over at least about 20 seconds is still further preferred.
Crenerally, after a useful loaded latex composition, as described hereinbefore, has been formed initially, some or all of the water-miscible organic solvent can optionally be removed from the composition without harming the valuable utility of such loaded latex composition. Removal of water-miscible organic solvent can pre~erably be accomplished by evaporation under any of a wide variety of conditions (at temperatures below about 40C, for example), preferably under reduced pressure. Preferably at least about half of the water-miscible solvent is removed from the initial compatible blend (of loadable polymeric latex/fluor/water-miscible solvent) to thereby ~orm one of the preferred useful loaded latex compositions of the present invention.
Such preferred useful loaded latex compositions retain their "latex" characteristics; that is, they have an aqueous continuous phase which optionally contains some of the water-miscible organic solvent (but preferably ~ot more ~-water-miscible solvent than about 30 weight percent of said .. . . . .
continuous phase), and a dispersed phase comprising loaded latex particles in which the fluor is uniformly distrlbuted.

Removal of the organic solvent and/or some water from the ' ' ~' .

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- ~97~5~6 initial blend of latex plus water-miscible solvent, of course, results in a composition having a higher "sollds" content.
Such latex compositions are useful as liquid scin~illator compositions in a conventional fashion.
When it is desired to lmprove the stability of a loaded latex composition to inhibit the tendency of the latex to settle out gradually upon prolonged storage, the composition can be intermixed with an aqueous solution of a hydrophilic colloid such as gelatin. Such an embodiment is speci~ically preferred. A preferred minimum amount of hydrophilic colloid and/or a starch such as grafted starch in the resulting mixtures is about 1 welght percent based on the weight of the loaded latex composition, although more hydrophilic colloid can be used, if desired, to form a stabili~ed latex product.
The following is an illustrative, non-limiting e~ample of the preparation of poly(n-butyl methacrylate-co-styrene-co-2-acrylamido-2-methylpropane sulfonic acid in a charge weight ratio of 50:40:10, which provides suitable 20 "loadable" polymeric particles as described above: ~-To a one-liter addition flask were added 200 g of n-butyl methacrylate, 160 g of styrene, and a solution con-sisting of 7.7 g of NaOH, 350 ml H2O, 40 g of 2-acrylamido-2-methylpropane sulfonic acid, and 2 g of an anionic sodium salt surfactant of an alkylaryl polyether sulfate available in liquid form under the trademark "Triton 770" (40%) from Rohm and Haas.
The mixture was stirred for 30 min. prior to the addition process.

"! In a 250 ml addition funnel was added 200 ml H2O
; containing 2 g of K2S2O8. Both the addition flask and the addition funnel were connected to a 3-liter reaction flask containing 800 ml H2O and 4 g o~ "Triton 770"
(40%) maintained at 95C with stirring. To start the pol~meri-zation, 1.2 g of Na2S2O5 was added to the reaction flask ~ ~
.
... . .

~795~6 immediately followed by the addition of monomer mixture and K2S208solution. The period of addition was about 30 min~ The polymeri-zation was allowed to proceed for an additional 30 min. The latex was then cooled and dialyzed ovexnight to give a solids content o~ 13.8~.
ELEMENT
According to a preferred embodimen-t of the present in-vention, a sta~ilized loaded lat~x composition such as described above is coated directly upon a suitable support by conventional means and the solvent or suspension medium is driven off to pro-vide a novel scintillation counting element. The ~upport can be omitted if the coating is self-supporting, or if the composition - -is to be used in block form. In the latter case, the polymeric particles must be formed from the monomers described above which ; do not cause a substantial decrease in efficiency as thickness increases. If a support is to be used, it can be a conventional photographic support. Typical supports include transparent sup-ports, such as film supports and glass supports as well as opa~ue supports, such as metal and photographic paper supports. The support can be either rigid or flexible. The most common supports for most applîcations are paper or film supports, such as poly (ethylene terephthalate) film. After coating the support, a substantial amount (generally at least about half, but preferably at least about 80 weight percent) of the water in the resulting coated wet layer is removed (preferably by evaporation) from said coated wet layex to form the desired, "substantially dry" coated ; substrate product. The dried layer preferably contains polymeric particles derived from the latex, calculated apart from the fluor, in the range of about 1 to about 5 g/100 cm .
` Any coating technique involving the use of coating hop-pers and/or other apparatus can be used to apply one or more layers of the compositions of the presen~ invention to a support.
Useful coating techniques and supports are described in the -~

publications listéd in Product Licensing ~-, Index, vol. 92, page 109, Dece~er, 1971. Typical coating com~
positions contain from about 3 to 25 percent and preferably about 10 to 20 percent by weight of solids and the wet coating of such composition can be about 5 to 40 millileters/100 cm , and prefer-ably 10 to 30 ml/100 cm2.
It has been found that as much as 25% of the dry coat-ing weight, which includes the binder, can be the fluor, using the above-described methods. Preferably, the latex polymer com- ~-prises between about 33 to about 80~ of the dry coating weight.
BINDERS
If the novel scintillator composition of the present invention is to be coated on a support to provide a novel element as described hereinabove, a hydrophilic binder can be added to retain the individual particles of the latex residue in a relatively fixed physical relationship on the supporting substrate and to assist in absorbing aqueous samples. In addition to providing a suitable medium or matrix for the residual latex particles, the !
binder preferably pcssesses certain other desirable characteris~
tics. Among these are that the binder be substantially non-quenching, i.e., it ~hould not absorb to any significant extent (i.e., more than about 1%) incoming emissions or inhibit to any significant extent the mobility of such particulate or wave form emissions in the scintillator composition or absorb in any inhibi-ting ~ashion the emissions of the fluor once excited.
In this regard, gelatin and starches which impart stability to the late~ as just described also serve the binding function when used at concentrations ranging from about 3.0 to abou~ 50 percent by weight of the latex or from about 2.0 to about 35 percent ~y dry weight of the coated scintillator compo-sition. The increased viscosity provided by the binder makes itparticularly useful for machine coating the counting composition.

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~ gra~ted starch such as that available ~rom General Mills has been found to ~e a particularly good binder which possesses each o~ the properties specified above. Other useful binders include poly(vinyl alcohol) and poly(acrylamide).
When a stabilizing colloid such as gelatin is also to be used as a binder for the dried residue of the loadable polymeric latex, the wei~ht ratio o~ loaded latex residue to binder should range from about 1.0:0 75 to about 10.0:1Ø A particularly useful overall weight ratio of the solids components is 1 part fluor, 3 parts polymer, and 0.33 parts colloidal binder such as gelatin. A high ratio of residue to binder is desi~able so that the polymeric particles are packed closely together Too much binder may tend to cause detrimental quenching and a decrease in -~
counting efficiency.
The process ~or preparing the loaded latex compositions, and ~or incorporating the resulting composition into a layer which contains at least one colloid, can be per~ormed at temperatures ranging from about 0C to about 40C or more~
care being necessary merely to prevent, or to encourage, as desired or necessar~, the setting up or gelling of the .- coating compositions at the appropriate times It has been determined that the binder can be omitted entirely, particularly when the amount o~ acrylic ester monomer is increased to exceed the weight percent of the other monomers.
Although the resulting coating prepared from such a composition i may be somewhat tacky, the counting efficiency is still at least about 23~.
In those instances in which the coated latex is somewhat brittle, it is preferred that increased amo~lnts of binder be used.

Element Use In use, a radioactive sample is applied to the preferably "dry"-coated scintillation counting element.
Such sample can be delivered in any suitable manner, such as by depositing an aqueous test sample on the sur~ace of the composition, resulting in s~elling thereof in response to 5~

the water of the sample. After permitting the sample to disperse throughout the portion of the coating to be examined, the coating then is positioned under a fluorlmeter of conventional design, such as is obtainable under the trademark "Tri-Carb Liquid Scintillation Counter," from Packard Instruments, to detect the amount of fluorescence which corresponds to the radiation of the test sample. It is the highly concentrated, uniform dis-persion of fluors by the techniques described above which brings the sample now in the coating into very close proximity with the - 10 fluors. In this fashion it is possible to have a counting efficiency which is high enough to detect emission energies as low as about 0.01 Mev.
Optionally, the element plus sample can be dried to evaporate the water from the sample, to increase the counting efficiencies by 1 or 2%. However, the efficiency provided by the invention is so high that such a drying step is not critical or necessary.
: Examples The practice of the invention is further illustrated ; 20 by the following non-exhaustive examples.
Ex. 1 - 3 , To make a dispersion for coating, 3 g of PPO fluor and `
., 15 mg of POPOP fluor were dissolved in 90 ml of tetrahydro~
furan, then ~0 g of poly(n-butyl methacrylate-co-styrene-co- :~
2 acrylamido-2-methylpropane sulfonic acid) (50/40/10 weight ratio), hereinafter '1Polymer 1", aqueous latex prepared as described above, containing 9 g of polymer, was added gradually, with stirring at about room temperature. The solvent was removed by evaporation in a rotary evaporator. After filtration 25 g of 10% gelatin was added. The final dispersion contained 3% of PPO, 1.5 x 10 2% of popop, 9% of Polymer 1 and 2.5% of gelatin, measured per dry weight of solids.

~ .

This dispersion was cast at a wet coverage of lO ml /lO0 cm2 on subbed poly(ethylene terephthalate) and evaporated to clryness. For the three examples, three strips 2" x l/2" were cut and treated with .Ol ml Benzoic Acid-3H
solu~on in water, Benzoic Acid-3H solution in p-Dioxane, and Benzoic Acid-l4C in water, respectively. Each solution when coated had approximately 22,000 disintegrations/Min. The strips were evaporated to clryness, mounted in 20 ml glass counting vials, and counted in a Packard Tri-Carb 1iquid Scintillation Counter Model 3380 at 12C. The strips were aligned normal to the axis o~ the 2 photomultiplier tubes. The counting efficiency was determined by comparing the detected emission against the theoretical disintegrations per minute.
The results appear in Table I.
Table I

Sample ! Counting Ex. ConstituencyEfficiency _ _ l 3H Benzoic Acid in Water 31.8%
2 3H Benzoic Acid in p-Dioxane 25.6%
~` 20 3 l C Benzoic Acid in Water 89.5%

Ex. 4-7 To determine the effect of the thickness of the coating, Examples 1-3 above were repeated, except that four coatings were made, two at 20 ml/lO0 cm2 and ~wo at 30 ml/lO0 cm2, wet thickness, respectively, and only tritium-containing benzoic acid in water and tritium-containing benzoic acid in p-dioxane were used as the test samples. The results appearing in Table 2 : indicate that the ef~iciency increased as the coa-ting thickness increased O

:

~L~79~

Table 2 Counting Wet Efficiency Ex. Thickness Test Sample (%)

4 203H Benzoic acid in 32.9 " 34.5 6 203H Benzoic acid in --p-dioxane 7 30 " 30.0 10Ex. 8-12 Coatings were prepared as in Ex. 1, except that the disper-sion thickness was 30 ml/100 cm2. For each of these 5 examples,

5 different isotopes identi~ied in Table 3 were chosen as the test samples. The results are given in Table 3.

` Table 3 -~

Counting Energy Efficiency Ex. Isotope(Mev.) (%) 8 C in H200~156(~) 89.5 20- 9 C in p-dioxane " 82.5 45Ca0.252(~) 100 11 36c10.714(~) 100 12 5I 0.035(Y) 48 Ex. 13-19 The same procedures were followed as that of Ex. 1, except that 360 g of styrene was used without any butyl meth-acrylate monomer, to ~orm as the polymer, hereina~ter "Polymer 2", ~ ~;
poly(styrene-co-2-acrylamido-2-methyl propane sulfonic acid) with a charge weight ratio o~ 90:10. The total solids 3 content was 16.2%.

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~ 7~5~L6 A dispersion of PPO and POPOP was made by using Polymer 2 in the procedure described in Ex. 1. The final dispersion contained 2% of PPO, 1 x 10 2% of popop, 4% of Polymer 2, and 2% of gelatin. For each of the seven examples, coatings were made as in Ex. 1, except that the dispersion thicknesses and the test samples were varied as shown in Table 4. The counting efficiencies also appear in Table 4.

Table 4 Wet -~-Dispersion Counting Thickness2Test Efficiency Ex. (ml/lOOcm )Sample (%) 132 3H Benzoic Acid 39.2 H
in H20 1410 ll 39.7 1520 " 38.3 163:0 - " 25.1 1710 3H Benzoic acid 39.7 in p-dloxane 1~3 20 " 28.3 1930 " 23-7 .

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9S~6 E~. 20 It has been found that a coating prepared identically to that of Ex. 1, except with butyl acrylate as a fourth monomer in a charge welght ratio of 10:10:70:10, the 70 weight percent being styrene, to form poly(n-butyl acrylate~co-n~butyl meth- ~
acrylate-co-styrene-co-2-acrylamide-2~methylpropane sulfonic ~ : .
acid), will also give a satisfac~ory scintillation counti.ng composition with a counting efficiency at least as high as 40~
when used to measure the radiation of tritium-containing benzoic acid in H2O.
, Ex. 21 - 25 ~
.,, :
To determine the effect of drying the sample and element prior to reading the fluorescence, five elements were prepared -as in Ex. 20, and coated at 20 ml/100 cm2. Upon each was : deposited tritium-containing benzoic acid in H2O. Drying time and conditions were varied as shown in Table 5, which illustrates the counting efficiencies.

Table 5 - Effect~ of Drying Counting 20 Ex. Drying Conditions Efficienc~ (%) 21 1 hour at 65C 40.9 22 2 hours, ambient temperature 39.8 23 4 hours, ambient temperature 41.3 24 5-1/2 hours, ambient temperature 41.9 25 24 hours, ambient temperature 40.9 Clearly, the effect of the moisture in the element is not enough to prevent a high counting efficiency, and can be accommodated by appropriate calibration.

-28- ~

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Ex. 26-27 Two coatings o~ 30 ml/100 cm2 wet ~hickness were prepared identically to that of Example 1, except with the sulfonic acid monomer omitted and the amount of styrene increased. In Example 26, the acrylic ester monomer was butyl.
methacrylate to form poly(n-butyl methacrylate-co-styrene) (35/65 weight ratio), while in Example 27 it was butyl acrylate to form poly(n-butyl acrylate-co-styrene) (35/65 weight ratio).
These gave a satisfactory scintillation counting composition with a counting efficiency of about 38% when used to measure the radiation of tritium-containing benzoic acid in H20.

Ex, 28 A coating prepared as in Ex, 1 except with a monomer ratio of (55/40/5) and no binder, and a latex to fluor ratio of 3:1, gave a counting efficiency of 22.6~ when used to measure the radiation of tritium-containing benzoic acid, The film so formed was tacky, but nevertheless gave successful counting results. ~-:
Ex. 29 ..
A coating prepared as in Ex. 1 except with a monomer ~ :
weight ratio of (30/60/10), and which had a weight ratio of polymer:gel binder:fluor of 3:3:1, gave a reduced counting efficiency of 17.92~ -- a value that is quite sufficient for ;., .
high energy emissions.
Ex, 30 -- -:
A coating prepared as in Ex. 29 except with a polymer:
fluor:starch binder:gel binder ratlo of 5:1:0.1:0.2 was prepared ~:
to demonstrate that a reduced amount of fluor concentration will also function satisfactorily. The counting efficiency . 30 when measuring tritium-containing benzoic acid in H20 in - -a coating wet thickness of about 30 ml/100 cm2 was 34.8~.

~ ' .

~x. 31 A coating was prepared as in Ex. 16 except that the polymeric latex was changed so that 3-methacryloyloxy propane-l sulfonic acid was substituted for 2-acrylamido-2-methyl propane sulfonic acid monomer. The final latex:fluor:gel binder ratio was 3:1:1. The counting efficiency, when measured as in Ex. 30, was 30.4%. In this example, the increased amount of binder was found to be useful for coating the otherwise brittle latex.
The invention has been defined in detail with partieular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications ean be effeeted within the splrit end seepe of the invention.

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Claims (28)

What is claimed is:

1. A scintillation counting composition comprising loaded polymeric particles derived from a latex, said particles being loaded with at least one hydrophobic fluor, said fluor being present in an amount sufficient to give said composition a counting efficiency of at least about 23%, when used as a substantially dry layer coated with a maximum wet thickness of 30 ml/100 cm2 and tested with a water solution of tritium-labeled benzoic acid.

2. The composition as defined in claim 1 wherein said fluor comprises at least about 16% of the dry weight of the composition.

3. The composition as defined in claim 1 wherein said polymer is copolymerized from at least two ethenic monomers one of which is a styrene monomer having the formula wherein R1 is hydrogen or methyl; R3, R4 and R6 are hydrogen or lower alkyl of 1 to 4 carbon atoms; R5 is hydrogen or with R4 constitutes the atoms necessary to complete a fused benzene ring.

4. The composition as defined in claim 3 wherein one of said ethenic monomers is a sulfonic acid or a sulfonate monomer in an amount between about 0 and about 10 weight percent of the composition.

5. The composition as defined in claim 3 wherein one of said monomers is an acrylic ester monomer having the structure H - ? = ? - ? - O - R2 wherein R is hydrogen or lower alkyl, R1 is hydrogen or methyl, and R2 is an aliphatic group containing from 1 to 6 carbon atoms.

6. The composition as defined in claim 1 wherein said fluor is selected from the group consisting of 2,5-diphenyloxazole; 2,2'-p-phenylene bis(5-phenyloxazole), p-bis(o-methylstyryl)benzene, and 1,4-bis-2-(4-methyl-5-phenyloxazolyl)-benzene.

7. The composition as defined in claim 1, and further including, in admixture, a substantially non-quenching binder, the weight ratio of said particles to said binder ranging from about 1.0:0.75 to about 10.1:1Ø

8. The composition as defined in claim 1 wherein two different fluors are present, one of which is a primary fluor and the other of which is a wave shifter.

9. A scintillation counting composition, comprising 1) a polymer latex exhibiting essentially no visible coagulation or settling when 250 ml of the latex containing about 12 to about 20 weight percent synthetic polymeric particles dispersed discontinuously in an aqueous continous phase is slowly stirred at 25°C into 250 ml of acetone over a 1 minute period at a uniform rate, and the blend is thereafter allowed to stand at 25°C for about 10 minutes, and 2) at least one hydrophobic fluor uniformly dispersed throughout said composition and distributed among said particles in an amount sufficient to give to said composition a counting efficiency of at least about 23%, when used as a substantially dry layer having a maximum thickness of 30 ml/100 cm2 and tested with a water solution of tritium-labeled benzoic acid.

10. The composition as defined in claim 9 wherein the weight ratio of said fluor to said loaded synthetic polymer in said particles is from about 1 to 5 to about 4 to 3, respectively.

11. The composition as defined in claim 9 wherein said particles comprise a polymer copolymerized from at least two ethenic monomers one of which is a styrene having the formula wherein R1 is hydrogen or methyl; R3, R4 and R6 are hydrogen or lower alkyl of 1 to 4 carbon atoms; R5 is hydrogen or with R4 constitutes the atoms necessary to complete a fused benzene ring.

12. The composition as defined in claim 11 wherein one of said ethenic monomers is a sulfonic acid of a sulfonate in an amount no greater than about 10 weight percent.

13. The composition as defined in claim 12, and further including as an additional monomer, an acrylic ester having the structure H - ? = ? - ? - O - R2 wherein R is hydrogen or lower alkyl, R1 is hydrogen or methyl, and R2 is an aliphatic group containing from 1 to 6 carbon atoms.

14. The composition as defined in claim 9 wherein said composition is substantially dry and further including in admixture, a substantially non-quenching binder, the weight ratio of said latex to said binder ranging from about 1.0:0.5 to about 10.0:1Ø

15. The composition as defined in claim 9 wherein said fluor is selected from the group consisting of 2,5-diphenyloxazole; 2,2'-p-phenylenebis(5-phenyloxazole), p-bis(o-methylstyryl)benzene, and 1,4-bis-2-(4-methyl-5-phenyloxazolyl)-benzene.

16. The composition as defined in claim 9 wherein two fluors are present, one of which is a primary fluor and the other of which is a wave shifter.

17. A scintillation counting composition comprising:
(I) the dried residue of an aqueous latex composition comprising a dispersed phase of solid particles of a copolymer comprising:
(a) from about 0 to about 10 weight percent of a hydrophilic ethenic monomer containing a sulfonic acid group;
(b) from about 0 to about 95 weight percent of one or more acrylic ester monomers having the structure H - ? = ? - ? - O - R2 wherein R is hydrogen or lower alkyl, R1 is hydrogen or methyl, and R2 is an aliphatic group containing from 1 to 6 carbon atoms, (c) from about 1 to about 99 weight percent of styrene monomer having the formula wherein R1 is hydrogen or methyl; R3, R4 and R6 are hydrogen or lower alkyl of 1 to 4 carbon atoms; R5 is hydrogen or with R4 constitutes the atoms necessary to complete a fused benzene ring; and (d) at least one hydrophobic fluor uniformly distributed among said particles in an amount sufficient to give to said composition a counting efficiency of at least about 23%, when used as a substantially dry layer having a maximum thickness of 30 ml/100 cm2 and tested with a water solution of tritium-labeled benzoic acid; and (II) a substantially non-quenching binder, the weight ratio of said latex residue to said binder ranging from about 1.0:0.75 to about 10.0:1Ø

18. The composition as defined in claim 17 wherein said fluor is selected from the group consisting of 2,5-diphenyloxazole; 2,2'-p-phenylenebis(5-phenyloxazole), p-bis(o-methylstyryl)benzene, and 1,4-bis-2-(4 methyl-5-phenyloxazolyl)-benzene.

19. The composition as defined in claim 17 wherein two fluors are present, one of which is a primary fluor and the other of which is a secondary fluor.

20. A scintillation counting element comprising 1) a support, and 2) coated over the support, a dry residue of latex composition which comprises loaded polymeric particles derived from a latex, said particles being loaded with at least one hydrophobic fluor in an amount sufficient to give to said com-position a counting efficiency of at least about 23%, when used as a substantially dry layer having a maximum thickness of 30 ml/100 cm2 and tested with a water solution of tritium-labeled benzoic acid, and 3) a substantially non-quenching binder, the weight ratio of said latex residue to said binder ranging from about 1.0:0.75 to about 10.0:1Ø

21. The element as defined in claim 20, wherein said weight ratio ranges from about 1.0:0.5 to about 10.0:1Ø

22. The element as defined in claim 20 wherein said fluor comprises at least about 25 weight percent of the solids content of said residue.

23. A scintillation counting composition comprising a dispersed phase consisting essentially of solid particles of a synthetic polymer derived from a latex and loaded with at least one hydrophobic fluor distributed throughout said particles;
the weight ratio of said fluor to said loaded synthetic polymer in said particles being from about 1 to 5 to about 4 to 3, re-spectively, and the average diameter of said particles being no greater than about 0.2 micron.

24. The composition as defined in claim 23 wherein said particles comprise a polymer copolymerized from at least two ethenic monomers one of which contains from about 1 to about 99 weight percent of the monomer having the formula wherein R1 is hydrogen or methyl; R3, R4 and R6 are hydrogen or lower alkyl of 1 to 4 carbon atoms; R5 is hydrogen or with R4 constitutes the atoms necessary to complete a fused benzene ring.

25. The composition as defined in claim 23 wherein said composition is substantially dry, and further including in admixture, a substantially non-quenching binder, the weight ratio of said particles to said binder ranging from about 1.0:0.75 to about 10.0:1Ø

26. The composition as defined in claim 23 wherein said fluor is selected from the group consisting of 2,5-diphenyl-oxazole; 2,2'-phenylenebis(5-phenyloxazole, p-bis(o-methylstyryl) benzene, and 1,4-bis-2-(4-methyl-5-phenyloxazolyl)benzene.

27. The composition as defined in claim 23 wherein two different fluors are present, one of which is a primary fluor and the other of which is a wavelength shifter.

28. A process of detection of low-energy emission of about 0.01 Mev. comprising the steps of 1) depositing an aqueous sample of low energy-emitting material upon a coating of a scintillation counting composition comprising polymer particles derived from a latex and loaded with at least one hydrophobic fluor in an amount sufficient to give to said composition a counting efficiency of at least about 23%, when used as a substantially dry layer having a maximum thickness of 30 ml/100 cm2 and tested with a water solution of tritium-labeled benzoic acid; and 2) after the sample has uniformly dispersed throughout the volume of the coating to be detected, detecting the amount of fluorescnece of the coating in response to the energy emission of the sample.