DE2904656A1 - MEANS OF COUNTING SCINTILLATION - Google Patents

Description

DR. BERG DTPL.-ING. STAPF DIPL.-ING. SCHWEBE DR. DK. SANDMAIR

PATENTANWÄLTE Z ΰ U 4 D D

P.O. Box 860245-8000 Munich 86

Attorney's file: 29 837 7 - February 1979

CIBA-GEIGY AG Basel / Switzerland

Scintillation counting means

Case: 1-11609 / +

90983 5/0581

• (089) 988272 telegrams: Bank accounts: Hypo-Bank Munich 4410122850

988273 BERGSTAPFPATENT Munich (BLZ 70020011) Swift Code: HYPO DE MM

⁹⁸⁸²⁷⁴ TELEX: Bayer Vereinsbank Munich 453100 (bank code 70020270) ⁹⁸³³¹⁰ 0524560 BERG d Postscheck Munich 65343-808 (bank code 70010080)

CIBA

CI3A-GEIGY AG. CH-4002 Basel

Case 1-11609 / + 2904656

Scintillation counting means

The present invention relates to means for scintillation counting containing a stabilizing agent organic compound of divalent sulfur and the use of these means for liquid scintillation counting.

It is known to those skilled in the art that scintillator counts must be kept (equilibrated) in the dark for some time before counting, as this is what they do tend to temporarily increase the count value (cpm »counts per minute) due to exposure to light. to surrender. This leads to incorrect measured values, which are all the more disruptive as they are only available for the blank value without Tracer clearly come to light. It is not certain whether this is phosphorescence, Chemiluminescence or other phenomena. But since this is an apparently slow process acts, there is an undesirable delay between the preparation of the count sample and its undisturbed Measurement.

In order to eliminate this disadvantage, it has been necessary up to now to start the scintillator preparation in good time prepare and use them at constant, if possible

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low temperature (0 to + 4 ⁰ C) _{31 to be kept} under exclusion of light. This "adaptation time" varied within wide limits, ie between at least 30 minutes and 24 hours.

According to the disclosure in German Offenlegungsschrift 20 22 390, the chemiluminescence postulated there can to an acceptable blank value, i.e. to a Blank value between 48 and 120 pulses / minute (cpm = counts per minute) can be reduced if the scintillator » Preparation treated with certain basic compounds, but the effect is only of a very limited duration.

It has now been found that you can reduce the photosensitivity in an advantageous manner if you adding stabilizing organic compounds of divalent sulfur to the stintillator preparations. These additions enable a long adaptation time to be avoided and a possible source of error during the measurement to be eliminated.

The means according to the invention for scintillation counting are characterized in that they contain at least one such stabilizing compound.

Such stabilizing compounds are compounds of divalent sulfur which have a reducing effect as well as their mixtures into consideration.

Mercaptans whose dissociation constant is greater than that of phenol are preferred Sulfides that are of the formula

(DR ₁ -SR ₂

correspond, where R and R ₂ independently of one another an aliphatic radical with preferably 1 to 8, in particular 1 to 4 carbon atoms or R ₁ and R ₂ together with the sulfur atom also mean a 5- or 6-membered ring.

"Aliphatic" means acyclic, straight-chain ones or branched, saturated or unsaturated, unsub-

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Hydrocarbon radicals which are substituted or substituted by non-homomophore and non-ionic groups and preferably have 1 to 8, in particular 1 to 4, carbon atoms. Particularly suitable non-chromophoric and non-ionic groups are: hydroxy, ammonium, mercapto and carboxy groups and the phenyl radical. Preferred aliphatic radicals are straight-chain groups with 1 to 4 carbon atoms. Aliphatic radicals R- and R ₂ can also contain other heteroatoms, for example oxygen or sulfur atoms. Heterocyclic rings which are formed by R and R 2 together with the sulfur atom are preferably saturated rings which can contain further heteroatoms. Mercaptans are preferably aromatic and heterocyclic mercaptans, which include, for example, compounds which, in addition to the mercapto group, can also have other substituents on the aromatic or heterocyclic ring, such as alkyl radicals with 1 to 4 carbon atoms, amino groups, hydrazino groups, hydroxyl groups or another mercapto group.

Examples of such mercaptans and sulfides are: l-methyl-2-mercapto-imidazole, 2-mercapto-benzimidazole, 4-mercapto-pyridine, 2-mercaptopyridine, 2-mercapto-4,6- -dimethy1-pyrimidine, 2-mercapto-4-hydroxypyrimidine, pyridinthione-1-oxide, 2-mercapto-benzothiazole, 2-mercapto-benzoxazole, thiophenol, 2-mercapto-A4-thiazoline, 2,5-dimercapto-l, 3,4- -thiadiazole, 3-mercapto-4-amino-5-hydrazino-4, l, 2-triazole, thioanisole, dibutyl sulfide, 3,3-thiodipropionic acid, thiodiethylene glycol, 1,3-dithiane, diammonium sulfide, 3,3-thiodiproprionitrile, 2-mercaptoethyl sulfide and tetrahydrothiophene.

With the compounds which can be used according to the invention one achieves that freshly prepared scintillation counts must be equilibrated much shorter or not at all in the dark prior to the count, until the

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Has stabilized the blank value to the minimum. This advantage is clearly evident, e.g. with one as a secondary solute 4,4'-bis (2 ", 5" -dimethylstyryl) -biphenyl containing Liquid scintillator, which according to the invention without additive usable compounds even with a moderate exposure to light indicates temporarily increased blank values. The effectiveness of the compounds which can be used according to the invention becomes clear when the scintillation counts are extreme by exposure to an additional UV light source Suspends conditions. Despite such extreme conditions, the blank value is at least 15 minutes after exposure a factor of 10 smaller than that of a control sample without a compound which can be used according to the invention.

The agents according to the invention contain the stabilizing additive in amounts of up to 100 percent by weight, particularly from 0.005 to 100 percent by weight and preferably from 0.05 to 10 percent by weight, based on the scintillator -Active substance. In ready-to-count solutions, are obtained on these solutions, 0.00005 to 1 percent by weight, preferably 0.0005 to 0.1 percent by weight of the stabilizing agent Addition used.

The surprising thing about the use of these stabilizers is that the expected extinction (chemical quenching) remains limited to an acceptable level.

Both primary solutes and mixtures of primary with secondary solutes can be used as scintillator substances for the agents according to the invention, such as those from Nucleonics _13, No. 12, December 1955, pages and 44, from Journal Chem. Physic _50, No. 11, June 1969, page 4962 and the compounds known from German Offenlegungsschrift 20 22 309. _{4,4'-bis- (2>} 5-dimethylstyryl) - can also be used as scintillator substances

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-biphenyl and 4,4'-bis- (2,4,5-trimethylstyryl) -biphenyl which are known from US Pat. No. 3,984,399 can be used.

The agents according to the invention are either ready-to-use liquid scintillators or solute concentrates, used for the production of liquid scintillator preparations for liquid scintillation payment can be.

Suitable solvents for liquid scintillation counting are primarily aromatic solvents at room temperature liquid hydrocarbons or mixtures, such as benzene, toluene, xylenes, ethylbenzene, 1,3,5-triethylbenzene, Cumene, cymene, phenylcyclohexane, and ethers such as Anisole, dioxane, 1,2-dimethoxyethane, non-aromatic hydrocarbons such as cyclohexane, heptane, etc., or finally solvent mixtures such as toluene / methanol and optionally Water, toluene / ethanol, naphthalene / dioxane, naphthalene / toluene and optionally water, naphthalene / dioxane / water, methyl cellosolve / naphthalene / toluene and optionally water, naphthalene / tributyl phosphate, other commercially available ones for these Aromatic hydrocarbon mixtures or mixtures of aromatic hydrocarbons recommended for purposes, e.g. the above, with surfactants such as ethoxylated alkylphenols, ethoxylated fatty alcohols, polyoxyethylene alkylphenyl sulfates, Polycarboxylic ester sulfonates, alkyl sulfonates, alkyl sulfates, alkyl naphthalene sulfonates, alkylaryl polyglycol ethers, sulfated ethylene oxide adducts and fatty acid sulfates.

The concentration of the scintillator substances in preparations according to the invention can in principle be within vary widely and are determined or limited out of practical needs. For example, it must be in the lower Limit to be dimensioned so that an adequate transmission

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to the scintillation recording system (photomultiplier) is guaranteed, while the upper limit is set by the noticeable absorption of self-emission ("self-quenching"). Although, for example, for the production of stock solutions (which are diluted accordingly for use), concentrations of 10% and higher are easily possible, the practically interesting working concentrations are between approximately O ₃ O and 5%, especially 0.1 and 3%. and preferably 0.4 to 2% (always weight percent based on the total weight of the solution) »

In addition to toluene and the xylenes, preferred solvent systems are the systems toluene / methanol (1: 1) with the addition of about 2% water, methyl cellosolve / toluene / naphthalene (40: 60: 8) with up to 4% water, dioxane / toluene / naphthalene (40: 60: 8) with up to 10% water or toluene / methanol / ethanolamine (50: 44: 6) or the corresponding mixtures with the xylenes. The arrangement of the solvent system depends primarily on the nature of the one to be measured Substrate or the isotope to be measured, whereby for the latter, for example, C, "3 _O 35 32" 59 _ 55 _T 125, _T 131

H, S, p, Fe, Fe, 1 and I are called sexen.

The following examples illustrate the invention without restricting it. Percentages are percentages by weight .

example 1

A ready-to-use scintillator solution which, dissolved in 100 ml of toluene, contains 800 mg of 2- (4'-tert-butylphenyl) -5-biphenylyl-1,3,4-oxdiazole (butyl-PBD) as the primary solute and 180 mg containing 4.4 ^I-bis- (2 ^ri, 5 "-dimethylstyryl) biphenyl, can be added as a stabilizer, 100 mg of 2-mercaptobenzothiazole.

909835/0581

K)

20 ml of this solution are exposed to a UV lamp (366 mu) for 15 minutes. The immediately following measurement of the impulses per minute shows in comparison to a Probi
Blank value.

4 a sample without stabilizer is about 10 times smaller

After equilibration in the dark for 22 minutes

3 ⁰ C the non-stabilized sample still has an approx.

3
10 times higher than the stabilized sample.

Results of the same order of magnitude are obtained if, instead of 2-mercaptobenzothiazole, 3,3-thiodipropionic acid, 2-mercapto-1-methy! Imidazo1 or 2-mercaptobenzimidazo1 is used.

Example 2

Proceeding as described in Example 1, but using 1,4-bis (2 "-methylstyryl) benzene as secondary solutes, in this way one arrives at similarly good results.

Example 3

If to prepare the scintillator solution of Example 1 instead of toluene, a mixture of toluene and a surfactant, such as ethoxylated isooctylphenol, (approx. 1: 1) is used, an equally excellent stabilization is obtained. Example 4

If the procedure is as described in Example 1, used but thiodiethylene glycol as a stabilizing compound, Dibutyl sulfide, 1,3-dithiane, pyridinthione, thiophenol, 2-mercaptobenzoxazole, 2-mercaptothiazoline or tetrahydrothiophene instead of the 2-mercaptobenzothiazole, then achieved

2 3

one blank values that are 10 to 10 times smaller than those of non-stabilized samples.

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Claims (9)

Attorney's file: 29 837 "'^ i.': ;;" ^{1st 3} '' - ^D - ~ ^: Γ> Π. Gandmair- Patent claims I., - means for scintillation counting _s containing a stabilizing organic compound of the bivalent
Sulfur. 2. Means according to claim I ₅ containing the stabilizing compound in amounts of O ₅ 005 to 100 percent by weight based on the scintillator active substance. 3 »A composition according to claim 2 _S containing as stabilizing compound is a mercaptan _s Dissosiationskonstante which is larger than those of the phenol" 4. A composition according to claim 2, containing a sulfide of the formula as the stabilizing compound TJ Q TJ wherein R 1 and R 2 are, independently of one another, an aliphatic Radical with 1 to 8 carbon atoms or R, and R2 together with the Sulfur atom also mean a 5- or 6-membered ring. 5. A composition according to claim 3, containing a 2-mercaptoazole as the stabilizing compound. 6. Agent according to claim 5, wherein 2-mercaptobenzimidazole is used as 2-mercaptoazole. 7. Agent according to claim 5, wherein 1-methyl-2-mercapto-imidazoI is used as the 2-mercaptoazole. 8. Agent according to claim 5, wherein 2-mercaptobenzothiazole is used as 2-mercaptoazole. 909835/0581 29CU656 - y- 9. Use of the agent according to claim 1 for Preparation of a liquid counting sample for the liquid -S ζ int ilation counting. 909835/0 5 81