DE2004847A1 - Liquid scintillator preparations for counting gamma rays and thermal neutrons - Google Patents

Description

DR. BERG DIPL.-ING. STAPF

8 MUNICH 2. HILBLESTRASSE 2O |

* Pr. Berg Dlpl.-Ing. Stopf, 8 Munich 2, HllblestraBe 20

Your sign

our sign 19 323 ^{l date} 3 February 1970

Attorney file number, 19 323

■ Monsanto Company

800 North Lindbergh Boulevard St. Louis, Missouri / USA

"■ Liquid scintillator preparations for counting,,,

Gamma rays and thermal neutrons ". ^: ..

■■ .. '■. ·. ■■. - - j ■

Addition to P 19 18 ^283.3:.! ■ '* ■ ■ 1

The present invention relates to the liquid scintilla} tion-counting "In particular, the present invention relates an improved preparation and method for Liquid scintillation counting and for recording -of- thermal-

^f X

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; see or slow xieutron and gamma rays.

In recent years, liquid scintillation counting has been used radiation a very popular tool for industry and research. In short, the liquid scintillation counting technique includes the interaction of radiation, usually with organic molecules, including emission caused by light impalses caused by the organic molecules and the light pulses are proportional to the radiation. ™ The light pulses are generated using a suitable The apparatus is counted and the radiation level is determined by this technology. In general, this is the liquid scintillation counting method used Plüssig scintillator made of a dissolved in an aromatic solvent

Fluorine. While such scintillators for .Iessung of

14 35 Beta emitters of low energy, such as C, S

and H, are suitable, but are not suitable for the detection of thermal neutrons or gamma rays, fl | When thermal or slow neutrons are absorbed by carbon, hydrogen and oxygen atoms normally found in such organic scintillators, they do not produce scintillation light . Diepe's problem became a certain «ϊϊ örad / '

10 ^{e! A} /

The addition of boron -containing compounds is necessary

, j; Saintillator solution overcome. Boron has a sufficient i

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- "Z mm

high cross-sectional area for. Neutron reactions such that the thermal neutrons are efficiently absorbed; / Which leads to an emission of alpha particles. The alpha particles act alternately on the liquid organic scintillator to produce scintillation light, which is then detected, as described above ^. Unfortunately, it has been since the time when the 3zihϋ'jllla & o.r ^ L · Öätmgen ^ organic] ^ - ^ atμr'sind _ί; . necessary to use organoboron compounds to achieve these "laden" solutions. Organic boron compounds are usually expensive to manufacture, often very toxic and; ■ "'difficult to handle and very often it is · still; not possible

·· - "'■'

lica, a sufficiently high concentration of boron present notify to "- adequate absorption of neutrons to ensure.

Gamma rays of holier energy are not sufficiently absorbed by the CHO atonies as they are normally found in organic saintillators. This problem su overcome the Szintillatorlösungen Λ vmrde 2U a gevrissen AusEiaß by Sugabe of Schwerlaetall-containing compounds. The to exist a Schvierr.etalls to the orsanischen Szinrillator increases the density oer solution, and causes - '"so that the Cranuna rays v; iri: sair, he will absoroieru in the medium, and so detects Un; is lückseligerweise. it,

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since the scintillator solutions are organic in nature, it is necessary to use organo-IIetal compounds for them to achieve "laden" solutions. Organo-metal compounds however, are usually quite expensive to manufacture,

r / often very toxic and difficult to handle and often it is not even possible to obtain a high enough concentration of the particular metal present to ensure adequate absorption of the gamma radiation.

A liquid scintillation counting preparation is known from the prior art, to which a neutron-capturing solute, often also ^t; It has now been found that the liquid scintillation preparation according to the prior art produces safe, inexpensive preparations which are excellent and particularly valuable for counting and detecting thermal neutrons or gamma rays are for very large-volume observation systems if they are combined with certain loading media.

The present invention, in one of its preferred embodiments, is a preparation for use in the liquid scintillation counting and for the detection of slow neutrons or ganma rays, containing

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at least 30% by weight of a scintillator solution, these Scintillator solution an aromatic hydrocarbon solvent, a dissolved scintillation substance and a ' contains ethoxylated alkylphenol in which the alkyl substituent has from 7 to 16 carbon atoms and the ratio the number of carbon atoms in the alkyl substituent to the average number of ethoxy groups in the mentioned ethoxylated alkylphenol is from 0.83 to 1.67, and a loading means.

The loading agent contains Mr thermal neutrons aqueous solution of a compound of an element, which has a sufficiently large, neutron-capturing cross-section possesses to cause the absorption of thermal neutrons, this element being one <which after trapping a thermal neutron, an exotherm Suffers nuclear reaction.

For gamma rays, the selected loading agent increases the absorption of the mentioned gamma rays and usually it contains an aqueous solution; a compound of a "■ element having an atomic number of higher than 20-;.

The preparations of the present invention contain zw.ei fundamental components, namely the scintillator solution and,

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the loading device. The scintillator solution contains im generally an aromatic solvent, an ethoxylated alkylphenol and a dissolved scintillation substance, whereas the loading agent is an aqueous solution of compounds of certain elements.

The ethoxylated alkylphenols, which are useful for the preparation of the scintillator solution, can in their structure can be represented by the formula below

° n ^K 2n + l

v / orin η has a value from 7 to 16 and χ the average Means number of ethylene oxide groups. The value of χ is of course dependent on the number of carbon atoms in the alkyl substituent vary. In general, however, the value of χ will be so large that the value of n / x in the range from 0.63 to * 1.67 lies. Examples of suitable ethoxylated alkyl

phenols and preferred ranges of n / x include ethoxylated heptylphenol r /. with a range of 0.83 to 1.08, ethoxylated octylphenol with one. Range from 0.83 to ; 1.11, ethoxylated ionylpheriol with a range of 0.89 to 1.11, ethoxylated decylphenol with a range of

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0.90 to 1.17, ethoxylated undecylphenol with a range from 0.93 to 1.22, ethoxylated dodecylphenol with a range from 0.95 to 1.27, ethoxylated tridecylphenol with a range from 0.97 to I ₃ 3 ^ * Ethoxylated tetradecylphenol with a range from 1.08 to 1.55, ethoxylated pentadecylphenol with a range from 1.15 to 1.67 and ethoxylated hexadecylphenol with a range from 1.33 to 1.51. As already stated above, χ means an average number of ethoxy groups per molecule. Accordingly, if one m

ethoxylated alkylphenol with 10.0 ethoxy groups speaks, Molecules are present which have both more and less than 10 ethoxy groups.

The ethoxylated alkylphenols useful in the present invention as well; Methods of making them are well known. Usually the ethoxylated alkyl phenols are prepared by the condensation of Sfchylenoxy.d with the desired alkylated phenol. Es'wird generally preferred that a ethoxylated alkylphenols of the present invention is mainly, ie, to about 5.0 | are in the para form. However, it is particularly preferred to use those in which at least 80 g of the ethoxylated alkylphenol '* is in the para form, the remainder essentially consisting of the ortho form.

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The solvents generally found useful in making the scintillator solution are the liquid ones aromatic hydrocarbons. Non-limiting examples of the latter include benzene, toluene, o-, m-, p-xylenes and mixtures thereof, cumene, the ethylbenzenes and ilesitylene. In particular, it has been found that xylene, Toluene and ethylbenzene give the highest number-performance. Particularly preferred solvents are the xylenes, i. the ortho, meta or para isomers, either alone or in admixture. The volume ratio of the solvent too the ethoxylated alkylphenol which can be used as a scintillation solution is usually from 3: 1 up to 1: 1. The ratio applied is determined by the requirements the sample stability, the temperature at which the samples are measured, the requirements for number performance and the percentage of the sample which one fsu measure wishes, definitely. The most useful ratios of solvent to ethoxylated alkylphenol are in Range from 2.4: 1 to 1.6: 1.

The dissolved scintillation substances that can be used to produce the scintillator solution are those which are known to those skilled in the art and the present invention is not intended to run on use any particular scintillation solute

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is limited, be it that it contains only one fluorine or be it that it also has a secondary solute, such as a spectral shifter or a waveband shifter contains. Some of the better known fluors, which are useful in the present invention para-terphenyl, the; Oxazoles and / or the oxadiazoles. Probably the one on; best known is oxadiazole fluorine PDD [2- (4-biphenylyl) -5-phenyl-1,3,4, -oxadiazole] and the am; best known oxazole fluorine is PPO [2,5-diphenyloxazole]. .,

- ■ - ■■. ■ ■ ■ ■ ■ "■ ■ i

Some of the better known secondary solutes that can be combined with the aforementioned primary solutes are POPOP [1,4-bis-2- (5-phenyloxazo-IyI) -benzene], alpha-NOPON [p-bis- 2- (5-l-naphthyloxazQlyl) -benzene], DPH [!, E-diphenyl-l ^ j ^ -hexatriene] ., Alpha-IJPO [2- (l ~ haphthyl) -5-phenyloxazole] and MSB [p- bis-colethylstyryD-benzene]. Another solved. Scintillation agent known in the art is m-terphenyl plus $ 0.5 anthracene. The dissolved scintillation substances only need to be present in amounts which are sufficient% to enable the preparations of the present invention to be useful as liquid scintillators. The optimal amount will vary according to the particular component or components making up the scintillation solute, and the amount will usually be in a balance between cost, solubility and

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Implementation information is available. The dissolved scintillation agent will usually be present in narrow ranges from 0.5 to 50 g per liter, but more often in narrow ranges from 1 to 12 g per liter. It is particularly preferred that the scintillator solutions of the present invention have about 4 to 6 grams per liter of dissolved. Scintillation substance included. Therefore, if only primary dissolved substances or fluorene are spoken of, these are usually present in a narrow range of about 0.5 to 12 tons per liter of the scintillator solution. Secondary solutes are generally present in relatively small amounts compared to those of the fluorine, that is, in amounts of about 0.05 to 3 grams per liter. The preferred scintillation solute of the present invention contains PPO and POPO? for thermal neutrons and PPO and --ISB for gamma rays.

The scintillator solution is at least 30% by weight, and preferably from 40 to 99% by weight, of the total scintillator formulation contain.

The processing selected for the production of the loading equipment. _v . bonds for the detection and counting of thermal neutrons should ideally be compounds of elements with high atomic density and low atomic number and they should have a strong neutrons interaction, polygamy _{: s} .

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causes a single measurable physical event, that is, an exothermic nuclear reaction. Such a reaction typically produces the emission of (1) substantial ionizing radiation, such as gamma rays, or (2) an energy particle, such as an aipha particle. An example of the neutron reactions that the. Neutroneh capture brings by a member having good neutron capture Charakterist ika with it is shown in the following, boron -containing equation.

«7 + η Li '+ α

The generated alpha particles then interact with the organic scintillator to generate scintillation light and can be detected with almost 100% yield . The selected compound is preferably a water-soluble one of an element, namely boron, lithium ⁶ , cadmium ¹¹³ , gadolinium ¹⁵⁵ , gadolinium ¹⁵ *, samarium ™ and / or samarium ^5, with water-soluble compounds of boron and lithium being particularly preferred .

In practice, any water-soluble compound of the above elements can be used. Non-limiting examples include sodium and lithium borate,

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Boric acid, boron fluoride, lithium acetate, chloride and bromide of samarium, the acetate, bromide and iodate of cadmium and other such connections.

The compounds chosen for making the loading means for detecting and counting the gamma rays will be ideally have the characteristics of high density and good water solubility, the former property is essentially fulfilled by a compound of an element W, which has an atomic number of above 20 having. As a general rule, the higher the the density of the compound used, the higher the density of the total scintillator preparation and accordingly the more effective gamma-ray capture ability. There are numerous connections which the above mentioned have listed characteristics with regard to the atomic number of the element and the water solubility. Be it j does not try to open all possible connections here.

t! however, typical examples of I.

generally available compounds that are suitable are given: the water-soluble halides, acetates and nitrates of cadmium, lead, zinc, cesium and barium; the nitrites, nitrates, and acetates of silver and gold; the bromides and iodides of sodium, potassium and lithium.

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If, a connection, .a. Element, which is a., Qrd-. .._ · number higher than 20 occupied, in the Scint.illafeor solution ■ is present, the incoming gamma rays with ... ". high energy are essentially caused by collisions with the - elements "slowed down" .- These collisions .continued the energy of the gamma "rays" so strongly that. · they then are able to work with the organic scintillator under Er.—. generation of scintillation light to interact, which then by conventional liquid saintillation. . Counting clmics can be measured.

In preparing the loading agents of the present invention, it is preferred to reduce the water soluble compound of the particular element present at a relatively high level. . Concentration to ensure maximum neutron or gamma-ray capture and consequently high detection performance. It should be understood that relatively low concentrations of the compound. in which loading means can be used. For example, results in an aqueous solution containing as little as I wt ■ -.% Of the selected -äh-. Connection satisfactory. Results. The amount of verb induing in the middle of the load becomes in a. Ausmaß'von 'water ^solubility:;

dependent on the same ^; -aMn, - Generally jedoeh-advertise ·. Loading means used, which weight-wise, from Lö

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up to 90 % of the maximum amount of compound also contained by weight, soluble in ./asaer at the temperature at which the scintillator preparation is to be used.

The loading rack is dependent on the particular, compound used in the preparation of the present invention in amounts ranging up to 70%, however, preferably from 1 to GO wt .- ;. · present.

To produce the preparations used here, the scintillator solution and the loading device are simple mixed together until a clear or translucent solution or gel is obtained. Although the scintillator solution, the water and the water-soluble compound, the latter two being the starting components for the loading agent, all of which can be mixed at the same time, it is preferred to first prepare the loading means by dissolving the compound in water and then add this aqueous solution, i.e. the loading agent, to the scintillator solution. To the invention To further explain, the following examples are presented. -ν.; · ::,. ' : ..: ■: ■.

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example 1

A variety of scintillator solutions were used of various ethoxyated alkylpnenols and xylene

produced as a solvent. A volume ratio of

Xylene to the ethoxyiated alky! Phenol of 1.7: 1 was in all cases-applied. Each one for capturing and counting Scintillator solution made by thermal neutrons contained 0.55 as the scintillation solute; (Weight / volume) »

PPO and 0.15 £ (w / v) POPOP. ^

The loading agents were made by dissolving appropriate Compounds made in water at room temperature.

The scintillator preparations for Weutronen detection were then followed by mixing the above Sgintillator solutions made with the loading means. Table I shows the preparations of the scintillator solutions.

The loading means and the scintillator accessories obtained i (| reitungen »The number power for the alphar particles, which

generated from neutrons became 1005S in all cases found, all of the preparations being either clear or translucent liquids or gels.

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Table I.

Scintillator - preparation! Loading; s medium

Scintillator strain phenol preparation

Average number

Ethoxy groups /
molecule

Wt. -JS
Scintillator solution
· in the
x / n scintillator preparation

link

Weight-3

g HpO tor acces

b "

friction

O A. CD CO B. OO CJ C. cn
* >> D. CD E. F.

Nonylphenol 9.460 Dodecyl
phenol 10.0 Nonylphenol 9.460 Dodecyl
phenol 10.0 Octylphenol 9,629 Pentadecyl
phenol 9.0

50
60

50
60
70
40

Lithium 50

acetate

Lithium 50

acetate

Sodium tetraborate

sodium 8 tetraborate

Lithium chloride

Cadmium nitrate

50

50 40 30 60

Ψ% C ₁ V ^; - lf.

■. _v - J. ._ I,,

In order to apply the present invention to gamma! ^: >StrahXeiaep-fas.surig; and counting; in more detail · to explain »; the following examples presented: In all cases the ZuiQeFexfcuBgeia nnfce-i ¹ use of a Cs / gamma * '. :

esi TFi-oarb-Model 5310-

ln _: s |? ruiv £ eriit

-Company, -counted. ■ «, '

ice pi e 1 2

A Szlafeillato-r-solution for ^ / detection and counting 'γόη

Murde using Uit with a cross section of 9 "2 above; per, molecule and an n / x ~ ratio: of 1, 02 and xylene as a solution ^ smittel ujngesetzt \, Ss, a volume ratio; from ZSylol to ethoxylated Honylphenol of 1 ^ f applied · ^ * .- * The Saint ■ iliator-L · .ösun { ^: ϊ contained as dissolved-SZintillaticina-

Substance ΰ, .55 % CGeM./Voa,,y to PjPO and Q; _v 20; i ^? CGeW-ZVoO, 4 & n '

Table II explains ^ d; xe ZahlgeSiQhwinöigkedt für wrsohiecien-like cones.t% atio4eEi _: des gleäohen, loading means _} . fine.

alternately dividing '.I means ^, uria compares dxe; counting < > gkeiV with e ^ ne ^ 'iommer / zie;!;!: · ve5pugtüai? en Plüssigkelt ^

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T a b e 1 1 e II

Gannia-ütralilen

Saint ill at or-Lüsunf .: Loading agent

Gzintillator preparation

fcJtamru-fhenol

Ourciinchnitt borrowed number of

molecule

link

Zij ^f hlgeschwincti, jkeit g / 10 ml per TEC. 10; al .. Q Beladun.vsMittel-

Losunn z \ x 10 rl

Scintillator solution

ü ^ jonylphenol ii Wonylphenol ι iMoiiylpnenol J Wonylphenol

1.02 : ', nßr Iu 1.02 Z η br 113 1.02 ■ Znbr , 4 ^N 1 T NaI

173'I 19 Qb

t; ine commercially available, flüaai-ne üarnina radiation ^ uhlCinde LiVsun ^, containing 5 Gev /, -. / Much in the form of a?

organic halide> roi! iüuru-; uiitor use of the pcleicnen

lkik

from a comparison of the data in Table II ent

can be taken are the scintillator preparations

present invention to a large extent the present

superior to the available liquid gamma-ray counting solutions. Such scintillator preparations, as they have been disclosed here, are used in particular in

large number systems, such as the human one

■ 'I ■■ "■■■■:

Radiation counting where they are instead of inorganic
Crystals such as sodium iodide (Tl), which are normally used, can be used.
Crystals of such materials, large enough for use in human counters and the like, are extreme
expensive and very difficult to obtain. As the scintillator preparations as described in this invention
are very effective in absorbing gamma rays, they allow the construction of large volume
Counters at a much lower price than what you get at
the; Expect to use the above solid crystals or the currently available liquid formulations

f ■

korinte. .

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Claims (6)

Claims / lJ scintillator preparation for use in the liquid scintillation counting of thermal neutrons or gamma rays, characterized in that it contains at least 30 Gevi .-% of the above-mentioned preparation of a scintillator solution containing an aromatic hydrocarbon solvent, a dissolved Scintillator substance and an ethoxylated alkylphenol, wherein the alkyl substituent contains from 7 to 16 carbon atoms and the ratio of the number of carbon atoms in the mentioned alkyl substituent to the average number of ethoxy groups is 0.63 to 1.67, and up to 70 wt. ·! the mentioned preparation of a loading agent, containing an aqueous solution of an iileü.entes which causes an increase in the scintillation light. 2. Preparation according to claim 1, characterized in that the he-mentioned dissolved scintillation substance in one Amount of 1 to 12 g per liter of the aforementioned scintillation solution is present and contains a fluorine and a Wellenbanu shifter. 3. Preparation according to claim 1, characterized in that 009835 / U16 - 21 - BATH ORIGINAL that -. "that mentions" element one of boron, lithium, cadmium *, gadolinium ¹ * adoli he- 1-57 j samarium '* ^iy or thought nuclear radiation are thermal neutrons ". 4, preparation according to claim 3> d.adurcij that the dissolved scintillation substance comprises 2, S-diphehyloxazole and ly4-bis "2- (5-t ⁾ lienyioxazolyl) -benzene, 5 »Preparation according to claim" 1, "characterized in that that the mentioned'Element is a water-soluble compound of an element with an ordinal number is higher than 20 and the nuclear radiation mentioned are gamma rays. 6. Preparation according to Claim _{5 S,} characterized in that the above-mentioned dissolved scintillation substance comprises 2,5-Diphe.nyloxazol and p-bis- (oi-iet: hylstyryl) -benzene .. f0t835 / U16 BATH ORIGINAL