US2519864A - Geiger-mueller counter tube - Google Patents

Description

Aug. 22, 1950 P. B. wmsz GEIGER-MUELLER coumrsx TUBE 3 Sheets-Sheec 1 Filed Sept. 2'7, 1948 W BYM %W Aug. 22, 1950 P. B. wasz 2,519,864

GEIGERMUELLER COUNTER TUBE Fi1ed Sept. 27, 1948 3 Sheets-Sheet 3 IOOO FIG 4 LOWEST OPE RATING VOLTAGE CARBON NUMBER INVENT R.

Fatente Aug. 22, 1950 UNITED STATES PATENT OFFICE GEIGER-MUELLER COUNTER TUBE Paul Burg Weisz, Swarthmore, Pa.

Application September 27, 1948, Serial N o. 51,401

special gas mixtures, certain compositions cf which Will result in tubes having what is known as self-quenching operating properties. The particular gas fillings employed 610 not only determine whether a given tube can thus be operated as a self-quenching GM-tube but also determine very largely its qualities which can be measumd by such major characteristics a the operating potential, natura of the counting plateau, the dead-time and the temperature sensitivity 01 the taube. This invention is concerned with new and specific gas mixtures which when employe in GM-tube of generally accepted designs will not only result in reliable selfquenching operation but will result in impnoved operating characteristics such as mentioned above, as compamd 120 those possessed by GM-tubes employing present1y known gas fillings.

A further object of this invention is 130 provide specia1 gas mixtures which, be;;ides offering improvements in the operaticn of GM-tubes, are easily prepared stored anal managelL in Iarge quantities in connection with the manufacture of such GM-tubes. 'Ihis is a considerabl improvement since presently known ga fillings are not easily handled when mixed in quantity, mainly because cf the W natural vapor pressure Which a1: least one of their components has ab ordinary room temperatures.

The GM-tube is now a well-known instrument for the detection of radiations. Figure 1 shows a typica1 GM-tube, having a cylindrical vacuumtight enve1ope I which containg an electrically c0nducting cylindrical electrode 2 which serves as a. cathode a. thin coaxially suspended metal wire 3 which serves as an anode and a gas fining which is introduced into the space 4 through a seal-*off stub 5. The tube is essentially gasfil1ed type electronic discharge tube which is so designed that no discharge current flows between its electrodes 2 and 3 until an ionizing event such as produced by radiations takes place within the sensitive volume of the tube. In a properly designed GM-tube such an event is followed by the development of a brief electrical discharge through the gas space 4 which is measurable by suitable electrical recording equipment, the latter being diagrammatically indicated by 6 When an operating voltage l is p1aced across the tube. An ordinary co-mbination of e1(ectr0des Contained in a gas spar;e will continue in a state of breakdown or electrical conduction through the gas space, once the operating voltage across it hag been raised high errough so th-at a discharge has been initiated. In order tha1: a discharge tube be capable cf detectihg individual ionizati0n events, so that it can properly be designated as a (EM-taube, it is necessary therefore that in the design means are provided extinguish the disch=arge after it has been initiated and afte1 it has manifestecl itself in a measurable current impulse following each individual ionization event. In the achievement of this end, namely the achievement of repetitive operation in the Form of single electrical impulses rather than continuous electrical breakdown or even trains Of repetitive pulses, lies the art of design and construction of tubes known as Geiger-Mueller tubes. The particular dass of GM-tubes known as self-quenching tubes and to which this invention refers is characterized by the fach that th repetitive extinction of each discharge i accomplished automatically by the tube itself and not by external artificial means cf special circuitry which complicates their use and in fach 1imits the speed of counting of such non-selfquenching tubes. Furthermore, such operating conditions must prevail 0Ver reasonable ranges, cf operating voltages, temperatures and other operational variables, in order that a GM-tube may be a practical device.

When a tube of the design of a GM-tube is filled with any gas, an ionizing event Will produce a current impulse whenever an electric potential is applied to the electlodes, and the magnitude cf that impulse will increase rapidly with increasing electrode potential. A1; sufficiently high voltage, any such tube Will give rise to impulseg 0f a fevv millivolts up to, in some cases, the order of a volt. These are in a sense seliquenching since they do nct result in extended electrical breakdown. I-Iowever, the individual impulses are not equal in size but consist 0f a Wide distribution of sizes. This type 0f operation is impractical for counting purposes. It can only be accomplished b the use of sensitive amplifiers with considerable amount of amplification. It is clear that for any finite sensitivity for such an amplifier those impulsz:s cf the pulse size distribution will not be counted whi ;h have an amplitude lass than the minimum recordablc we're again similar in all cases to the typical exampleg in Figure 3.

Furthermore it was found that the ubstitution of the normal hydrocarbons by any of their isomeric forms ha-ving the same composition C1H2+2 did not appreciably efiect the electrical operating characteristics. This finding was. 120 be expected in line With scientific findings coucerning the fact that the ionization potential 01 various isomers does 'not =appreciably change with alteration 01 isomeric structure. Thus, identical results were obtained for th electrical oparating chara.cteristics for the following examples tested: n-butane and iso-buane, n-pentane and di-methyl-propane, n-octane and 1-1 di-methyl-hexane.

Furthermore, it was found that essentially identical results were obtained with the cyc1ic forms of the hydrocarbons having the composition CuH2n, as seen by identical resu1ts obtained from n-hexan and cyclo-hexane.

It was further found that the presence of a double carbon-carbon bond in Ehe hydrocarbon molecule, such hydrocarbons being known a.s olefins and having the composition CH2n did not interfere With its qualities in producing good quenching characteristics, although the operating voltage for the olefins is generally somewhat 1ower than in case of its equivalent parafiin hydrocarbon compound, as seen by the following examples in Table I which were studied With the olefin anc1 argen under conditions equivalent 110 the previous examples.

It was found, however, that when using olefinic hyclrocarbons as indicated the life-time of such tubes was somewhat unpredictable, and this limitation was thought to be caused by a tendency towards polymerization of such olefins caused by the action of the discharge. The use of the 01efin hydrocarbons is not considered to be preferable 110 the use of the paraffin type hydrocarbons.

Now several advantages connected with the hydrocarbon gases as quenching components will be seen when other characteristics are compared.

The dead-time was measured for such hydrocarbons and for other customarily used quenching components, and a comparison can be made by comparing the results a5 tabulated in Table II.

Table II Hydrocarbon Dead-time Micro. seconds Ethane. 42 Propane Butane n-Pentane Neo-ppntanp Hexane.

Amyl ace Ethylene dibromide It is obvious that practically all the hyr carbons result in short dead-times, and inparticular the dead-times of the lighter hydrocarbons, ethane and propane, for example, are strikingly short and superior to equivalent standard type of gas fillings.

The property of tubeg, to fai1 at lower operating temperatures has been found to b@ connected With the fact that at a, given 10W temperature part or all of the quenching gas comp-onent begins 120 remove itself from the gas space by condensation. The temperature at which this failure Will set in will be the lower drop with lower boiling points of the pure quenching gas com ponent.

It is easi1y observed that such kn-own quenching vapors as alcohols, ethers, and halogenated hydrocarbons as we1l as organo-metal compounds ashave been found useful as quenching gases in the past all have relatively hig=h boiling points while amongst the unsubstituted hydroca.rbons many can be found with boiling points considerab1y lower.

As a result, such hydrocarbons will a1low operation at considerably lower temperatures than a'il 0f the vapors known for otherwise equivalent conditions.

In Tab1e III, boiling points a1e cmnpared, and in Table IV the approximate temperatures are she-wn at which tubes actually begin to fai1 when using various quenching gases under the Same conditions as in all the above examples.

Table III k Oompou.nd (o1d) B. P. Compound (new) Ethyl ether Ethy1 ah01 Tetramethyl lead Ethylene dibromide.-.. Amyl acetate Ethane Iso-butane n-Pentane Iso-pentane. Neo-pentane. n-Hexane Propylne Table IV Approx. Term).

Compound (new) below 78 below 78 -65 ho1ow 78 below 30 15 bolow -78 Ethyl ether Ethyl alchol. .I Am y1 acetate I Ethylene dibromide Tetramethyl lead Iso-butane Neo-pentano n-Hexane Ethylene However, Tab1e III and Table IV Show how the new quenching gas component leacl to lower criical temperatures than known types of quenching gas components under similar conditions.

According to this invention, the new typenf of tiie types*presehtly known-airi sonnection xwith; custmary non-se1f quenching gas components su'ch asargon; neon, h'elim;=hydrogen ethers,

and# relative concentrations anal total gas-- pregsures genera-1ly acceptabl a'for known quencb;v i11gcomponents.

I-Iwever, it was fund th'at such:quenching.. gases*as-.are presentedaby this im ention can2be used over wider ranges frelative -concentratiom and -total'gas pressure than is thecase. of;eth3rl" aioohoi'andbther=knbwn:gases withouo seriously afictingtheresultingoperating qualities of tubea.

Whi1e Ehe optimum pressure ranges depend largely onithe a-n0d wire-. diameter; it lwas found th-at--optimum -operating characteristicsrwere at4 tainedas i0l1owsz- (a-) Withanodewvire dia1neter-s; of.approxi mately .008i inchaor less, With partial pressures of the new quenching gases: rapproximately equal: tobetween one (l) and; twenty'-fivei(2=) mm; (I-Ig) and total gas pressures 0f apDroximately betweenz:fiffiy mm.z(I-Ig) and atmospheric pressure;:

(b) Withanode wire diameters of approxi mately .008 inch to .035 inch, with paroial pres+ sures of-tthe new quen=chingt gases approximately equal 130 between cne-tenth (.1) and.ten* (1010) mm; (Hg) andi total gascpressures ofapproxi. mately between fifty (50) mm. (I-Ig-) a11d atmospheriopressnre.

In particular, it was fiound that these nevv quenchin gases are capa;bl6 of yielding success fu1 auch hih quality operation 0f Gl\f-tubes when the total ixuternabpressure: is nearlyas high o1 actuallyequal t0 the pressure of the externat atmosphere. None of the quenching gaseg heretof0re described -h2uve voperafoed. a1; total pressures siderable pressure difierence between theat-- mosphere=and the tub interic-r. Such. limitation virtually. disappears when the new atmospheric gas fillings are used. Also, it is possible to fi11 such tubes without empioying vacuum equipinent otherwise requi-red to obtain -the:frac* tional internai gas pressures.

Iir was: found. that in operating; GB/L-tubesa esseni1ia11y equal-:to atmospheric* total internal are: to'- be preferredbecausetof :the '10\VMODGT&1TE" veltages-whieh resuitwhenthey are useci in pfeference to others.

.Elov such uses itwas found thatpmferrecl .gas mixtures were obtaincd by providingcomposi;- tion3- which ccnsisted of. either: a saturatedaor cyelic: hydrccarbon With three:;tafivea carbom at0lns, in connection with. arg onas themajor 1gas. coniponent. 'Ih0: gasesufound: 130 be. preferred :as hydrocarbon constituentsfor atmospheric pres=' sure :oneration can belchflracterieithereforezby the=forrriuiaesCI-E C3I-IG, C3Hzi', C4H8,CC4HIO;;C5HiI and C5H12. The optimum conditionszweraaata tained when. the concentration of the hydmcarbon* componentwas about 1% tg 6%.of the total.- gaamiXture; when..the GM4sube in.:whichtther. gases were used: ihad an anode diameten:bf: about: .008 inch .on1es3. For larger=anodediameters;theg optimum A hydrocarbom concentration was .foundt to begmal'ier. For=anode diameters ranging ftom .G08"ineh to a.bout1.35 inch heabest;sllitable hy drocarbom concentrationswere: found im: range: froml% 130 10% ofthertotal gasspressura.

An impgrta11tzadvantage-can bezderivedirom the use:of :most of the: gases theuse ofiwhichzis taught by this invention inthe processe's: cone nected with the preparation 01. th quenching gas mixtures, their storage,. and'. their:use when =GM-tubesare. be constructed 01:: manufacturecL I1;Lis weil. known :that .presently kn0wn quensehing compounds are1liquidg.atnormal tem.perature./ andi pressure and: thatthe1ef0re: they exhibita definitely. limited..vapor. pressurerat such teme peratures.at whicthey are-:handled; In;-the process of Tpreparing the gas.mixtureg this.amust.t always ba taken intmaccount and:presents 1imi tations on.. procedure as weil asuon. thetotal. amoum= ofaz.given gas mixturewhich; can be prepared iorstored' in:areservair of given volume.-

Fl'on. a givenvoiume of a.storagereservoir only 1ittle gas-volmeacanba stored for:any attempt so: c0mpress thec mixture would lead to partial: liquefaction of quenching,component,.and. in such a case the relativacomposition of the .gases removed. continuously changes with the amount of gases removed as we1l as With the temperature of the environment.

N0W, because of the 10W boiling points demonst'tat(ed in 'Ifb1ie HI'for the new quenching gases,

it.ispossible 110 handle many o- F them such as etha'ne, propane, butana, neo-pentane, ethylene; propylene as gases in any mixing equipment.

Furthermore.some of them.are.readily com+- pressed without danger of liquefactionbysuchi facbors which make the storage of large quantities of pre-mixed gas mixtures possible =and esono-mical.

F01 exampie, it i3 welI known that'nlqutarie* Will not be iiquified sc longas itspartial Dressure ina compressed'cylihder isiessthan about 15 p. s. i. Thus ifit Wfe' desired"to'makeand" store a gas t0 be used as filliilggas forselfquenchingGM-tubes; COntainin ultimately 1.0; cm: (Hg) of n=b-utane anti 30.*cm. (Eig) 'of argen one partbutane 00 30 part3 of argon, it'w ould be possiblto make* andstore such a.gas mixtura in a pressuri2e' cylinder a1; a totaipre'ssm7e of ab'out450'p. s. i; representing a volumelof" thhwy.times the cylinr er v0111me when refrred to standard cc-nditins. Even larger quantities of mixture could be madanol stored in case of isobutane, propane and 0ther hydrocarbons with boiling=points below that 0f n-butane under 0011- ditiong otherwise equal.

Whiiein all exampleg given he gas fillings were cc nsidered as consisting cf two gaseous 00m:

po nents name1y the quenching gas component and the non-quenching g-as component, itmust. baunderstood that by a11- known principles th'e us'e of two or more gases known individually 'to have the desired quenching properties, as weil asthe use of tvvcor more non-quenching:gas components eaeh beim; kng wn-to-lzmeth'e d:3 sired characteristics indWiduaI-Iywouldb bez ms-- 9 sible and Ieads to similar resulcs as does the use of ju'st two-component mixtur es. The teachings cf this invention are 120 be understood theref0re 130 include the possibilit of combining more than two components of such gases as it teaches to be applicable and usab1 in case cf th describcd two-component mixtures.

I clim a my invention:

1. A gas mixture for the filling of Geiger- Mueller tubes for the purpose of providing such tubes with self-quenching properties with pulse equalization at substantiallyatmospheric internal g=as pressure, consisting of a. major anal a minor component the formerof Which comprising at least one Of the gascs hydrogen, nitrogen, argen, neon, and helium, and;the latter cf which comprising at least one offt he hydrocarbons selected from the group of compounds described by the ch'emical formulae CnH2n+2 a.nd C1H2n wherein the carbon number n be a number between two and eight inclus'ively, said hydrocarbon coxhponent making up from 0.1% to 6%, approximately, of the total gas pressure.

2. A gas mixture for the fllling of Geiger- Mueller tubes for the purpcse of providing such tubes with self-quenching properties with pulse equalization a.t substantially atmospheric internal gas pressure, consisting of argen and C4Hm, ancl where the latter gas constitutes from .1% 130 6%, approximately, of the total gas pres w sure.

3. A gas mixture for the filling of Geiger= Mueller tubes for the purposa cf providing such tubes with self-quenching properties with pulse equalization at substantially atmospheric internal gas pressure, consisting of helium and C4H1o, am). where the 1atter gas constioutes from .1% to 6%, appmximately, of th total gas pressure.

4. A gas mixture for the filling of Geiger- Mueller tubes fo1 the purpose cf providing such tubes with self-quenching properties with pu1se equalization ab substantially atmospneric internal gas pressure, comisting cf argon and C2H4, and where the latter gas constitutes from .l% to 6%, approximately, o1" the total gas pressure.

PAUL BURG WEISZ'.

REFERENCES CITED Korff: Electron and Nuclear Ccunters, 1946, D. Van Nostrand Co., Inc., New York, page 107.

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