US2612615A - Cathode for ionization detection devices - Google Patents

Description

p 9 E. B. FEHR ET AL I 2,612,615

CATHODE FOR IONIZATION DETECTION DEVICES Filed July 22, 1949 DETECTING MEANS lnventorsi Edith B. Fehr, William T Poseg,

by Their- Attorney.

tube or envelope to give the same efiect. Preferably the tin chloride is dissolved in alcohol or an alcohol-water solution and sprayed into the vitreous counter chamber or envelope which is maintained at a temperature of about 400 C. to 700 C. and preferably at least500 C. The concentration of tin chloride in the alcohol may vary widely, the smaller the concentration of. the chloride, the more the amount of solution which is required. A preferred spraying solution consists of fifty parts by Weight of tin chloride dissolved I in forty-five partsby weight of ethyl alcohol. The exact nature or character of the conductive film produced on the heated glass, vitreous or ceramic wall by the tin chloride or other I I metal halides is not known. Analysis has shown that the film has no halide content. The tin or other metal, which is known to be present, is in combined form, perhaps as a tin. or. metal oxide, or even conceivably in combination with the constituents of the vitreous surface. The

absence of the usual gray cast of elemental metal militates against the presence of tin orother metal in this state on the envelope wall.-

Attention is invited to the drawing f'or typi cal examples of the use of the present cathode v film in counter devices. In Fig. 1 is shown a radioxide film of this invention to conduct oft electric charges which collect on the mica surface during operation of the device and may produce faulty operation or false impulse signals.

Another modification of the tube is shown in Fig. 2. This tube has no mica window, the radiation 'to be measured passing directly through the relatively thin side walls H of the tube which are coated on their inner surface with a 1 conductive surface film 12 :as described herein.

I ,Wire anode i3 is mounted longitudinally in the i tube and passes out of the tube through a gastight seal. The usual glass bead I4 is fused to the-inner tip of anode 13. Electrical contact is made with the cathode coating [2 in any con- 'venient-mannen For example, a split ring or ation'or ionization measuring device, or-counter of the Geiger-Muller type. The tube orenvelopel of the counter is fabricated of non-conduct-, ing vitreous material such as glass or a ceramic material. ,-The cylindricaltube is flared outwardly at-one end as at 2 to receive thin ;mica sheet or window 3. which is-sealed gas-tight to tube 1 by means of a low melting point glass 4,1;

Generally the mica window variesin weight from about one to five milligrams per square centi'-' meter, the lower weight or thinner material ad-. mitting softer radiation.v The end ofthe tube opposite the mica window 3 is also sealed gaselectrons to be swept to the'po'siti've electrode.

tight. Mounted within the tube along the. ma

jor orlongitudinal axis thereof is an elongated tubewall as shown and thus is made-externally wire anode 5 of chromium-iron alloy, tungsten or other suitable metal which passes through the a accessible. The diameter ofthis wire may vary,

usually being about five to fifty mils. A" glass bead -6 is normally fused to theinner endeof panod-e 5 to prevent leakage of the discharge from V the sharp point which in turn would prevent the wire'from attaining al-ongits entire length a proper voltage gradient. 'An electrically conductive-coating 1, produced byftreatment-with' tin chloride as described 'above,- covers'" the -inner surfaceof tube orenvelope l' as shown serveshas the cathode. j Making electric contact With'ftheicathode"coating "l is a split ring or band a of metal such' as stainless steel which fits tightly within the "periphery of coating I.-

' This band, as well as all other metal parts err-.- posedto the counteriatmospherafis polishedand oxidized to g prevent corrosion or absorption of g the.{halogeri;content of the atmosphere. Wires] electrically joined to: ring 8 by any convenient means and passes through the "wall cfthe tube; as shown. The atmosphere in the tube which" is generally -maintained ata pressure of from '-'five"--.to fifty centimeters} of, mercury is 'made up of "a, halogen and other inert gas, oi g ases;. a typ- I icailt composition being one part by volume of halogen to 760 p rts by volume of neon .andf

' fourp'arts by volume of argon,' .II

The mica wind-ow used in somlc ounters'may also, advantageouslybe coated with the. .metal .75},

mg a, vitreous=envelope containing band, 15 of polished and oxidized metal such as stainless steel'may'be slipped inside the tube .beforeit is sealed and lead Wire l6 fixed thereto and passed through the tube wall as shown.

In Fig. 3 there is illustrated a schematic circuit for anionization detection device of the presenttype which is represented by cathode shell I8 and anode wire 19. A source of potential, V, is providedin'series with the counter The resulting electrical impulse flows through the circuit and registers'in thedetecting mea Th'ere is produced byffollowing the teachings of this invention an ionization detection-device whichmay" operate effic'ien'tly with corrosive" The halogenabsorbing surfaces'are reduced to a minimum and so constancy of halogen content'anddetec tion performance is'insured. I The device described also hasa minimum number of glass Sto" metal seals and avoids sharp met-a1 edgesi'whi'ch' q halogen-containingatmospheres.

produce arcing or corona efiects.

What we claim as new and desire to secure by LettersPatentof the United-States is: 1. Anionization' detection device comprising a vitreous envelope containing an atmosphere of ionizablegases' including a h'aloi-- gensanzanode within said envelope, a cathod'e' comprising a .non metallic 'filmpf electrically. conductive corrosion-resistantwmetal compound 9 on'the inner suflaceofiisaid envelope, said film being non-corroding in =the'.presence of a halogen, .2 gas and being obtained bya'pplyinga metal halide to the inner surface ofsaid envelope whileijsaidnon-conducting,

.2; ionization:fdetection ldevicev e pts;

mosph ere of ionizable gas 1 including gen, ;a wire anode ,within said envelope, 'non metallic electrically conductive film compri .iflg liiae uad. l g n s a i i m a i-.1 a 118,10?

anode mounted within said tube along the major axis thereof, a cathode coating of a non-metallic tin compound which is non-corroding in the presence of chlorine on the inner surface of said tube, said cathode coating being obtained by applying a tin chloride to the inner surface of said envelope while said surface is maintained at a temperatureof from 400 to 700 C.,;.and externally accessible terminals connected with said anode and said cathode. I

4. An ionization detection device comprising a closed glasstube containing an atmosphere of chlorine, neon and argon, a wire anode mounted within said .tube along the longitudinal axis thereof, a cathode coating of a non-metallic iron compound which is non-corrosive in the presence of chlorine gas on the inner surface of said tube,

said cathode coating being obtained by applying an iron halide to the inner surface of said envelope while said surface is maintained at a temperature above the boiling point of said iron halide, and terminals connected with said anode and said cathode and passing through said tube.

EDITH B. FEHR. WILLIAM T. POSEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,118,795 Littleton May 24, 1938 2,429,420 I McMaster Oct. 21, 1947 2,474,851 Liebsen July 5, 1949 2,516,663 v Zunick July 25, 1950 FOREIGN PATENTS Number Country Date 234,906 Great Britain June 8, 1925

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