US3048730A

US3048730A - Counter tube

Info

Publication number: US3048730A
Application number: US780641A
Authority: US
Inventors: Talbot A Chubb
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-12-15
Filing date: 1958-12-15
Publication date: 1962-08-07
Anticipated expiration: 1979-08-07

Description

Aug. 7, 1962 .T. A. CHUBB COUNTER TUBE Filed Dec. 15, 1958 TALBOT A. CHU B B ATTORNEYj 3,048,730 C(EUNTER TUBE Talbot A. Chubb, 319 Onondaga Drive, Forest Heights, Md. Filed Dec. 15, 1958, Ser. No. 780,641 tClaims. (Ci. 31393) (Granted under Title 35, US. Code (1052), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to an improved counter tube and has particular reference to a photon counter which as a result of this invention has greater stability, lgnger life and improved plateau characteristics.

, In the construction and operation of Geiger counters,

employ organic vapors which have aromatic and un- I fhotodetectors and the like, it is frequently necessary to saturated type molecular structures. For instance, a photon counter which responds by photoionization of the enclosed gas alone, in the narrow range of radiation between 1425 and 1500 Angstroms, requires xylene vapor as the photoionizable and quenching medium of the tube. While other organic vapors might be employed in this type of photon counter, ionization yields are considerably higher with xylene and for this reason it has been the photoionizable vapor favored and found most effective for this range of UV. light. Xylene vapor, however, has been found to be unstable and decomposes with continued usage and following heavy excitations, causing the tube to remain electrically conductive. It is believed that this electrically conductive condition is due to breakdown products of xylene and of other aromatic or of the unsaturated type vapors recombining in the inter-electrode space and forming insulating films on electrode surfaces. These insulating films accumulate an electrical charge during counter operation and become a source of spurious electrons which prevent normal quenching of the counter, as a result of which, the counter goes into discharge.

The present invention is concerned with a novel gaseous filling for Geiger tubes, photon counters, proportional counters, etc., which include in the filling thereof a vapor having a certain degree of aromaticity in its chemical structure. Counters that incorporate the gaseous admixture in accordance with this invention become stabilized and do not show the symptoms heretofore attributed to film formations on electrode surfaces.

It is accordingly an object of the present invention to provide an improved counter tube that is more stable and has improved plateau characteristics.

Another object of the present invention is to provide a novel gaseous filling for a photon counter having a very selective range of response to radiation between 1425 and 1500 Angstroms.

A further object of the invention resides in the provision of a counter tube containing an aromatic or an unsaturated aliphatic vapor which is prevented from forming dielectric films in the operation of said counter.

For a better understanding of the invention reference may be had to the accompanying drawing in which;

The figure is a longitudinal cross-section view of a sidewindow photon counter containing the gaseous filling described herein.

In accordance the present invention a gaseous filling consisting of a vehicular gas, which is one of the inert gases, such as neon; a photoionizable as well as quenching medium, which for the purposes of this invention is an aromatic vapor, for instance xylene, and hydrogen gas are added to a photon counter tube of the type shown in the drawing. The novel gaseous filling is especially prescribed in the illustrative example herein for a photon inc counter which responds by photoionization of the enclosed gas to a selected range of ultraviolet light. The use of this gaseous admixture provides for a stable, photoionizable photon counter, exhibting a wider plateau than the prior art tubes operated in the ultraviolet range of radiation of less than 1500 Angstr'oms. The photon counter remains in operation after sustained usage and following heavy excitations Without any tendency on the part of the tube to remain conducting or in any way to alter its pulsating characteristics. The xylene vapor does not form insulating films which heretofore limited the life of the tube. In the improved counter tube the presence of hydrogen prevents the formation of a film deposit. Unsaturated bonds which become available during the breakdown of xylene are linked to hydrogen atoms and form unreactive gaseous products which donot interfere with the operation of the tube.

In the illustrative example, the photon counter tube consists of a metal cylinder or envelope 11 coaxially arranged with respect to anode 12. The envelope structure is made of chrome-iron or of any other suitable metal while the anode is preferably a tungsten wire 0.005 inch in diameter mounted along the axis of the cylinder. Ceramic ring plugs 13 and 14 extend from the ends of the metal cylinder and are sealed thereto with fused powder glass, as shown at 15; the interior portion of said ceramic ring plugs serve to confine the tube space 16 and also to insulate the anode terminal from the metal cylinder which serves as the cathode. The surface of the ceramic rings is arranged with a series of annular convolutions 17, while annular rims 18 extend from the end of each ring insulator. A chrome-iron lug 21, which may be constructed of any other suitable metal, passes through ceramic ring plug 13 to provide a terminal 22 to which the anode wire is connected. A flange 23 extending laterally from the lug is fastened over annular rim 18 with powdered glass seal 24. That portion of the lug which extends to the rear of the flange is threaded at 2.5 to provide a means for attaching a cap (not shown) for protection of the glass tube seal 26. At the other end of the tube, an annular flange cap 27, having tubular extension 28, is fastened to ceramic ring 14 with powdered glass seal 29.

The metal envelope ll is provided with a side-window 30 by cutting an opening 31 into the envelope and welding a circular sill 32 on a level indent 33 surrounding said opening. A sapphire plate 34- is mounted on a ridge in the side window and is fastened thereto with powdered glass seal 35, so that radiation transmitted by the sapphire enters through opening 31 into the interior of the tube. The anode wire is connected to lug terminal 22 by passing the wire through a small hole in the tip of the lug terminal; a ball member 36 soldered at the end of the wire is retained in the lug terminal. The other end of the anode wire passes through the tubular extension 28; the wire is stretched tightly and welded to the metal at 28. The assembled tube is sealed to a vacuum system and exhausted to obtain a high vacuum. A fiilling of about 2 mm. Hg of xylene, 10 mm. Hg of hydrogen and 400 mm. Hg of neon gas is introduced through exhaust tube 37, the filling enters the counter space through a small bore drilled in the side of the lug member 21 (bore not shown in the drawing).

The photon counter shown in the drawing operates when radiation in the UV. region between 1425 and 1500 Angstroms enters side-window 30 producing ionization in the xylene molecules, Radiation of wavelength shorter than 1425 A. is absorbed by the sapphire crystal in the side-window while radiation of wavelength longer than 1500 A. fails to ionize the xylene molecule. When the potential across electrodes 11 and 12 is in the magnitude of about 1000 volts, a chain of ionizations occurring asters spas,

within the inert gas molecules transmit the gaseous discharge in a matter of microseconds to the anode 1-2. The quenching vapor deionizes the inert gas ions produced during the charge transfer, the gaseous discharge is stopped and the counting cycle is ready to begin again.

The xylene vapor has been found to be effective in performing the photoionizing function in the spectral region between 1425 and 1500 Angstroms. The addition of hydrogen gas to the admixture of xylene and neon makes possible the production of a practical and reliable counter tube. The addition of hydrogen prolongs the life of the counter and greatly reduces the tendency of the conventional xylene photon counter to remain in discharge after excessive excitation. This form of photon counter is especially useful in detecting oxygen in concentrations as little as one part per million in compressed inert gases and in the detection of molecular oxygen in the upper regions of the atmosphere.

Organic vapors other than xylene may also serve as photoionizable' quenching media and many of these vapors are characterized as aromatic or with some degree of unsaturation in their molecular structures. Typical of such vapors are the aromatics, for example, benzene, and the open-chain unsaturated hydrocarbons, for example, ethylene gas. The addition of hydrogen to a counter tube containing an aromatic or unsaturated type vapor reduces the tendency of the counter to go into discharge. The hydrogen need be present only in an amount sufficient to combine chemically with the breakdown products of such vapor. Care should be exercised where the metal present in a counter may have a catalyzing effect on hydroen and cause it to add more readily to unsaturated molecules. Preferably, of course, the metal in the counter should not affect the reaction between the organic vapor and hydrogen.

It will be apparent to one skilled in the art that the present invention is by no means limited to the particular photon counter device shown and described and that many modifications may be made of the tube structure without departing from the scope of this invention as set forth in the appended claims.

What is claimed is:

1. A counter tube comprising in combinataion a radiation permeable envelope, a gaseous filling therein consisting of an inert gas, a quenching medium which is xylene vapor, and hydrogen gas, plus means for producing a unidirectional electric field across said gaseous filling.

2. A counter tube comprising in combination a radiation permeable envelope, a gaseous filling therein consisting of neon, xylene and "hydrogen gas, plus means for producing a unidirectional electric field across said gaseous filling.

3. A photon counter tube comprising in combination an envelope with a window therein capable of ,transmitting radiation in a first selected Angstrom range, said envelope enclosing therein a gaseous filling consisting of an inert gas, an aromatic vapor responsive to radiation in a second selected Angstrom range overlapping a portion of said first selected Angstrom range, and hydrogen gas, plus means for producing a unidirectional electric ileld across said gaseous filling.

4. A photon counter tube comprising in combinati n a metal envelope with a window therein capable of transmitting radiation in a first selected Angstrom range, sail envelope enclosing therein a gaseous filling consisting of about 2 mm. Hg of xylene, which is responsive to radiation in a second selected Angstrom range, a portion of said second selected Angstrom range overlapping a portion of said first selected Angstrom range, 10 mm. Hg of hydrogen and 400 mm. Hg of an inert gas, plus means for producing a unidirectional electric field across said gaseous filling.

5. A photon counter tube comprising in combination a metal envelope with a window therein capable of transmitting radiation of wavelength longer than about 1425 Angstrorns, said envelope enclosing therein a gaseous filling consisting of about 2 mm. Hg of xylene, 10 mm. Hg of hydrogen and 400 mm. Hg of neon.

References Cited in the file of this patent UNITED STATES PATENTS 2,489,627 Dudley Nov. 29, 1949 2,612,615 Fehr Sept. 30, 1952 2,765,418 Weisz Oct. 2, 1956 2,776,390 Anton Jan. 1, 1957

Claims

4. A PHOTON COUNTER TUBE COMPRISING IN COMBINATION A METAL ENVELOPE WITH A WINDOW THEREIN CAPABLE OF TRANSMITTING RADIATION IN A FIRST SELECTE ANGSTROM RANGE, SAID ENVELOPE ENCLOSING THEREIN A GASEOUS FILLING CONSISTING OF ABOUT 2 MM. HG OF XYLENE, WHICH IS RESPONSIVE TO RADIATION IN A SECOND SELECTED ANGSTROM RANGE, A PORTION OF SAID SECOND SELECTED ANGSTROM RANGE OVERLAPPING A PORTION OF SAID FIRST SELECTED ANGSTROM RANGE, 10 MM. HG OF HYDROGEN AND 400 MM. HG OF AN INERT GAS, PLUS MEANS FOR PRODUCING A UNIDIRECTIONAL ELECTRIC FIELD ACROSS SAID GASEOUS FILLING.