US2936388A - Counters with a negative-ion-forming vapor additive - Google Patents

Description

May 10, 1960 CHUBB ETAL COUNTERS WITH A NEGATIVE-ION-FORMING VAPOR ADDITIVE Filed Dec. 15, 1958 m m m 55ml VUR mHE CP P m TE.

A m J ATTORNEY Unite States Patc'ntO 2,936,388 COUNTERS WITH A NEGATIVE-ION-FORMIN VAPOR ADDITIVE Talbot A. Chubb, Forest Heights, and James E. Kupperian, Jr., Glassmanor, Md.

Application December 15, 1958, Serial No. 780,643

6 Claims. (Cl. 313-93) (Granted under Title 35, US. Code (1952), 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 counters which respond by ionization of the enclosed vapor and more particularly to counters wherein electron emissions from the cathode are undesirable in their operation and should be suppressed.

In photon counters whose ultraviolet sensitivity depends on gas ionization the choice of an ionizable vapor determines the lower frequency limit or cut-off to which the counters respond, and when radiation filters or other screening means are provided to furnish a high frequency cut-oif these counters become selectively sensitive to radiation of definite frequency bands. Ionized vapors for these counters are selected mainly on the basis of their response to definite spectral regions; these vapors on the other hand may not be adequate in themselves to prevent spurious responses caused by trailings of electrons emitted from the cathode. Very often, therefore, it has been found desirable to screen out electrons in the low field region around the cathode and to suppress electrons contributed by the photoelectric eifect in coun- .ters Where only the photoionization of the gas molecules is desired; Suppression of such electrons also improves the counting characteristics of some types of Geiger counters.

It is therefore an object of the present invention to provide counters wherein any photoelectric contribution from the cathode is eifectively suppressed.

Another object of the present invention is to provide a gaseous additive which is chemically inert and can be utilized in small concentrations for the purpose of improving the performance of counter devices.

It is a further object of this invention to provide a photon counter whose pulsating output is free from spurious electrical counts.

The invention itself together with further objects and advantages thereof may best be understood by reference to the following specification taken in connection with the following drawing which is a longitudinal crosssection view of a side-window photon counter that contains the novel gaseous filling in accordance with the present invention.

Sulfur hexafluoride (SP is added to the gaseous filling of a photon counter shown in the drawing; said gaseous filling contains a photoionizable quenching vapor, for instance, alcohol, acetone, nitric oxide, ethylene bromide, or ethyl formate, and an inert gas which may be any from the group of neon, argon, helium, etc. The addition of SP to the filling of the photon counter results in an improved counter that is now capable of sharper, clearer responses free from background output. Electrons which cause erratic and undesirable, counts are effectively prevented from contributing such counts as a result of this invention.

The present invention, therefore includes photon ice counters containing therein a gaseous admixture of an inert gas, a photoionizable quenching vapor and an additive, namely a small amount of SP The invention also includes Geiger counters containing therein a gaseous admixture of an inert gas, a quenching vapor and an additive, namely a small amount of SP The SP is suflicient for the purposes of this invention when present in amounts of from 0.01% up to about 1% of the gaseous filling in these counters.

Referring now to the drawing, the photon counter shown comprises a tubular metallic cathode member 111 surrounding a coaxial anode wire 12; the tubular member forms the body portion of the envelope and has fused or joined thereto ceramic members 13 and '14 by means of fused powered glass seals 15. The ceramic members confine the tube space 16 and also insulate the anode wire from the metallic cathode 11. The surface of said ceramic members isarranged with a series of annular convolutions 17 and annular rims 18 protrude from their circular end surface. A chrome-iron lug '21, which may be constructed of any other suitable metal, passes through ceramic member 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. A portion of the lug member which extends to the rear of the flange is threaded at 25 to provide a means for attaching a cap (not shown) for protection of glass tube seal 26. An annular flanged cap 27 with tubular extension 28 is fastened to ceramic member 14 with powdered glass seal 29.

The anode wire is connected to lug terminal 22 by initially passing the wire through a small hole in the tip of said lug terminal until the ball member 36, which is, soldered to the end of the wire is retained by the lug terminal. The other end of the wire is passed through tubular member 28, drawn tightly to form a taut wire across the tube space, clamped to the tubular extension 28 and welded thereto.

The metal envelope is provided with a side-window 30. Welded around an opening 31 in the metal envelope is a circular sill 32 which fits into a flat indent 33 cut out of the envelope surface. A LiF plate 34 is mounted within circular sill 32 on a ledge, provided in the side-window for this purpose, and is fastened thereto by means of a powdered glass seal 35. Radiation transmitted by the LiF crystal enters through opening 31 into the interior of the tube. Ceramic member 14 is provided with a glass tube 37 by means of which the counter may be exhausted and filled with the desired filling. In a typical embodiment, a gaseous filling consisting of neon at a pressure of about 700 mm. Hg, NO at a pressure of about 10 mm. Hg and SP at a pressure of about 0.5 mm. Hg is introduced through glass tube 37 and enters the counter space through a small bore in the side of lug member 21; the glass is subsequently sealed as shown at 26.

The photon counter operates when radiation of wavelength over 1050 A., which is capable of transmission through the LiF window, enters the window and produces ionization in the nitric oxide molecules. When the potential across the electrodes 11 and 12 is in the magnitude of about 1000 volts, a chain of ionizations within the inert gas molecules transmit the gaseous discharge in a short time interval to anode 12. The quenching vapor deionizes the inert gas ions produced during the charge transfer, the gaseous discharge :is then stopped and the counting cycle is ready to begin again.

SP is a unique chemical molecule: It has an outstandingly large cross-section for formation of negative ions. SE; is chemically inert and does not combine readily with vapors or with the metal electrodes in the tube. It has also been discovered that SP, is eifective as an electron absorber in extremely small concentrations, considerably more than other vapors that show this property. In fact it can be used with other common electronegative vapors with beneficial results. The addi tion of this vapor in amounts of from about 0.01 to about 1% is sufiicient to suppress cathode photoelectrons from contributing spurious counts.

SF' additions to counters impart other beneficial effects to the discharge characteristics. The plateau is increased considerably, in some cases as much as a factor of 3. In a tube containing acetone and neon which normally exhibits a plateau with a voltage range of about 1000 to 1200 volts, the voltage is increased to 1600 volts and in some instances as high as' 2400 volts when SE, is present in the filling. The tube is also capable of passing more intense count discharges.

A further example of a counter in which SE improves the discharge characteristics concerns the photon counter with an admixture of about 5 mm. Hg of acetone, 700 mm. Hg of neon and 0.5 mm. Hg of SP said photon counter is provided with a Li'F filter for a cut-off at 1050A. As a result of this novel filling, the counter is not troubled with spurious counts and has a response to radiation limited more strictly to the 11801050 A. range.

It is therefore apparent that SP as an additive to counters operating by gas ionization alone provide (1) an efiicient electron absorber in the low field region around the cathode (2) a chemically inert additive in admixtures containing active vapors to improve the discharge characteristics.

()bviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

'1. A counter tube characterized by the suppression of photoelectrons from the cathode comprising a radiation permeable envelope, a gaseous filling therein consisting of an inert gas, a quenching medium and sulfur hexafluoride; plus means for producing a unidirectional electric field across said gaseous filling.

2. A Geiger tube characterized by the suppression of photoelectrons from the cathode comprising a radiation permeable envelope, a gaseous filling therein consisting of Chemical A g a. 4 of an inert gas, an electronegative quenching medium and sulfur hexafluoride; plus means for producing a unidirectional electric field across said gaseous filling.

3. A photon counter characterized by the suppression of photoelectrons from the cathode comprising an envelope with a window therein capable of transmitting radiation in a first selected Angstrom range, a gaseous filling therein consisting of an inert gas, a photoionizable quenching medium 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, and sulfur hexafluoride; plus means for producing a unidirectional electric field across said gaseous filling. I

4. A photon counter characterized by the suppression of photoelectrons from the cathode comprising an envelope with a LiF window, a gaseous filling therein consisting of neon, nitric oxide and sulfur hexafluoride; plus means for producing a unidirectional electric field across said gaseous filling.

5. A photon counter as claimed in claim 4 in which the gaseous filling consists of about 700 mm. mercury pressure of neon, about 10 mm. mercury pressure of nitric oxide and about 0.5 mm. mercury pressure of sulfur hexafluoride. V

6.- A photon counter as claimed in claim 3 in which the inert gas consists of about 700 mm. mercury pressure of neon, the photoionizable quenching medium'consists of about 5 mm. mercury pressure of acetone, and sulfur hexafiuoride is present therein in concentration of about 0.5 mm. mercury pressure.

References Cited in the file of this patent UNITED STATES PATENTS Fehr Sept. 30, 1952 OTHER REFERENCES Chubb et al.: Photon Counters for The Far Ultraviolet, Review of Scientific Instruments, vol. 26, No. 5, May 19-55, pages 493 to 498.

Liu et al.: The Absorption Spectrum of Sulfur Hexafiuoride in The Vacuum Ultraviolet Region, Journal Physics, vol. 19, pages 71 and 72, January

Claims (1)

1. A COUNTER TUBE CHARACTERIZED BY THE SUPPRESSION OF PHOTOELECTRONS FROM THE CATHODE COMPRISING A RADIATION PERMEABLE ENVELOPE, A GASEOUS FILLING THEREIN CONSISTING OF AN INERT GAS, A QUENCHING MEDIUM AND SULFUR HEXAFLUORIDE, PLUS MEANS FOR PRODUCING A UNDIRECTIONAL ELECTRIC FIELD ACROSS SAID GASEOUS FILLING.

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