US2776390A

US2776390A - Radiation detector tube

Info

Publication number: US2776390A
Application number: US392604A
Authority: US
Inventors: Anton Nicholas
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-11-17
Filing date: 1953-11-17
Publication date: 1957-01-01
Anticipated expiration: 1974-01-01

Description

Filed Nov. 17, 1953 United States Patent O RADIATION DETECTOR TUBE Nicholas Anton, Brooklyn, N. Y.

Application November 17, 1953, Serial No. 392,604

8 Claims. (Cl. 313-93) The present invention relates to the art including radiation detectors and is more particularly concerned with improvements in the structure of proportional and Geiger counter tubes.

Geiger and proportional counter tubes have been found to be useful in X-ray spectroscopy, particularly for soft X-rays such as obtained from copper. In such tubes, the use of krypton gas has been found to be advantageous, but such use has been inhibited because of the former difficulty of reducing spurious counts.

According to the present invention, simple and effective means have been discovered which eliminate spurious counts in such tubes, and accordingly it is a primary object of the present invention to provide an improved radiation detector tube structure in which spurious counts are eliminated or minimized.

Other advantages and objects of the present invention will become more fully apparent from consideration of the following description taken in conjunction with the appended drawing, which in its single figure shows a longitudinal cross sectional view of an axially symmetrical detector tube according to the present invention.

Referring to the single figure of the drawing, the tube of the present invention comprises a cylindrical cathode electrode 11 forming also a major portion of the envelope of the device. Sealed to the cathode 11 at one end 32 thereof is an insulator 12, such as of ceramic material or the like, to which in turn at 33 is sealed the anode support 13 formed of conductive material. The anode 14 is supported in cantilever fashion from the anode support 13 and is formed by a stiff wire such as .025" diameter stainless steel wire. The anode support 13 has a bore 16 extending transversely thereof and a bore 17 extending axially thereof. An exhaust tubulation communicates with and is sealed with the bore 17 of anode support 13. The remainder of the enclosure of the device is provided by a radiation-permeable window 19 formed of plastic, mica or the like, and sealed at 31 to cathode 11. The material of this window is not critical, provided that it has a low weight per unit area and may, for example, be 1.4 milligrams per square centimeter in area density.

In usual fashion the envelope formed of window 19, cathode 11, insulator 12 and anode support 13 is evacuated through the tubulation 18 and is then filled with a suitable gas and a quenching agent. The preferred gas lling is krypton at pressures ranging from 300 -to 600 millimeters of mercury, and the quenching agent used is a halogen, such as bromine, chlorine or a mixture of both. An anode terminal 21 is secured to the anode support 13 as by threading and/or soldering to form one terminal for the device, the other terminal being formed by the conductive cathode casing. A glass or other insulating bead 22 is formed at the tip of the anode wire 14 to prevent accidental contact with cathode 11 and to avoid corona discharge at the tip of the anode wire.

A tube such as that just described is subject to the spurious count disadvantage indicated above. According to the present invention, this spurious count formation is eliminated by introducing a cathode insulator sleeve 23 Within the cathode 11 at the window end thereof and extending for a short distance inwardly, such as of the ICC order of 1A to 1/2 inch out of a total length of cathode of approximately 5 inches. This insulator is short in an axial direction to allow the electric field to extend close to the mica window 19 to permit counting of the electrons generated by 'the impinging X-ray beams as soon as they enter the tube.

While the manner in which this sleeve 23 operates to eliminate spurious counts is not fully clear, it is believed 4that it does so by eliminating the field concentration due to termination of anode Wire 14 in insulating bead 22.

it will be understood that in some cases it may be advantageous to omit the glass bead 22 entirely or to form a conductive bulbous tip at the end of the anode Wire 14.

it is to be understood that the above description is to be taken as illustrative only since the present invention may assume apparently widely different forms without departing from the spirit thereof, the scope of the invention being defined solely by the appended claims.

What is claimed is:

l. A radiation detector comprising a cylindrical cathode electrode, a radiation-permeable window sealed across one end of said cathode, an insulator sealed at the other end of said cathode, an anode support mounted on and sealed to said insulator, an anode wire mounted coaxially within said cathode and supported only at one end by said insulator and terminating at the other end in a tip adjacent said window, said tip being within said cathode, an exhaust tubulation sealed to said anode support and completing the envelope of said tube, and an insulating sleeve lining the interior of said cathode adjacent said window and surrounding said anode wire tip for reducing spurious counts.

2. A detector tube as in claim l, wherein said anode wire tip is formed by an insulating bead sealed to the end of said anode wire.

3. A detector tube as in claim 2, wherein said anode wire tip is formed by a glass bead sealed on the end of said anode wire.

4. A detector tube as in claim 1, wherein said envelope contains krypton gas at a pressure between 300 and 600 millimeters of mercury.

5. A radiation detector tube as in claim 4, wherein said envelope also contains a halogen quenching gas.

6. A detector as in claim l, wherein said window is permeable to soft radiation and has an area weight of the order of 1.4 milligrams per square centimeter.

7. A radiation detector tube comprising a gas-tight envelope, said envelope comprising a cylindrical cathode and an'insulating radiation-permeable window sealed at one end of said cylindrical cathode, a krypton gas filling within said envelope, an anode mounted coaxially within said cathode and insulated and spaced therefrom, said anode being supported only at the end thereof opposite said window and terminating adjacent said window in-a tip, said tip being within said cathode, and an insulating sleeve lining said cathode adjacent said window and surrounding said anode tip whereby spurious counts are inhibited.

8. A radiation detector tube comprising a gas-tight envelope comprising a hollow axially symmetrical conductive cathode having a radiation-permeable window at one end, an anode mounted coaxially within said cathode and having an end adjacent said window and Within said cathode, and an insulating sleeve lining the interior of said cathode adjacent said window and surrounding said anode end, whereby spurious counts are inhibited.

References Cited inthe file of this patent UNITED STATES PATENTS 2,479,201 Bleeksma Aug. 16, 1949 2,542,440 Victoreen et al Feb. 20, 1951 2,612,615 Fehr et al. Sept. 30, 1952