US3047760A - Geiger-muller counting tube - Google Patents

Description

July 31, 1962 J. HERMSEN ET AL 3,047,760

GEIGER-MULLER COUNTING TUBE Filed March 13, 1959 INVENTOR JO HANN ES HE RM SEN P TER JOHANNES KRAAIJEVELD N COLAAS WABRvOLTZ M l-iGENii 3,047,769 Patented July 31, 1952 ice p 3,047,7tit) GEEGER MIJLLER C(HJN HNG TUBE .Iohannes Hermsen and Pieter Johannes Kraaiieveld,

Amsterdam, and Nieolaas Warmoltz, Eindhoven,

Netheriands, assignors to North American Philips Company, Inc, New York, NY, a corporation of Delaware Filed Mar. 13;, E59, Ser. No. 799,147 Claims priorit application Netherlands Apr. 8, 1953 (til. Mfr-93} This invention relates to Geiger-Muller counting tubes for indicating radiation, more particularly aor ,B-particles and 'y-radiation. It also relates to a device comprising such a counting tube.

For indicating radiation, Geiger-Muller counting tubes of the most diiferent forms and with much varied arrangements of the electrodes are known. The term Geiger-Muller counting tube is to be understood in this specification to mean a counting tube, the arrangement of the electrodes and the gas-filling of which are such that for a given range of the operating voltage the strength of the pulse given oil by the counting tube is independent of the primary ionization brought about by the incident radiation.

In order to improve the properties of such counting tubes, it has previously been suggested to use as a gas filling a mixture of gases containing at least 0.001% of halogen as a quench. Argon, neon, xenon or krypton may then constitute the balance of the gaseous atmosphere, as is well-known.

An important factor is the so-called resolving power of the counting tube, which is inversely proportional to the dead time. In the case of a small-size counting tube, the resolving power for the ordinary gas-fillings is usually greater than for counting tubes of a larger volume.

The measuring accuracy which may be obtained with a given intensity of radiation is determined inter alia by the counting velocity or rate. In order to obtain a high counting velocity, a large active surface of the counting tube is necessary. The term active surface is to be understood herein to mean the size of the projected surface of the sensitive part of the counting tube.

A Geiger-Muller counting tube according to the invention comprises a space surrounded by an envelope and filled with a mixture of gases containing at least 0.001% of halogen, and it is characterized in that the space enclosed by the envelope comprises two joined, distinctly separate parts of different volumes, the part of the smaller volume containing the cathode and the anode of the counting tube.

The invention is based on the discovery that, when rays to be registered are incident, photons are produced in a counting tube as a result of ionization of the filling gas. These photons are capable of igniting the counting tube. However, it has been found that it is not necessary for the photons to be produced between the cathode and the anode. In the counting tube according to the invention, by tar the largest proportion of the photons is produced in the larger part of the space of the counting tube, which contains neither the cathode nor the anode of the counting tube.

The volume of the larger part or" the space filled with the gas mixture is preferably chosen at least five times as large as the volume of the smaller part.

It is desirable that a considerable proportion of the photons produced can see and penetrate the space between the cathode and the anode of the counting tube. In order the invention, use is made of electrostatic or electromagnetic means for accelerating and concentrating the electrons produced towards and onto the opening or aperture provided between the two parts of the counting tube. If desired, said means may be arranged outside the counting tube.

It is also possible to arrange electrodes in the part of the larger volume, which electrodes are connected to a source of direct voltage or alternating voltage, resulting in a potential field being produced in said space of a strength such that formation of an avalanche and multiplication of the gas occurs. As a matter of fact, this also results in greater efiiciency of the total counting tube.

It is alternatively possible for the wall of the larger part of the tube to be internally covered with a photosensitive layer. This results in a considerable increase in efliciency more particularly for 'y-rays.

In order that the invention may be readily carried into eifect, it will now be described in detail, by way of eX- ample, with reference to the accompanying drawing, in which:

FIG. 1 shows a device and a counting tube according to the invention having two co-aXial cylindrical parts;

FIG. 2 shows a counting tube according to the invention having a mirror for the concentration of the photons;

FIG. 3 shows a counting tube and a device according to the invention containing electrodes in the larger part of the discharge space and electromagnetic means for the concentration of electrons and negative ions;

FIG. 4 shows a counting tube according to the invention, comprising two straight circular cylinders and having a window to allow the passage of the radiation to be registered.

Referring now to FIG. 1, the counting tube comprises a cylindrical part 1, for example of glass, closed at one side by means of a circular glass window 3 and, at the other side, by means of an annular glass closure piece 5. A metal cylinder 9 having an insulating seal 11, for example of glass, hermetically adjoins an opening or aperture 7 provided in the ring 5. A rod-like electrode 13 is hermetically passed through the seal 11. The electrodes 9 and 13 constitutes the cathode and the anode respectively of the counting tube. A photon produced in the cylindrical space 1 by incident radiation causes ignition of the counting tube containing the cathode 9 and the anode 13, if, during operation, the cathode 9 is connected to the negative terminal of a battery 15 and the anode is connected to the positive terminal thereof. An extinction resistor 17 is arranged between the cathode 9 and the negative terminal of battery 15. The pulses produced are derived from a tapping on resistor 17 and supplied through a capacitor 19 to a counting device 21.

FIG. 2 shows a counting tube comprising a cylindrical part 23 having a glass wall which merges, at one side, into a conical glass part 25 closed by means of a glass window 27. The cylindrical part 23 is closed by means of a glass window 29 in which an anode 31 is hermetically secured. The cathode of the counting tube is constituted by a metal layer 33 on the inner side of cylinder 23. A reflecting metallic layer 35 is provided on the inner side of the window 27. The curvature of the window 27 and the layer 35 is such that the opening between the cylindrical and conical parts of the counting tube lies approximately at the focus of mirror 35.

FIG. 3 shows a counting tube according to the invention which has a shape substantially identical with that of the tube shown in FIG. 1. The larger part 37 of this tube contains an annular electrode 39 and a plate-like electrode 4-1. These electrodes are connected to the positive and negative sides, respectively, of a battery 47. The wall of the smaller cylindrical part constitutes the cathode 43 of the counting tube. The anode is indicated by 45. Said electrodes are connected in the same manner as shown in FIG. 1. The performance of this tube may briefly be described as follows. Radiation, either of electromagnetic or corpuscular nature, which enters the larger space 37, ionizes a gas molecule, resulting in a photon. This photon can directly ignite the gas discharge between the anode 45 and the cathode 43 of the counting tube. If, at the same time, an electron is produced, then due to the electric field produced between the electrodes 39 and 41 by means of the battery 47, this electron may give rise to the formation of an avalanche due to sequential ionizations. Said field also causes the electrons produced to be slightly concentrated onto an opening 53 provided between the parts of the tube.

The formation of an avalanche may be slightly enhanced by means of the field produced by a coil 49 surrounding the cylindrical part 37 and fed by a battery 51. Furthermore, the electrons are then focussed further to the aperture 53 between the two parts of the counting tube, igniting there a gaseous discharge between the cathode 43 and the anode 45. Since due to the multiplication of the gas in the larger portion of the tube a much larger number of electrons is available for the ignition of the gaseous discharge, such a device has a very high efficiency.

FIG. 4 shows a counting tube according to the invention which comprises a straight circular-cylindrical part 55 and a straight circular cylindrical part 57, the diameter of which is considerably larger than that of the part 55.

The whole wall of the tube is of glass except the window 59 which consists of a thin mica disc. As may be seen from the figure, the axes of the two cylinders are parallel. The opening between the two cylinders thus has a rectangular shape. A rod-like anode 61 of the counting tube is located in the axis of cylinder 55. The cathode is constituted by a conductive coating 63 which extends throughout the wall of the part 55. In order to increase the efficiency for electromagnetic radiation and more particularly 'y-radiation, a large portion of the cylindrical Wall of part 57 is covered with a photo-sensitive layer 65. This photo-sensitive layer may consist of known photosensitive materials, for example cesium-antimony or cesium-cesiumoxide. Due to the cylindrical shape of coating 65, the flow of photons is also concentrated to a certain degree to the rectangular opening between the parts 55 and 57.

What is claimed is:

1. A Geiger-Miiller counting tube comprising an envelope having closely-spaced wall portions forming a first smaller counting discharge space and widening extensions of said wall portions and integral therewith forming a second larger radiation-receiving space communicating with the first space via an opening located at the junction of the closely-spaced wall portions and Widening extensions, an ionizable gaseous filling including at least 0.001% of a halogen-type quench within said envelope, and cathode and anode electrodes adapted and arranged to sustain a discharge within only the first smaller space and being i '4 located in positions permitting the passage of particules generated substantially anywhere in the second space by incident radiation to the first space between the electrodes to initiate discharges therein.

2. A Geiger-Muller counting device comprising an envelope having closely-spaced wall portions forming a first smaller counting discharge space and widening extensions of said wall portions and integral therewith forming a second larger radiation-receiving space communicating with the first space via an opening located at the junction of the closely-spaced wall portions and widening extensions, a quenched ionizable gaseous filling within said envelope, cathode and anode electrodes adapted and arranged to sustain a discharge Within only the first smaller space and being located in positions permitting the passage of particles generated substantially anywhere in the second space by incident radiation to the first space between the electrodes to initiate discharges therein, the volume of the larger space being at least five times greater than that of the smaller space, said envelope being adapted to permit incident radiation to enter the second space, and a counting circuit coupled to the said cathode and anode electrodes.

3. A counting device as set forth in claim 2 wherein a reflecting surface is provided on envelope wall portions forming the second space opposite the said opening for reflecting photons toward the said opening.

4. A counting device as set forth in claim 2 wherein an accelerating electrode is provided in the second space for propelling free electrons toward the said openin.

5. A counting device as set forth in claim 2 wherein means are associated with the second space for directing particles toward the opening and into the first space.

6. A tube as set forth in claim 1 wherein a layer of photo-sensitive material is provided on an envelope wall portion defining the larger space.

7. A counting tube as set forth in claim 2 wherein the two spaces are generally cylindrical but of different diameters and in parallel relation, the anode electrode constituting a wire-like member extending along the axis of the smaller cylinder.

8. A counter as set forth in claim 2 wherein the envelope has a window permeabl to radiation adjacent the larger space.

Reierences in the file of this patent UNITED STATES PATENTS 2,141,655 Kott Dec. 27, 1938 2,523,132 Mason et al. Sept. 19, 1950 2,599,352 Schneider June 3, 1953 2,638,560 Borkowski May 12, 1953 2,666,865 Borkowski Jan. 19, 1954 2,671,868 Evans Mar. 19, 1954 FOREIGN PATENTS 656,681 Great Britain Aug. 21, 1951 566,525 Canada Nov. 25, 1958

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