US2742586A - Multi-section geiger-mueller counter - Google Patents

Description

April 17, 1956 Filed April 18, 1952 H. FRIEDMAN MULTI-SECTION GEIGER-MUELLER COUNTER HERBERT 2 Sheets-Sheet l INVENTOR FRIEDMAN flaw/41.4%

ATTORNEYj April 17, 1956 H. FRIEDMAN 2,742,586

MULTI-SECTION GEIGER-MUELLER COUNTER Filed April 18, 1952 2 Sheets-Sheet 2 H3 Ill H 4 1| 2 5 I00 INDICATOR INVENTOR HERBERT FRIEDMAN BY ,ML/

M ATTORNEYJ nited States Patent V r 2,742,586 I v MULTI-SECTIGN GEIGER-MUELLER. (IOUNTE-R 7 Herbert Friedman, Arlington; Va. 7 V V i Application-.April-18, I952,-:Serial No. 283,111 J '6 Claims. (Cl; 313 83) (Granted under Title 35, U. S. Code (1 95 2), sec.. 265) This'invention relates'to multi-section radiation de- Anotherobject of this invention is to form a radiation detector having a multi-segment cathodein which the cathodestructure is divided into a number of distinct sections so that the spread of an ionization discharge along a centrally disposed-wire .anode may be'confined to the section or sections actually penetrated by an ionizing particle.

A further object of this invention is to provide a novel radiation detecting devicecapable of distinguishing between dischargesv produced by beta and gamma radiation.

A'still further object of 'thisinvention is to reduce background count .when counting. beta radiation with a Geiger- Mueller type counter.

Other objects and advantages. of. .the. invention will be evident to those skilled in .the art from the following description. a

It' has been knownformany years that the discharge along the wire anode of a Geiger-Mueller type radiation counter that is caused by entry into the tube of an ionizing ray,:m ay be readily confined-to specified sections of the wire by any procedure which interferes with the step by step process of ionization propagationatthe boundaries of each section. As is well known, the discharge caused by the entry into the tube of an ionizing particleis confined to the immediate vicinity ofthe wire and the spread of the discharge along the wire. is produced by ultraviolet radiation appearing as a result ofan ionizing event. If an obstacle such as aglass bead issealed round the wire, the discharge will jump theobstacleonly. if the obstacle has 'less than a critical minimum diameter which may be as smallas 3 or 4 times thediameter or" the anode area, or if the ratio of field strength to. pressure in the counter tube exceeds a critical value. As it isdesirable to operatein the Geigerregion at high anode voltage to obtain large voltage pulses, it can be seen that under such operating conditions the probability of the discharge jumping the wire is enhanced. Reference is made to applicants article titled Geiger counter tubes appearing in July 1949 Proceedings of .thel. R. E., at pagel791, for a mOIC'CXhZiUSiiVE treatment of this phenomenon.

Likewise, Geiger-Mueller type counters utilizing multisegment anodes to reduce the electric field intensityv below the value necessary to develop a complete avalanche have been-known-andused. for some years. Typical prior art devices'of this ,type are described by Wilkening and Kanne,

in Physical Review 62, page 534 (1942); by-W. 13. Ramsey, in Physical Review 61, page 96 (1942'); and by H. G.

Stever, in Physical. .-Review v.62, page. 38 (1942).- .The devices described in these articles. are disadvantageous-in thatftheyare relatively large, due tofthe spacing required between sections, and are not easily manufactured. 'However, .this type of construction has peculiar: advantages in determining thedirectonfrom which radiationis emanating, and in distinguishing between beta and gamma radiation. As noted by Ramsey and by Steverin the. articles cited above, the sections may be used in conjunction with a coincidence counter to distinguish between beta.and gamma radiation. "The advantage-of. themulti-segment cathode over counters utilizing beaded .anodesato interrupt the discharge along the anode. is that voltage pulses may be-taken directly from the individual cathodesegments. The disadvantage of the counters that havebeen suggested heretofore lies in their difliculty vof construction and in thefa'ct that they are rather large due tothe spacing required between. cathodes.

- Stever suggests the use of glass beads on the anode-in conjunction with a divided cathode, theglass beads being placed on the section of the anodebetween .thecathode segments. However, ascan be readily seen, the placing of these beads on the anode is somewhat-difiicult and there is no absolute assurance that there will be no interaction between. a given cathode segment andthosesectionsof the anode lying within the spacedefinedby an adjacent cathode segment. This is particularly true with nonselfi-quenching. tubes, or when tubes utilizinghalogen'admixtures for quenching are used. Under .these circumstances, the photoelectric emission responsible for spreading' the discharge-along the anode occurs at the. cathode rather than in the gas. There is no negligible. absorption in the gas itself of ultraviolet radiation responsible for such photoelectric emission. This has been demonstrated by experiments in which a discharge Was spread from. one cathode section to another cathode section across a. gas path of 20 to 30 cm. with almost 100% efiiciency.

For abetter understanding of applicants .invention, reference maybe had to the accompanying :drawingsin which: r

Figure lis a detailed view of one embodiment of: applicants novel counter tube.

Figures 2 and 3 show embodiments of applicants invention utilizing av plurality ofwire electrodes.

Figure 4 is aview of applicants tube used inconjunction with a coincidence counter for distinguishing between distincttypes of radiation.

'With reference to Figure 1, they multiple cathode elements of the tube are designated as 1, 2, 3,. 4, 5 and 6. The

ends ofthe cathode elements :may be provided With-mating recesses to provide a secure joint. that will decrease the possibility of separation of the sections due to rough treatment. I V V The cathode sections may be conveniently constructed of stainless steel. tions from each other and sealed thereto in the recesses 7a, and at the same time isolating thespace defined by the annular sections, are thin windows or plates of mica-designated'7,'8, 9,10 and 11. Aplate 12, which may be-mica, aluminum or other suitable radiation permeablematerial, seals the free end of annular section 1. This plate must be of sufficient thickness to resist the pressure differential between the interior of the tube and'the atmosphere, but the other plates may be as thin as the mica canbe cut inasmuch as the pressure of the gas within the tube is substantially the same in all parts of the tube.

Small vent holes 13, 14,15, 16 and 17 may be used to aid in filling the tube and in maintaining the same'pressure throughout the various sections of the tube. As will be apparent from the discussion below, these vent holes should be relatively closer to the cathode sections than Patented Apr. 17,1956,

Electrically insulating the individual: secto the anode wire, so as to insure complete blocking of the ultra-violet radiations. The holes should also be very small; mere pin holes will sufiice.

An anode wire 18 passes through cathode section 6 and is insulated therefrom by bushing B. It also passes through mica plates 7, 8, 9, 10 and 11 and may be securedto the individual plates by any of a number of suitable sealing compounds or simply by a very snug fit. If possible, the anode should be positioned along the axis of the cathode, although this is not an absolute requisite.

Thus, beta radiation can enter the tube only in a direction preclude penetration of alpha and beta particles except through window 12. This window can be thick enough to filter out alpha radiations if such filtering is desirable.

Thus, beta radiation can enter the tube only in a direction roughly defined by the axis of the cathode cylinder. Such a particle will easily traverse two or more of the compartments 33, 34, 35, 36 and 37 causing an ionization avalanche, in the direction of the anode structure. The neutral gas molecules are excited during the avalanche by electron collisions. In returning to the ground condition, they emit ultraviolet quanta of relatively low ionization potential from the vicinity of the anode which, if the fill gas is a polyatomic vapor such as alcohol mixed with a simple gas such as argon, will ionize the polyatomic gas and cause a new avalanche. If the fill gas is a halogen admixture combined with a rare gas or a non-self-quenching gas, the new avalanche will be brought about by a photoelectron emitted from the cathode.

mica shield is reached. As the ultraviolet radiations under 2500 Angstrom units are almost completely absorbed in the thin mica sheets, a discharge will spread along that part of the anode 18 within compartment 33 only until it reaches mica shield 11. At this point it is stopped, and the original ionizing particle must pass through mica shield 11 into compartment 34 if there is to be a discharge within compartment 34. Therefore, for there to be a discharge in any of the compartments 33, 34, or 36, the original will be limited to the compartment in which the electron is emitted. Soft X-rays will also produce a discharge in only one compartment. The ray after entering the tube through the end window, will eject but one electron from a molecule of the fill gas in one of the compartments. This characteristic is valuable in reducing the effects of dead time, as other compartments are free to receive a discharge when one of the compartments has broken down and the positive ion sheath around the anode has not been drawn to the cathode.

The multi-section tube of this invention may conveniently be used to distinguish between beta ray and gamma or soft X-ray counts when used in conjunction with a coincidence circuit, as shown in Figure 4. Potential source 20 is connected to the various cathode sections through load resistors 21, 22, 23 and 24. Blocking condensers 25, 26, 27 and 28 couple the various cathode sections to a coincidence circuit generally designated as 33. A discharge in compartment 111 will produce a positive pulse on the grid of vacuum tube 102. This in turn will produce a negative pulse on the grid of tube 106 and thus, a positive pulse on the grid of coincidence amplifier tube 170. The grid bias on this tube is set high enough so that the pulse voltage produced by a discharge through a single compartment of the counter tube 100 is not sufficient to cause flow of current through tube 170.

As a result of this process, the discharge will spread down the anode until As the plate circuits of tubes 106, 107, 108 and 109 are connected to a single source of potential through a common resistor, simultaneous discharges through two or more of compartments will be additive. Therefore, if the grid bias of tube is set so that plate current will flow only when discharges occur in two or more compartments, a pulse will appear at the output of tube 170, when a beta particle penetrates the counter 100, but no pulse will occur when a gamma ray penetrates the counter.

When it is desired to measure pulses from the anode rather than from the individual cathode sections, a simple pulse amplitude discriminator may be conveniently used to reject pulses having an amplitude less than that produced by discharges in a given number of tube compartments.

Figure 2 presents an embodiment of applicants novel radiation counter in which a separate anode is disposed in each compartment. Anodes 18 may be in the shape of loops, and are supported by leads brought into the compartment by means of bushings B through the walls of the cathode segments.

Figure 3 illustrates another embodiment of applicants novel radiation counter utilizing three anodes. The advantage of this type of construction is that, when an ionizing particle has caused a discharge to one anode and the positive ion sheath surrounding the anode has not yet been swept to the cathode, the other anodes are free to receive avalanches if another ionizing particle penetrates the counter. Applicants invention 15 particularly adapted for use with such multi-anode tubes. It can be seen that, if the glass bead and multi-segment cathode type of construction is used, there is a problem in placing the beads in corresponding positions on each of the anode wires. Applicants use of mica shields obviates this difiiculty, as the exact position at which the shields encompass the wires can in no way become critical.

Although certain specific embodiments of this invention have been shown and described herein, many modifications thereof are possible. Therefore, this invention is not to be restricted except insofar as is necessitated by the scope of the dsiclosure.

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.

What is claimed is:

1. In a radiation detecting device of the counter type, a plurality of mutually insulated hollow outer cathode members with mating recesses assembled end to end, and a separate insulating partition separating said cathode members at each point of juncture between said mating recesses and across at least one end of the assembly and at least one anode means disposed within said cathode members and aflixed to said insulating partitions.

2. A radiation detecting device of the counter type comprising a plurality of tubular open-ended stainless steel cathode sections with mating recesses assembled end to end, a separate transverse mica insulating partition between each cathode section at the points of junctions of said mating ends and across at least one end of the assembly, axially disposed wire anode means extending through and sealed to all of said mica sealing means except the mica means sealing the end cathode means.

3. A radiation detecting device comprising a plurality of stainless steel tubular cathode sections with mating ends assembled end to end, at least one wire anode disposed within said cathode sections and mica means for sealing at least one of the ends of the assembled cathode sections, mica plates fitted between said mating ends of said adjoining cathode sections electrically insulating said adjoining sections, bonding said mica plates and said mating ends of said cathode sections, and encompassing the individual anode sections, and means sealing the anode sections to the said mica plates.

4. A radiation detector comprising a plurality of holverse mica partition members; intersecting said outer conductors at the points of juncture thereof along its length to form a series of distinct radiation detector cells.

5. A radiation detector comprising .a plurality of tubulow outer conductors with mating endfsurfaces, a substana tially coaxial inner conductor and a plurality of transbly, and a plurality of conductors individually disposed ing the compartments defined by said tubularconductors and said mica partitions: V v 6. A radiation detector comprising a closed end radiation impermeable wall portion comprising a plurality of electrically conductive sections forming said impermeable I wall portiomsaid sections having mating recesses on the proximate end portions, parallel transverse insulating partitions bonded at the juncture of each successive conductive I "section; to form separate ionization chambers, radiation, permeable material bondedto the outer-endof the outer-V most conductive section whereby radiation passing through said permeable material may also pass through a number of said partitions depending upon the energy level of said entering radiation, an anode within each chamber formed by the conductive sections and the partitions, a gas coutained in each chamber ionizable by radiation entering the chamber; and voltage shift responsive counting means coupled separately to each of a plurality of cathode sections independently of the other sections of the plurality.

References Cited in the tile of this patent UNITED STATES PATENTS- 2,397,661 Hare Apr. 2, 1946 2,445,305 Hochgcsang July .13, 1948 2,457,781 'Metten et al. Dec. 28, 1948 2,519,007 Wilson L. Aug. 15, 1950 I 2,536,314 Scherbatskoy Jan. 2, 1951 2,552,723 Koury May15, 1951 2,559,526 Van de Graaf et a1. July 3, 1951 2,612,615 Fehr et al Sept; 30, 1952 2,649,554 Anton Aug. 1.8 1953 Goldstein Oct. 27, 1953

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