US2161979A - Apparatus for detecting ionizing radiations of very low intensity - Google Patents

Description

L. R'OVNER Filed April 22, 1938 June 13, 1939.

APPARATUS FOR DETECTING IONIZING RADIATIoNs oF VERY Low 'INTENSITY NNJ NN www MN m\ Kx .S 7 WN l Patented June 13, 1939/ J t APPABATS FOR DETECTING IONIZIN RADIATIONS OF VERY LOW INTENSITY Leopold Bovne'rpChica-go, Ill., assignor of onehalf to Prothero Rad-lum Memorial, Aa corporation oflllinoian Application April zz, 193s, serial No. 203,716v 1 (ci. 25o-ss) This invention relates generally to a novel and improved apparatus in which a counter tube is employed for observing ionizing radiations of very low intensity and has for its main object a 5 novel and improved construction of counter tube and apparatus whereby the same may be employed as a minimum signal directional device for detection of, and for directional localization of, a small source of penetrating radiation.

70 Another object of the invention is to provide in an apparatus of the character'I described, a novel and improved construction of counter tube so proportioned as to have directional characteristics whereby the same may be effectively used for directional localization of a small source of penetrating radiation.

A further object of this invention is to provide in an apparatus of the character described a novel and improved construction ofcounter tube, comprising a cathode cylinder containing an axially mounted central anode filament, the cathode cylinder being made of such dimensions that the longitudinal cross-section area in relation to the end-on cross-section area is much greater than unity. f

A still further object of this invention is to provide a counter tube for the purpose hereinabove described having its cathode cylinder so proportioned that its length is relatively great as compared to its diameter, whereby the same will be-highly effective for directional localization of a small source of penetrating radiation. l

A still further object of this invention is to provide a novel and improved construction of appa- .i5 ratus within which a counter tube of the abovedescribed characteristics may be mounted, said apparatus including an axially mounted radiation stopping shield.

A stillv further object of, this invention is to provide in an apparatus of the character described, a counter tube for the detection of a smallsource of penetrating radiation, said apparatus having mounted therein means for excluding radiations coming in along the direction of the longitudinal axis of said tube.

A still further object of `the invention is to provide iri an apparatus of the character described, a novel and improved construction o'f counter tube so arranged therein as to be capable 59 of indicating direction of a small source of penetrating radiation by registering a minimum in the rate of the signal pulses.

A stili further object of the invention is to provide in an apparatus of the character described a novel and improved electrical pickup circuit, within which said counter tube may be arranged.

A still further object of the invention is to provide an apparatus of the character described, which will be simple in construction, assembly and operation, winch willbe compact and durable,

v'and which will at the same time be highly emcient for carrying out the purposes for which it is designed.

With the foregoing and other objects in view which will appear as the description proceeds, the

invention consists in certain novelA features of construction, arrangement and combination of Vparts hereinafter fully described, illustrated in the accompanying drawing, and particularly pointed out in the appended claims, it being understood that various changes in the form proportion, size and minor details of the structureA may be made withoutdeparting from the spirit or sacrificing any of the advantages of the invention.

For the purpose of facilitating an understanding of my invention, I have illustrated in the accompanying drawing, a preferred embodiment thereof, from an inspection of which, when considered in connection with the following description, my invention, its mode of construction, assembly and operation, and many of its advantages should be readily understood and appreciated.

Referring to the drawing in which the same characters of reference are employed to indicate corresponding or similar parts throughout the several figures of the drawing:

Fig. 1 is a longitudinal cross-sectional view through an apparatus constructed in accordancev with the principles of my invention;

Fig. 2 is an electrical wiring diagram, showing` an improved electrical circuit for my apparatus;y

Fig. 3 is a modified electrical circuit that may be used with my improvedapparatus.

'I'he counter tube which is generally referred to as a Geiger-Muller tube is essentially'a gas-lled diode consisting of a hollow cylindrical conductor mounted axially about a central conducting filament. Under the influence of an external source of penetrating radiation (which may project ionizing particles to Within the sensitive volume of the tube, or which may effect the release of ionizing particles within that volume) the counter tube mechanism initiates a process of collision ionization that produces an electrical l cathode cylinder) nue to uns mt, most counter tubes have inherent directional properties whenever-they areconstructed with cathode cylinders whose dimensons result in a ratio oi' longitudinal vcross-section toV end-on cross-section area not equal *to one. -In general, these tubes present 'more area from'ftheirsides than from their ends.

having a perpendicular component) Athan to radiation directed along the axis. It is "one of the fea- -turesof this invention to utilize this property of the tubes In making directional counter tube apparatus for detecting and locating small sources of penetrating radiation.

In the use heretofore made of this type of counter, tube `for locating ordetecting small sources of penetrating radiation, the counter tube is mounted within a massive cylinder of radiation-shielding material made so as to provide'.

enough metal thickness to exclude radiation from all directions except through a portal at one end on the axis'of the tube. In this known apparatus ,the direction is indicated by a maximum in vthe rate of the signal pulses. The counter tube necessarily receives the radiation along the direction of its least efllcient response,that is, along the axis. Furthermore-the apparatus as heretofore used is sensitive toradiations from only a very limited portion of the whole geometrical sphere and hence is a'low efficiency detector, since it will have a very weak response in the presence of an active source unless it is properly aimed.

Furthermore, in order to properly shield an apparatus of thischaracter, a considerable weight rangingv anywhere from twenty to fifty pounds of metal isrequired for even a small portable detectorunit, such, for example, as that used for nding radium, thereby making the apparatus unwieldy.

In my improved construction, I provide a counter tube arrangement, designed to receive most of the radiation in the direction of the optimum response of the tube (direction vperpendicular to axis of tube). In order to exclude radialtions coming in along the direction of the axis,

I provide a very small radiation-shielding cylinder of proper length at one end on lthe projected axis of a long cylinder counter tube. My improved apparatus will, therefore, indicate direction by a minimum in the rate of the signal pulses. With this improved ltype of apparatus, it will be noted that the same -will be sensitive to radiation over yalmost the whole geometrical sph'ere and will readily respond without being aimed whenever it is In the presence of a radioactive source oi' penetrating radiation.

In the drawing, I have illustrated one embodiment of my improved invention, which is an instrument particularly adapted for detection oi and for directional localization ofY a small source l of penetrating radiation, that is, radiations such j as gamma rays, X-rays, or high-speed ionizing particles.A a A Referring to the drawing more specifically by characters of reference, my improved instrument comprises a tube of the Geiger-Muller type gen-. erallyde'signated by thereference character I0, formed of glass or any other radiation-transparend material, said tube having mounted therein a hollow cylinder II of suitable conducting material, such as metal or metal gauze, said cylinder being relatively long with relation to its diameter and forming the cathodeof, my improved counter tube.

Mounted within the. tube III and extending I axially through the hollow'conducting cylinder II. is the centralconducting filament I2,v which forms the anode of my improved counter tube.

v'.l'he tube I0 is filled with a suitable gas and 'is suitably sealed, as shown in the drawing, and

suitable metal such'as lead or the like. 'Ihis cyl.'-`

inder I is comparatively light in weight, weighsuch small weight, the entire cylinder I3 with the tube Il and cylinder I5 disposed therein may be f mounted in. a comparatively small instrument which may be conveniently held in one hand, thereby greatly facilitating the ease with which 'jing approximately a few ounces, and because of eov the 'instrument may be used. Thus, in the'eml bodiment illustrated, the cylinder I3 has a portion of it disposed within a hollow tube I6, which,

inurn, is supported' in a holder I1, which holder has formed integral therewith a depending extension I3, so shaped as to be adapted for gripping in the hand of the operator.

The holder t3 is hollow and is, adapted for receiving therein an extension I il of the tube II),-

within which extension is disposed a conductor 20, one end of which is connected to the cathode Il, as shown at 2l, and the other end of which is connected, as shown at 22, toa conductor 23 leading to a high voltage plug (not shown). The.

filament I2 is connected, as shown at 24, toa conductor 25, which leads to acondenser 28, and the other end of said condenser being connected by means of the conductor 21 to a. p hone tip plug "23. The filament I2 is also connected, as shown at 2l, to a conductor 29, which leads to a resistor 30, said resistor being connected by means of a conductor 3| to the other phone tip plug 32, and from there to the plus of the ground 33.

I have found from actual practice that vthe voltage pulse across the tube at time of discharge is sumcient to actuate a volt sensitive (piezoelectric) phone set in .direct coupling, as set forth in Fig. 2, without the aid of an intervening arnpliiler arrangement.

- In the electrical wiring diagram, shown in Fig. 3, the current pulse through the tube circuit is sufficient to actuate current sensitive (magnetic) head phones without the aid of an intervening amplification arrangement.l Thus, it will be noted, that with my arrangement, it is possible to use a direct phone coupling circuit for a counter tube, therebygreatly simplifying the circuit by eliminating therefrom the amplifier means heretofore thought .necessary with a tube of the .Geiger-Muller type.

In operation, when' thevcathode cylinder II) intercepts ionizing radiations, the counter tube mechanism when arranged in the electrical circuit hereinbefore described produces sharp, dis- 'A ing source is accomplished after the presence of the source has been detected. The apparatus is then turned in all directions until that direction is found at which the pulse rate is a minimum.

in prising a holder When that occurs, the apparatus will be aiming directly at the radiation source with the radiation shielding end nearest the source.

If desired, electrostatic shielding may be provided for the holder unit, which may be done by plating the entire outside of the casing and then grounding the same to the left hand phone connection, which is the ground for my improved electric circuit. s

From the above, it will be apparent that I have provided a novel and improved apparatus, including a counter tube,'so arranged and proportioned, as to render the same more effective fr locating a small source of penetrating radiation. It will also be noted that the device may be assembled in a small and compact unit, easily and conveniently handled by the observer. It will also be noted that I have provided a novel phone coupling circuit directly connected with the counter tube, thereby eliminating the vnecessity of intervening amplification means between the tube and the phone, all of which makes for a more simplified and cheaper construction, while, at the same time, being highly eilicient for carrying out the purposes for which my improved apparatus is de.- sisned.

It is believed that my invention, its mode of construction and assembly, and many of its advantages should be readily understoodv from the foregoing without further description, and it should also be manifest that while a preferred 4embodiment of the invention has been shown and described for illustrative purposes, the structural details are nevertheless capable of wide variation 'within the purview of my invention as deinedn in the appended claims.

f I claim:

1. An apparatus of the character` described, comprising a holder, a counter tube mounted within said holder and radiation excluding shielding carried by said holder and disposed adjacent one end. of said tube only lso as to exclude only radiations coming in along the direction of the longitudinal axis of said tube.

2. An apparatus of the character described, comprising a holder, a counter tube mounted within said holder and having cathode and anode leads at one end of said tube, and an axially mounted radiation stopping shield disposed adjacent the other end of said tube, said radiation stopping shield having substantially no portion thereof in the path of radiations strik-- ing the sides'of said tube, said arrangement serving to exclude from said tube only radiat'iins coming in from the direction defined by said eld. 3. .An apparatus of the character described for detecting a small source of radiation, comadapted to be held in the hand of the observer, a counter tube mounted within said holder, and a radiation stopping shield disposed within. said holder and arranged axially adjacent the operating end of said counter tube, said radiation stopping shield having substantially no portion thereof rearward of the operating end of said counter tube, whereby only radiations coming in ,from the direction defined by the shield and the longitudinal axis ofsaid counter tube will be excluded.

4. An apparatus of the character described for detecting smallsources of penetrating radiation comprising a holder adapted to be held in one hand by the observer to be aimed at the' source of radiation, a hollow cylinder disposed within said holder, a counter tube supported within said cylinder, one end of said cylinder extending beyond one end of said counter tube, a radiation stopping shield mounted in said extended end of said cylinder and being effective for excluding only radiations coming in to said carried by said holder and disposed substantially at right angles to said grip. a radiation excluding shield disposed within said holder and arranged axially of said counter tube and in front of the forward end thereof with no portion of said shield extending substantially rearward of said front portion of said counter tube whereby only radiations coming in along the forward end of the longitudinal axis of said tube i will be excluded from impinging on said tube.

6. An apparatus of the character described, comprising a holder provided with a hand grip and a portion extending forwardly and substantially at right angles to said grip, a counter tube mounted in said forwardly extending portion, and. radiation excluding 'shielding provided for said tube and carried by said holder, said shielding being arranged in ,said holder at the forward end of said tube with no portion thereof extending substantially rearward of said tube so as to exclude from said tube only those radiations coming in along the line of the forward end of the longitudinal axis of said tube.

7. An apparatus of the characvter. described ltion comprising a holder adapted to be held in one hand by the observer to be aimed at the than said end of said counter tube.

LEOPOLD iaxovNEri..

for detecting small sources of penetrating radiad

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