US2584844A - Geiger tube radiation meter - Google Patents

Description

Patented Feb. 5, 1952 UNITED STATES PATENT OFFICE GEIGER' TUBE RADIATION METER James M. Constable, Ozone Park, N.Y. Application November 26, 1949, Serial No. 129,543

- solaims. (ci. 25o-83.6)

' The present invention relates to a Geiger tube radiation meter and more particularly to a meter which is light in weight and has a long* lived power supply.

As the science of nuclear physics advances and the discovery, mining, purification and application of radioactive materials becomes more widespread both in a civilian and military sense,it becomes increasingly important that simple, rugged, accurate, and lightweight detecting and measuring instruments for beta, gamma, and alpha rays and particles be made available. Heretofore, the most successful instruments were of the type employing Geiger-Mueller tubes and various types of vacuum tube amplifying means for increasing the output of the Geiger-Mueller tubes sufciently to be readable on a microammeter integrating circuit. While these instruments are far superior to any previously available,` they still have several serious disadvantages in'that the vacuum tubes require both filamentV and plate supply batteries which are of considerable weight because of the added necessity of supplying rela# tively high voltages to the Geiger-Mueller tube therefrom, the vacuum tubes had to be miniaturized to reduce the drain on the batteries thereby to increase their lives which resulted in adelicate structure, and the vacuum tube amplifiers are both complex and, because of their complexity, inaccurate. v

To obviate some of these disadvantages, special small high voltage batteries have been yprovided for use with these instruments. However, vthe weight of the batteries is still excessive, becausethey are non-standard they are not readily available so that prospectors for radioactive ores could not secure them in remote localities nor would they be on hand in areas of great emergency as when an atomic bomb has fallen, and the lives of such batteries by reason of their extremely small cell size is short and unreliable.

To eliminate the use of such batteries, special vibrators and transformers have been developed to convert the output of 3 volt batteries tothe high voltage necessary tothe operation of a" Geiger-Mueller tube which ranges between 500`- to 1500 volts. lIn this type of supply, the .battery has one terminal connected to the mid-point of the primary of the transformer, the other ter. minal of they battery being connected toeither, end of the primary alternately by operation of the vibrator. The step-up ratio of the turns on the primary and secondary windings of the .trans-.3 former is proportional to the ratio of the batteryv voltage tothe desired voltage and, because the" 2 desired voltage is high, the turns on the secondary winding must also necessarilybe high. It is obvious then that such a winding has both high resistance and inductive impedance which leads to large power losses in both the resistance of the winding and the iron in the transformer core. Because the vibrator has to have its armature driven at its high resonant frequency andwith considerable amplitude in order to swing between its two opposing contacts, a considerable mechanical loss is engendered thereby so that it has been found that by reason of the high resistance, magnetic and mechanical losses, this arrangementA has a power conversion efciency of only 5 to 10%. Other arrangements have been found to be equally inefficient by reason of the high electrical, magnetic, and mechanical losses inherent in their construction. The present invention was designed after a thorough analysis of the foregoing disadvantages and with a view to producing an instrument that is simple, rugged, accurate, and requires Asuch low battery consumption as to be Aboth lightweight and long-lived. These results have been achieved a' by the total elimination of all filament type vacuum tubes with the consequent elimination of the necessity for filament supply batteries and a considerable enhancement in the ruggedness and simplicity of the arrangement without'any' sacrice of its accuracy. The accuracy has been further increased by the provision of special integration and calibration circuits whereby both low Ycount and high count radiations may be indicated with great precision by a simple switching between circuits of greater or lesser sensitivity. Further reduction in battery weight is accomplished, not only by the elimination of the lament supply battery, but also by providing a highly eficient power supply for the Geiger- Mueller tube which likewise serves as the source of power for such cold-cathode electronic tubes as are found necessary to the operation of the instrument. Because of the elimination of the filament battery and the high efficiency of the main power supply, battery life is also greatly extended beyond the maximum heretofore achieved. In a final attempt to secure simplicity, the power supply has been designed to operate from a single standard flashlight cell of the type readily available in any five-and-ten-cent store or cross-roads country store.

Specifically, the apparatus of the present invention comprises a Geiger-Mueller tube having its voltage supply connected thereacross. vA stepdown transformer is so connected to the tube that pulses corresponding to the tube pulses pass through its primary winding and appear across its secondary winding at considerably decreased voltage but higher amperage. These low-voltage hgh-amperage pulses are rectified and supplied to a microammeter having an integrating condenser connected thereacross whereby the microammeter will indicate a value dependent upon the number of pulses produced by the tube per unit of time. The aforesaid rectification can be switched to be either half-Wave or full-wave, the half-wave rectification having been found to be more sensitive for low tube counts and the full- Wave rectification providing greater resolution for high tube counts.

For even greater sensitivity when the number of pulses from the tube is low, a storage condenser may be provided across the tube so as to enhance the intensity of the pulses and a variable calibration resistor is provided for simultaneously ad- .I

justing the effective value of the storage condenser and variably shunting themicroammeter for calibration purposes. When full-wave rectication is employed, a second variable resistoris connected to shunt the microammeter tof'provide calibration thereof.

The novel power supply includesa closed core inductor having a low resistance primary winding in series with the winding and normally closed contacts of a vibrator relay, the series circuit being connected to a single dry cell of theilashlight type. The inductor is also provided with a fairly low resistance secondary winding connected in series with a gaseous tube rectier'to a storage condenser, the latter in turn being connected through a loading resistor to a voltage regulating tube. The voltage regulating tubeis connected through either a surge limiting'resistor or rectifier to a condenser which'acts as 'the power supply for the Geiger-Mueller tubeandits associated meter circuit.

An object of the present invention is the y'provision of a radiation meter in Whichalllamenttype tube amplifiers have been eliminated.

Another object is to provide a radiationmeter having as its only source of power a single dry cell of the flashlight type.

A further object of the invention is rthe provision of a high eiciency low-drain .powerconversion system between a dry cell anda Geiger- Mueller tube.

Still another object is to provide an-amplication means which converts the high-voltage'lowcurrent pulses of a Geiger-Mueller tube tolowvoltage high-current pulses without the intervention of electronic tubes.

Yet another object of the present invention is the provision in a radiation meter of .readily adjustable circuits which are capable of detecting low count pulses from a Geiger-Mueller tube with great sensitivity and high count pulses with great accuracy.

It is also an object of the invention to provide a radiation meter which is selectively responsive to both low and high count pulses from a Geiger- Mueller tube with simple calibration means.

A further object is to provide in the power supply system of a radiation meter, a voltage regulation means arranged to prevent surges produced by such regulation lfrom having a deleterious effect on the operation of a Geiger-Mueller tube energized therefrom. Y

Other objects and many of the attendant advantages of this invention will be readily apprecated as the same becomes better understood iii -known in the art as Geiger-Mueller tubes.

vof la. 'resistor 4.

4 by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the gures thereof and wherein:

Fig. 1 is a diagram of the preferred form of circuit employed in the radiation meter of this invention, and

Fig. 2 is a diagram of a modified circuit intended Vto replacea portion of the circuit of Fig. l.

Referring now to the drawings, there is shown in Fig. 1 a gas-filled tube I of the type which discharges when the gas therein is excited by external radiations as from gamma, beta or alpha rays or particles, such tubes being generally The tube I is vprovided with the usual cathode 2 and anode 3. the anode being connected to one end The other end of resistor 4 is connected to one end of the primary winding 6 of fa. step-down transformer 5, the other end of theprimary winding 6 being connected to `one end ofa condenser 'I which has its other end connected to the cathode 2 and is grounded. The condenser 'I is maintained charged at the operating voltage of the tube I by power supply equipment to .bedescribed hereinafter and serves therefore as the source of high Voltage for making tube I .operative when radiations excite the gases therein.

The transformer 5 is of the closed core type, as illustrated, and is provided with a center tapped secondary winding 8 having considerably fewer turns than the primary winding 6, a ratio of about 40 to 1 being preferred. One end of the secondary winding 8 is connected through a recti-l fier 8 to one end of a microammeter I0, the other endof which -is connected to the center tap of the secondary winding. Connected across the S microammeter I0 is an integrating condenser II.

The other end ofthe secondary winding 8 -is connected to one end of a second rectifier I2, the other end of which isadapted to be disconnected from or vconnected to the same end of the microammeter I0 as is the rectier 9 by the switch I3. The rectiers 9 and I2 are poled to produce fullwave rectication of the output of the secondary winding 8 when both rectiers are connected to the microammeter I0.

Connected between the anode 3 andthe resistor 4 is one sid-e of a condenser I5 of much smaller capacity than the power supply condenser 1, the other side of condenser I5 being connected to one end of a resistor I5 havingan 'F- adjustable sliding contact thereon as illustrated.

A second switch I4 mechanically interconnected with switch I3, as shown, to provide simultaneous operation thereof is arranged in its left-handv positionto connect the sliding contact of resistor I6 tothe grounded lead I8 of the power supply and in its right-hand position to connect a sliding contact on a resistor Il to the grounded lead IE for a purpose to be made apparent hereinafter. It vwill be noted that one end of the resistor I'I is connected to one end of the microammeter I8, the other end of the microainmeter being connected by lead Ia to the grounded lead I8. In its left-hand positionthe switch I3 con-A nects the lower end of resistor I6 to the end 'of the microamm'eter I0 which is not connected tov lead IBa.

In order to maintain the condenser 'l chargedat a high voltage, a voltage conversion and regu. lating system energized from a single dry cell I8. whichfmay be ofv the flashlightlcattery or equ,iva-.

lent low voltage, lightweight type, is provided. The voltage conversion V'portion of Vthe system comprises a relay 2li having a coil and normally closed contacts in Vserieswith the battery IS' and the primary winding 22 'of an inductor 2l, the inductor having a closed core 30 and a secondary winding 23 thereon. l

The relay 20 is a current operated relay'A designed so that a minimum arnountrof power is required to eiieet opening of its contact, andthe mechanical movement of the relay armature need be very slight and only great enough to break the contact as, distinguished from the operation of the usual full-wave vibrator which must have suiiicient mechanical movement in its' armature to close a pair ofback contacts. It is apparent that this type of construction reduces the battery drain considerably over other arrangements. I

The primary winding 22 has very few turns and therefore low resistance loss to limit further the drain on the battery I9, the high induotanoe of the closed core 38 providing considerable magnetic energy storage therein to cause the primary winding 22 to have a large impedance therebyto slow down operation of' the relay 20 with'a further saving of mechanical energy and consequent reduction of the drain on battery I9. Opening of the contacts of relay 20 produces a large magnetic surge through the core 30 and this produces in the relatively few turns of lthe winding 23 a considerable voltage which is greater than the` magnitude needed to operate the tube I'. The ratio or the turns of primary windingl 22 tosecondary winding 23 need not approach li that of the ratio of the voltage of battery I"9 to that needed to operate'tube I as the voltage' produced by winding 23 is not onlya function of'its turns but also of the rate ofV change of v'fluir in core 30 which, as stated above, is very high. The use of a closed core provides high inductance and eliminates the losses inherent in an open core whereby the size and weight of the core'can be made quite small. Thus the weight of inductor 2.! is considerably reduced v`when compared with that of a step-up transformer or an open core induotor.

The secondary Winding 23 has one side connected to grounded lead I8 and theotlier side is connected to the anode of' a cold-cathode, high voltage rectier 2li, the cathode of which is connected to one side of a condenser 25 having its other side connected to grounded lead I8. Connected across the condenser 25 isa voltage regulator ltube 25 of the ionization type having an anode 28 and a cathode 2i connected to grounded lead I8, `a current limiting resistor Z9 being arranged in the circuit between tube 26 and condenser 25. The resistor 2S andthe tube 26 act to produce a load on condenser 25 which limits the peak voltage on the latter and therefore thel voltage across the turns of secondary'winding 23 and primary winding 22, the number of turns 'on winding 22 being selected to limit the voltage across the contacts of relay 2B to a safe value.

to prevent impropereperation thereof.

i'f desired, the anode 28 may be connected directly to the primary 5. of transformer thereby to eliminate the condenser 'i but it has `been found.. more desirable to employ the'condenser I-V to'reduce the eiectof surges likely'to` b'e produced bythe voltage regulator tube 25 whenthe voltageY of battery I9 is low. To achieve this result, the condenser I is connected through a rectiiier 3| across the tube 26,- the4 rectier being Tir poled soth'at surges vfrom the-tube 26 arei'solated from condenser 'I'. When Geiger tubef i ispulsing to cause thereby'a drain on the power supply anda drop inits voltage during eachpulse, the regulator tube `will momentarily stop conducting fdurin'g' each` pulse if the battery 'voltage is low rand asurge will result when conduction resumes. This surge is blocked by rectifier 3l which acts as a low resistance in one direction and a high resistance in the other permitting thereby charging of condenser 'I but opposing the eiiect of surges. If desired, rectifier 3| may be replaced by a resistor which will permit condenser 'I to supply the peak currents while the condenser need supply only an average current to the condenser 1.

Referring now to Vthe arrangement of Fig. 2, there is disclosed therein a modification in all respects similar to'that ofFig. 1 except that the primary Winding 6 of transformer 5 is connected in series with condenser I5 across the tube I, it" being apparentfthatdisoharges of tube I` will produce pulses in secondary winding 8 in a manner 'similar to the arrangement of Fig. 1.

The :operation of the radiation meter described hereinabove will now be disclosed. Referring to Fig. l, as soon as the battery I9 is connected in circuit' as by a switch, the relay 2U commences to vibrate producing thereby intermittent high intensity iiux surges in the closed core of inductor 2l whenever the contacts Yof relay 26 open, it being apparent that the building up or' the flux in core 30 is relatvely'slow when the contacts close. These high intensity flux surges link the turns of secondary winding 23 to prod-uce' high Voltagev pulses therein which are rectitled by 'rectiiier 24, the direction of winding 23' and poling of rectier 24 being arrangedto permitthis. Tlie'intermittent'high voltage pulses charge the 'condenser 25 to a voltage determined by the voltage regulator tube 26 and the loading resistor 29, such voltage being of a magnitude to produce vdischarge of the Geiger tube I in the presence of radiations. The condenser 25 vgradually charges the condenser 'I through the resistance of4 the'rect'ier 3l, or a resistonwhich maybe vsi'ibstitutedtherefor as described above, the voltageof` thecond'enser 'l remaining substantially constant th-erec'tiiier 3l. Y

The meter is now ready for calibration, it beingmerely necessary to select the positions ofi switchesv i3 and I li and set the calibration of' resist'cnrsv 'I6' or I'I 'depending on whether a low of a. Ahigh radiation count is to be detected.

Assuming that a low radiation count is to be detected, it is obvious that the instrument shouldV Y have high'sensitix'fity even at the sacrifice of good resolution. For high sensitivity, the switches I 3 and I4 arethrown to the left or into `the position shown in `vlig. 1", in which position the condenser I5 is connected in series with a portion of resistor IG and through its movable contact and the switch I4 to the grounded lead I8. It is thus apparentv thatthe condenserV and the upp'erpoition ofv resistor I6 are connected across the anode and cathode of tube I and that the cha'rge inthe condenser will'be discharged, when the tube I becomes conductive, at a rate determined by the poitionofV the resistor I6 in lseries witlii the? ciziiidenser.l It will be apparent, also, that the'condenser t5' acquires its chargefr'om the condenser Ithr'ough the andcurrent limiting resistor 4L vWithr the switchv` I3-thrown to' the left,-V the by reason ci.v the 'presence of primary winding 6"' rectifier 9 only is connected to the microammeter I and the lower portion of resistor I6 is oonnected across the microammeter by means of leads I8a and I8 and switches I4 and I3. It will be noted that when the adjustable tap on resistor I8 is moved downwardly to increase the amount of resistance in series with condenser I and thus decrease its rate of discharge and therefore the size of the pulse passing through primary winding 6, the amount of resistance introduced by resistor I6 across the microammeter I0 is reduced simultaneously to increase the shunt across the microammeter thus reducing its sensitivity. Thus, resistor I8 acts as a calibration means and it may be so adjusted when a standard source of radiations is placed adjacent Geiger tube I to provide any desired scale reading on microammeter I8.

The condenser I5 is a recognized means for increasing the pulse size of the Geiger tube when greater sensitivity is desired as it is obvious that it permits an enhanced discharge across the Geiger tube by reason of the charge stored in the condenser. An additional increase in sensitivity is achieved by the use of half-wave rectification in employing the rectifier 9 alone as this leads to pulse stretching in the winding 8 of transformer 5 by reason of the inductive lag in the core of the transformer when the entire pulse passing through the core is not utilized. Because of the latter means for securing greater sensitivity, the condenser I5 may be omitted.

From the foregoing, it will be understood that the meter is first calibrated against a standard source and that when the tube I is placed near a source of low count radiations, the pulses passing through primary winding 6 will induce pulses of a considerably higher amperage but lower voltage in the output of secondary winding 8 of transformer 5 which are rectified by rectifier 9 and integrated by condenser II to produce an average reading on the microammeter I0, the latter being properly calibrated to give a direct reading of the number of radiations received by the instrument.

For higher count radiations, the switches I3 and I4 are thrown to the right, thereby disconnecting condenser I5 and resistor I6 from the circuit but connecting rectifier I2 to the microammeter Ill to provide full-wave rectification of 'the output of transformer secondary Winding 8, the calibration resistor II being also connected across the microammeter. The removal of the condenser I5 lowers the sensitivity of the meter but sensitivity is unnecessary when high radialtion counts are to be detected. Likewise, as soon as the output of winding 8 is connected for fullwave rectification, the inductive lag in the core of transformer 5 is eliminated along with the pulse stretching produced thereby with a consequent reduction in sensitivity, now no longer necessary, but with a corresponding increase in resolution so that each pulse will produce a definite eect on the integrating condenser I I thereby to increase the accuracy of the readings of microammeter I8. As before, the calibration of the meter is determined by a standard source, the resistor I1 being adjusted to produce a desired initial reading on the microammeter.

The operation of the modification of Fig. 2 is essentially the same as in Fig. 1. The condenser I5 is charged from the power supply through resistor 4. When Geiger tube I discharges by reason of radiations impinging thereon, the discharge of' condenser I5 causes a high-voltage.

low-amperage pulse to pass through primary winding 6 and produces a low-voltage, high-amperage pulse in secondary winding 8 which is rectiiied by rectifier 9, integrated by condenser II, and indicated by microammeter I8. As in Fig. 1, full-wave rectification may be employed for the output of secondary winding 8 and the various calibration means disclosed in Fig. 1 may be employed.

From the foregoing description, it will be apparent that a radiation meter has been provided which is simple, lightweight, and has Very few parts while maintaining great efficiency and accuracy in its operation. Tests have shown that its power conversion efficiency is in the neighborhood of 40% whereas the highest previously known for this type of supply is 17%. The unit is so efficient that 70 hours of operation may be expected from one standard ashlight battery Whereas heretofore twice the weight of batteries in other arrangements has given less than 8 hours of operation.

The power supply is inherently self-regulating in that when the battery voltage drops, the output high voltage does not drop in proportion as the relay 20 merely slows down but continues to produce practically the same induced voltage in the secondary winding 23 of the inductor 2I, any drop in voltage being produced merely by the demands on the charge in condenser 25.

The tube I does not necessarily have to be a Geiger-Mueller tube as any counter tube which operates to produce small pulses may be employed in its stead. The indicating means need not be restricted to the microammeter I0 and the integrating condenser II as these may be replaced by other indicating or recording means satisfactory for the purpose.

Various modifications are contemplated and may obviously 'be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter defined by the appended claims as only preferred embodiments thereof have been disclosed.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. A radiation meter comprising a gas-filled tube subject to discharge by radiations when energized, a source of electric power supply for energizing said tube, a step-down transformer having a primary winding and a secondary winding, said primary winding being connected to the source of power supply for said tube and responsive to the discharge of the latter, an indicating means connected to said secondary winding and energizable therefrom for indicating the rate of discharge of said tube, and a rectifier interposed between said secondary winding and said indicating means to supply the latter with unidirectional current.

2. A radiation meter comprising a gas-filled tube subject to discharge by radiations when energized, a source of electric power supply for energizing said tube, a step-down transformer having a primary winding and a secondary winding, said primary winding being connected to the source of power supply for said tube and responsive to the discharge of the latter, an indicating means connected to said secondary winding for indicating the rate of discharge of said tube. a rectifier interposed between said secondary winding and said indicating means to supply the latter with unidirectional current, and an integrating condenser connected across said indicating means and in series with said rectifier.

3. A radiation meter comprising a gas-filled tube subject to discharge by radiations when energized, a source of electric power supply for energizing said tube, a step-down transformer having a primary winding and a secondary winding, said primary winding being connected in series with the source of power supply for said tube and responsive to the discharge f the latter, an indicating means connected to said secondary winding and energizable therefrom for indicating the rate of discharge of said tube, and a rectier interposed between said secondary winding and said indicating means to supply the latter with unidirectional current.

4. A radiation meter comprising a gas-filled tube subject to discharge by radiation when energized, a source of electric power supply for energizing said tube, a step-down transformer having a primary winding and a secondary winding, said primary winding being connected to the source of power supply for said tube and responsive to the discharge of the latter, an indicating means connected to said secondary winding for indicating the rate of discharge of said tube, a rectifying arrangement interposed between said indicating means and said secondary Winding for producing half-wave or fullwave rectication of the output of the secondary winding, and switching means operable for selectively connecting said indicating means to said rectifying arrangement to subject said indicating means to half-Wave rectication for low rate tube pulses and to full-wave rectification for high rate tube pulses.

5. A radiation meter comprising a gas-filled tube subject to discharge by radiation when energized, a source of electric power supply for energizing said tube, a step-down transformer having a primary winding and a secondary winding, said primary winding being connected to the source of power supply for said tube and responsive to the discharge of the latter, an indicating means connected to said secondary winding for indicating the rate of discharge of said tube, a rectifying arrangement interposed between said indicating means and said secondary winding for producing half-wave or fullwave rectification of the output of said secondary winding, switching means operable for selectively connecting said indicating means to said rectifying arrangement to subject said indicating means to half-wave rectication for low rate tube pulses and to full-wave rectification for high rate tube pulses, and an integrating condenser connected across said indicating means and in series with said rectifying arrangement.

JAMES M. CONSTABLE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,920,569 Koros Aug. 1, 1933 2,026,421 Fecker Dec. 31, 1935 2,225,700 Laing Dec. 24, 1940 2,231,873 Barrett Feb. 18, 1941 2,401,723 Deming June 11, 1946 2,474,581 Howell June 28, 1949 2,531,106 Brown et al Nov. 21, 1950 OTHER REFERENCES Nucleonics, Oct. 1948, pp. 52 and 55.

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