US2532503A

US2532503A - Electronic counting circuits

Info

Publication number: US2532503A
Application number: US532566A
Authority: US
Inventors: Joseph W Kennedy; William R Baker; Clyde E Wiegand
Original assignee: Individual
Current assignee: Individual
Priority date: 1944-04-24
Filing date: 1944-04-24
Publication date: 1950-12-05
Anticipated expiration: 1967-12-05

Description

Dec. 5, 1950 J. w. KENNEDY ETAL ,532,503

ELECTRONIC COUNTING cIRcuf'rs Filed Ap-ril- 24, 1944 INVENTORS JOSEPH w: KENNEDY, WILLIAM R. BAKER BY CLYDE E. WIEGAND W a. .1 M

ATTORNEY.

Patented Dec. 5, 1950 UNITED STATES PATENT OFFICE "R; Baker, Berkeley, Calif., and Clyde E. Wieg'a-nd-, Santa Fe, N. lVIex., a'ssignors to the United States of America as represented by the United States AtoinicEnergy Commission "Application Aptii 24, 1944; Serial No. 532,566

"Still another object"of'the invention -isto provide a counting defice'that has incorporated therein an integrating arrangement,- the accuracy of the integrating "arrangement being substantially "independent of the time interval between "the integrated pulses. 7

Otherobjects of the-present invention will be apparent from the following description and the accompanying-drawing which illustrates a preferred embodiment thereof.

' Thedrawing is" a schematic "View of an '-improved= counting "mechanism that embod-i'es the "present invention and "essentially comprises a b'attery source of "potential "and anarrarigement foi emplifying the battery potential"- to a volt- "'agesufiiciently high for 1 use with an ionization "chamber-incorporated -in the oouriting mech- 'arfis'm. I'he pulses resultingin-the ionization chamber are amplified by" a multi-stage linear amplifier of variable -sensitivity, the "output of I which -is fedeither directly or through an inte- "grator to a discrimineitor 'stage. The purpose of the discriminator stage is to distinguish between -pu1ses ofthe desired:counted; particles and other ionizing particles or radiation or other background noises which are-necessarilypresent The output 'of' the discriminator stage in mm triggers ""a -grid controlle'd gas discharge tube which actuates'an electrical recording device or register.

Referring to 'the drawing, the "present" device includes a power supply comprising a "filament battery "2 -0f'1;5 -volts plate supply series c'on- -""nected"batteries '3 totaling 135 volts, and a 45- volt grid bias supply battery 4 having 1 "a 22=yolt *tap. The negative terminal of i the 'pl'ate' supply batteries 3 *andthe positive teri'ninal of the grid bias "supply battery; '4 are grounded through an octal "c'onn'ectora. The other "terminals of 'the "plate supply batteries '3 "andthe filament battery "2 are 'alsoconnectedto the circuitthrough the "o'etal' connector'8.

f The arrangement for amplifying thevoltaige "of the plate supply batteryto the high potential required "for an ionization "chamber 1 comprises tubesvsuna V9 "and theirassoci'ated circuitnetcharge tube; 'in the present embodiment it is shown as a coldcathode thyratron,the=-plate 0f which is unemployed, thecontrol' grid thereof acting asone el'e'etrodeand thecathode thereofas the other electrode. One terminal of theprin'iary of the transformer" 91* neon-nemesto the control grid 95 0f the tubeVQ; the other terminal-thereof being connected' to' thehigh positiveterminal of the plate supply-"batteries 3 through a 0:10-

- megohm resistor'QB; switches- 92 and-"9t,- and the Octal-connector 8. The transjformer' e'iid of the resistor i 96' is connected through a l microfalad condenserwi to the "cath6de 98 of--'the tube V9,

'whichcathode is in turn 'grounded. "It should be noted that'the control -gri'd lad-nhd "the cathode lead-of tube'VQ are shielded. 'A terminal of the secondary or the transformer "is connected to the plate'85 of' the tube V8; the other terminal thereof being gro'un'ded. The tube V8 is shown as atriode whereinthe grid aiid filament are tied together, thus practicallyresulting-in a diode; but-it'is apparentthat an ordinary diode may be 'used in its stea'd. The-filament st of the tube V8 "suppliedeurrentby -a' battery 8| through aswitch82,-the 'fi1ament 86 being connected through-a -1o-meghm res1swr 83 to the electrode'fi of'the ionization; chamber 1, the two terminals of the resistor -83' being grounded through .05-microfarad condensers 84, the resistor 83 and condensers 84 forminga filter network The other electrode 9 of i the ionization chamber '1 is connected t'o the control grid l 0 of a'tube V1, the filament of 'the tube 'Vl' beingconnected-to ground-and through'ja switch ll to-a filamentflsupplybus. *Although'the tube V1 is shown as a pento'de-having its suppressor grid tied to the filament and-its'screen-grid connected through a -1-megolim resistor l2 to the -v'olt positive potential and-beingby-passed to ground through an s-microra mq condenser '13, itis obvious that other types oft'ubes may *be' substituted in its pla'ce -In'thi's first 'stage a tube havihg "avery low noise level is required, inasmuch as the pulses supplied to th'e'control' grid thereof are very weak. It has been found that a- 959 type of Acern tube is satisfactory. The plate' of the tube 'V1 is connected i to series oc'inn'ected resistors i It and 16, theresistordt being of 0.1-meg0hm"and the resistor l4 being of .65 nie'g'olim "an'd'through' a switch Site the 45 vo1t positive' potential. The Junction point between resistors i4 "and it is --grounded through an 8 'nii carofarad T decoupling 'conden'ser'l'l. The plate *of "the tube Vlis also connected through a I0005micr6fajrad coupling condenser l3 to the control gri'd or a pentode V2, which control grid is gr'ounded throug'h a .25- megohm resistor 20. Tlie suppressor grid of the pentode V2 is tied to theffilament-thereof,which 'filament is in turnco'nnected'tothe filament supply bus. 'Connoted intheusualmanner through a by-pass condenser 23 to ground and through resistor 22 to the high positive plate supply bus is the screen grid of the pentode V2, the anode being supplied a positive potential from the high voltage bus through the resistors 25 and 26, the junction point between the resistors 25 and being grounded through a decoupling condenser 2's. The anode of the pentode V2 is also connected to ground through a coupling condenser 28 and the tapped potentiometer resistor 2% The values of the resistors and condensers of the stage including the pentode V2 are those usually employed, the by-pass condenser 23 being of 8 microfarads, the resistor 22 of 1.5 megohms, the resistor 25 of .25 megohm, the resistor 25 of .05 megohm and the condensers 2i and 28 being 8 microfarads and 0.1 microfarad respectively. The following two stages of amplification have substantially the same element values.

Connected to the adjustable arm of the potentiometer 29 is the control grid of the pentode V3, the filament of which is connected to the filament supply bus and has tied thereto the suppressor grid. The screen grid of the pentode V3 is connected through a resistor 32 to the high positive plate potential bus and is grounded through a by-pass condenser 33. The plate of the pentode V3 is supplied a positive potential through series-connected resistors 35 and 31, the junction point of which is grounded through a decoupling condenser 34. The output of the pentode V3 is connected through a coupling condenser 39 through a potentiometer resistor -lil to ground, the adjustable arm of the potentiometer being connected to the control grid of a tube V4. The filament, suppressor grid and screen grid of the tube V4 are connected in a manner similar to the connections in the pentode V3, the plate voltage being applied through a resistor M and an impedance element 42, the inductive impedance of the impedance element being about 60,000 ohms at 1000 cycles. The output of the tube V4 is connected through a coupling condenser 43 and switches 44 and 5 to the junction point of .Ol-microfarad condensers and H, the other terminal of the condenser 5i being connected to one pole of a switch 52 and the other terminal of the condenser 50 being connected to the control grid of a pentode V5.

The control grid of the pentode V5 is supplied a 22-volt negative bias through a l-megohm resistor 53. The suppressor grid of the pentode V5 is tied to the filament, which in turn is connected to the filament supply bus, the screen grid of the pentode V5 being grounded through the by-pass condenser 54. Also connected to the screen grid is the adjustable arm 55 of a 10- megohm potentiometer 55, one terminal of the potentiometer 56 being grounded and the other terminal being connected through a switch 5? to the 90-volt positive potential of the plate supply batteries 3. The anode of the tube V5 is connected to the 90-volt positive potential through a condenser 58 in parallel with a seriesconnected .OZ-megohm resistor 59 and glow discharge lamp 60, which glow discharge lamp may be of the ordinary neon or argon type. It should be noted that the anode of tube V5 is, except for negligible leakage, in an isolated condition.

The junction point between the resistor 50 and the glow discharge lamp 60 is connected through a coupling condenser GI to a pole 53 of the switch '52, which pole is grounded through a 1.0-megohm resistor 64. Connected to the blade of switch 52 is the control grid of a tube V6,

which control grid is supplied a negative bias of 22 volts through a 2-megohm resistor 65. The filament of the tube V6 is connected to the filament supply bus and has tied thereto a suppressor grid, the screen grid being grounded through a condenser 66 and being connected through the switch 57 and a .25-megohm resistor 68 to the -v0lt positive plate potential, the same potential being applied to the anode of the tube V6 through a .25-meg0hm resistor 69. The output of the tube V6 is led through a coupling condenser 70 to the control grid of a gas discharge tube V7, which control grid has a negative 45- volt bias applied thereto through a l-megohm resistor H. The cathode and anode of the tube V7 are shunted by a l-microfarad condenser 72, the anode being connected through an electromagnetic register 13, a .0025-megoh1n resistor 14 and the switch 45 to the high positive plate potential, the cathode being connected directly to ground. The register 13 may be of any wellknown electromagnetic type that has a substantially high counting rate.

The improved counting device has been described and specific values applied to the component parts thereof, but it is obvious that these values, as well as the component parts thereof, may be changed or altered to suit a particular purpose. For example, the ionization chamber has been illustrated merely as a pair of electrodes; however, it should be understood that any other Well-known type of ionization chamber may be used, such as a proportional counter, as well as a Geiger-Muller tube supplied with external or internal quenching. Also the design of the amplifier may be modified, but in any case the amplifier should be one having a low noise level and a high degree of stability with respect to overall gain.

The device operates as follows. The high voltage plate supply is fed to the stage comprising the tubes V8 and V9, the tube V9 and its associated elements acting as a relaxation oscillator forming high voltage periodic pulses having a steep wave front, which pulses are in turn amplified by the step-up transformer 9l' and thence rectified and filtered by the tube V8 and the resistor condenser network resulting in a voltage output of the order of 1500 volts. The positive potential output of the supply is applied to the electrode 6 of the ionization chamber, the other electrode 9 being connected to the grid of tube V1. There is a high potential existing between the electrodes of the ionization chamber 1 and any ionizing particle introduced between these electrodes will produce ionization of the gas between the electrodes 6 and 9, resulting in a momentaryv surge of current which impresses a pulse on the control grid of the tube V1. This pulse is amplified through the four stages of amplification including the tubes V1, V2, V3 and V4, the sensitivity of the amplifier being adjustable by means of the potentiometers 29 and 40. The scaling circuit including the tube V5 integrates the output pulses of the last stage of the amplifier, the output of the scaling circuit or the output of the amplifier being fed through the double throw switch 52 to the discriminator stage including the tube V6. The condenser 58 of the scaling circuit is step charged for each pulse applied to the control grid of the tube V5. The condenser 58 will retain its charge except for negligible leakage. Inasmuch as the anode of the tube V5 and the side of the condenser 58 connected thereto is in an isolated condition except voltage the condenser .rr the afcresaia negligible leakage, the 'f'c'ondenser 58 has no discharge path except through the gas tube 60 upon firing. when the potential across the condenser 58 reaches a predetermined will dischargefthrough the gas tube 50, thus. sendinga pulse 'throughthe condenser- 6]. It is obviousfthat the frequency of dis rgeiof the condenser '58- is dependent "n-thefiequency'of'the pulses fed'tothe control grid of tube 'V5, as Well. as upon the duration and intensity of these pulses. 'Theaforesaid can be varied by means of the po-tentiometers 29 and 40 of the amplifier. By adjusting the potentiometer 56, the scale of the integrator may also be changed. The discriminator stage consists of the tube V6 biased beyond cutoff, which tube is responsive only when a pulse of a predetermined voltage is applied to its control grid. In this way any undesired pulses which are below the predetermined voltage will have no eifect on the subsequent stages of the counter.

The output of the discriminator stage triggers the cold cathode thyratron V? which in turn becomes conducting, causing the condenser 12 to discharge, thereby allowing the thyratron V7 to de-ionize, thereby returning the grid thereof to control. Thereafter the condenser 12 is charged through the resistor 13 and the resistor M, causing the register 13 to advance; More specifically, the time constant of the resistor-condenser network 'I4-'I2 is of such value as to permit the thyratron V7 to de-ionize before the potential on the condenser 12 reaches a value sufilcient to maintain the thyratron discharge, thereby allowing the grid of the thyratron V7 to regain control.

Considering now the calibration and application of the improved apparatus, a standard sample having a known count is positioned between the electrodes 6 and 9 of the ionization chamber 1 and the gain of the amplifier is adjusted by means of the potentiometers 29 and 40. The scaling circuit is adjusted to any desired value by varying the potentiometer 56, thus establishing the screen An apparatus count is then taken of the standard sample and by comparing the known count of the standard sample with the apparatus count the calibration factor of the apparatus at the set adjustments is determined. standard sample is removed and the test sample, the count of which is desired, is inserted between the electrodes 6 and 9 of the ionization chamber 1 and the apparatus count is obtained. By multiplying the apparatus count of the test sample by the calibration factor the absolute count of the test sample can thus be determined.

Of course, the kind and mean energy of the particles emitted by the standard sample should be substantially the same as of the particles emitted by the test sample, .and the effective thickness of the two samples should be substantially the same, so that energy losses within the sample are the same on the average, for the two samples, and the samples should be so positioned that the average path length of the particles within the ionization chamber is the same for the two samples. For example, if it is desired to count alpha :particles from a test sample containing unknown amounts of the uranium isotope, it would be adequate for approximate work to use as a standard sample one containing a known amount of uranium having the normal ratio of isotope concentrations, since the alpha particles from these isotopes all have the same grid potential of the pentode V5. 1

Thereafter the energies within about 15%. "'Hdwevr f it probably would not be satisfactory touse poloniuin .0 1j*'a a t e r, Care s fldfi ui's e 'sr 186d that the amplifier does not change appreciably between calibration and use.

A preferred embodimen'toi the invention has been shown, but xitjis obvious that, numerous alterations and omissions may beymade without departing from the spirit thereof.

What is claimed is:

1. A self-contained portable counter comprising an ionization chamber, a power supply for furnishing a high potential to said ionization chamber, a pulse amplifier, a scaling circuit the input thereto being the amplified pulses, a register, and switching means for impressing the output of the scaling circuit or the amplified pulses to said register.

2. A self-contained portable counter comprising an ionization chamber, a power supply for furnishing a high potential to said ionization chamber, a pulse amplifier, a scaling circuit the input thereto being the amplified pulses, means for varying the scale of said scaling circuit, a register, and switching means for impressing the output of the scaling circuit or the amplified pulses to said register.

3. A self-contained portable counter comprising in combination an ionization chamber, a battery source of potential, electronic means for amplifying said potential, means for applying said amplified potential'to the electrodes of said ionization chamber, a preamplifier stage controlled by the output of said ionization chamber, a pulse amplifier, the output of said preamplifying stage feeding said pulse amplifier, a scaling circuit, an electromagnetic register, and switch means for selectively conducting the output of said pulse amplifier directly or through said scaling circuit to said register.

4. In a scaling circuit, an electron tube having an anode, a cathode, a screen grid and a control grid, said anode being substantially isolated, a condenser, a source of potential connected. through said condenser between said anode and said cathode, a series-connected glow discharge tube and first resistor connected to shunt said condenser, and a second resistor connected across said power supply, said second resistor having an adjustable contact connected. to said screen grid whereby the scale of said scaling circuit may be varied.

JOSEPH W. KENNEDY. WILLIAM R. BAKER. CLYDE E. WIE'GAND.

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

UNITED STATES PATENTS Number Name Date 1,762,712 Charlton June 10, 1930 1,933,976 Hanson Nov. 7, 1933 1,979,692 -Knowles Nov. 6, 1934 2,037,924 Rentschler Apr. 21, 1936 2,049,376 I-Iartwig July 28, 1936 2,061,733 Jobst Nov. 24, 1936 2,075,140 Schlesinger Mar. 30, 1937 (Other references on following page) 8 STATES PATENTS Lewis, Electrical Counters, Cambridge, 1942, Number Name Date 7146- 0 1 07 Strauss Ntay 18, 93 Locher 8t 21., Radlology. V01. 27, 1936, pp. 2,097,400 Batchelor Oct. 26, 1937 2,163708 Schimkus et a1 June 27 1939 5 Geophyslcal Instrument C0. C1rcu1a-r E Wash- 2,191,903 Aldous Feb. 27, 1940 mgtm' 4 2,203,382 Shore June 11 1940 Huntoon, Artlcle 1n Revlew of Sc1ent1fic In- ;2 321 2 5 Howell June 8 943 Strumen'BS, June 1939, V01. 10, pp. 176-178.

Curtiss, Journal of Research of the National OTHER REFERENCES H) Bureau of Standards, v01. 23, July 1939, R. P. 1223,

Lifschutz, Review of Scientific Instruments, ppvol. 10, January 1939, pp. 21-26.