US2689309A - Discharge device responsive to molecular density - Google Patents

Description

Sept. 14, 1954 J. R. MAHONEY DISCHARGE DEVICE RESPONSIVE TO MOLECULAR DENSITY Filed Jan. 30, 1951 2 ShGtS-Sheet 1 Discharge Poi n l Z 0,0 firnum m k l Q Q IN VEN TOR.

John ,Q Md/zonqy BY V ATTORNEY Sept. 14, 1954 J. R. MAHONEY 2,689,309

DISCHARGE DEVICE RESPONSIVE TO MOLECULAR DENSITY Filed Jan. 30, 1951 2 Sheets-Sheet 2 INVENTOR. John A? Mabaney ,4 7" TOPNEY Patented Sept. 14, 1954 DISCHARGE DEVICE RESPONSIVE TO MOLECULAR DENSITY John 1%., Mahoney, Oak Rid the United. States Tenn.,, assignor to of America as represented by the United States Atomic Energy Commisslon Application; January 30, 1951, Serial .N 0. 208,489

5 Claims.

This invention relates to control or regulatin; devices, and more particularly to a device which is responsive to changes. in the molecular density or composition of gases for altering the current flow through and/or the voltage drop across a circuit which includes the. device In conventional counters such asv the air proportional counter, theimostsatisiactory balance betweensensitivity and background is achieved when the operating voltage lies within a limited range, referred. to as the. optimum range. This optimum voltage range. also lies somewhat below the. voltage at. which the counter goes into continuous discharge, and varieswith it. Changes in. the. continuous discharge voltage are effected by variations in the molecular density of the counter gas, that is, a given decrease in atmospheric temperature or increase in atmospheric pressure. raises the counter discharge. point and the optimum operating. voltage. In other counters subject. to. the influence of, or used in connection with gases of different or varying compositions, such changes tend. to alter their operating characteristics fand this results in. th necessity for frequent manual adjustment to.- maintain. the counter in the optimumvoltage range. Further, it becomes a complicated and difficult problem to regulate several counters or probes having difi'erent characteristics when supplied from a single voltage source. Another problem of keeping a counter within theoptimum voltage range arises when it is-operated from a source under changlngvoltage supply-conditions."

Applicant with a knowledge of these problems in the prior art has for anoba'ect of his inventiorr the provision of a regulating or control device responsive to changes in temperature-and/ or pressure for adjustingthe potential across a circult; v

Applicant. has as another object of his invention' the. provision of an electric discharge device responsive to changes in temperature and pressure for adjusting the potential, of a source. for a counter to maintain it within a predetermined optimum range and insure substantially uniform operation of the counter as the operating characteristics change in response to changes in atmospheric conditions or molecular density.

Applicant has as another object of his, invention the provision of an electric discharge device responsive to changes in the composition of gases for regulating the voltage across and the current through a circuit.

Applicant has as another object ofhis invention the provision of an electric discharge device 2 for continuous discharge which is responsive to changes in temperature or pressure to alter the voltage across a circuit, and is especially adaptable.- for use in airborne laboratories which. may

be subjected to rapidly changing atmospheric conditions over wide ranges.

Applicant has as a further object-of his invention the provision of an electric discharge device for regulating the potentialacross; a circuit utilizin a filar electrode which is adjustable with respect to the other electrode or the discharge device.

Applicant has as a still further objectof his invention the provision oi an. electric di charg device having voltage-resistance characteristics which are responsive to changing conditions of temperature or pressure; for indicating changes therein as a function of current change.

Applicant has, as a still further object of his invention the provision oi an electric discharge device for determining the composition. of gases including argon, helium, trichloroethylene, and water vapor through the measurement of ibsdischarge voltage and/or current. i 1

Other objects and advantages or my invention will appear from the following specification and accompanying drawings and the novel: features thereof will. he particuiarly; pointed out in. the

annexed claims, i

In. the drawings, 1 ice setof characteristic curves taken atdifiercnt temperatures and pressures. for a counter where pulseheight isplotted against voltage. Fig-.2v isa plan view of'oneiorm of my proportional counter or probe witlr'thc cover removed, incorporatingmyimproved. regulating or control deviceanother probe, with the cover removed, incorporating a modified. form. of regulating device. Fig. 4 is. a plan view of, a conventional proportional counter or probe which includes a. modifled. form of an improved regulating. or; control device mounted externally thereof. Fig. 5.- is a schematic. oi a preferred form of circuitcmployin my improved; regulatingor control device.

Referrin to the drawings in detail, Fig. 1 shows. two characteristic curves with lines intersectihg them, indicating the; optimum operating voltage ranges on each curve. As will he seen from curve A, the optimum voltage range lies slightly below the point at which the countergoes into continuousoperation. However, as the molecular density of the gas surroundin the counter is altered, the point of continuous discharge is moved, as indicated in curve B,,andj theoptimnm operating range is likewise altered. Thus it is Fi 3 is. a plan view of apparent that with changing atmospheric conditions, regulation of the voltage across the counter is required in order to maintain proper operation.

In the circuit of Fig. 5, the regulating or control tube I is fed from a high voltage D. C. source 2 of conventional type through a relatively large resistor 3 of preferably about 9,000 megohms and is coupled to a conventional probe 4 preferable of the standard air proportional type although not necessarily restricted to this type, through a resistor 5 or preferably 22' megohms. Bridged across the regulating or control tube I is a by-pass condenser B of preferably .002 mfd., for passin high frequency or other transient disturbances such as those resulting from inter ruptions in the operation of tube I as well as the high frequency transients characteristic of this type of discharge. The output of this circuit is coupled to a preamplifier (not shown) through a conventional coupling condenser I. In this circuit resistor 3 functions as the regulating resistor, that is, as the high voltage supply voltage regulator. The current through the discharge device tends to increase but the voltage across the resistor 3 will increase to return the discharge voltage to almost its original magnitude. Resistor 3 also functions to allow the discharge voltage to change in response to the gas conditions. Resistor 5 allows the voltage across the probe to vary when an alpha pulse changes the resistance of the probe momentarily.

The regulating or control tube I i vented to an atmosphere identical to that of probe 4, and includes a filar electrode 8, as indicated in Fig. 2. This filar electrode or wire 8 extends longitudinally of the case and is suspended between spring fingers 9, 9 carried by insulator supports I0, I mounted on the inner walls of the case II of the probe. The wire 8 is maintained taut by tension spring I interposed between the end of wire 8 and finger 9. The case II acts as the fixed electrode and also carries a pair of spaced screws I2, I2 of insulating material threaded into the wall thereof and with tapered ends for engagement with the bowed portions of spring fingers 9, 9 to move them outwardly and alter the distance or spacing between the filar electrode 8 and the case I I. In addition, the usual spaced wire electrode I3, I3, I3 of the conventional probe are included and they are suspended between the wire supports I4, I4 within the case II. Also included within the case I I, and connected in the manner indicated in connection with the schematic of Fig. 5, are the resistors 3, 5 and condenser 6. In the usual operation of this system, the optimum operating voltage for the standard probe is determined by any suitable means such as by plotting a curve similar to Fig. 1, after which the spacing between the filar electrode 8 and the case II is adjusted by screws I2, I2 so that the control device I will go into continuous discharge at the selected voltage. Since the discharge device I is the electrical equivalent of the standard probe, being of similar construction, and being vented to a like atmosphere any atmospheric change, shifting the discharge point of.

the probe 4, also shifts the discharge point of device I to substantially the same degree. Consequently, once the device I has been adjusted as outlined above, it maintains the voltage across the probe 4 at the desired magnitude, and somewhat below the probe discharge voltage, despite shifts in characteristics of the probe and the voltage range thereof.

In the modification of Figure 3 the filar electrode 8' is made stationary and is suspended between the guard rings I6, I6 of the insulator assembly positioned in the case II. However, instead of employing the case II as the other electrode, a rigid form of bar II of conducting material is utilized. This electrode is joined to the ends of a bowed leaf spring I8 through screws or other appropriate means while the central portion of the spring is mounted through screw I9 on case II. Screws 20, 20' pass through the case II near the ends of bar electrode I1 and coact with the screw threads of the sockets in the case through which they pass. As these screws are advanced, the ends thereof bear against the bar electrode I1 and move it inwardly of the case I I, away from the walls thereof, and toward the filar electrode 8. As the screws 20', 20 are withdrawn from the case, the bowed spring I8, joined to the electrode IT, project from the central portion of the case M towards the walls thereof.

In another modification, the regulating or control device is mounted externally of the counter, as shown in Figure 4. This makes it easier to incorporate the device into the arrangement of existing counters. In this assembly the discharge device I", along with resistors 3", 5" and condenser 6", are disposed within an enclosure or housing 2I" positioned on the back of case II". Insulators 22", 22 mounted on the inner walls of housing 2| serve to suspend the filar electrode 8" which remains stationary. The other electrode takes the form of a screw 23" threaded into the wall of housing 2I" and having a head 24" on its free end. Lock nut 25" serves to maintain the screw electrode 23" in adjusted position.

In one test of the arrangement of Fig. 4, a 20,000 count per minute alpha source was employed, and the assembly was placed in a bell jar with the alpha source joined thereto or otherwise associated therewith. The output of the probe was connected to a conventional rate meter circuit having an output proportional to the probe sensitivity, and this gave the following results:

Vacuum (in mm. mercury below atmosphere) Ratemeter Reading 13.5 31

In the embodiment of the invention of the foregoing test, electrode 8" was made two inches in length and electrode head 24" was made one and one-half inches in diameter. In a subsequent test, slightly inferiorregulation was obtained where the electrode 8" was one inch long 3.2161 the head 24" three-quarters inch in diame er.

Although the primary purpose of the subject. invention is to function as already described, it may also serve as a voltage regulator for the probe high voltage supply. For example, the

arrangement employed in the first test cited above was connected to a high voltage supply Whose output voltage was varied stepwise. The assembly successfully regulated the probe voltage, as is indicated below.

Supply voltage: Voltage across standard probe This invention thus not only serves to accomplish the functions of a regulator responsive to atmospheric changes, but also obviates the need for a high voltage regulating system. Other uses or applications are: (a) a plurality of probes modified as shown in Figs. 2, 3 and 4 may be operated in parallel from a single high voltage supply, each probe being regulated to operate in its optimum voltage range; (5) a probe modified as shown may be used with any one of several supplie having dissimilar voltage ratings; and (c) a given high voltage supply provided with the circuit of Fig. 5 is made quickly adaptable to any conventional probe. It is noteworthy, also, that the invention eliminates the necessity of making probe voltage adjustments in the field.

Having thus described my invention, I claim:

1. A system for regulating the operation of a radiation detecting device comprising a radiation detecting space discharge device for operating in a predetermined voltage range, a source of high voltage potential connected to said space discharge device, and a voltage regulator including an electric discharge device subject to the same atmospheric conditions as said spaced discharge device and electrically coupled to the source and said radiation detecting discharge device for altering the voltage impressed on said space discharge device in response to changes in atmospheric conditions for maintaining the operation of the space discharge device.

2. A system for controlling the operation of a counter comprising a Geiger Mueller counter operable within a critical voltage range, a source of high potential connected to said counter, a voltage regulator including an electric discharge device set to conduct at a predetermined voltage and subject to the same atmospheric conditions as said counter electrically coupled between said source and said counter and responsive to changes in atmospheric conditions for altering its contion.

3. A system for controlling the operation of a counter comprising a source of high voltage, a counter for operating over a changing voltage range at atmospheric temperature and pressure, resistance means for coupling said counter to said source, and a voltage regulator including an electric'discharge device electrically coupled to the counter and set to continuously discharge at a predetermined voltage and responsive to changes in atmospheric conditions for adjusting the voltage to maintain it Within the operating range of the counter.

4. A system for controlling the operation of a counter comprising a source of high potential, a radiation detecting probe operable over a critical voltage range which is dependent upon atmospheric conditions, a pair of resistors for connecting the probe to the source, and a voltage regulator including an electric discharge device,

continuously operable at a predetermined potential coupled between said resistors and responsive to changes in atmospheric conditions for altering its current flow adjusting the voltage across said probe to maintain it in operation.

5. A system for controlling the operation of a counter comprising a source of high potential, a counter operable over a critical voltage range which is effected by changes in atmospheric conditions for detecting radiation, a plurality of series connected impedances for connecting the counter to the source, and. a voltage regulator including an electric discharge device coupled between said impedances for continuous discharge above a predetermined potential, said discharge device beingresponsive to the same changes in atmospheric conditions as those to which the counter is subjected for controlling the voltage across the counter to maintain it in operation.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,490,674 Christ et al. 1- Dec. 6, 1949 2,496,886 Molloy et al. Feb. '7, 1950 2,505,919 7 Simpson, Jr May 2, 1950 2,522,902 Shamos Sept. 19, 1950 2,531,804 Carlin et a1 Nov. 28, 1950 2,532,956 Simpson, Jr. Dec. 5, 1950 2,602,904 Simpson, Jr. July 8, 1952 2,611,268 Mellen Sept. 23, 1952

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