US2963589A

US2963589A - Automatic ionization chamber

Info

Publication number: US2963589A
Application number: US578454A
Authority: US
Inventors: Neher Henry Victor; Alan R Johnston
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-04-16
Filing date: 1956-04-16
Publication date: 1960-12-06
Anticipated expiration: 1977-12-06

Description

Dec. 6, 1960 H. V. NEHER ET AL AUTOMATIC IONIZATION CHAMBER Filed April 16, 1956 TIME BETWEEN DISCHAEGES SECS. i; u\

APPLIED POTENTIAL T0 SHIELD I4AND FIBEEZA' INVENTOR5 Heme) Wcroe Nev/5e BY '44 /v Eda/v 8729/ United States ate AUTOMATIC IONIZATION CHAlVlBER Henry Victor Neher and Alan R. Johnston, both of 1201 E. California St., Pasadena, Calif.

Filed Apr. 16 1956, Set. No. 578,454 Claims. (Cl. 250-83.6)

This invention relates to automatic ionization chambers and included in the objects of this invention are:

First, to. provide an automatic ionization chamber which is an improvement in the automatic ionization chamber' is directed to the accompanying drawings in which:

Figure 1 is a fragmentary, partial elevational, partial sectional view of the automatic ionization chamber.

Figure 2 is an enlarged fragmentary, transverse sectional view taken through 22 of Figure 1 with the surrounding shell of the ionization chamber removed.

Figure 3 is a transverse, sectional view through 3--3 of Figure 2.

Figure 4 is a transverse, sectional view through 44 of Figure 2.

Figure "5 is a diagrammatical view showing the electrical connections immediately associated with the ionization chamber.

Figure 6 is a graph or chart to illustrate the lack of influence of change in voltage on the operation of the ionization chamber.

The automatic ionization chamber includes a shell or envelope 1 which is preferably spherical in form and constructed of metal or of any other suitable material having a conductive coating. The shell 1 is provided with a mouth 2 having a flange 3 which co-acts with a clamp ring 4 and suitable screws to secure the margin of a terminal base 5. The terminal base forms the lower end of a mounting unit 6 which projects into the mouth of the shell 1. A seal ring 7 is provided between the flange 3 and the margins of the terminal base 5.

The mounting unit 6 includes a glass seal 8 centrally disposed in the terminal base 5. Leads 9 extend through the seal, the outer extremities of which are connected to terminals 10 suitably supported in an insulating memger 11 forming the lower extremity of the terminal ase 5.

The inner end ofthe mountingunit 6 supports-an outer shield ,12 which is cylindrical in form and projects into ;the .Shfillpr envelope 1. The inner extremity of the shield ,1; 2,is clgsed except for a central aperture .13. Supported .withintheouter shield 12 is an inner orelectrostatic shield 14 which is also cylindrical and closed at its .inner end except for anaperture .15 which. is co-axial with theaperture 13. The inner or electrostatic shield 2,953,589 fiatented Dec. 6, 1960 14 is supported by extensions 9a of several of the leads 9 (in the construction illustrated, three of such extensions 9a are provided) which extend upwardly or inwardly from the glass seal 8. The electrostatic shield is centered relative to the outer shield 12 by means of glass or ceramic spacer tubes 16 held in place by tabs 17 offset outwardly from the electrostatic shield and inserted in the ends of the tubes 16.

The mounting unit 6 includes a supporting plate 18 disposed within the lower end of the outer shield 12 and spaced from the lower end of the electrostatic shield 14. The supporting plate 18 is provided with peripheral apertures which clear the leads 9. Centered in the plate 18 is a socket member 19 which receives the lower end of quartz rod 20. A suitable cement 21 secures the quartz rod within the socket member. By way of example, the socket member may be formed of silver and a silver chloride cement may be employed.

The quartz rod 20 extends co-axially with respect to the outer shield 12 and inner or electrostatic shield 14 and projects through the

apertures

15 and 13. The extended portion of the quartz rod 20 is plated or otherwise coated with metal, as indicated by 22, to form a conductive surface. The protruding coated rod 20 func tions as an ion collector. The metal coated portion extends into the electrostaticshield 14. Fused to the quartz rod 20 is an L-shaped arm 23 also formed of quartz and which includes a portion extending parallel with the quartz rod 20. The upper extremity of the arm 23 tapers virtually to a point to form a fiber 24 of extremely small diameter. The fiber 24 is bent horizontally and positioned so that it may flex to and from contact with the metal coated side of the quartz rodion collector 20 and, when connected with a source of potential, forms an element for recharging the ion collector whenever the potential of the ion collector has fallen to a predetermined value. The fiber 24 and adjacent portion of the arm 23 is coated with metal as indicated by 25 to provide a conductive surface. The metal coating 25 is electrically connected to a wire 26 which in turn is connected to an extension 9b of one of the leads 9 which projects upwardly through a suitable aperture in the supporting plate 18.

In use, only three of the terminals 10 are employed; namely, the terminal connected with the lead having the extension 9b, one of the terminals having the extension 9a, and one of the remaining terminals is connected to the plate 18 or otherwise grounded by a lead 1c.

Reference is directed to Figure 5. The electrostatic shield 14 is placed at a high potential relative to the outer shield 12 and seal 1, the outer shield and seal being grounded. This terminal is connected through a resistor to the terminal connected with the lead extension 912.

' Under the conditions of operation, the voltage drop across the resistance 27 is negligible so that the electrostatic shield is virtually the same potential as the fiber 24. The fiber is connected through its terminal and a condenser 28 to a suitable amplifier such as shown in the aforementioned Patent 2,617,044 or other conventional type of amplifier.

Operation of the automatic ionization chamber is as follows:

The ionization chamber formed by the shell 1 is filled with argon of high purity to a pressure of several atmospheres. A pressure of eight atmospheres has been found satisfactory. The argon gas is ionized by the artificial or by cosmic radiation to which-the instrument is exposed. The projecting plated portion 22 of the quartz rod 21) forms an ion collector for the ion charges fQlmed inthe argon gas.

Assuming an initially charged state of the collector element, the fiber 2,4 occupies a repelled position shown 3 by solid lines in Figure 4. ion charges resulting from ionization of the argon gas within the ionization chamberformed by the shell 1 are attracted to and cumulatively reduce the potential of the ion collector 20. The apparatus is pre-designed to receive from 10,000 to 50,000 ion charges before discharging the ion collector sufiiciently to cause contact by the fiber or charging element 24.

When the potential of the ion collector 22 drops to a value to which the electrostatic element or fiber 24 touches it, current flows from the fiber 24 on to the ion collector rod 20, thereby lowering the potential of the fiber and with it the potential at the input of the amplifier which is connected to the fiber through the condenser 28. This potential drop due to the mechanical contact of the fiber and collector occurs in a very short time; that is, a few micro-seconds. After the initial, very rapid potential drop the potential of the fiber is restored by current flow through the resistance 27 and approaches closely to theapplied potential after fifty to one hundred microseconds. Due to mechanical inertia, the fiber remains in contact with the collector longer than this period. Therefore, when it returns to its repelled position the collector rod 20 has been recharged to substantially the same voltage applied to the electrostatic shield 14. The cycle then repeats. A charge of 1O- coulombs has been found adequate to recharge the collector rod.

The pulse which occurs on contact of the fiber with the collector element is employed in a conventional manner to operate a trigger circuit which in turn controls a suitable recording, transmitting, or telemetering apparatus, not shown.

The time interval between such pulses vary inversely as the rate of ionization in the ionization chamber, and may range from a count or pulse each half hour to several counts per second. By the use of known sources of radioactivity, the ionization chamber may be calibrated so that the number of ion charges represented by each output pulse is known.

The electrostatic shield 14 plays a very important function in that it eliminates, for all practical purposes the effect of change in the applied voltage or potential, so that the accuracy of the instrument is not dependent upon the maintenance of a constant voltage supply as long as the supply is above a predetermined threshold value.

The reason for this may be explained as follows:

The fiber 24 is moved away or toward the collector rod by the electrostatic forces carried by the charges induced in the fiber by all the conductors near the fiber. In the construction illustrated the only effective neighboring conductors are the shield 14 and the collector 20. The shield 14 almost completely surrounds the fiber and effectively shields it electrostatically from any outside potentials. Except during the first instant of the recharging operation the shield is at the same potential as the fiber irrespective of the applied voltage and therefore cannot exert an electromotive force on the fiber. However, the collector rod 20 does exert an attractive force on the fiber which increases as its potential is lowered below that of the fiber and the shield.

When a critical potential difference between the collector rod 20 and the fiber obtains, the force is large enough to attract the fiber into contact. The critical potential difference is determined by the mechanical characteristics of the fiber and thus remains constant. As the force which attracts the fiber to the collector is due to the potential difference therebetween rather than the obsolute potential of the fiber and shield, change in the value of the charging voltage, above a threshold value has no appreciable effect. This is illustrated in the graph, Figure 6.

After the potential has exceeded a certain threshold value, which .is indicated in the graph at less than fifty volts, further change in voltage has only the slightest effect on the change in time between the discharges. In

4 fact the change in interval may be in the order of 0.005 percent per volt change in potential.

This is highly important in view of the fact that devices of this character may be employed for long periods of time or used under conditions where the voltage may not be held at constant level.

Having thus described certain embodiments and applications of our invention, we do not desire to be limited, but intend to claim all novelty inherent in the appended claims.

We claim:

1. An automatic ionization chamber, comprising: a sealed envelope, a first shield extending into said envelope and maintained at the same potential as said envelope; a second shield disposed within said first shield and insulated therefrom; an ion collector extending from within said second shield into said envelope, there being accommodation apertures in said shields to clear said collector; a charging element within said second shield and tending to move away from said ion collector when their potentials are the same and to move into contact with said ion collector when a predetermined potential diiference therebetween occurs; and a source of electrical potential connected with said charging element and with said second shield for maintaining the charging element and second shield at substantially the same potential.

2. An automatic ionization chamber, comprising: a sealed envelope, a first shield extending into said envelope and maintained at the same potential as said envelope; a second shield disposed within said first shield and insulated therefrom; an ion collector extending from within said second shield into said envelope, there being accommodation apertures in said shields to clear said collector; a charging element within said second shield and tending to move away from said ion collector when their potentials are the same and to move into contact with said ion collector when a predetermined potential difference therebetween occurs; a sourec of electrical potential connected with said charging element and with said second shield for maintaining the charging element and second shield at substantially the same potential; and means for transmitting a signal each time contact is made between said ion collector and said charging element.

3. An automatic ionization chamber, comprising: a sealed envelope; a first shield extending into said envelope and maintained at the same potential as said envelope; a second shield disposed within said first shield and insulated therefrom; an ion collector extending from within said second shield into said envelope, there being accommodation apertures in said shields to clear said collector; a charging element within said second shield and tending to move away from said ion collector when their potentials are the same and to move into contact with said ion collector when a predetermined potential difference therebetween occurs; means for maintaining a potential on said charging element and second shield above a predetermined threshold value whereby change in said potential above said value does not appreciably affect the period between contact of said charging element and ion collector; and means for transmitting a pulse each time contact is made between said ion collector and said charging element.

4. An automatic ionization chamber, comprising: an envelope having a conductive surface; an ion collector therein; means for periodically recharging said ion collector; an inner and an outer shield within said envelope and surrounding said recharging means and a portion of said ion collector, the outer shield being grounded to said envelope, the inner shield being insulated therefrom; and means for maintaining said recharging means and said, inner shield at substantially the same potential.

, .5. An automatic ionization chamber, comprising: an

References Cited in the file of this patent UNITED STATES PATENTS Victoreen Nov. 6, 1951 Neher Nov. 4, 1952 Keyes July 17, 1956 Borzin May 20, 1958