US3579017A

US3579017A - Harp electron multiplier

Info

Publication number: US3579017A
Application number: US737490A
Authority: US
Inventors: Marvin L Vestal
Original assignee: Scientific Research Instruments Corp
Current assignee: ALLEGHENY INTERNATIONAL MEDICAL TECHNOLOGY Inc; Scientific Research Instruments Corp
Priority date: 1968-06-17
Filing date: 1968-06-17
Publication date: 1971-05-18
Anticipated expiration: 1988-05-18

Abstract

An electron multiplier having a plurality of dynodes wherein each dynode includes two wire layers located in staggered relationship with one another and wherein each of the dynodes is located with a first one of its wire layers aligned with the immediately adjacent wire layer of an immediately preceding dynode and with its second wire layer aligned with the immediately adjacent wire layer of an immediately following dynode. The wires in each layer of each of the dynodes are spaced so that the open space between them is less than the diameter of the wires, with the exception of the first wire layer in the first dynode wherein the wires may be of a noncircular cross section or of a smaller diameter and wherein they are spaced apart by a distance greater than the diameters thereof.

Description

United States Patent [72] In Marvin vesial 2,821,637 1/1958 Roberts et a1 313/105 Baltimore, Md. 3,182,221 5/1965 Poor 313/103 [21] P 737490 Primary ExaminerRoy Lake [22] Filed June 17, 1968 As szstant Exammer-Darwm R. Hostetter [45] Patented May 18, 1971 At C h D b & C h [73] Assignee Scientific Research Instruments t0mey at y us man Corporation Baltimore, Md. ABSTRACT: An electron multiplier having a plurality of dynodes wherein each dynode includes two wire layers located in staggered relationship with one another and [54] i E wherein each of the dynodes is located with a first one of its wire layers aligned with the immediately adjacent wire layer of [52] US. Cl 313/105, an immediately preceding dynode and with its second wi e 323/243 layer aligned with the immediately adjacent wire layer of an [5 l] lnt. Cl H01] 43/00 immediately following dynode, The wires in each layer of each [50] Field ofSearch 328/243; of the dynodes are paced so that the open space between 250/207 them is less than the diameter of the wires, with the exception of the first wire layer in the first dynode wherein the wires may [56] References cued be of a noncircular cross section or of a smaller diameter and UNITED STATES PATENTS wherein they are spaced apart by a distance greater than the 2,342,986 2/1944 Van Den Bosch 328/243 diameters the pZ/MflE Y EVA 043E #4 Vanna ZZ-l- Q NOFE Patented May 18, 1971 2 Sheets-Sheet 2 Rev/m4? Y 52 5c rev/v 354M INVENTOR Mew/V L %J2'AL BY wfw HARP ELECTRON MULTIPLIER BACKGROUND OF THE INVENTION The present invention relates generally to improvements in electron multipliers and the like, and more particularly to a new and improved electron multiplier wherein the electrode configuration and electrical potential distribution are such that the electrons emitted from an active surface of one stage are effectively removed from that surface and transmitted to the active surface of the next stage.

In the field of electron amplifiers or multipliers it has been the general practice to employ devices having a plurality of dynodes to perform the multiplying function. Although such devices have served the purpose, they have not proved entirely satisfactory under all conditions of service because the electrode configurations and electrical potential distributions have not been such that electrons emitted from an active surface are most effectively removed from that surface and transmitted to the active surface of the next stage of the multiplier.

SUMMARY OF THE INVENTION Accordingly, the general purpose of this invention is to provide an electron multiplier which embraces all of the advantages of similarly employed multipliers and possesses none of the aforedescribed disadvantages. To attain this, the present invention contemplates a unique dynode arrangement in the electron multiplier wherein each dynode is comprised of two staggered layers of wires wherein the centers of the wires of one layer are located centrally over the open space between wires of the other layer in the dynode. When a plurality of dynode stages are utilized by the invention, each dynode stage is located so that the first layer of wires in that stage is aligned with the second layer of wires in the preceding stages. This is accomplished with a series of identical dynodes with alternate ones inverted.

An object of the present invention is the provision of an electron multiplier having an electrode configuration and electrical potential distribution such that electrons emitted from an active surface of one stage are effectively removed from that surface and transmitted to the active surface of the next stage.

Other objects and features of the invention will become apparent to those of ordinary skill in the art as the disclosure is made in the following description of a preferred embodiment of the invention as illustrated in the accompanying sheets of drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a plan view of one dynode in a preferred embodiment of the invention;

FIG. 2 illustrates an end view of a portion of the dynode represented in FIG. 1;

FIG. 3 shows a diagrammatic view of a preferred embodiment of the invention; and

FIG. 4 shows the approximate potential distribution occurring between the first and second dynodes of the invention with 100 volts impressed across the dynodes.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. I a plan view of one dynode stage of the multiplier. Each stage is comprised of a pair of

mounting elements

12 and 14, which are preferably of a conducting material that is the same as the material in the wires 16 in order to prevent differential thermal expansion problems between the mounting elements and the wires. The mounting elements are also preferably composed of an electrically conducting material in order to maintain all of the wires of a particular stage at the same electrical potential. The end or mounting elements, however, may be nonconductive if means (not shown) are provided to maintain the wires within a particular stage at the same potential.

FIG. 2 more clearly shows the staggered relationship of the wires 16 with respect to the wires I8 in the dynode of FIG. 1. The wires of each of tee layers are spaced so that the distance between the wires is less than the diameters thereof. One example of dimensions for an electron multiplier dynode constructed in this manner is as follows: wire diameter 0.025 inch, gap between wires 0.020 inch, and thickness of mounting elements 0.020 inch.

FIG. 3 illustrates an arrangement of these dynodes into a four-stage electron multiplier. Each stage is located so that the upper layer of wires therein is aligned with the lower layer of wires in the stage above. This is accomplished by the use of four identical dynodes as set forth in FIG. 1 wherein every other dynode is inverted. Each stage is spaced from the stage above and below, e.g., a distance of 0.0l50.020 inches, by suitable insulating spacers (not shownlwhich are adapted to fit through the apertures 20 in the

mounting elements

12 and 14. In addition, a high voltage source 22 is coupled across the dynode stages by means of

resistances

24, 26 and 28 so that a potential difference is applied between each pair of dynodes. Another resistor 30 is coupled between resistor 28 and the positive side of voltage source 22 and a junction 32 is connected to load resistor 34, which in turn, is connected to the anode 36.

The first wire layer 16 in the'first stage or dynode of the multiplier maybe composed of relatively small diameter wires with respect to the diameters of the wires in the second layer of the first stage and with respect to the wires in the remaining dynodes. However, instead of using smaller diameter wires, the wires in the first wire layer 16 of the first dynode may be of a triangular cross section and be oriented with an apex of the triangular cross section pointing toward the direction from which the electron beam is originating from. The use of the smaller size wires will have the effect of isolating the remaining stages of the multiplier from exterior fields while the use of wires of triangular cross section will tend to focus electrons from the impinging electron beam more efficiently on the active surfaces of the wires 18 in the second wire layer of the first dynode.

An approximate potential distribution occurring between two dynode stages for a volt applied potential therebetween is shown in FIG. 4 wherein the electric field at or near the active surface of the wires causes electrons to be swept from one stage to the next so that the stage from which an electron is generated repels that electron and causes it to be attracted by the next stage. Although the use of 100 volts between stages is described, it should be understood that many other voltages could be so applied.

The operation of the multiplier base on the electrode configuration and the electrical potential distribution can best be described by reference to FIG. 4. In a typical electron mul tiplier, the energy of the primary electrons striking the active surface of the dynode, and the condition of that surface must be such that substantially more than one electron is emitted from the surface for each electron striking thereupon. The electron energy of the primary electron beam may typically be in the range of 100 to 300 electron volts. The active surface of the dynode may be prepared by heat treating certain alloys, such as beryllium-copper or silver-magnesium in a properly controlled atmosphere. A detailed representation of the electrode configuration and electrical potential distribution between two dynode stages of this invention is shown in FIG. 4 wherein the electrical field at or near the active surface of the wires within each stage is such as to cause electrons to be swept on to the next dynode stage. For example, a primary electron, represented at 38 in FIG. 4, may pass between two wires 16 of the first layer of wires of dynode one and strike one of the active surfaces of wires 18 in the second layer of wires in dynode one. Because of the preparation of the active surfaces of the wires, substantially more than one electron will be emitted therefrom as represented by paths 40 and 42. Also, because of the electrode configuration in the adjacent dynodes and because of the electrical potential distribution associated therewith, the negatively charged electrons 40 and 42 are then swept away from the wire 18, as shown, and on to the second dynode and a wire 16 therein. At this point, the process repeats with each of the electrons 40 and 42 causing the emission of more than one electron, respectively, from dynode stage two.

This invention provides an electron multiplier comprising a unique electrode configuration and electrical potential distribution with respect to its dynodes wherein the electric field at or near the active surfaces of the wires of the dynodes acts to repel electrons secondarily emitted so that they are swept on to the next dynode stage.

Obviously many modifications and variations of the present invention are possible in view of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

I. An electron multiplier comprising:

a plurality of serially related dynodes including a first and a last dynode and wherein each of said dynodes includes at least first and second spaced-apart layers of wires,

said wires in each of said layers except the first layer of said first dynode being spaced apart less than a wire diameter,

said wires in said first layer being staggered with respect to wires in said second layer,

said plurality of dynodes being mutually oriented wherein wires in the first layer of each dynode except said first dynode are aligned with the second layer of wires in an immediately preceding dynode and wires in the second layer of each dynode except said last dynode are aligned with the first layer of wires in an immediately succeeding dynode,

all of the wires in each dynode comprising both said first and second layers being electrically connected together,

insulating means for electrically isolating each of said dynodes from every other dynode, and

an anode for collecting electrons from said plurality of dynodes.

2. An electron multiplier as in claim 1 wherein each of said dynodes comprises two spaced-apart end elements with a continuous wire wound around said elements to form said first and second layers of wires.

3. An electron multiplier as in claim 2 wherein said end elements are formed of the same electrically conducting material as said wire and electrically connected to all the wires in said first and second layers.

4. An electron multiplier as in claim 3 wherein alternate dynodes are assembled in inverted relationship to achieve said alignment between the first layer of one dynode and the second layer of an immediately preceding dynode and between the second layer of each dynode and the first layer of an immediately succeeding dynode.

5. An electron multiplier as in claim 3 including impedance means electrically connected between said dynodes for providing an electrical potential difference between successive ones of said dynodes when connected to a voltage source.

6. The multiplier of claim 1 wherein the first wire layer in the first of said dynode means is comprised of wires having a diameter less than the diameter of the wires in the second layer thereof.-

7. The multiplier of claim 6 wherein the first wire layer in said first dynode means is comprised of wires spaced apart a distance greater than the diameters thereof.

8. The multiplier of claim 7 wherein the second wire layer in said first dynode means is comprised of wires spaced apart a distance less than the diameters thereof.

9. The multiplier of claim 8 wherein the wires within each of the layers in the remaining ones of said dynode means are spaced apart a distance less than the diameters of the wires.

10. The multiplier of claim 1 wherein the first wire layer in the first dynode means is comprised of wires having a triangular cross section. y

11. The multiplier of claim 10 wherein the wires in said first wire layer in said first dynode means are spaced apart a distance greater than the length of any side of said triangular cross section.

12. The multiplier of claim 10 wherein the wires having a triangular cross section are oriented with an apex of the triangular cross section pointing toward the direction from which the primary electron beam originates.

Claims

1. An electron multiplier comprising: a plurality of serially related dynodes including a first and a last dynode and wherein each of said dynodes includes at least first and second spaced-apart layers of wires, said wires in each of said layers except the first layer of said first dynode being spaced apart less than a wire diameter, said wires in said first layer being staggered with respect to wires in said second layer, said plurality of dynodes being mutually oriented wherein wires in the first layer of each dynode except said first dynode are aligned with the second layer of wires in an immediately preceding dynode and wires in the second layer of each dynode except said last dynode are aligned with the first layer of wires in an immediately succeeding dynode, all of the wires in each dynode comprising both said first and second layers being electrically connected together, insulating means for electrically isolating each of said dynodes from every other dynode, and an anode for collecting electrons from said plurality of dynodes.

6. The multiplier of claim 1 wherein the first wire layer in the first of said dynode means is comprised of wires having a diameter less than the diameter of the wires in the second layer thereof.

10. The multiplier of claim 1 wherein the first wire layer in the first dynode means is comprised of wires having a triangular cross section.