Electron Multiplier With Preamplifier

Abstract

A spiraled electron multiplier assembly fabricated of six twisted channels fused into a solid bundle or array, the input section of the electron multiplier being provided with a flared input section formed of a straight channel portion and a flared input portion integrally formed therewith. The input section is assembled with a spiraled multiplier section by means of a collar-like or tab-like electrode for establishing a voltage potential at the output section of the flared section and the input to the multiplier section, the flared input section being slightly spaced from the spiraled electron multiplier.

Description

BACKGROUND AND SUMMARY OF THE DEVELOPMENT

This invention relates generally to an electron multiplier assembly and more particularly to an electron multiplier assembly which includes a spiraled multichannel electron multiplier section which is provided with an input preamplifier formed with flared input and either straight or curved channel preamplifier portions.

Spiraled electron multipliers have been the subject of previous applications, namely, the application of William Balas and Bagdasar Deradoorian, Ser. No. 772,527, filed Nov. 1, 1968. The spiraled electron multiplier of this application has the characteristics of providing high gain at low voltages, substantially zero feedback at relatively high gain, and low noise.

While prior art spiraled electron multipliers provide extremely high reliability and relatively efficient operation, it has been found that certain differences may exist in the input apertures of the independent channels of the electron multiplier, dead area is created by the presence of the wall of each individual channel, even though the channels are fused into a solid array, and the input area for a specific configuration is relatively fixed.

Further, it has been found that a need has arisen for higher gain channel multipliers, channel multipliers with improved full width half maximum characteristics, and a capability of varying the input area and input configuration independently of the configuration of the electron multiplier.

The assembly of the present invention incorporates a spiraled electron multiplier, which may be of the type disclosed in the above referenced application, and further provides an input preamplifier in the form of a single channel device which may be flared, the preamplifier being adapted to be positioned at the input end of the spiraled electron multiplier section. With the addition of the preamplifier section, the output gain of the entire assembly has been appreciably increased with an improved full width half maximum characteristic, resulting in a more uniform electron gain per occurrence. Further, the addition of the pre-amplifier has been utilized to limit the effects of difference in input apertures in the individual channels of the spiraled electron multiplier. This reduction in the effect of a variation in input areas occurs because of the fact that each occurrence which enters the funneled aperture of the pre-amplifier is sufficiently amplified before entering the spiraled electron multiplier section so that there is a high statistical probability any multiplied occurrence will enter all of the individual channels. Thus, a single channel amplification of occurrences at the input to the multiplier section does not occur because all of the channels are triggered by a single input event. Thus, the output pulse of the electron multiplier is a summation of all the individual channels of the spiraled electron multiplier.

Further, the use of a pre-amplifier section, either flared or unflared, substantially eliminates the effect of any dead area created by the interstitial spaces in certain cases or the presence of solid glass at the input section of the spiraled electron multiplier in all cases. In this situation, the only dead area which may be encountered would be an occurrence that exactly avoids the flared section and the additional single channel section of the pre-amplifier and happens to strike an interstitial space or glass at the input face of the spiraled electron multiplier.

Further, the pre-amplifier of the present invention provides the user with the capability of varying the area of the input for collecting the occurrences, within limits, and also enables the user to vary the configuration of the flared input surface, which for example, can have inter alia, a circular, rectangular, or elliptical cross section. Also, it has been found that damage may occur to the input portion of the spiraled electron multiplier which necessitated the replacement of the spiraled multiplier. With the system of the present invention, the damage to the multiplier section is effectively reduced by the pre-amplifier and the pre-amplifier may be separately replaced if damage should occur.

Accordingly, it is one object of the present invention to provide an improved electron multiplier.

It is another object of the present invention to provide an improved electron multiplier having higher gain capabilities through the use of a pre-amplifier.

It is still a further object of the present invention to provide an improved electron multiplier having improved full-width half-maximum characteristics.

It is still a further object of the present invention to provide an improved electron multiplier of the type having an array of individual channels which substantially alleviates the effects of differences in the input apertures of the multiplier array.

It is still a further object of the present invention to provide an improved electron multiplier which substantially eliminates the effective dead area of the electron multiplier.

It is still a further object of the present invention to provide an improved electron multiplier assembly having the capability of varying the area of the input and effective input configuration of the pre-amplifier.

It is still a further object of the present invention to provide an improved electron multiplier having an input section which is separately replaceable from the main amplifying section.

Further objects, features, and advantages of the present invention will become apparent from a consideration of the specification, claims and drawings, in which:

FIG. 1 is a perspective view of an electron multiplier assembly incorporating the features of the present invention;

FIG. 2 is a side view of the electron multiplier assembly of FIG. 1 taken along line 2--2 thereof;

FIG. 3 is an end view of the electron multiplier assembly of FIG. 2 taken in the direction of arrow 3 and particularly illustrating a preferred configuration and relative area of the input section thereof;

FIG. 4 is an end view of the electron multiplier assembly of FIG. 2 taken along line 4--4 thereof and particularly illustrating the output aperture;

FIG. 5 is an end view of a modified form of input aperture; and

FIG. 6 is an end view of a second modified input aperture.

Referring now to FIGS. 1-4, there is illustrated an electron multiplier assembly 10, which, in the illustrated embodiment, includes a six or seven channel spiraled electron multiplier section 12, which may be formed in accordance with the methods disclosed in the aforementioned U.S. Pat. application, and an input pre-amplifier section 14. The spiraled electron multiplier section l2 includes a plurality of six or seven individual channels which have been formed with a central cane, in the case of a six channel configuration, or the central portion thereof has been formed with a seventh channel in lieu of the cane. In this latter case, certain feedback effects may be experienced due to ion feedback from the output of the electron multiplier assembly toward the input section thereof. The six channel configuration is spiraled to eliminate any straight through path thereby substantially eliminating any feedback effects from the output. For details of the fabrication of the spiraled section 12, specific reference is made to the aforementioned patent application, the disclosure of which is incorporated herein by reference. It should be understood that the individual channels of the assembly need not be of circular cross section and can inter alia be triangular or hexagonal.

The pre-amplifier portion 14 is shown as a substantially straight single channel 16 having an inside diameter which is approximately equal to the diameter of a circle which circumscribes all six of the spiraled channels forming the multiplier portion of section 12. The channel 16 can be curved if desired. In addition, the channel 16, whether straight or curved, can be provided with a slotted longitudinal aperture through which input signals can be received for multiplication. A flared cone section 18 can be formed integrally with the channel portion 16 and may be shaped by heating the glass from which the pre-amplifier section is fabricated and forcing the input aperture thereof over a mandrel, the mandrel being the complimentary shape of the final desired shape of the flared input section.

The spiraled and pre-amplifier sections 12, 14 are fabricated of lead or bismuth glass and are hydrogen reduced in a heated environment to form an electron emitting coating on the interior surfaces thereof. For specific details of the formation of the electron emitting surfaces, reference is made to application Ser. No. 660,142, filed Aug. 11, 1967 now U.S. Patent No. 3,492,523. Other methods of forming the emissive coating on the interior surfaces of the sections 12 and 14 may also be utilized, these other methods being presently known to those skilled in the art.

Further, it has been found that the optimum length for the section 16 is 20 diameters. It should have a 20 to 1 length to diameter ratio if the channel cross section is circular. If a non-circular cross sectional configuration is used, a length to effective diameter ratio of 20 to 1 can be used. The term effective diameter here refers to the diameter of a circle encompassing an area equal to the cross sectional area of the channel.

The assembly 10 is further provided with a plurality of electrode connectors 22, 24, 26, the first 22 of which is positioned adjacent the input portion of the section 16, the second 24 of which bridges the output portion of the section 16 and the input portion of the spiraled electron multiplier 12, and the third 26 being attached adjacent the output portion of the spiraled electron multiplier 12. The electrode 22, in the preferred embodiment, is supplied with a fixed potential of preselected magnitude, in this case zero, and the electrode 24 is supplied with an electrical potential which is approximately 800 volts above the potential at electrode 22, and the third electrode 26 is supplied with a voltage which is 3,000 volts above the input electrode 22. In this way, the necessary accelerating field is established within the interior of the sections 16 and 12. The foregoing voltage values are illustrative of values which can be used with the invention, but it should be understood that many other sets of values can be utilized and satisfactory performance obtained therewith. Electrical connections are made between the electrodes 22, 24, 26 and the various portions of the 16 l6 and 12 by means of methods which are common in the art, as for example a conductive adhesive and the coating formed on the glass by hydrogen reduction of the glass.

It is to be noted that the output face of the section 16 is spaced from the input face of the spiraled electron multiplier section 12 to preclude damage to either of the aforementioned faces in the event that bending of the pre-amplifier 14 occurs relative to the spiraled electron multiplier section 12.

There will be noted that the input flared section 18 shown in FIG. 3 has a round, conical configuration. However, other configurations and areas may be utilized, such as the flared rectangular cross section input surface 28 illustrated in FIG. 5. The input surface 30 of FIG. 6 has an elliptical cross section. The term "input surface" refers to the inner surface of the funnel like configuration shown in FIGS 1-3, 5, and 6, but does not refer to any part of the channel 16. The spacing between the two sections is, in the preferred embodiment, nominally 1 millimeter and it is further contemplated that the assembly may be utilized in a two terminal configuration whereby there is no connection of an electrical potential to the terminal 24. Further, the terminals 22, 24, and 26 are generally of metal foil bonded to the respective pre-amplifier or spiraled sections, and the associated resistive coating, to provide the necessary connections to the internal resistive coating within in the channels 16 and 12. Further, it is to be understood that the input surfaces of FIGS. 1-3, 5, and 6 are coated or formed with a resistive coating as described above, which coating provides the electron emissive surface. The surface of the outside of the funneled portion of the pre-amplifier from the base of the funnel to the point of contact with terminal 22 is coated with a conductive material to permit current flow from the terminal 22 to the resistive coating on the inside of the funnel. Thus, the base of the input surface is maintained at the same potential as terminal 22. From the foregoing, it is seen that the present invention has provided an electron multiplier with the improved gain, full-width half-maximum characteristics while eliminating the effects of variations in channel aperture configuration and dead area and also enables the user to variably select the input areas and configuration. Further, greater flexibility is provided in packaging and also provides a wide choice of input apertures which could be easily furnished at the user's convenience.

While it will be apparent that the preferred embodiments of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

Claims

What is claimed is:

1. An electron multiplier assembly including a multi-channel electron multiplier section, said assembly comprising: a single channel electron multiplier preamplifier means positioned, relative to the path of an occurrence, ahead of the electron multiplier section; said preamplifier having an integrally formed flared input portion, said preamplifier being removable from said multi-channel multiplier section so that the area and configuration of the input surface to said multi-channel multiplier is variable, said preamplifier section being positioned to have an output end in the close proximity of the input end of said multi-channel multiplier section;

and means for establishing an accelerating field within said preamplifier and multi-channel electron multiplier.

2. The improvement of claim 1 further including a metal terminal having a generally round portion and an elongated tab portion, said round portion being attached to said input and output portions to support said pre-amplifier relative to said multi-channel electron multiplier section.

3. The electron multiplier of claim 1 wherein said preamplifier means has an inside diameter approximately equal to the diameter of a circle circumscribing all channels of said multi-channel multiplier section.

4. The electron multiplier of claim 1 wherein said preamplifier means has a length which exceeds its diameter by at least an order of magnitude.

5. The electron multiplier of claim 1 wherein said preamplifier has a length in the order of twenty times its diameter.