JPS5947426B2 - Secondary electron multiplier dynode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dynode of a secondary electron multiplier tube, and more particularly, to a dynode of a secondary electron multiplier tube in which the arrangement of thin plates constituting the dynode is improved.

Hereinafter, in this specification, a thin plate constituting a dynode refers to a single thin plate on which at least one surface has the ability to emit secondary electrons, and a plurality of these thin plates form the basic unit of the dynode. used for

In addition, the secondary electron multiplier of the secondary electron multiplier is formed by one or more dynodes arranged perpendicularly to the main axis of the tube of the secondary electron multiplier. .

A secondary electron multiplier tube is generally placed in a vacuum tubular container.
It contains an electron source, followed by a secondary electron multiplier consisting of a series of dynodes, and finally an electron collecting electrode (collector).

These electrodes are arranged along the main axis of the tube in substantially the order described above.

During operation of the secondary electron multiplier, appropriate voltages are applied to these electrodes in order to generate an electric field that accelerates electrons along the principal axis.

At this time, the electrons emitted from the electron source collide with each dynode in order along the tube axis, are multiplied each time, and collected by the collector.

One type of dynode is known as the inesian type.

An inesian-shaped dynode consists of a plurality of rectangular laminae, the long sides of which are perpendicular to the main axis of the tube, and the short sides inclined to the same axis.

Two consecutive dynodes are arranged so as to be inclined in opposite directions with respect to the tube axis.

Usually, a mesh electrode is provided on the side of each dynode on which electrons are incident, to which the same potential as that of the dynode is applied.

Hereinafter, a conventional secondary electron multiplier formed by an inesian type dynode will be described by way of example.

FIG. 1 is an enlarged view of a part of the cross section of a conventional inesian type dynode.

In the figure, reference numerals 11 and 12 are thin plates forming a dynode located at a relatively earlier stage.A cross section of the short side of the thin plate is shown in the paper.

Each thin plate is inclined at 45 degrees to the main axis of the secondary electron multiplier.

Further, in the figure, 2L 22 is a thin plate forming a dynode located at a relatively later stage.

The thin plates 2L and 22 of this dynode are inclined at 45 degrees in the opposite direction to the thin plates 11 and 12 of the front and rear dynodes.

Note that each thin plate has the same shape, and the length of the short side of the thin plate is 3.
It is 5m+++.

In a conventional inesian type dynode, the pitch d in the direction perpendicular to the main axis of the secondary electron multiplier of the thin plate forming the dynode, and the thickness t of the dynode in the direction of the main axis of the secondary electron multiplier (the above example) Then t=3.5X0.7=2.
45) was approximately 1.

1 between the front stage dynode 1 and the rear stage dynode 2
A voltage of 0.00 volts is applied, and this voltage gives the electrons sufficient collision energy to emit secondary electrons.

If electrons are incident on the above-mentioned dynode parallel to the main axis of the secondary electron multiplier tube, d/l=1 and there is no gap, so all the electrons will definitely collide with one of the thin plates.

The shape of such a dynode is referred to as optically opaque or simply opaque.

However, in the conventional inesian type dynode, the rate at which secondary electrons emitted from the dynode reach the next stage and collide with each other is extremely low for the following reason.

In other words, the electrons emitted from the part near the dynode in the previous stage are moved by the electric field caused by the dynode in the previous stage, as indicated by the arrows ai
, a2, it is returned to the dynode again.

A part of the electrons emitted near the center of the dynode thin plate has an extremely weak electric field, so that the electrons emitted near the center of the dynode thin plate have an extremely weak electric field. As shown in b2, it collides with an adjacent thin plate of the same dynode.

These electrons have substantially low energy and do not emit secondary electrons.

An object of the present invention is to provide a dynode for a secondary electron multiplier tube that can efficiently cause secondary electrons generated on the surface of a thin plate to reach the next stage dynode.

To achieve the above object, the dynode of the secondary electron multiplier according to the present invention is arranged perpendicularly to the main axis of the secondary electron multiplier, and the dynode of the secondary electron multiplier of the secondary electron multiplier is In the dynode to be formed, the pitch in the direction perpendicular to the main axis between the plurality of thin plates arranged at an angle with respect to the main axis to form the dynode is d, and the thickness of the dynode in the main axis direction is t. 1.5 between them
The structure is such that the relationship ≦d/l≦1.75 holds true.

According to the above structure, it is possible to improve the transfer efficiency of the secondary electrons generated in the dynode to the next stage dynode, and the object of the present invention can be completely achieved.

The dynode of the secondary electron multiplier according to the present invention will be explained in more detail below with reference to the drawings and the like.

FIG. 2 is a partially enlarged cross-sectional view of an inesian-type dynode according to the present invention.

The thin plates 31 and 32, at least on which the electrons are incident, have the ability to emit secondary electrons, are thin plates constituting a part of the n-th stage dynode 3.

Similarly, thin plates 41 and 42 constitute the n+1st stage dynode 4.

In the inesian type dynode according to the present invention, the ratio of the pitch d of the thin plates constituting the dynode in a plane parallel to the main axis of the tube to the distance t of the thin plates in the tube axis direction is selected in the range of 1.5 to 1.75. .

When viewed from the incident electrons, such a dynode has a geometrically optically transparent part.

In other words, it appears that the light passes through without contacting the thin plate forming the dynode and directly collides with the dynode at a later stage.

However, this is not a problem for the following reasons.

Electrons emitted from the front and back enter the dynode of the relevant stage with a certain degree of convergence so that they are difficult to escape.

The electrons from the previous stage are incident on the stage with a distribution having the same pitch as the thin plate of the previous stage dynode, and two consecutive
Since the inclinations of the thin plates of the two dynodes are in the opposite direction to the tube axis, the following measures can be taken.

That is, by shifting the dynode by an appropriate distance from directly below the thin plate of the dynode in the preceding stage in the direction of the arrangement of the thin plates, most of the electrons incident on that stage can be made to collide with the thin plate of the dynode.

In addition, the dynode according to the present invention has a small portion that emits electrons such that the emitted electrons are returned to the dynode by the electric field of the front and rear dynodes, and a portion that emits electrons that collides with an adjacent thin plate or does not exist. .

The reason for this will be explained qualitatively with reference to the drawings.

FIG. 3A is an explanatory diagram showing electrodes and an electric field in a partially enlarged cross-section of a conventional inesian type dynode.

The mesh electrode 10 is at the same potential as the dynode 1 or the thin plates 11.12 of the dynode 1.

The mesh electrode 20 is connected to the thin plate 1 at the same potential as the next dynode (not shown), i.e. 100 volts higher than the dynode 1.
Since the gap between 1 and 12 is narrow, the electric field generated by the mesh electrode 20 cannot enter the gap.

On the other hand, the electric field generated by the front dynode (not shown) creates an electric field that pushes the emitted electrons back through the gap between the mesh electrodes 10 to the surface area 13 of the thin plate 12 of the dynode near the front dynode.

Although this electric field is extremely weak, the initial velocity energy of the emitted electrons is also extremely small, so the vicinity of the center of the three-dynode thin plate 12, where there is a possibility of being pushed back, is not affected by the electric field from the front-stage dynode and the rear-stage dynode.

Furthermore, since the main component of the initial velocity of the emitted electron is perpendicular to the surface of the dynode 12, there is a high possibility that the electron emitted from here will collide with the adjacent dynode 11. FIG. 2 is an enlarged view of a part of the cross section of a dynode showing an electrode and an electric field.

The mesh electrode 30 is at the same potential as the thin plates 3'l, 32 of the dynode 3.

Since the mesh electrode 40 has a voltage higher than the dynode 3 by 100 volts and the gap between the thin plates 31 and 3.2 is wide, the electric field generated by the mesh electrode 40 enters the gap between the thin plates 31 and 32.

Therefore, the secondary electrons emitted from near the center of the thin plate 32 enter the next stage dynode (not shown) through a trajectory as indicated by the arrow d.

Furthermore, the electric field generated by the mesh electrode 40 affects the surface of the thin plate 32 near the front dynode (not shown), and the electric field from the front dynode (not shown) passes through the mesh electrode 2° to the front of the thin plate of the dynode. It is not possible to create an electric field on the surface near the dynode that would push the secondary electrons back.

Next, a quantitative explanation will be given with reference to experimental results.

The inventors of the present invention have gradually increased only the pitch d of the thin plates in the direction parallel to the main axis of the conventional dynode as previously explained in FIG. compared.

The horizontal axis is (d/l), and the vertical axis η is as follows.

The arrival at the next stage when (d/l) -1 (point p in FIG. 4) is defined as η1, and the reaching degree ηX when arbitrary d=dx is defined as η-ηX/η1.

From Fig. 4, when d/l is from 1.0 (d/l = 1 is a conventional dynode) to 1.5, the above ratio η increases monotonically, and d
It can be seen that η>2 when /l is between 1.5 and 1.7.

Among them, it was the highest at 1.64. When d/l becomes larger than 1.7, η decreases).

This is because the effect of the electric field mentioned above is d/l from 1.5 to 1.
It saturates between 75 and d/l is 1.5 to 1.7.
This is thought to be due to the fact that when the value exceeds 5, the transparent part becomes thicker than the thin plate part of the dynode when viewed from the incident electrons, and the number of electrons passing through the dynode increases without colliding with the dynode and being amplified.

As explained in detail above, the dynode of the secondary electron multiplier according to the present invention has a ratio of (d/l) of 1.5 to 1.75, thereby allowing the dynode of the secondary electron multiplier to reach the next stage, which is more than twice as high as the conventional device. The achievement level was obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a dynode of a conventional secondary electron multiplier tube, and FIG. 2 is a schematic diagram showing an embodiment of a dynode of a secondary electron multiplier tube according to the present invention. FIG. 3 is a schematic diagram for explaining the change in electric field when the interval between the thin plates is widened, and FIG. 3A shows a conventional dynode, and FIG. 3B shows a dynode according to the present invention. FIG. 4 is a graph showing changes in the degree of secondary electron reach to the next stage when the pitch d of the thin plate of the dynode in the direction parallel to the tube axis is changed.

Claims (1)

[Scope of Claims] 1. In a dynode arranged perpendicularly to the main axis of a secondary electron multiplier tube and forming a secondary electron multiplier of the secondary electron multiplier tube, in order to form the dynode, the When the pitch in the direction perpendicular to the main axis between a plurality of thin plates arranged at an angle with respect to the main axis is d, and the thickness of the dynode in the main axis direction is t, the following relationship holds between them: A dynode of a secondary electron multiplier tube, characterized in that it is configured to. 1.5≦d/l≦1.75 2 The dynode of a secondary electron multiplier tube according to claim 1, wherein the d/l is 1.64.