JPH01292737A - Secondary electron multiplying device - Google Patents

Abstract

PURPOSE:To make a channel wall obtain a broad linearity and a high multiplication gain by making the cross sectional area near an output end of a multiplied secondary electron smaller than the cross sectional area near an input end which emits a secondary electron against an incidence of a charged particle. CONSTITUTION:In a secondary electron multiplying device equipped with a secondary multiplier 2 having a cylindrical channel 2b made up of semiconductor material which can emit a secondary electron, the channel 2b of the secondary electron multiplier 2 is formed such that the cross sectional area near an output end 2c which outputs a multiplied secondary electron is made smaller than that near an input end which emits a secondary electron against incidence of a charged particle. Thereby, the wall of the channel 2b functions as a secondary electron multiplied face, and also as a kind of bleeder resistance with the result that the resistance of the channel 2b become greater at the output end 2c side and a field strength becomes greater than that of any other portion so that an increase in the space charge density of a secondary electron can be controlled. Accordingly, a linearity can be obtained until a high output region in case of application to current amplification and a large gain can be obtained until a high counting rate in case of application to pulse count.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a secondary electron multiplier, and more particularly, to a secondary electron multiplier having a cylindrical channel made of a semiconductor material having a secondary electron emitting ability. The present invention relates to a secondary electron multiplier that detects ions and electrons in space by detecting secondary electrons output from a secondary electron multiplier.

[Prior Art] In recent years, devices for detecting ions and electrons existing in outer space, or mass spectrometers for analyzing the mass of various ions and atoms, have been using semiconductor materials with secondary electron emitting ability in a cylindrical shape. A secondary electron multiplier device called a channel electron multiplier is used, which uses a secondary electron multiplier tube formed in .

This type of secondary electron multiplier multiplies the secondary electrons generated in the secondary electron multiplier by applying an electric field and pulling them, so the ions, electrons, etc. in the secondary electron multiplier are The input end becomes the cathode, and the output end becomes the anode. And 2
In secondary electron multipliers, there are two grounding methods: an anode grounding method and a cathode grounding method, depending on whether the anode of the secondary electron multiplier tube is grounded or the cathode is grounded.

To detect positively charged ions, an anode grounding method as shown in FIG. 5 is used.

The secondary electron multiplier has a channel 2b made of a cylindrical semiconductor material made of zinc titanate ceramic having secondary electron emission ability, and has a channel 2b in which positive (plus) ions i are formed on one end side. A secondary electron multiplier tube 2 in which a cathode 1 is formed on the outer peripheral surface of a cone-shaped portion 2a constituting an input end.
It is equipped with Then, from the output end of channel 2b of this secondary electron multiplier tube 2, 0.51II to 1, OL
A collector 3 made of a circular metal plate is arranged with a gap g of 1.1 m, and a voltage of -3 KV is applied to the cathode 1 with respect to the ground.
While applying a high voltage EH of 1 to 14 KV, an accelerating voltage EL of 1+00 V to 1200 V relative to the ground is applied to the anode 4 formed on the other end side of the secondary electron multiplier tube 2.
The multiplication current is collected in the collector 3 using this acceleration voltage EL. The accelerating voltage EL applied to the anode 4 is
The voltage is obtained by a voltage drop caused by a resistor R such as a metal film or carbon connected between the anode 4 and the ground.

The output secondary electron current collected by the collector 3 is charged to the stray capacitance Cs generated between the collector 3 and the ground, and the charged charge is discharged through the load resistor R1, and at this time, a voltage is generated across the load resistor. is amplified by the preamplifier 5.

In the above, the acceleration voltage E applied to the anode 4 is
The accelerating voltage Et is obtained by the voltage drop caused by the resistor R connected between the anode 4 and the ground, but the acceleration voltage Et is applied between the anode 4 and the ground as shown in FIG. A DC power source Ea may be connected.

On the other hand, to detect negatively charged electrons, a cathode grounding method as shown in FIG. 7 is used.

In the cathode grounding type, the cathode 1 is directly grounded, but a relatively low positive DC voltage is applied by the DC power supply Eb. In this cathode grounding type, the collector 3 has a positive (plus) high potential with respect to the ground, so a coupling capacitor C for DC blocking is inserted between the collector 3 and the preamplifier 5. Even with this cathode grounding method,
Instead of the DC power supply Ea for applying the acceleration voltage Eb, a resistor (
Not shown.

) may also be connected.

[Problems to be Solved by the Invention] By the way, in the secondary electron multiplier shown in FIGS. 5, 6, and 7, the channel 2b of the secondary electron multiplier 2
The wall functions as a secondary electron multiplier surface and also acts like a bleeder resistor in a multistage secondary electron multiplier, and has a -like resistance value distribution. In such a secondary electron multiplier, unlike those shown in FIGS. 5, 6, and 7 above, when the channel 2b has a linear shape, the operating voltage is increased to obtain a large multiplication gain. A disadvantage was found that when increasing the value, an ion feedback phenomenon occurred and the operation became unstable. It has also been confirmed that this phenomenon becomes more pronounced as the operating vacuum pressure becomes higher, that is, as the vacuum becomes lower.

For this reason, the external shape of the channel 2b is shown in FIG.

The ion feedback phenomenon is suppressed by using a waveform as shown in FIGS. 6 and 7, a spiral shape, an arc shape, etc. Even with this shape, when operating at a higher vacuum pressure or increasing the operating voltage for the purpose of increasing the multiplication gain, the channel near the output end of channel 2b of the secondary electron multiplier 2 The secondary electrons multiplied in channel 2b concentrate and become high space charge density, and some of the secondary electrons return to the input end side of channel 2b, resulting in an ion feedback phenomenon, or the above-mentioned high density space There is a problem in that the multiplication gain decreases due to the increase in charge.

The purpose of the present invention is to provide a secondary electron multiplication system that has wide linearity in current amplification devices, high multiplication gain up to high counting rates in pulse count devices, and secondary electron multiplication that prevents ion feedback from occurring. The purpose is to provide equipment.

[Means for Solving the Problems] Therefore, the present invention provides a secondary electron multiplier comprising a secondary electron multiplier having a cylindrical channel made of a semiconductor material having secondary electron emission ability. , the cross-sectional area of the wall of the channel near the output end where multiplied secondary electrons are output is smaller than the cross-sectional area near the input end where secondary electrons are emitted in response to the incidence of charged particles. It is a feature.

[Function] The wall of the channel of the secondary electron multiplier tube functions as a secondary electron multiplier surface and also functions as a kind of bleeder resistance. It has a resistance value distribution according to its cross-sectional area. Further, since the cross-sectional area of the channel on the output end side is smaller than the cross-sectional area on the input end side, the resistance of the channel is larger on the output end side than on the input end side of the channel. As a result, the electric field strength on the output end side of the channel becomes larger than on other parts, and an increase in the space charge density of secondary electrons on the output end side of the channel is suppressed.

[Effects of the Invention] According to the present invention, the electric field strength at the output end side of the channel of the secondary electron multiplier becomes larger than other parts, and the space charge density of secondary electrons at the output end side of the channel decreases. This suppresses the increase in current amplification, so secondary electron multipliers for current amplification can achieve linearity up to a high output range, and secondary electron multipliers for pulse counting can achieve high gain up to high counting rates. At the same time, ions are prevented from returning from the output end of the channel to the input end, and ion feedback is also suppressed.

[Example] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The present invention provides, for example, in the secondary electron multiplier explained in FIGS. 5, 6, and 7, the cross-sectional area near the output end that outputs multiplied secondary electrons is The channel 2b of the secondary electron multiplier 2 is formed so as to be smaller than the cross-sectional area near the input end where the secondary electrons are emitted.

A specific configuration of the secondary electron multiplier tube 2 of the secondary electron multiplier according to the present invention is shown in FIGS. 1 and 2.

In the secondary electron multiplier 2 shown in FIG. 1, the thickness of the wall of the channel 2b is constant, but the diameter of the output end portion 2C from near the output end of the channel 2b to the output end is larger than that of the other portions. It is designed to be smaller than the diameter.

The secondary electron multiplier 2 in FIG.
b has a constant wall thickness, but its diameter gradually decreases from the input end to the output end.

The wall of the channel 2b of the secondary electron multiplier 2 functions as a secondary electron multiplier and has a resistance value distribution according to its cross-sectional area. And the above channel 2b
Since the cross-sectional area on the output end side is smaller than the cross-sectional area on the input end side, the resistance value per unit length on the output end side is larger than the resistance value per unit length on the other parts. As a result, the electric field strength E on the output end side of the channel 2b of the secondary electron multiplier 2 is higher than the electric field strength E1 on the input end side.

becomes stronger, and an increase in the space charge density of secondary electrons on the output end side of the channel is suppressed. Therefore, while ion feedback is suppressed, linearity is maintained up to high output,
Moreover, a high gain is maintained up to a high counting rate. In the above embodiment, the thickness of the wall of the channel 2b may be smaller on the output end side than on other parts.

By the way, we used a linear secondary electron multiplier tube as shown in Figure 3, and the inner diameter of the tube was 1.0 mg + over the entire length.
The outer diameter of both points A and B is 4.0 mm (conventional example), and the outer diameter of point A is 4.0 mm. The gain characteristics and ion feedback were investigated using a device with Oes and point B set to 3.0all (the present invention).

Figure 4 shows the gain characteristics, where the gain at 10" cps is Go, the gain at higher counts is G, the gain is expressed as G / Go, and the count is expressed as The graph shows the tendency when the output voltage is changed.As is clear from FIG. 4, the linearity of the device according to the present invention is better than that of the conventional example, and the input-output dynamic range is wider. , even when examining the l1n-E out characteristics in measurements during current amplification,
The linearity of the present invention was better.

Table 1 shows the frequency of ion feedback when changing the voltage, and the present invention has a greater effect of suppressing ion feedback than the conventional example, and the higher the voltage, the greater the effect. I understand.

Table 1

[Brief explanation of the drawing]

1 and 2 are partially cutaway front views of a secondary electron multiplier of a secondary electron multiplier according to the present invention, and FIG. 3 is an explanatory diagram of a specific example of the secondary electron multiplier. be. FIG. 4 is a multiplication gain characteristic diagram. FIG. 5, FIG. 6, and FIG. 7 are explanatory diagrams of conventional secondary electron multipliers, respectively. 2... Secondary electron multiplier tube, 2a... Cone part, 2b...
...Channel, 2C...Output end part. Patent applicant Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] (1) In a secondary electron multiplier comprising a secondary electron multiplier tube having a cylindrical channel made of a semiconductor material having secondary electron emitting ability, the wall of the channel is formed by the multiplied secondary electrons. 1. A secondary electron multiplier characterized in that a cross-sectional area near an output end that outputs secondary electrons is smaller than a cross-sectional area near an input end that emits secondary electrons in response to incidence of charged particles.