JPH04233151A - Ion detector - Google Patents

Abstract

PURPOSE:To provide an ion detector, which can detect ions with high sensitivity and lengthen the life of a secondary electron multiplier tube by operating the secondary electron multiplier tube at low operating pressure. CONSTITUTION:This is equipped with the first conversion dynode 15, to which the negative ions from an ion source enter, the second conversion dynode 16, to which the positive ions from the first conversion dynode 15 enter, and a secondary ion multiplier tube 14, to which the electrons 22 generated by this second conversion dynode 16 enter. The negative ions, which have entered the first conversion dynode 15, being drawn by the positive high voltage applied to the first conversion dynode 15, collide against the first conversion dynode 15, and are converted into positive ions. These positive ions enter the above second conversion dynode 16, being sucked by negative high voltage applied to the second conversion dynode 16, and are converted into electrons. The converted electrons are sucked by the voltage applied to the secondary electron multiplier tube 14, and enter the second electron multiplier tube 14 and are doubled.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention uses a secondary electron multiplier called a continuous dynode electron multiplier (CDEM), which has a cylindrical structure and is made of a semiconductor material having a secondary electron emission ability. The present invention relates to an ion detection device that detects negative ions.

0002

2. Description of the Related Art In recent years, in the field of analysis, there has been a demand for highly sensitive detection of high mass number ions and negative ions.

[0003] The detection efficiency of high mass number ions increases as the speed of the ions colliding with the secondary electron multiplier increases. In order to increase the speed of ions, an accelerating electrode may be provided and the accelerating voltage applied thereto may be increased. The easiest way to do this is to increase the negative voltage applied to the incident section of the secondary electron multiplier. However, in this case, there is a limit because the higher the voltage, the more the multiplier tube is simultaneously operated at a higher gain, which shortens the life of the secondary electron multiplier tube. In addition, when detecting negative ions, in order to extract the output signal in analog form, it is necessary to set the collector to ground potential, which requires applying a high negative voltage to the ion incidence part of the secondary electron multiplier tube. It is impossible in principle to collide negative ions there.

[0004] Conventionally, therefore, an ion detection device having a configuration as shown in FIG. 5 has been developed, in which the negative ions are detected by converting negative ions into positive ions and detecting the converted positive ions. has been proposed (for example, see Japanese Patent Publication No. 58-7229).

The ion detection device 1 includes a conversion anode 3 that generates positive ions when negative ions 2 are incident and collide with each other. That is, the ion detection device 1 has a grid-like holed screen 4 provided therein, as shown in FIG. Received from analyzer 6. Then, the ion detection device 1 collides the negative ions 2 with the conversion anode 3 to convert them into positive ions 7, and inputs the converted positive ions 7 into a secondary electron multiplier 8 to generate secondary electrons. Multiply the secondary electrons and take out the multiplied secondary electrons as an output signal. A voltage of +3 KV is applied to the conversion anode 3 in order to attract the negative ions 2 from the mass spectrometer 6. Further, a voltage of -1KV to -3KV is applied to the cathode of the secondary electron multiplier tube 8 in order to attract the positive ions converted by the conversion anode 3.

[0006]

However, in the conventional ion detection device 1 described above, the conversion anode 3 generally has a low conversion efficiency when converting the negative ions 2 into positive ions 7. Therefore, the secondary electron multiplier tube 8 has a normal operating voltage (2
KV or less), it is not possible to obtain a sufficient output signal. In order to compensate for this, the operating voltage of the secondary electron multiplier tube 8 is increased to increase the gain, thereby obtaining a practical level output signal. As a result, the operating voltage is about 2.8 KV. When the secondary electron multiplier 8 deteriorates and its gain decreases, the applied voltage is further increased to compensate for this.

However, the operating voltage is 2.8K as mentioned above.
If V is high from the beginning, the upper limit of the general-purpose high-voltage power supply used in the ion detection device 1 is 3.0 KV, and the operating voltage of the secondary electron multiplier tube 8 is generally 3 KV or less, so the general-purpose There is a problem in that both the high voltage power supply and the secondary electron multiplier 8 do not have enough margin to compensate for gain deterioration, and the life of the secondary electron multiplier 8 becomes relatively short.

[0008] Furthermore, in the conventional ion detection device 1,
Most of the positive ions 7 generated by the conversion anode 3 are attracted to the cathode of the secondary voltage multiplier 8, but since they are isotropically dispersed immediately after colliding with the conversion anode 3, some of them are absorbed by other ions. The ions were absorbed by the metal, and the ions generated at the conversion anode 3 could not be completely focused. This is also a cause of not being able to obtain high sensitivity in the conventional ion detection device 1 described above.

An object of the present invention is to detect ions with high sensitivity, and to extend the life of the secondary electron multiplier by operating the secondary electron multiplier at a low voltage. The purpose is to provide equipment.

0010

[Means for Solving the Problems] Therefore, the present invention provides an ion detection device for detecting negative ions incident from an ion source, in which the negative ions are incident and collided with each other, and a proportionate amount of positive ions are generated. a first conversion dynode that generates a It is characterized by comprising a secondary electron multiplier tube into which electrons enter and from which multiplied secondary electrons are output from an output end.

[0011]

[Operation] Negative ions incident on the first conversion dynode are converted into positive ions by being attracted by the high positive voltage applied to the first conversion dynode. The converted positive ions are attracted to the negative high voltage applied to the second conversion dynode, enter the second conversion dynode, and are converted into electrons. The converted electrons are attracted by the voltage applied to the secondary electron multiplier, enter the secondary voltage multiplier, collide with its inner wall, and generate secondary electrons. In the process of repeating the process of colliding with the inner wall of the secondary electron multiplier tube to generate secondary electrons, the secondary electrons are multiplied in a so-called mouse equation. The voltage applied to the cathode of the second conversion dynode and the voltage applied to the secondary voltage multiplier are applied separately,
controlled.

0012

According to the present invention, the voltage applied to the cathode of the secondary electron multiplier is lower than the negative high voltage applied to the second conversion dynode, and Since the voltage and the voltage applied to the secondary voltage multiplier can be applied and controlled separately, the conversion efficiency from positive ions to electrons is increased depending on the voltage applied to the second conversion dynode. As efficiency improves, the voltage applied to the secondary electron multiplier can be lowered, and the life of the secondary electron multiplier can be significantly extended.

Further, according to the present invention, the ions generated in the first conversion dynode are focused and incident on the second conversion dynode, and the electrons generated in the second conversion dynode are also focused, resulting in secondary electron multiplication. Since the ions are incident on the tube, there is no loss of ions and high sensitivity can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows the configuration of an embodiment of the ion detection device according to the present invention.

The ion detection device 11 shown in FIG. 1 has a holed screen 13 and a secondary electron multiplier tube 14 installed behind a holed screen 13 having holes 13a through which negative ions 12 from an ion source (not shown) pass. placed between
All are Cu-Be, Ag-Mg, Au-Al, Au-
It is made of a metal such as Si, a semiconductor ceramic such as ZnO-TiO2 type, BaTiO type, or a thin film thereof. First conversion dynode 15 and second conversion dynode 16
Equipped with. The first conversion dynode 15 and the second conversion dynode 16 each have a rectangular parallelepiped box shape, as shown in FIGS. 2 and 3. Both the first conversion dynode 15 and the second conversion dynode 16 have an ion incidence window 17 on one of their four sides, and a mesh 18 is attached to cover the opening of the ion incidence window 17. ing. Further, the first conversion dynode 15 and the second conversion dynode
One end face of each of the conversion dynodes 16 serves as an exit opening for positive ions 21 and electrons 22, respectively. When ions collide with the ion incidence surfaces of the first conversion dynode 15 and the second conversion dynode 16, charged particles with different charges are generated. For example, negative ions 12 generate positive ions 21, and positive ions 21 generate electrons 22.

As shown in FIG. 1, the first conversion dynode 15 has its ion incidence window 17 facing the hole 13a of the holed screen 13.
It is placed behind 3. On the other hand, the second conversion dynode 16 is arranged behind the holed screen 13 with its ion incidence window 17 facing the ion exit opening 19 of the first conversion dynode 15 . The secondary electron multiplier 14 is arranged such that the trumpet-shaped entrance end 14a of the secondary electron multiplier 14 faces the electron exit opening 19 of the second conversion dynode 16.

A positive high voltage of, for example, +3 KV is applied to the first conversion dynode 15. In addition, the second
A negative high voltage of, for example, -3 KV is applied to the conversion dynode 16 so that the positive ions 21 are efficiently converted into electrons. A voltage of, for example, -2 KV is applied to the secondary electron multiplier tube 14.

Negative ions 12 are introduced into the inner wall of the first conversion dynode 15 from the hole 13a of the holed screen 13 through the ion incidence window 17 of the first conversion dynode 15.
When the two collide, positive ions 21 are generated. The generated positive ions 21 are attracted to the potential of the second conversion dynode 16, are repelled by the voltage applied to the first conversion dynode 15, are converged, and are directed to the exit aperture 1.
9 to the ion incidence window 17 of the second conversion dynode 16
fire towards.

The positive ions 21 entering the second conversion dynode 16 from the ion incidence window 17 of the second conversion dynode 16 collide with the inner wall of the second conversion dynode 16, and
Generates electrons 22.

The electrons 22 generated above are attracted to the potential of the incident end 14a of the secondary electron multiplier 14, which has a lower potential than the second conversion dynode 16, and are applied to the second conversion dynode 16. The electrons are repelled by the voltage and converge, and enter the incident end 14a of the secondary electron multiplier 14 through the exit aperture 19 with directionality. Then, it is multiplied by this secondary electron multiplier tube 14, and a multiplied output is obtained from the output end 14b,
Electrons emitted from the output end 14b are received by the collector.

As described above, the electrons 22 converted by the second conversion dynode 16 enter the secondary electron multiplier tube 14 and are detected.
In order to make the electrons 22 incident on the secondary electron multiplier 14, it is necessary to accelerate the electrons 22 toward the incident end 14a of the secondary electron multiplier tube 14. In order to do this, the operating voltage of the secondary electron multiplier 14 must be lower than the negative high voltage of the second conversion dynode 16 to which a negative high voltage (for example, -3 KV) is applied as described above. It is also necessary to lower the voltage (for example, -2 KV), and the operating voltage of the secondary electron multiplier 14 can necessarily be lowered.

Further, the positive ions 21 and electrons 22 generated in the first conversion dynode 15 and the second conversion dynode 16 are not lost on the way, but are converged and directed to the second conversion dynode. 16 and the secondary electron multiplier 14 . It can be seen that this significantly improves the sensitivity of the ion detection device 11.

In the above embodiment, the first conversion dynode 15
A box-shaped one was used as the second conversion dynode 16, but as shown in FIG. 4, the positive ion 21 generation surface and the electron 22 generation surface have a parabolic shape. Good too. In this case, in order to prevent the electrons 22 from returning from the second conversion dynode 24 to the first conversion dynode 23, the potential gradient between the second conversion dynode 24 and the first conversion dynode 23 is dynode 2
4 and the incident end 14a of the secondary electron multiplier 14 must be increased. For this purpose, the secondary electron multiplier 14 may be placed as close as possible to the second conversion dynode 24. Furthermore, by setting the holed screen 13 and the first conversion dynode 23 at the same potential, it is possible to obtain the same effect as a box-shaped dynode. In addition,
In FIG. 4, parts corresponding to those in FIG. 1 are indicated with corresponding symbols, and redundant explanations will be omitted.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the configuration of an embodiment of an ion detection device according to the present invention.

FIG. 2 is a perspective view showing the configuration of a first conversion dynode and a second conversion dynode of the ion detection device of FIG. 1;

FIG. 3 is a longitudinal sectional view of a first conversion dynode and a second conversion dynode of the ion detection device of FIG. 1;

FIG. 4 is a perspective view showing the configuration of another embodiment of the ion detection device according to the present invention.

FIG. 5 is an explanatory diagram of a conventional ion detection device.

FIG. 6 is an explanatory diagram of a mass spectrometer.

[Explanation of symbols]

11 Ion detection device 12 Negative ions 13 Screen with holes 13a Hole 14 Secondary electron multiplier 14a　Incidence end 15 First conversion dynode 16 Second conversion dynode 17 Ion incidence window 19 Output aperture 21 Positive ions 22 Electron 23 First conversion dynode 24 Second conversion dynode

Claims (1)

[Claims] 1. An ion detection device for detecting negative ions incident from an ion source, comprising: a first conversion dynode for generating an amount of positive ions in proportion to the incident and colliding negative ions; The above-mentioned positive ions generated from the first conversion dynode enter and collide, and the second conversion dynode generates an amount of electrons proportional to the positive ions. The electrons generated from this second conversion dynode enter and are multiplied from the output end. An ion detection device comprising: a secondary electron multiplier that outputs secondary electrons.