JPH0368503B2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to an ion detector.

<Prior Art> Charged particle detection devices using microchannel plates have recently come into widespread use in radiation measurement and mass spectrometry. A microchannel plate is an element with an apparent plate-like shape that multiplies the number of secondary electrons produced by collisions of charged particles (ions, electrons) that are incident on it, but it is used for ion detection. When used in a device, due to the general characteristics of secondary electron emitters, the secondary electron emission capability of the microchannel plate decreases for slow heavy ions, and thus the ion detection efficiency of the device decreases. To deal with this, there are two methods: accelerating the ions before they are incident on the microchannel plate, and coating the microchannel plate with a cesium film to increase its secondary electron emission ability.

However, accelerating heavy ions and colliding particles with large momentum will stop the deterioration of the microchannel plate, and the improvement in secondary electron emission ability by coating with a cesium film is not that great. .

For this reason, ions can be directly transferred to microchannels.
There is an ion detection device that uses the so-called ion-electron exchange method, in which the secondary electrons are not made incident on a plate, but are made to collide with a separately prepared strong electrode, and the secondary electrons emitted from there are guided to a microchannel plate. . However, conventional devices using this method have various difficulties in efficiently guiding secondary electrons generated elsewhere to the microchannel plate; The disadvantage is that the structure of the device is complicated, as it requires the application of a magnetic field.

<Problems to be Solved by the Invention> The present invention solves the above-mentioned drawbacks of conventional ion detection devices using microchannel plates, namely, the problem of microchannel plate deterioration due to ion acceleration, and the problems of ion detection devices using microchannel plates. This solves the problem of decreased secondary electron collection efficiency associated with the electron exchange method.

<Means for Solving the Problems> In order to solve the above problems, the device according to the present invention employs an ion-electron conversion method and converts the secondary electrons emitted from the ion-electron conversion electrode into It is characterized by the provision of an electron repelling electrode for directing electrons to the channel plate.

<Operation> By keeping the electron repelling electrode at an optimal negative potential lower than that of the ion-electron conversion electrode, almost all the secondary electrons emitted from the ion-electron conversion electrode are
The electron repelling electrode bends its path towards the microchannel plate.

<Example> Examples of the present invention will be described below based on the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, the main parts 5 of which are a grid-like electron repulsion electrode 1, a Venetian blind ion-electron conversion electrode 2, a microchannel plate 3, and an electron collection electrode. It is composed of 4. In addition, the electron repulsion electrode 1
The screen electrode 6 placed on the left side is an electrode for electrostatically shielding the main part 5 of the device from the ion flight part (not shown), and is also arranged in a grid pattern to allow ions to pass through. It is formed.

In the above configuration, the ion-electron exchange electrode 2
is kept at a negative potential, the electron repulsion electrode 1 is kept at an even lower negative potential, and the electron collection electrode 4 is kept at a positive potential with respect to the microchannel plate 3. When ions 7 accelerated to a constant velocity by a lattice-shaped screen electrode 6 and an electron repulsion electrode 1 are injected, the ions pass through a lattice-like screen electrode 6 and an electron repulsion electrode 1, resulting in Venetian blind ion-electron exchange that is oriented obliquely. collides with electrode 2. Due to the collision of ions, the ion-electron exchange electrode 2 emits secondary electrons, but the emitted secondary electrons are kept at a negative potential lower than that of the electrode 2, so that their trajectory is directed to the right. and reaches the microchannel plate 3. Microchannel plate 3 reaches 2
The secondary electrons are further multiplied in a chain reaction manner by the secondary electron emission action. The electrons finally emitted from the microchannel plate 4 flow through the electron collection electrode to the resistor 8, generating an output voltage thereon. This voltage is amplified by a conventional electronic circuit 9 and the arrival of ions 7 is detected electrically.

FIG. 2 is a diagram showing the path of secondary electrons emitted from the ion-electron exchange electrode 2, obtained by computer simulation. In Figure A, the electron repelling electrode 1 is kept at the same potential as the ion-electron exchange electrode, and in Figure B, the electron repelling electrode 1 is kept at an optimal potential that is more negative than the ion-electron exchange electrode 2. In this case, Figure C shows the secondary electron travel paths when the electron repulsion electrode 1 is kept at a potential more negative than the above-mentioned optimum potential. As can be seen from these figures, by selecting an appropriate potential difference between the electron repulsion electrode 1 and the ion-electron exchange electrode 2, virtually all of the emitted secondary electrons are transferred to the microchannel plate. It can be bent in the direction of 3. Incidentally, FIG. 3 is a diagram showing the relative positional relationship between the ion-electron exchange electrode 2 and the microchannel plate 3.

<Effects of the Invention> As is clear from the above explanation, according to the present invention, ions are detected via secondary electrons emitted from the ion-electron exchange electrode, so that the microchannel plate is not affected by collisions of high-speed ions. In addition to preventing deterioration, by adding a grid-like electron repulsion electrode with a simple structure, secondary electrons can be efficiently guided to the microchannel plate, resulting in a simple structure and high sensitivity. An ion detection device is obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is a secondary electron travel path map created by computer simulation. FIG. 3 is a perspective view showing the relative positional relationship between the ion-electron exchange electrode and the microchannel plate in the above embodiment. 1...Electron repulsion electrode, 2...Ion-electron exchange electrode, 3...Microchannel plate.

Claims (1)

[Claims] 1. An ion-electron conversion electrode that emits secondary electrons upon collision with ions to be detected; a microchannel plate as an element that multiplies and emits the secondary electrons emitted from the ion-electron conversion electrode;
an electron collection electrode that collects secondary electrons emitted from the microchannel plate; and an electron repulsion electrode that repels the secondary electrons emitted from the ion-electron conversion electrode toward the microchannel plate. An ion detection device consisting of: