JPS6371680A - Ion detector - Google Patents

Abstract

PURPOSE:To improve detection limit and sensitivity and to enable detection of both positive and negative ions with the same gain by disposing a meshed electrode between an ion-electron converter and scintillator and forming a curved shape to focus secondary electrons to a scintillator surface by using the surface of the meshed electrode and the surface of the scintillator. CONSTITUTION:The surfaces of the meshed electrode 2 and the scintillator 4 are shaped to the spherical surface having the same center so as to focus the secondary electrons generated by the ion-electron converter 1 onto an aluminum film 3. Ions 9 past a mass spectrometer 8 are converted to the secondary electrons 7 by the ion-electron converter 1 and are passed through the meshed electrode 2; thereafter, the ions arrive at the scintillator 4, by which the ions are converted to light. The light is amplified by a photomultiplier 5 and is detected. The value which is nearly 100% is obtainable for the count efficiency of the ions to be detected in the case of using a pulse counting system to count the number of pulses by converting the output of the photomultiplier 5 to voltage pulses. The detection limit of the detector is thereby improved to a greater extent.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ion detector, and particularly to an ion detector suitable for detecting positive and negative charged particles with the same gain, high sensitivity, and good quantitative performance. Regarding ion detectors.

[Conventional technology]

A conventional ion detector consists of an ion-to-electron converter, a scintillator, and a photomultiplier, as described in Patent No. 888,821. In this configuration, ions as a signal are first converted into electrons, which are accelerated and irradiated onto a scintillator and converted into light.Finally, the optical signal is amplified by a photomultiplier tube and detected as an electrical signal. .

[Problem that the invention seeks to solve]

The above conventional technology does not consider the focusing of secondary electrons generated in the ion-electron converter onto the scintillator surface, and does not consider the efficiency of secondary electron utilization (how many of the generated secondary electrons ) is low, and as a result, the amplification factor of the detector is correspondingly low, resulting in a problem that the counting efficiency is low when pulse-counting signals.

The purpose of the present invention is to improve the above-mentioned problems in the prior art,
It is an object of the present invention to provide an ion detector that can improve the detection limit as a detector, has high sensitivity, and can detect both positive and negative ions with the same gain.

c. Means for Solving Problems] In order to achieve the above object, the present invention employs the following configuration. That is, an ion-electron converter that converts detected ions into electrons and outputs them, and the ion-electron converter that converts the detected ions into electrons and outputs them.
Ion consists of a scintillator or phosphor (hereinafter referred to as scintillator) that converts electrons output from an electronic converter into light, and a photoelectric converter that amplifies the light from this scintillator and detects it as an electrical signal. In the detector, a mesh-like electrode or a perforated electrode (hereinafter collectively referred to as mesh-like electrode) is inserted between the ion-electron converter and the scintillator, and the surface shape of the mesh-like electrode and the scintillator is inserted between the two. The scintillator has a curved surface so that electrons are focused on the scintillator by the generated electric field, and the ion-electron converter is set at ground potential.

[Effect]

Electrons are accelerated in the opposite direction to the electric field. Therefore, by making the surface shapes of the mesh-like electrode and scintillator curved so that the opposite direction of the electric field is focused on the scintillator surface, the secondary electrons generated in the ion-electron converter pass through the mesh-like electrode. The secondary electrons become focused on the scintillator surface, increasing the efficiency of secondary electron use. Further, the reason why the ion-electron converter is set to the ground potential is to receive positive and eclipsed ions having the same energy and opposite polarity with the same energy.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, 1 is an ion-electron converter, 2 is a mesh electrode, 3 is an aluminum film attached to the surface of a scintillator 4, and 5 is a photomultiplier tube.

Reference numeral 6 denotes a high voltage power source that applies a high voltage for electron acceleration between the mesh electrode 2 and the aluminum film 3. here,
The surface shapes of the mesh-like electrode 2 and the scintillator 4 were spherical with the same center so that the secondary electrons 7 generated in the ion-electron converter 1 were focused on the aluminum film 3.

The photomultiplier tube 5 was designed for photon counting and had a relatively small light entrance window of 5 nu x 8 m so as to reduce the generation of thermoelectrons from the photocathode, which would cause noise.

Next, the operation will be described. Here, a case will be described in which secondary ion detection is performed using an ion microanalyzer.

First, the case of positive ion detection will be described. Ions 9 accelerated at +3 kV and passed through the mass spectrometer 8 are first converted into secondary electrons 7 by the ion-electron converter 1 at ground potential. After passing through the mesh-like electrode 2, these secondary electrons 7 are accelerated in the direction opposite to the direction of the electric field generated by the accelerating voltage applied by the high-voltage power supply 6, and are focused and irradiated onto the surface of the aluminum film 3. . Here, the secondary electrons 7 reach the scintillator 4 and are converted into light.

This light is amplified and detected by the photomultiplier tube 5.

When a pulse counting method was used in which the output of the photomultiplier tube 5 was converted into voltage pulses and the number of pulses was counted, the counting efficiency for the ions to be detected was close to 100%. This made it possible to significantly improve the detection limit of the detector. In the case of negative ion detection, ions accelerated to -3 kV enter the ion-electron converter 1, but can be detected with the same gain as in the case of positive ions described above.

According to this embodiment, the secondary electrons generated from the ion-electron converter can be focused and used efficiently, so it can be used particularly in photomultiplier tubes with a small light entrance window to achieve low noise for photon counting. However, if a pulse counting method is used, a high counting efficiency close to 100% can be obtained, and the noise can be reduced to less than 1 per second, which limits the detection limit of the detector. can be significantly improved. Therefore, it is possible to quantitatively analyze extremely trace amounts of components, such as a few secondary ions. Furthermore, since positive and negative ions having the same energy can be measured with the same gain, it is possible to quantitatively compare the positive secondary ion strength and the negative secondary ion strength.

〔Effect of the invention〕

According to the present invention, (1) the secondary electrons generated in the ion-electron converter can be used efficiently and have a high gain as an ion detector; (2) when combined with the pulse counting method, the gain is close to 100%. (3) In the case of (2) above, even if a particularly low-noise photomultiplier tube is used, light can be efficiently guided to the photocathode, and a signal can be generated with a noise of less than one per second. (4) Positive and negative ions with the same energy can be measured with the same gain; (5) The device is simple and inexpensive. This produces effects such as reducing

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention. Explanation of symbols 1...Ion-electron converter

Claims (1)

[Claims] 1. An ion-electron converter that converts ions into electrons, a scintillator that converts secondary electrons emitted from the ion irradiation surface of the converter into light, and converts this light into an electrical signal. In the ion detector, which is composed of a photoelectric converter that detects the An ion detector characterized in that the surface of the mesh electrode and the surface of the scintillator are formed into curved shapes that focus secondary electrons on the surface of the scintillator. 2. The ion detector according to claim 1, wherein the surfaces of the mesh electrode and the scintillator are formed into concentric hemispherical surfaces to focus secondary electrons toward the center thereof. . 3. The ion detector according to claim 1, wherein the ion-electron converter is held at ground potential. 4. The ion detector according to claim 1, wherein the photoelectric converter is a photomultiplier tube. 5. The ion detector according to claim 1, wherein the photoelectric converter comprises a photomultiplier tube and a pulse counter that counts the output thereof.