JPH04132152A - Charged particle detecting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a charged particle detection device such as an ion detection device in a mass spectrometer.

(Prior Art) When charged particles are detected by an analyzer using a charged particle beam, a channeltron, a microchannel plate (MCP), or the like is used as a secondary electron multiplier. All of these are based on the principle of signal amplification using secondary electrons, but secondary electron multipliers use multiple dynodes separated from each other, while Channeltrons and MCPs use continuous dynodes. It is something. Currently, continuous dynode type detectors such as channeltrons and MCPs are often used from the viewpoint of longevity.

By the way, since the channeltron has a single tube for the secondary electron multiplication path, the output is easily saturated and the dynamic range is narrow. Since an MCP has many secondary electron multiplication paths, even if the input is saturated with just one channeltron, if it is distributed over the entire surface of the MCP, the load per microchannel is reduced and the dynamic range is expanded. It should be done. However, conventional MCPs have been used to detect the density distribution of charged particles within an area such as an image of charged particles, and have not been used for the purpose of expanding the dynamic range of charged particle detection.

(Problem 1g to be Solved by the Invention) The present invention aims to expand the dynamic range by using an MCP instead of a channeltron.

<Means for Solving the Problems> A lens system for diverging a charged particle beam is placed in front of the MCP, and electrons emitted from the MCP are made to enter the common anode.

(Function) Since the charged particle beams emitted from the exit slit of a mass spectrometer or charged particle energy analyzer are narrow, conventionally they were detected by entering them into a channeltron. Simply placing an MCP behind this exit slit will not result in M
Only a few central channels of the CP's many channels are used for measurement, and the input level at which the output is saturated is low. However, in the present invention, a beam diverging lens system is placed in front of the PvI CP, so even if the beam emitted from the analyzer is narrow, the beam can be distributed over the entire surface of the MCP, and - the load per microchannel can be reduced. is reduced and the saturation level is increased.

(Example) Figure 1 shows an example of the present invention. In this example, the present invention is applied to the ion detection section of a quadruple barrel mass spectrometer. In the figure, 1 is a quadrupole electrode. , 2 is an exit slit, and the ion beam advances from the left, and ions with a specific mass pass through the exit slit 2.The ions that have passed through the exit slit 2 pass through the base plate 3, lens electrode 4, and then to the microchannel plate. (MCP) 5, MC
All electrons emitted from P5 enter a common anode 6, and an anode current is sent to an amplifier 7. Output slit 2
The optical axis is vertically shifted between the ion beam and the base plate 3, and a deflection electrode 8 for deflecting the ion trajectory is placed between the two, but this is because the ion trajectory is straight in the quadruple barrel mass spectrometer. Therefore, the ion source can be seen from the ion detector through the exit slit, and the light from the filament in the ion source enters the ion detector and emits photoelectrons, which becomes noise and reduces the noise from the ion source. The ion trajectory is bent so that the light does not enter the ion detector.

The present invention is based on base plate 3. Lens electrode 4. The point is that an ion beam diverging optical system is constructed by the three MCP5s. Figure 2 shows base plate 3° lens electrode 4, MCP
5 shows each potential on the surface of No. 5 and the spatial equipotential surface distribution. The base plate 3 is OV. There is an ion acceleration effect from the base plate 3 toward the lens electrode 4, and a deceleration effect with a potential difference of 0.5 KV between the lens electrode 4 and the MCP5, but the overall distance from the base plate to the MCP is 1
It has an accelerating effect of ~2KV. The lens electrode 4 has a potential valley, and although the ion beam is somewhat converged between the base plate and the lens electrode, it is diverged in the deceleration field after passing through the lens electrode, and as shown in the figure, the ion beam is approximately focused in front of the MCP. It is distributed throughout the entire area.

(Effects of the Invention) According to the present invention, the charged particle beam is diverged and distributed over the entire surface of the MCP. Since the load on each channel is reduced, it is possible to sufficiently respond to inputs that would otherwise be saturated in the case of a single channel, and it is possible to detect and measure charged particle beams with a wide intensity range. It becomes possible.

[Brief explanation of the drawing]

FIG. 1 is an inverted view of an embodiment of the present invention, and FIG. 2 is an enlarged view of a portion of a diverging lens system. 1... Quadrupole electrode, 2... Output slit, 3...
Base plate, 4... Lens electrode, 5... MCP
, 6... Anode, 7... Amplifier, 8... Deflection electrode. Agent Patent Attorney Kosuke Agata

Claims (1)

[Claims] A microchannel plate is used as a charged particle detector, and a lens system that diverges the charged particle beam is placed in front of the microchannel plate so that the charged particle beam to be detected is dispersed and incident on almost the entire surface of the microchannel plate. A charged particle detection device characterized in that the electrons emitted from each channel of the microchannel plate are received by a common anode.