JPS6264042A - Detector for charged particle or the like - Google Patents

Abstract

PURPOSE:To enable easy maintenance, long life of a scintillator and measurement in a wide dynamic range, by providing the scintillator near the last stage of a secondary electron multiplier and selecting two measurement modes, high sensitivity mode and normal measurement mode. CONSTITUTION:Mode 1 is selected by operating switches S1-S3 to disconnect a dynode Dyn at the last stage from a dividing resistor and connect it to an amplifier 38, in order to amplify ion current incident on Dy1 and feed it to a signal processing circuit. Voltage -Vs is impressed from a high voltage power soppy 34 on the metal film 24 of a scintillator 22 to repel electrons emitted from Dyn. In the case of mode 2, switches S1-S3 are placed on 'a'- contact side with voltage -Vd impressed on Dy1 from a high voltage power supply 32 and divided voltages impressed respectively on Dy1-Dyn. Voltage +Vs is impressed on the scintillator 22 by the power supply 34 to accelerate incident ion current, which has been amplified an Dy1-Dyn, and convert it into photons which are then fed to amplifier 38 via a photomultiplier 30.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a detector that is used in a measuring instrument such as a mass spectrometer and detects positive ions, negative ions, and the like.

(Prior Art) Secondary electron multipliers, channeltrons, and the like are widely used as detectors for detecting minute ion currents and electron currents in mass spectrometers and the like.

A Daly type secondary ion detector is also used, which includes a scintillator placed opposite an ion-electronic converter and a photomultiplier tube that receives light generated from the scintillator.

In a Dalley-type secondary ion detector, electrons generated from an ion-electron converter are drawn in by an electric field between the scintillator and the scintillator and collide with the scintillator, and the light generated from the scintillator is detected by a photomultiplier tube.

In addition, a secondary electron multiplier is inserted between the collector slit and the secondary electron multiplier, and the ions passing through the collector slit are accelerated by the inserted secondary electron multiplier, increasing the sensitivity. It has been reported that the detector has increased
MASS 5PECTRO5CO
PY) Magazine, Vol. 33, No. 2, pp. 145-147 (1
985)).

According to this detector, it is reported that detection sensitivity can be obtained about three times as much as that of a conventional detector using only a secondary electron multiplier.

However, in the case of these detectors, there is a limit in terms of detection sensitivity in trace analysis such as analysis of biological components and pollution analysis, for example, the limit is about pg/lμQ.

When the voltage applied to the dynode of a secondary electron multiplier is increased, the gain increases, but since the noise is amplified along with the signal, the S/N ratio (signal-to-noise ratio) is not improved, and therefore the sensitivity is not increased.

(Problems to be Solved by the Invention) Therefore, the present invention has developed a detector that can significantly improve the detection limit, for example, about 10 times or more, compared to conventional secondary electron multipliers. We developed a detector with the structure shown in Figure 3.

In FIG. 3, 14 is a secondary electron multiplier tube as a multiplier, and seven stages of dynodes Dy+ to Dy7 are provided. The number of dynode stages can be changed as appropriate. A voltage is applied between the dynodes Dy+ to Dy7 so as to amplify the secondary electrons generated at each stage. A channeltron can also be used as a multiplier instead of the secondary electron multiplier tube 14.

A scintillator 22 is provided on the exit side of the secondary electron multiplier tube 14. The scintillator 22 is, for example, a glass plate 20.
A metal film 24 is formed on the surface of the scintillator 22. A scintillator 22 having a metal film 24 is placed at the outlet of the secondary electron multiplier tube 14 so as to face inside the secondary electron multiplier tube 14, and is integrated with the secondary electron multiplier tube 14 via an insulator 26. is firmly fixed. The scintillator 22 can also be separate from the secondary electron multiplier 14.

A photomultiplier tube 30 is provided on the back side of the scintillator 22 via a light guide 28. The light guide 28 is made of synthetic resin, quartz glass, or the like, and has a structure that allows light to pass through efficiently.

Note that 16 is a deflector that controls the direction of charged particles incident on the first stage dynode Dy+, and 18 is a deflector that controls the direction of secondary electrons emitted from the final stage dynode DY7 and guides them to the scintillator 22. It is.

Various materials are used for the scintillator 22, but
- For example, phosphor Y3AQsO with RMA number P46
+ 2 ; C8 can be mentioned.

The metal film 24 is, for example, an aluminum vapor-deposited film.

In the detector shown in FIG. 3, when a charged particle or a neutral particle is incident on the first stage dynode Dyl of the secondary electron multiplier 14, secondary electrons are generated from the dynode Dy+. The secondary electrons are amplified by the second stage dynode DY2, and the amplified secondary electrons are further amplified by the third stage dynode D31.
The dynode DV4.3 is amplified by the dynode DV4. Dy
5. Dye.

The secondary electrons are sequentially amplified at Dy7 and generated at the final stage dynode Dy7, and enter the scintillator 22. The light generated by the scintillator 22 is guided to a photomultiplier tube 30 through a light guide 28 and detected.

It is believed that once the secondary electrons from the multiplier 14 are converted into light by the scintillator 22, noise is reduced and the S/N ratio is improved.

In the detector shown in FIG. 3, the metal film 2 on the surface of the scintillator 22 is
By applying a voltage to the terminal 4, the secondary electrons generated at the final stage dynode Dy7 can be accelerated and made to enter the scintillator 22.

By the way, component parts such as multipliers such as secondary electron multipliers and channeltrons, scintillators, and photomultipliers deteriorate with long-term use. In particular, scintillators are susceptible to deterioration.

In the detector shown in FIG. 3, the present invention uses a scintillator and a photomultiplier tube only for high-sensitivity measurements, and uses a scintillator and a photomultiplier tube when measurements can be made with normal sensitivity. The purpose of this is to protect the scintillator by not using it, and to simplify maintenance by limiting the parts where deterioration occurs to the multiplier.

(Means for Solving the Problems) In the detector of the present invention, a scintillator for converting electrons into light is provided near the final stage dynode or exit of a multiplier that converts incident particles into secondary electrons and amplifies them, A metal film is formed on the surface of this scintillator, and a photomultiplier tube is provided at a position that receives light from this scintillator, and a first measurement mode in which the output of the multiplier is extracted. , a second measurement mode in which a voltage is applied to the metal film so as to accelerate secondary electrons generated from the final stage dynode or outlet of the multiplier and guide them to the scintillator, and the output of the photomultiplier tube is extracted; It can be used by switching between the two.

(Embodiment 1) FIG. 1 shows an embodiment in which a secondary electron multiplier is used as a multiplier. Note that the same parts as in FIG. 3 are given the same symbols and their explanations will be omitted.

Dy+ to Dyn are dynodes of a secondary electron multiplier.

A resistor r is provided between each dynode from the first stage dynode Dy+ to the (n-1)th stage dynode Dyn-+. A high voltage power supply 32 for amplifying secondary electrons between the dynodes is connected to the first stage dynode Dy+. A switch Sl is connected to the (n-1) stage dynode Dyn-r, the a contact of the switch S1 is grounded through a series circuit of a resistor r and a resistor R, and the b contact of the switch S+ is connected to the resistor r. is grounded through.

A switch S2 is connected to the final stage dynode Dyn, and the a-contact of the switch S2 is connected to a node N of a series circuit of a resistor r and a resistor R at the a-contact of the switch S1.

A scintillator 22 is provided opposite the exit of the final stage dynode Dyn of the secondary electron multiplier. The scintillator 22 is provided, for example, on a glass plate 20, and a metal film 24 is formed on the scintillator 22. A high voltage power source 34 is connected to the metal film 24.
4, a voltage is applied to the scintillator 22 via the metal film 24.

A photomultiplier tube 30 is provided on the back side of the scintillator 22 via a light guide 28. A high voltage power supply 36 for signal amplification within the photomultiplier tube 30 is connected to the photomultiplier tube 30 .

The output terminal of the photomultiplier tube 30 is connected to the a contact of the switch S3, and the switch S3 is connected to the preamplifier 38,
The output of the preamplifier 38 is connected to a signal processing system. The b contact of the switch S2 and the b contact of the switch S3 are connected to each other.

Switch St, S2. For example, a relay is used as S3, and the relay is driven by an external signal to switch S1.82.
S3 can be switched.

40 is a wall of the vacuum device. A scintillator 22, a light guide 28, and a photomultiplier tube 30 are integrated, and the light guide 28 is supported by a wall surface 40 of the vacuum apparatus. Then, as shown in the figure, the dynodes Dy+ to Dy
A secondary electron multiplier with n=8− and a scintillator 22 are housed in a vacuum, a photomultiplier tube 30, high-voltage power supplies 32, 34, 36, and a switch 81.
, S2. S3. The preamplifier 38 is provided on the atmospheric side.

The operation of this embodiment will be explained for the case of detecting + ions. Switch S+, S2. By switching S3, the mode (Mode 1) takes out the output current from the secondary electron multiplier.
) and a mode (mode 2) in which the output current is extracted from the photomultiplier tube 30.

First, the case where it is used in mode 1 will be explained.

Switch S1. S2. S3 is switched to the b contact side. At this time, a voltage divided by the resistor r is applied to the dynodes Dy1-Dyn.

The final stage dynode Dyn is separated from the dividing resistor and connected to the preamplifier 38. A voltage of -Vs is applied to the scintillator 22 from the high voltage power supply 34, and the electrons flying out from the final stage dynode Dyn are driven back to the dynode Dyn.

In the case of this mode 1, dynodes Dy+ to Dyn-1,
An example of the voltage applied to the scintillator 22 will be shown below.

-Vd=-500V to -4kV -Vs=-1kV. Note that -Vd is set according to the amount of incident ions.

In the case of mode 1, ions incident on the first stage dynode Dy+ are amplified as an electron current between the dynodes Dyl''Dyn, are collected at the final stage dynode Dyn, and are sent to the signal processing system via the preamplifier 38.

Next, the case where it is used as mode 2 will be explained.

Switch St, 82. S3 is connected to the a contact side as shown in the figure. At this time, a voltage of -Vd is applied from the high voltage power supply 32 to the dynode Dy+, and each dynode D
A voltage divided by resistors r and R is applied to y+ to Dyn. A voltage of -Vd-R/((n-1)r+R) is applied to the final stage dynode Dyn. Here, the ratio of r and R is set so that the potential difference between the dynodes Dy+ and Dyn is 1 to 3 kV within the applied Vd range. A voltage of +Vs is applied to the scintillator 22 from a high voltage power supply 34.

Here, an example of the voltage applied to the dynodes Dy+ to D y n and the scintillator 22 is -Vd=-3k
V ~ -6kV + Vs = O ~ 6kV.

Ions incident on the first-stage dynode Dy+ are amplified as an electron current between the dynodes Dy+ and Dyn, then accelerated by the potential difference between the final-stage dynode Dyn and the scintillator 22, converted into light by the scintillator 22, and photoelectron multiplied. It is amplified in the tube 30 as an electron current. The output signal from the photomultiplier tube 30 is sent to a signal processing system via a preamplifier 38.

Mode 1 and mode 2 can be used depending on the amount of current to be measured. Normally, mode 1 is used, and mode 2 is used only when trying to detect extremely small currents.

In this embodiment, the axis of the secondary electron multiplier tube and the axis of the photomultiplier tube 30 are perpendicular to each other, but they may be changed so that their axes are parallel to each other.

(Embodiment 2) FIG. 2 shows an embodiment using a continuous dynode type channeltron as a multiplier.

Reference numeral 42 denotes a channeltron, and a voltage is applied between its inlet and outlet from the high voltage power supply 32. A collector 44 is provided opposite the outlet of the channeltron 42. A switch S4 is connected to the collector 44,
The a terminal of switch S4 is connected to high voltage power supply 46.

The scintillator 22 is also provided facing the collector 44. A metal film 24 is formed on the surface of the scintillator 22, and a voltage is applied to the scintillator 22 from a high voltage power source 34 through the metal film 24. The provision of a photomultiplier tube 30 is similar to the embodiment shown in FIG.

-12= The output terminal of the photomultiplier tube 30 is connected to the a contact point of the switch S5 connected to the preamplifier 38. The b contact of switch S4 and the b contact of switch S5 are connected to each other.

In this embodiment, the voltages applied from the high voltage power supplies 32, 34 when used in mode 1 or mode 2 are the same as in the case of FIG.

When measuring in mode 1, switch S4. Both S5 are connected to the b contact side. The electron current from the outlet of the channeltron 42 is collected in the collector 44 and sent to the preamplifier 3.
Guided by 8.

When measuring in mode 2, switch S4. Both S5 are connected to the a contact side as shown in the figure. By applying a voltage to the collector 44 from a high-voltage power supply 46, electrons from the outlet of the channeltron 42 are deflected by the collector 44 and enter the scintillator 22.

The light from the scintillator 22 is detected by a photomultiplier tube 30, and the output from the photomultiplier tube 30 is guided to a preamplifier 38.

(Effects of the Invention) According to the present invention, the following effects can be achieved.

(1) Normally, it is often used only in a multiplier (secondary electron multiplier tube or channeltron), and deterioration is likely to occur in the multiplier. Therefore, it becomes easy to determine which parts have deteriorated in terms of maintenance.

(2) The scintillator is subjected to electron bombardment in mode 2.
Only in the case of Therefore, the life of the scintillator can be extended.

(3) By performing measurements by switching between mode 1 and mode 2, measurements can be made over a wide dynamic range.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a first embodiment of the present invention, Fig. 2 is a schematic diagram showing a second embodiment of the invention, and Fig. 3 shows a detector developed by the present inventors. It is a schematic sectional view. 22...Scintillator, 24...Metal film, 30...Photomultiplier tube, Dy+~Dyn...Dynode, 5i-85.
·····switch.

Claims (1)

[Claims] (1) A scintillator that converts electrons into light is provided near the final stage dynode or exit of the multiplier that converts incident particles into secondary electrons and amplifies them, and a metal film is formed on the surface of this scintillator. , a photomultiplier tube is provided at a position that receives light from the scintillator, and a first measurement mode in which the output of the multiplier is extracted;
a second measurement mode in which a voltage is applied to the metal film so as to accelerate secondary electrons generated from the final stage dynode or outlet of the multiplier and guide them to the scintillator, and the output of the photomultiplier tube is extracted; A detector for charged particles, etc., characterized in that it can be used by switching between the two types.