JP4638792B2 - Charged particle measuring apparatus and operation method of charged particle measuring apparatus - Google Patents

Description

  The present invention provides: The present invention relates to a charged particle measuring apparatus that measures charged particles such as low-level α rays, and more particularly, to a charged particle measuring apparatus suitable for quantitative analysis of charged particles such as low-level α rays in various materials.

  In conventional charged particle measuring devices, especially for α-ray measurement among charged particles, a semiconductor detector and measurement sample are placed in a reduced-pressure measurement chamber, and charged particles such as α-rays emitted from the measurement sample are emitted. There is a low-level α-ray measuring device that measures the amount with a semiconductor detector (for example, see Patent Document 1).

  This low-level α-ray measurement device has a tray (sample pan) on which a measurement sample is placed facing a semiconductor detector in a measurement chamber equipped with a sealed door, and is connected via an exhaust pipe leading to the measurement chamber. A radiation measurement circuit comprising a preamplifier, a linear amplifier, and a pulse height analyzer connected to a semiconductor detector, after repeating evacuation and supply / replacement of clean gas by a set number of times by the evacuation apparatus and gas replacement apparatus The charged particle emission amount is counted by a charged particle emission amount calculation device that quantitatively analyzes the charged particles based on the output signal of the radiation measurement circuit.

Japanese Patent Laying-Open No. 2003-50279 (pages 4, 5 to 1 to 5)

  An extremely low level charged particle measuring device is desired for a radioactivity analyzer for environmental samples, a radioactivity analyzer for emission, and a material quality control device for the semiconductor industry. In particular, in the semiconductor industry, semiconductor memory becomes increasingly finer, and in order to cope with soft errors in which the accumulated charge of the semiconductor memory is reversed by α particles, a very small amount of natural α radioactive element contained in various materials is released. Interfering α-ray nuclide identification and low-level quantitative analysis are important.

  In the above-described conventional semiconductor detector type low-level α-ray measuring device, the inside of the measurement chamber is replaced with a clean gas, and charged particles emitting nuclides and charged particles emitting nuclides contained in the air are removed. .

  However, if air enters the measurement chamber when the closed door is opened and closed and airborne dust containing charged particle emission nuclides and charged particle emission nuclides adheres to the measurement chamber, the removal is complicated and the background count value Is difficult to reduce.

  An object of the present invention is to provide a charged particle measuring apparatus that can suppress a background count value to a low level, efficiently measure extremely low level charged particles, and maintain high sensitivity for a long period of time.

In order to solve the above problems, the present invention provides a sample pan on which a measurement sample is placed, a semiconductor detector facing the measurement sample, a measurement chamber having a sealed door and containing the sample tray and the semiconductor detector, and a measurement chamber Inside the measurement chamber with the upper and lower electrodes installed outside the sample pan and semiconductor detector, a dust collection power source that applies a dust collection voltage between the upper and lower electrodes, and clean gas that does not contain radioactive materials The system consists of a clean gas supply and replacement system that replaces air, a vacuum exhaust system that exhausts and decompresses air and clean gas in the measurement chamber, and a radiation measurement circuit connected to the semiconductor detector. The air in the measurement chamber is replaced with clean gas that does not contain gas, the air and clean gas in the measurement chamber are exhausted and decompressed, and a dust collection voltage is applied to the upper and lower electrodes. To electrostatic precipitator floating dust containing charged particle emitting nuclides and charged particle emitting nuclides contained in brought into the measurement chamber air Suggest charged particle measuring device.

The charged particle measuring apparatus is installed between a sample pan and a lower electrode during sample measurement, shields charged particle emission nuclides collected from the lower electrode and suspended dust containing charged particle emission nuclides, and semiconductors during background measurement. There may be provided a shielding plate that is installed between the detector and the sample pan and shields the measurement sample and the charged particle emission nuclide collected by the lower electrode and the floating dust containing the charged particle emission nuclide.

  According to the present invention, it is possible to obtain a charged particle measuring apparatus that can suppress the background count value to a low level, efficiently measure extremely low level charged particles, and maintain high sensitivity for a long period of time.

  Next, with reference to FIGS. 1-3, the Example of the charged particle measuring device by this invention is described. The charged particles in this embodiment are α rays.

  FIG. 1 is a diagram illustrating a system configuration of a charged particle measuring apparatus according to a first embodiment of the present invention.

  The charged particle measuring apparatus according to the first embodiment includes a measurement chamber 1, a semiconductor detector 2, a tray (sample tray) 5 on which a measurement sample 3 is placed, an upper electrode 4a, a lower electrode 4b, and a tray (sample tray) 5. , A vacuum door 8, a vacuum pump 8 b, a vacuum valve 8 c, a measurement chamber gas supply pipe port 9 a, an empty gas supply pipe port 9 b, and a gas cylinder 9 c. , Measurement chamber inlet valve 9d, vacant chamber inlet valve 9e, clean gas supply / substitution system 9 comprising pressure regulator 9f, signal line 10, dust collecting power source 11, vacant chamber (glove box) 12, vacant door 13, a globe 14, a replacement gas discharge port 15, and a shielding tray (shielding plate) 16.

  Although not shown here, the signal line 10 outputs the detection signal of the semiconductor detector 2 to the preamplifier of the radiation measurement circuit including a preamplifier, a linear amplifier, and a pulse height analyzer.

  An empty chamber 12 is provided adjacent to the measurement chamber 1 so that outside air does not flow into the measurement chamber 1 even when the closed door 7 is opened and closed.

  The vacant chamber 12 is a glove box, and opens and closes the vacant door 13 into which the measurement sample 3 is placed, the vacant gas supply pipe port 9b for filling the clean gas, the replacement gas discharge port 15, and the hermetic door 7. In addition, a glove 14 for installing the measurement sample 3 in the measurement chamber 1 is provided.

  The vacant chamber 12 is made of a transparent or translucent material such as acrylic so that the handling status of the sealed door 7 and the measurement sample 3 can be visually confirmed.

  The clean gas supply replacement system 9 (9a, 9b, 9c, 9d, 9e, 9f) is a system that replaces the inside of the measurement chamber 1 and the empty chamber 12 with a clean gas, that is, a gas not containing radioactive gas. Branched into two via the pressure regulator 9f, connected to the measurement chamber gas supply piping port 9a via the measurement chamber inlet valve 9d, and connected to the vacant gas supply piping port 9b via the vacancy inlet valve 9e. It is. Here, nitrogen gas is employed as the replacement gas. Other gases may be used as long as they are clean gases that do not contain radioactive gases.

  The evacuation system 8 (8a, 8b, 8c) exhausts the gas in the measurement chamber 1 so that the gas between the semiconductor detector 2 and the measurement sample 3 in the measurement chamber 1 does not attenuate alpha rays. This is a system for measuring α rays under reduced pressure. The vacuum pump 8b is connected to the exhaust pipe port 8a of the measurement chamber 1 through a vacuum valve 8c.

  In the air, radon, which is a decay product of uranium, and thoron, which is a decay product of thorium, are contained, and α rays emitted from radon and thoron become large interference radiation.

  When the replacement gas discharge port 15 is opened and the replacement gas is allowed to flow into the empty chamber 12 from the clean gas supply replacement system 9 (9c, 9f, 9e, 9b), the air in the empty chamber 12 can be excluded.

  When the replacement gas is introduced into the measurement chamber 1 from the clean gas supply replacement system 9 (9c, 9f, 9d, 9a) and exhausted by the vacuum exhaust system 8 (8a, 8c, 8b), the measurement chamber 1 is cleaned with clean gas. Can be substituted. If evacuation is further performed by the evacuation system 8 (8a, 8c, 8b), radon and thoron slightly remaining in the measurement chamber 1 can be discharged.

  When the closed door 7 is opened and closed in a state where the vacant chamber 12 and the measurement chamber 1 are filled with clean gas, and the measurement sample 3 is installed in the measurement chamber 1, the entry of charged particle emitting nuclides such as radon and thoron into the measurement chamber 1 Can be suppressed. Since the air remaining slightly in the measurement chamber 1 is replaced with clean gas and exhausted, the charged particle emission nuclides adhere to the measurement chamber 1 and the background count value is lowered to enable measurement. You can lower the value and maintain a measurable lower level.

  FIG. 2 is a perspective view showing the positional relationship between the tray (sample pan) 5 on which the semiconductor detector 2 and the measurement sample 3 are placed in the measurement chamber 1, and the upper electrode 4a and the lower electrode 4b.

  A signal line 10 from the semiconductor detector 2 arranged to face the measurement sample 3 is drawn from the upper part of the measurement chamber 1.

  The distance between the measurement sample 3 and the semiconductor detector 2 can be adjusted by changing the height at which the tray (sample dish) 5 on which the measurement sample 3 is placed is inserted into the slit 6.

  At the time of sample measurement, a shielding tray (shielding plate) 16 is inserted at the lowest stage of the slit 6 to shield α rays emitted from dust collected on the lower electrode 4b.

  At the time of background measurement, a shielding tray (shielding plate) 16 is inserted at a position closest to the semiconductor detector 2 at the top of the slit 6 to shield charged particles emitted from the measurement sample 3.

  An upper electrode 4a is installed at the upper part of the semiconductor detector 2 in the measurement chamber 1, a lower electrode 4b is installed at the lower part of the measurement chamber 1, and a space between the upper electrode 4a and the lower electrode 4b from the dust collection power source 11 in FIG. To be applied.

  It is known that the decay products of radon and thoron contained in the air are positively charged during the decay process, and the floating dust to which the decay products are attached is also positively charged.

  The upper electrode 4a and the lower electrode 4b provided in the measurement chamber 1 can collect radon and TRON decay products and floating dust in one of them when the direction of the applied voltage of the dust collection power supply 11 is selected.

  The tray (sample pan) 5 installed in the slit 6 holds the measurement sample 3 in a predetermined position in the measurement chamber 1 and also collects the charge collected by the lower electrode 4 b negatively charged at the lower part of the measurement chamber 1. It also has a role of shielding α rays emitted from particle emitting nuclides.

  As described above, when the upper electrode 4a and the lower electrode 4b are arranged inside the measurement chamber 1 and a voltage is applied, radon and tron decay products in the air that are slightly mixed in and floating dust to which the decay products are attached are collected. it can. If the α rays emitted from the collected charged particle emission nuclides are shielded by the tray (sample pan) 5, the background count value can be reduced, and the measurable lower limit level can be lowered.

FIG. 3 is a flowchart illustrating a procedure for measuring low-level α rays by the charged particle measuring apparatus according to the first embodiment.
≪Sample measurement≫
Step 100: Place the measurement sample 3 on the tray (sample pan) 5 placed in the vacant chamber 12, and close the vacant door 13.

  Step 101: In order to exclude air in the vacant chamber 12, the replacement gas discharge port 15 is opened, and a clean gas is allowed to flow into the vacant chamber 12 from the clean gas supply / substitution system 9 (9c, 9f, 9e, 9b). The air in the chamber 12 is replaced with clean gas.

  Step 102: A voltage is applied between the upper electrode 4a and the lower electrode 4b in the measurement chamber 1 in order to collect the interference nuclides slightly present in the empty chamber 12 when the sealed door 7 is opened.

  Step 103: Clean gas is filled into the measurement chamber 1 from the clean gas supply / substitution system 9 (9c, 9f, 9d, 9a).

  Step 104: Open the sealing door 7, insert the tray (sample pan) 5 on which the measurement sample 3 is placed into the slit 6 in the measurement chamber 1, insert the shielding tray (shielding plate) 16 at the bottom of the slit 6, Close the sealing door 7.

  Step 105: The supply of the clean gas circulated in the empty room 12 is stopped.

  Step 106: The inside of the measurement chamber 1 is replaced with clean gas in order to eliminate air that has entered slightly when the sealed door 7 is opened.

  Step 107: The inside of the measurement chamber 1 is depressurized by the evacuation system 8 (8a, 8c, 8b) in order to suppress the attenuation of α rays from the measurement sample 3 due to gas.

  Step 108: The voltage applied between the upper electrode 4a and the lower electrode 4b in the measurement chamber 1 is cut off.

Step 109: The signal output from the semiconductor detector 2 is taken into the preamplifier of the radiation measurement circuit by the signal line 10 and the α ray of the measurement sample 3 is measured.
≪Background measurement≫
Step 120: After the operation in Step 109, the shielding tray (shielding plate) 16 is placed in the vacant chamber 12, and the vacant door 13 is closed.

  Step 121: In order to exclude air in the vacant chamber 12, the replacement gas discharge port 15 is opened, and a clean gas is allowed to flow into the vacant chamber 12 from the clean gas supply / substitution system 9 (9c, 9f, 9e, 9b). The air in the chamber 12 is replaced with clean gas.

  Step 122: A voltage is applied between the upper electrode 4a and the lower electrode 4b in the measurement chamber 1 in order to collect the interfering nuclides slightly present in the empty chamber 12 when the sealed door 7 is opened.

  Step 123: Fill the measurement chamber 1 with clean gas from the clean gas supply / substitution system 9 (9c, 9f, 9d, 9a).

  Step 124: Open the sealed door 7, insert the shielding tray (shielding plate) 16 into the uppermost stage of the slit 6 in the measurement chamber 1, and close the sealed door 7.

  Step 125: The supply of the clean gas circulated in the vacant chamber 12 is stopped.

  Step 126: The inside of the measurement chamber 1 is replaced with clean gas in order to eliminate the air that has slightly entered the measurement chamber 1 when the sealed door 7 is opened.

  Step 127: The inside of the measurement chamber 1 is depressurized by the evacuation system 8 (8a, 8c, 8b) in order to suppress the attenuation of α rays by the gas.

  Step 128: The voltage applied between the upper electrode 4a and the lower electrode 4b in the measurement chamber 1 is cut off.

  Step 129: The signal output from the semiconductor detector 2 is taken into the preamplifier of the radiation measuring circuit by the signal line 10 and the α-ray as a background is measured.

  In Example 1, the present invention has been described using α rays as a measurement target. If the material of the shielding tray (shielding plate) 16 used for background measurement is changed, charged particles such as beta rays can be similarly measured.

  According to Example 1, charged particles that can reduce the influence of interfering nuclides contained in the air, suppress the background count value low, efficiently measure extremely low level charged particles, and maintain high sensitivity for a long period of time. A measuring device is obtained.

  In the first embodiment, a glove box type vacant chamber 12 is provided in consideration of work convenience and prevention of contamination of the measurement sample before measurement.

  The essence of the present invention is that an upper electrode 4a and a lower electrode 4b for collecting floating dust are installed in the measurement chamber 1, and charged particles emitted from the dust collected by the electrode 4 are measured in the background. The reason is that a shielding tray (shielding plate) 16 is sometimes shielded.

  Therefore, the vacant chamber 12 of Example 1 and its clean gas supply / substitution system 9 (9e, 9b) are not necessary for the configuration of the basic invention.

  The second embodiment is different from the first embodiment in the vacant chamber 12, the vacant door 13, the globe 14, the replacement gas discharge port 15, and the clean gas supply replacement system 9 (9e, 9b) to the vacant chamber 12. It is the structure which excluded.

Next, a procedure for measuring low-level α rays by the charged particle measuring apparatus according to the second embodiment will be described. The step number of each procedure is made to correspond to the step number of FIG.
≪Sample measurement≫
Step 100a: The measurement sample 3 is placed on the tray (sample pan) 5 placed in the measurement chamber 1, a shielding tray (shielding plate) 16 is inserted at the bottom of the slit 6, and the sealing door 7 is closed.

  Step 101a: In order to exclude air in the measurement chamber 1, the clean gas supply / substitution system 9 (9c, 9f, 9d, 9a) is used while the measurement chamber 1 is depressurized by the vacuum exhaust system 8 (8a, 8c, 8b). ) To flow clean gas into the measurement chamber 1 and replace the air in the measurement chamber 1 with clean gas.

  Step 102a: A voltage is applied between the upper electrode 4a and the lower electrode 4b in the measurement chamber 1 in order to collect the interference nuclides slightly present in the measurement chamber 1.

  Step 105a: The supply of the clean gas flowing through the measurement chamber 1 is stopped.

  Step 107: The inside of the measurement chamber 1 is depressurized by the evacuation system 8 (8a, 8c, 8b) in order to suppress the attenuation of α rays from the measurement sample 3 due to gas.

  Step 108: The voltage applied between the upper electrode 4a and the lower electrode 4b in the measurement chamber 1 is cut off.

Step 109: The signal output from the semiconductor detector 2 is taken into the preamplifier of the radiation measurement circuit by the signal line 10 and the α ray of the measurement sample 3 is measured.
≪Background measurement≫
Step 120a: After the operation of Step 109, the sealed door 7 is opened, the shielding tray (shielding plate) 16 is inserted into the uppermost stage of the slit 6 in the measurement chamber 1, and the sealed door 7 is closed.

  Step 121a: In order to eliminate the air in the measurement chamber 1, the clean gas supply and replacement system 9 (9c, 9f, 9d, 9a is reduced while the pressure in the measurement chamber 1 is reduced by the vacuum exhaust system 8 (8a, 8c, 8b). ) To flow clean gas into the measurement chamber 1 and replace the air in the measurement chamber 1 with clean gas.

  Step 122a: A voltage is applied between the upper electrode 4a and the lower electrode 4b in the measurement chamber 1 in order to collect the interfering nuclides slightly present in the measurement chamber 1 when the closed door 7 is opened.

  Step 125a: The supply of the clean gas flowing in the measurement chamber 1 is stopped.

  Step 127: The inside of the measurement chamber 1 is depressurized by the evacuation system 8 (8a, 8c, 8b) in order to suppress the attenuation of α rays by the gas.

  Step 128: The voltage applied between the upper electrode 4a and the lower electrode 4b in the measurement chamber 1 is cut off.

  Step 129: The signal output from the semiconductor detector 2 is taken into the preamplifier of the radiation measuring circuit by the signal line 10 and the α-ray as a background is measured.

  Also in Example 2, the background count value can be suppressed to a low level, extremely low level charged particles can be measured efficiently, and high sensitivity can be maintained for a long time.

It is a figure which shows the system | strain structure of Example 1 of the charged particle measuring apparatus by this invention. 3 is a perspective view showing a positional relationship between a tray (sample pan) 5 on which a semiconductor detector 2 and a measurement sample 3 are placed in a measurement chamber 1, and an upper electrode 4a and a lower electrode 4b. FIG. 3 is a flowchart illustrating a procedure for measuring low-level α rays by the charged particle measuring apparatus according to the first embodiment.

Explanation of symbols

1 Measurement Chamber 2 Semiconductor Detector 3 Measurement Sample 4a Upper Electrode 4b Lower Electrode 5 Tray (Sample Dish)
6 Slit 7 Sealed door 8 Vacuum exhaust system 8a Exhaust piping port 8b Vacuum pump 8c Vacuum valve 9 Clean gas supply replacement system 9a Measurement chamber gas supply piping port 9b Empty gas supply piping port 9c Gas cylinder 9d Measurement chamber inlet valve 9e Empty chamber inlet Valve 9f Pressure regulator 10 Signal line 11 Dust collection power source 12 Empty room (glove box)
13 Vacant door 14 Globe 15 Replacement gas discharge port 16 Shielding tray (shielding plate)

Claims (5)

A sample pan on which a measurement sample is placed;
A semiconductor detector facing the measurement sample;
A measurement chamber having a sealed door and containing the sample pan and the semiconductor detector;
An upper electrode and a lower electrode installed outside the sample dish and the semiconductor detector in the measurement chamber;
A dust collection power source for applying a dust collection voltage between the upper electrode and the lower electrode;
A clean gas supply and replacement system that replaces the air in the measurement chamber with a clean gas that does not contain radioactive material;
An evacuation system for evacuating and depressurizing air and clean gas in the measurement chamber;
Consisting of a radiation measurement circuit connected to the semiconductor detector,
Prior to measurement, the air in the measurement chamber is replaced with a clean gas that does not contain radioactive substances, the air and clean gas in the measurement chamber are exhausted and decompressed, and a dust collection voltage is applied to the upper and lower electrodes. The charged particle emission nuclides contained in the air brought into the measurement chamber and the floating dust containing the charged particle emission nuclides are electrostatically collected ,
The charged particle emission nuclide installed between the sample dish and the lower electrode during sample measurement and the suspended dust containing the charged particle emission nuclide collected by the lower electrode are shielded. A charged particle, comprising: a shielding plate that is installed between the sample pan and shields the measurement sample and the charged particle emission nuclide collected in the lower electrode and floating dust containing the charged particle emission nuclide. measuring device. A sample pan on which a measurement sample is placed;
A semiconductor detector facing the measurement sample;
A measurement chamber having a sealed door and containing the sample pan and the semiconductor detector;
A glove box having an internal space covering at least the sealed door;
An upper electrode and a lower electrode installed outside the sample dish and the semiconductor detector in the measurement chamber;
A dust collection power source for applying a dust collection voltage between the upper electrode and the lower electrode;
A clean gas supply replacement system that replaces the air in the glove box and the measurement chamber with a clean gas containing no radioactive substance;
An evacuation system for evacuating and depressurizing air and clean gas in the measurement chamber;
Consisting of a radiation measurement circuit connected to the semiconductor detector,
Prior to measurement, the air in the measurement chamber is replaced with a clean gas that does not contain radioactive substances, the air and clean gas in the measurement chamber are exhausted and decompressed, and a dust collection voltage is applied to the upper and lower electrodes. A charged particle measuring apparatus characterized in that the charged particle emission nuclides contained in the air brought into the measurement chamber and the floating dust containing the charged particle emission nuclides are electrostatically collected. The charged particle measuring apparatus according to claim 2 ,
The charged particle emission nuclide installed between the sample dish and the lower electrode during sample measurement and the suspended dust containing the charged particle emission nuclide collected by the lower electrode are shielded. A charged particle, comprising: a shielding plate that is installed between the sample pan and shields the measurement sample and the charged particle emission nuclide collected in the lower electrode and floating dust containing the charged particle emission nuclide. measuring device. An operation method of the charged particle measuring apparatus according to claim 1,
Place the measurement sample on the sample plate and insert a shielding plate between the sample plate and the lower electrode.
While depressurizing the inside of the measurement chamber with the vacuum exhaust system, the clean gas is flowed into the measurement chamber from the clean gas supply replacement system, and the air in the measurement chamber is replaced with clean gas.
Apply a voltage between the upper and lower electrodes in the measurement chamber,
Stop supplying clean gas and depressurize the measurement chamber using the vacuum exhaust system.
Cut off the voltage applied between the upper and lower electrodes in the measurement chamber,
The signal from the semiconductor detector is taken into the radiation measurement circuit and the radiation of the measurement sample is measured.
Insert the shielding plate between the semiconductor detector and the sample pan ,
While depressurizing the inside of the measurement chamber with the vacuum exhaust system, the clean gas is flowed into the measurement chamber from the clean gas supply replacement system, and the air in the measurement chamber is replaced with clean gas.
Apply a voltage between the upper and lower electrodes in the measurement chamber,
Stop supplying clean gas and depressurize the measurement chamber using the vacuum exhaust system.
Cut off the voltage applied between the upper and lower electrodes in the measurement chamber,
A method for operating a charged particle measuring apparatus, wherein a signal from a semiconductor detector is taken into a radiation measuring circuit and radiation serving as a background is measured. An operation method of the charged particle measuring apparatus according to claim 2 ,
Place the measurement sample on the sample pan placed in the glove box ,
Clean gas is supplied into the glove box from the clean gas supply and replacement system to replace the air in the glove box with clean gas.
Apply a voltage between the upper and lower electrodes in the measurement chamber,
Fill the measurement chamber with clean gas from the clean gas supply replacement system,
Insert the sample pan with the measurement sample into the measurement chamber, insert a shielding plate between the sample pan and the lower electrode,
Stop supplying clean gas and depressurize the measurement chamber using the vacuum exhaust system.
Cut off the voltage applied between the upper and lower electrodes in the measurement chamber,
The signal from the semiconductor detector is taken into the radiation measurement circuit and the radiation of the measurement sample is measured.
Pull out the shielding plate into the glove box ,
Clean gas is supplied into the glove box from the clean gas supply and replacement system to replace the air in the glove box with clean gas.
Apply a voltage between the upper and lower electrodes in the measurement chamber,
Fill the measurement chamber with clean gas from the clean gas supply replacement system,
Insert the shielding plate between the semiconductor detector and the sample pan ,
Stop the supply of clean gas circulated in the glove box ,
Replace the measurement chamber with clean gas and depressurize the measurement chamber with the vacuum exhaust system.
Cut off the voltage applied between the upper and lower electrodes in the measurement chamber,
A method for operating a charged particle measuring apparatus, wherein a signal from a semiconductor detector is taken into a radiation measuring circuit and radiation serving as a background is measured.

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