JPH0410349A - X-ray detector - Google Patents

Abstract

PURPOSE:To enhance X-ray detection efficiency by arbitrarily setting a pressure of operating gas of an X-ray detector by means of a regulating mechanism. CONSTITUTION:Operating gas incorporating, in a predetermined ratio, respective gas components from a plurality of gas bombs 22 with pressure reducing valves by means of a gas mixer 21 is introduced in an X-ray detector 2 via a pipe 31, to be exhausted through another pipe 32 by means of a rotary pump 20. A pressure of the operating gas is controlled by a pressure regulator 18 comprising a vacuum gauge, a variable leak valve and a controller. The pressure regulator 18 PID(proportional plus integral plus derivative)-controls the opening/closing of the variable leak valve of the pressure regulator 18 in accordance with a difference between a set pressure value and a measured pressure, to regulate conductance with respect to the operating gas, to thus supply the operating gas into an X-ray detector 2 while keeping it at a predetermined gas pressure. Therefore, setting of the pressure of the operating gas enables measuring accuracy of the X-ray detector 2 to be enhanced.

Description

[Detailed Description of the Invention] Field of Industrial Application] The present invention relates to a gas-filled X-ray detector for counting X-rays in an ultra-high vacuum atmosphere, and particularly for counting soft X-rays from synchrotron radiation. The present invention relates to an ultra-high vacuum X-ray detector suitable for use in ultra-high vacuum applications.

[Conventional technology] Conventional gas-filled X-ray counters include, for example, G and F.

As the principle of operation is described in "X-ray Measurement Handbook" by Robert Knoll (translated by Moku Moku and Sakai), Nikkan Kogyo Shimbunsha (1982), pp. 123-190, X-rays are applied to the sample, and in principle ionization occurs. A radiation detector operating as a box detects the transmittance of X-rays, detects the total reflection xg from the sample, detects the diffraction and scattering of X-rays by the sample, or simply measures the intensity of the X-ray source. I started doing things like that.

However, the radiation detectors mentioned above are classified into ionization chambers, proportional counters, Geiger-Mueller counters, etc.X4! This is a device that performs XIIA counting by measuring the ionization caused by the X-rays. Since the ionization of the synchrotron radiation is measured, the leakage of the operating gas from the xi transmission window causes the soft xi of the synchrotron radiation to be measured.
The problem was that it was not possible to obtain the ultra-high vacuum required for counting.

In order to reduce the leakage of the operating gas mentioned above, JP-A-61-0
In Publication No. 84584, a radiation detector equipped with the above-mentioned xi transmission window (made of a polymeric organic film) is housed in a vacuum container having an X-ray transmission window made of a thin beryllium plate, and the degree of vacuum is controlled by an external ultra-high vacuum. and the operating gas pressure in the radiation detector above to reduce the pressure difference acting on each of the polymeric organic film and the beryllium thin plate, and further reduce the pressure difference above that acts on the polymeric organic film and the beryllium thin plate, and further reduce the pressure difference above that leaks through the polymeric organic film. The exhaust of the working gas component is independently controlled to prevent the working gas from leaking into the ultra-high vacuum atmosphere.

[Problem to be solved by the invention] In the above conventional technology, in high-precision X-ray counting,
Since it is not possible to adjust the pressure of the working gas to an optimum value according to the photon energy of the rays, there is a problem in that it is not possible to increase the X-ray counting efficiency and make the measurement highly accurate.

Furthermore, in the conventional technology described above, the pressure of the operating gas is 1 s pressure, so it is necessary to use a membrane material that can withstand a pressure difference of about 1 atm for the X-ray transparent window material, for example, a 7.6 μm thick Kapton membrane. etc. were used. However, in the measurement of X-ray photon energy in the low energy region of 5 keV or less, which is the objective of the present invention, the xi absorption due to the film thickness is excessive, so the S/N (signal-to-noise ratio) of the radiation detector output
There was a problem that good counting accuracy could not be obtained due to a decrease in the number of counts.

An object of the present invention is to make it possible to adjust the pressure of the working gas according to the X-ray energy to be measured, and to thin the film thickness of the xi transmission window material and reduce its transmission loss6. An object of the present invention is to make it possible to reduce transmission loss while ensuring the required X-ray detection efficiency for the incident X-ray detector by adjusting the operating gas pressure,
The object of the present invention is to improve the detection efficiency of a detector for X-rays emitted from a sample.

In summary, it is an object of the present invention to provide an X-ray detection device capable of measuring X-ray photon energy in a low energy region of 5 keV or less.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a pressure regulator that controls the pressure of the working gas introduced into the X-ray detector.

Further, the X-ray detector is housed in a vacuum container part whose degree of vacuum can be controlled, and the vacuum container part is installed in an ultra-high vacuum chamber in the ultra-high vacuum atmosphere, and the pressure inside the vacuum container part is adjusted to the above-mentioned level. The pressure is lower than that of the ultra-high vacuum chamber, and the pressure inside the X-ray detector is set lower than the pressure inside the vacuum container.

Furthermore, the working gas is generated by a gas mixing device that mixes different types of gases to an arbitrary composition.

Further, the X-ray detector, the vacuum container section, and the ultra-high vacuum atmosphere section can be interconnected by a valve.

[Function] By using the operating gas composition and pressure adjustment mechanism in the X-ray counter, the counting efficiency and X-ray transmittance of the X-ray counter are adjusted to optimal values according to the energy of the X-rays to be measured. I can do it.

Furthermore, when measuring a low energy region of 5 keV or less, the pressure of the operating gas is made lower than atmospheric pressure to reduce the pressure difference between the inside and outside of the X-ray transmission window of the counter section. This results in 1
A thin film with low mechanical strength but low absorption of low energy X-rays can be used as the xi transmission window.

In addition, by providing a valve that connects the counter section, vacuum container section, and measurement chamber with an ultra-high vacuum atmosphere, the X Damage to the line-transmitting window can be prevented.

[Examples] First, the theoretical basis supporting the effects of the present invention will be explained, and then specific examples thereof will be explained.

FIGS. 2(a) and 2(b) are diagrams explaining the principle of the X-ray measurement method.

FIG. 2(a) shows a case where the X-ray absorption of the sample 100 is measured. The incident X-ray intensity is measured by the detector 21, and the detector 22
The intensity of X-rays transmitted through the sample 100 is measured using the following method.

Figure 2(b) shows the X-ray reflectance or diffraction of sample 100,
When measuring scattering intensity etc., the detector 21 detects the incident X
The X-ray intensity reflected, diffracted, or scattered from the sample 100 is measured by the detector 22.

In order to improve the measurement accuracy in FIGS. 2(a) and 2(b) above, the first step is to increase the X-ray transmittance of the detector 21 to
This prevents attenuation of the X-ray dose irradiated to the detector 22.
It is necessary to increase the X-ray detection rate.

The above-mentioned X-ray transmittance and X-ray detection rate of the detector change depending on the pressure of the operating gas inside the detector, as explained below, so in order to meet the above requirements, the above-mentioned operating gas pressure must be set to the optimum value. Must be set.

However, in the conventional Xl&detector, the operating gas pressure is fixed at a substantially constant value.

There were naturally limits to measurement accuracy.

Various types of X and II detectors are used depending on the purpose of measurement.

FIGS. 3 and 4 are cross-sectional views of an example of the XMc detector.

In Figure 3, XI! is incident through the X@@ pass window 61 and exits to the outside through the same window 62. Each X-ray transmission window 61, 62 is made of an organic polymer film with a thickness of about 2.5 μm, and is bonded to the housing 25 with epoxy resin.
It is attached to the detector section 2 via the connector 6. Working gas is supplied and exhausted into the housing 25 through pipes 31 and 32, and airtightness is maintained so that there is no leakage of the working gas to the outside. A high voltage is applied between electrodes 7 and 8 to collect ions ionized along the path of the X-rays. Note that 24 is a compensation electrode that compensates for disturbances in the electric field at the end of the electrode, which improves detection accuracy.

Figure 4 shows a gas-filled X# that requires a high electric field such as a proportional counter tube or GM tube! FIG. 3 is a cross-sectional view of a cylindrical electrode type counter section for a counter. The cylindrical electrode 27 also serves as a working gas container, and a 2.5 μm thick Mylar film coated with aluminum is attached as XIIIA transmission windows 61 and 62 in the same manner as shown in FIG.

The high voltage is connected to a cylindrical electrode 27 with a diameter of 8 μm in the center.
A voltage is applied between the wire anodes 29 of approximately

In the above X-ray detector, if Io is the incident X4I intensity and T is the emitted X-ray intensity that passed through the X@detector, then X#! Transmission $1/I is theoretical.

1/Io=exp(-tt A-tt wW)
It is expressed as (1). Here, A is the length of the Xg optical path in the working gas (am), μm is the linear absorption coefficient of the XR transmission window (cm-''), and W is the thickness of the X-ray transmission window (cm).

On the other hand, the detection efficiency of the above X-ray detector is expressed as μ
Linear absorption coefficient (cm-1), where L is the length of the electrode in the working gas (cm), theoretically 1-exp (-μL)
It is proportional to (2).

Equation (1) shows that the xi transmittance is inversely proportional to the X-ray absorption coefficient μ of the working gas, and Equation (2) shows that the detection efficiency is proportional to the above μ.

Therefore, for example in FIGS. 2(a) and (b),
The operating gas pressure of detector 21 is as low as possible;
I want to make the operating gas pressure in step 2 as high as possible. However, in the detector 21, when the operating gas pressure is lowered, although the transmittance is improved, the detection sensitivity of incident X-rays is lowered, so the operating gas pressure must be determined based on the balance between the two.

Normally, the appropriate transmittance of the detector 21 is about 90%.

In the case of the detector 22, it seems better to increase the operating gas pressure, but in reality, as shown in FIG. There is a permeation loss between .61 and .61, which increases proportionally with the operating gas pressure.

Therefore, in reality, equation (2) needs to be modified to (transmittance between the electrode end and each transmission window)X equation (2).

FIG. 5 shows an example of measurement data of the relationship between the above-mentioned operating gas and detection efficiency in the detector 22.

The working gas is Ne, the electrode 7 is 70.5 mm, the electrode 8 is 80.5 mm, and the transmission window 61.61 is a 2.5 μm mylar film, and the distance between the end of each electrode and the corresponding transmission window is is 15 mm.

C in FIG. 5 is a case where the energy of incident X-rays is 2 keV, and it is clearly seen that the detection efficiency is maximized at an operating gas pressure of 10 kPa. At this maximum point, the increase in detection efficiency due to the increase in working gas pressure is exactly balanced against the decrease in transmittance.

D in the same figure is incident X! This is a case where the energy of a is 3 kV, and the maximum point of detection efficiency has moved to the side where the operating gas pressure is higher.

This shows that it is necessary to optimally set the operating gas pressure according to the X-ray energy to be measured. Furthermore, the gas pressure needs to be adjusted depending on the composition of the working gas.

Figure 1 is a block diagram of an embodiment of the ultra-high vacuum X-ray detector of the present invention in which the operating gas pressure of the )l detector can be arbitrarily set according to the above-mentioned concept, and Figure 2 (a) ,(
A state in which only one of the detectors 21, 22, etc. shown in b) is accommodated is shown.

Incident X-rays 1 enter the X-ray detector 2 from the left side of the center of the figure in the direction of the arrow and ionize the working gas along the path. The ion pairs generated by this ionization are the parallel plate type electrodes 7 and 8.
The particles move according to the electric field between them and are collected by the electrodes.

The X-ray detector 2 is housed in a vacuum container section 3, and the vacuum container section 3 is placed in an ultra-high vacuum atmosphere 4 of about 10-'Pa.

12 and 13 are a turbo molecular pump and a rotary pump for generating ultra-high vacuum atmosphere 4, respectively.

The vacuum container section 3 is a device described in Japanese Patent Laid-Open No. 61-084584, which is provided to buffer an excessive pressure difference between the working gas pressure in the X-ray detector 2 and the ultra-high vacuum atmosphere 4.

The vacuum container section 3 is evacuated to a predetermined pressure by a rotary pump 15 and a turbomolecular pump 14, and is equipped with an X-ray transmission window 5.

xi detector 2 (7) X1ii pass window 61.62 niha 2.

A Mylar film with a thickness of 5 μm is used and is bonded to the housing 25 with epoxy resin.

A working gas in which each gas component of a plurality of gas cylinders 22 with pressure reducing valves is mixed to a predetermined composition by a gas mixing device 21 is introduced into the X-ray detector 2 via a pipe 31 .
Exhausted by.

20 is a rotary pump for exhaust.

The pressure of the working gas is controlled by a vacuum regulator 18 that includes a vacuum gauge, a variable leak valve, a control device, and the like. The vacuum regulator 18 controls the opening and closing of the variable leak valve of the vacuum regulator according to the difference between the set pressure value and the measured pressure using PID (Proportional Integral Derivative) control to adjust the conductance with respect to the operating gas, and adjusts the operating gas to a predetermined gas. It is maintained at a constant pressure and supplied into the counter section 2.

The measurement accuracy of the X-ray detector can be improved by setting the operating gas pressure.

If the X-ray transmitting windows 61, 62, etc. of the X-ray detector 2 are damaged, the operating gas leaks into the vacuum container section 3 and the pressure increases, causing the X-ray transmitting window 5 of the vacuum container section 3 to be damaged and the ultra-high vacuum atmosphere 4 to occur. There is a possibility of an accident that will increase the pressure on the people all at once. Therefore, the degree of vacuum inside the vacuum container section 3 is constantly monitored by the vacuum gauge 16, and when the degree of vacuum exceeds a predetermined value, the cutoff valve 17
automatically closes to stop the supply of operating gas.

When atmospheric pressure is leaked to the X-ray detector 2, the vacuum container 5, the ultra-high vacuum atmosphere 4, etc. at the end of measurement, the X-ray transmission window may be damaged due to pressure shock. In order to prevent this, it is necessary to proceed with the leak while balancing the pressure in each part. For this reason, first, the shutoff valve 17 is closed to reduce the pressure inside the X-ray detection rg2. Then,
Open the valve 9.10 to remove the X-ray detector 2, vacuum container section 5,
Equalize the pressure in the ultra-high vacuum atmosphere 4, etc. At this time, in order to minimize the differential pressure applied to the X-ray transmission window, the valves 9 and 10 are opened by making the fluid resistance values (conductances) equal from the leak valve to both surfaces of each X-ray transmission window. Thereafter, the leak valve 11 is opened to introduce dry air.

FIG. 6 is an example of the results of X-ray measurement by the apparatus of the present invention shown in FIG. X-rays are applied to a polycrystalline silicon sample 100 while continuously changing the energy E, and the incident X-ray intensity and transmitted X-ray intensity are measured by the apparatus of the present invention to obtain an X-ray absorption spectrum. The horizontal axis is the wave number k calculated from the difference between the above E and the energy E0 of the X-ray absorption edge of silicon, and the vertical axis is the vibration χ extracted and normalized from the Xi absorption spectrum of the sample6. The clearer the peaks and troughs of the measured waveform in the figure, the better the S/N (signal-to-noise ratio) and the more accurate the analysis.

In the conventional device f (a type in which the operating gas pressure within the X-ray detector 2 is constant), the waveform of the portion corresponding to A in the same figure was similar to that of the portion B. From this, when the effect of the present invention is converted into S/N, an improvement of more than 10 times has been achieved.

[Effects of the Invention] According to the present invention, since the pressure of the operating gas of the 1g detector can be arbitrarily set by the adjustment mechanism, the X-ray transmittance of the X-ray detector and xg can be adjusted according to the incident X-ray energy. The X-ray detection efficiency can be maximized by optimally balancing detection efficiency.

Furthermore, the operating gas pressure can be set lower than conventional atmospheric pressure, so X4! It is possible to reduce the pressure difference acting on the transmission window, which allows the use of a thin Mylar film as the X-ray transmission window8, thereby increasing the transmittance of the X-ray transmission window6. By improving the transmission efficiency, detection efficiency, etc. of each xi detector, the S/N of xg measurement can be improved by more than 10 times, making it possible to greatly advance the limits of fine analysis of the structure and characteristics of various samples. can.

This makes it possible to improve the accuracy of measurement in the low energy region of 5 keV or less, which has been difficult in the past.

Furthermore, xg detector 2. By installing valves 9.10, etc. that connect the vacuum container section 3 and the ultra-high vacuum atmosphere 4, etc., each xi transmission window 5.61.62 is installed when leaking these to atmospheric pressure.
It is possible to alleviate the pressure shock that acts on the parts, etc. and prevent their damage.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of an embodiment of the transmission type ultra-high vacuum X-ray detector according to the present invention, Figs. 2(a) and (b) are explanatory diagrams of X-ray measurement at various locations, and Figs. FIG. 5 is a cross-sectional view of a transmission type ultra-high vacuum X-ray detector, FIG. 5 is a characteristic diagram of X-ray detection efficiency by the device of the present invention, and FIG. FIG. 3 is a characteristic diagram showing an example of measurement results (absorption edge fine structure). DESCRIPTION OF SYMBOLS 1... Incident X-ray, 2... Counter part, 3... Vacuum container part, 4... Ultra-high vacuum atmosphere, 5... X-ray transmission window. 6... X-ray transmission window, 7... High voltage electrode, 8... Collector electrode, 9.10... Shutoff valve, 11... Variable leak valve, 12... Rotary pump, 13...・Turbo molecular pump, 14...rotary pump, 15・
...turbo molecular pump, 16... vacuum gauge, 17...
Shutoff valve, 18...Vacuum regulator, 19...Variable leak valve, 20...Rotary pump, 21...
Gas mixing device, 22... Gas cylinder, 24... Protective electrode, 25... Housing, 26...○-ring,
100...sample.

Claims (1)

[Claims] 1. In an X-ray detection device that measures X-rays incident from an ultra-high vacuum atmosphere using an ionization chamber type X-ray detector, the pressure of the working gas introduced into the X-ray detector is controlled. An X-ray detection device characterized by comprising a pressure regulator for controlling the pressure. 2. In an X-ray detection device that measures X-rays incident from an ultra-high vacuum atmosphere using an ionization chamber type X-ray detector, a pressure regulator for controlling the pressure of the working gas introduced into the X-ray detector; , a vacuum container part that accommodates the X-ray detector and whose degree of vacuum can be controlled, and the vacuum container part is installed in the ultra-high vacuum atmosphere.
Line detection device. 3. The X-ray detection apparatus according to claim 2, further comprising an ultra-high vacuum chamber for accommodating the vacuum container section. 4. The X-ray detection apparatus according to any one of claims 1 to 3, further comprising a gas mixing device that mixes different gases into an arbitrary composition to produce the working gas. 5. The X-ray detection device according to any one of claims 2 to 4, further comprising a valve that allows the X-ray detector, the vacuum container section, and the ultra-high vacuum atmosphere section to be connected to each other. 6. In claims 2 to 5, the pressure within the vacuum container section is set lower than the pressure within the ultra-high vacuum atmosphere section, and further the pressure within the X-ray detector is set lower than the pressure within the vacuum container section. An X-ray detection device characterized by the following. 7. In claims 2 to 4, X in the X-ray detector
An X-ray detection device characterized in that the radiation-transmitting window material is a thin film material with a pressure holding strength lower than atmospheric pressure.