JP2002365370A - X-ray detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray detector provided with an X-ray incident window improved in the transmittance of ultra-soft X-rays. SOLUTION: The X-ray incident window 7 mounted on a base 6 is fitted to the window part 8 of a housing 2, and the incident window 7 is fixed to the housing 2 with a base fixing cap 9 mounted on the housing 2. The incident window 8 comprises a mesh 12 adhered to the base 6 and an aluminum thin film 13 adhered thereon, and as the aluminum thin film 13, one having a thickness of 0.1 to 2.5 μm is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an X-ray detector such as a gas flow proportional counter.

[0002]

2. Description of the Related Art Heretofore, a gas flow proportional counter has been used as an X-ray detector for so-called soft X-rays having a wavelength of about 1 nm or more. As the X-ray incident window of the gas flow proportional counter, an organic thin film of polypropylene or the like having a thickness of about 1 μm and a conductive material coated with aluminum to a thickness of about 50 nm are used.

[0003]

However, carbon, which is a main constituent material of an organic thin film such as polypropylene, and oxygen contained depending on the type of the organic thin film, have a wavelength of about 20 to
High mass absorption coefficient for ultra soft X-ray of 40 nm. For this reason, in an X-ray incident window using an organic thin film, the transmittance of such an ultra-soft X-ray is extremely poor, and the detection efficiency of a gas flow proportional counter using such an X-ray incident window is very poor.

The present invention has been made in view of the above points, and an object of the present invention is to provide an X-ray detector having an X-ray entrance window with improved transmittance of ultra-soft X-rays. is there.

[0005]

The X-ray detector of the present invention that achieves this object has an X-ray incident window formed of an aluminum thin film.

[0006]

Embodiments of the present invention will be described below with reference to the drawings.

First, an electronic probe microanalyzer to which the X-ray detector of the present invention is mounted will be described with reference to FIG.

As shown in FIG. 1, in an electron probe microanalyzer, X-rays generated from a sample by irradiation with an electron beam e are separated by a spectral element. Then, among the X-rays of a specific wavelength separated by the spectroscopic element, the X-rays that have passed through the slit s are guided to the gas flow proportional counter of the present invention.

In the electron probe microanalyzer shown in FIG. 1, the sample, the spectroscopic element, and the slit s are located on a Rowland circle, and 2dSin θ = λ (d: spacing between spectroscopic elements, λ: X-ray to be split The spectral element and the slit s are moved so as to satisfy the condition of (wavelength). Further, the gas flow proportional counter is configured to move with the movement of the slit s.

Next, the gas flow proportional counter of the present invention in FIG. 1 will be described in detail with reference to FIG.

In FIG. 2, a housing 2 of a gas flow proportional counter 1 has a gas introduction duct 3 and a gas discharge duct 4.
have. Although not shown in FIG. 2, the gas introduction duct 3 is connected to a gas supply source via a pressure reducing valve.
For example, P-10 gas (90% argon gas and 1 methane)
0% mixed gas) is supplied into the housing 2 via the gas introduction duct 3. The pressure in the housing is maintained at about 1 atm. Also, housing 2
Is provided with a housing hole 5.

An X-ray incident window 7 attached to the pedestal 6 is fitted into a window 8 of the housing 2, and the incident window 7 is fixed by a pedestal fixing cap 9 attached to the housing 2. It is fixed to. The pedestal 6 has an X-ray passage hole 10.
An O-ring 11 is interposed between and the cap 9.

The entrance window 7 has a mesh 12 bonded to the pedestal 6 and an aluminum thin film 13 bonded thereon. The mesh 12 is made of a material that has a good X-ray transmittance and is not charged, for example, nickel. FIG. 3A is a view of the entrance window 7 as viewed from the slit s side, and FIG.
It is the figure seen from the side.

As described above, in the gas flow proportional counter of the present invention, the aluminum thin film 13 and the mesh 12 for reinforcing the mechanical strength of the aluminum thin film 13 form
A line entrance window 7 is configured. In this case, since the aluminum thin film 13 itself has conductivity, the conventional conductive coating is unnecessary. In addition, P-1 of the housing chamber 14
The aluminum thin film 13 is bonded to the pedestal 6 with an adhesive or the like so that the zero gas does not leak to the sample chamber side.

In the gas flow proportional counter of FIG. 2, reference numerals 15 and 16 denote electrical insulators.
Is fixed to the housing 2. A core wire 17 to which a positive potential is applied is stretched between the insulators. The core wire 17 stretched in the housing chamber 14 is connected to a pulse transmission line 18 in which a high voltage is applied to a terminal a having a high resistance r.

The terminal b of the high resistance r is connected to a pulse transmission line 19, and the pulse transmission line 19 is connected to a capacitor 20. The capacitor 20 is connected to a count processing circuit 22 via an amplifier 21.

Reference numeral 23 denotes a ground line, and the ground line 23 is connected to the housing 2.

The configuration of the gas flow proportional counter of FIG. 2 has been described above. In the electron probe microanalyzer of FIG. 1 equipped with such an X-ray detector, the X-ray generated from the sample by the irradiation of the electron beam e is used. When the above-mentioned ultra-soft X-rays among the rays are detected by the gas flow proportional counter 1, a spectroscopic element for dispersing the ultra-soft X-rays to be detected is selected.

Then, the super soft X separated by the spectroscopic element
Of the lines, the ultra-soft X-rays that have passed through the slit s enter the X-ray entrance window 7, and the ultra-soft X-rays that have passed through the X-ray entrance window 7 enter the housing chamber 14. The ultra soft X-rays that have entered the housing chamber 14 cause P-10
The gas is ionized, and electrons released at this time are captured by the core wire 17.

A charge pulse generated by the electrons captured by the core 17 passes through pulse transmission lines 18 and 19 and is further supplied to an amplifier 21 through a capacitor 20. The charge pulse output from the amplifier 21 is output to the counting circuit 2
The charge pulse is supplied to the counter 2 and the count processing circuit 22 counts the charge pulses. Based on the result of the X-ray counting, the concentrations of the elements constituting the sample are obtained.

In the gas flow proportional counter of FIG. 2, the aluminum thin film 13 and the housing 2 come into contact with each other, so that the housing 2 and the aluminum thin film 13 are electrically connected. For this reason, electric charges added to the aluminum thin film 13 and the surface of the housing 2 can be discharged through the ground line 23.

Hereinafter, the optimum thickness of the aluminum thin film 13 will be described. That is, the inventor of the present invention determines, based on the published mass absorption coefficient value, how much the thickness of the aluminum thin film 13 should be increased in order to improve the transmittance of the X-ray incident window as compared with the related art. Simulation calculated.

FIG. 4 shows the result of the calculation.
FIG. 4 shows NaL _2,3 rays (wavelength 40.72 nm) when a conventional X-ray incident window using an organic thin film is used and when the X-ray incident window 7 of the present invention shown in FIG. 2 is used. , MgL _2,3 line (wavelength 25.15 nm) and LiKα line (wavelength 23 to 24 nm) are shown. As shown in FIG. 4, this comparison shows that the thicknesses are 0.1 μm, 0.5 μm, 0.8 μm, 1 μm and 1.5 μm.
μm, 2 μm, 2.5 μm, 3 μm aluminum thin film 13
Made about.

FIG. 5 shows a conventional X-ray incident window used for comparison. The X-ray entrance window in FIG.
μm polypropylene organic thin film 24 and mesh 25
Is adhered to the pedestal 26, and as a conductive coating, 50 n
m aluminum coating film 27 is applied to the surface of the organic thin film. In FIG. 4, simulation calculation is performed on the assumption that the mesh 12 and the mesh 25 have the same X-ray transmittance.

From the comparative values shown in FIG.
The X-ray entrance window of an aluminum thin film of less than μm has a wavelength of about 20 to 40 nm compared to a conventional X-ray entrance window using an organic thin film.
It can be seen that the X-ray transmissivity for ultra-soft X-rays of Example 2 has been improved about twice or more.

From this, the present inventor believes that the thickness of the aluminum thin film of the present invention is preferably 0.1 μm or more and 2.5 μm or less in view of a balance between mechanical strength and transmittance of X-rays having a wavelength of about 20 to 40 nm. Was. As the aluminum thin film becomes thinner, pinholes tend to be formed on its surface, and it cannot be used as an X-ray entrance window of an X-ray detector that requires sealing.

Further, the present inventor has found that the wavelength is particularly about 20 to 25 n.
In view of the balance between the X-ray transmittance of m and the mechanical strength and gas tightness, it was concluded that 0.5 μm or more and 2 μm or less were more preferable. In fact, as shown in the comparative values of FIG. 4, in the X-ray incident window of the aluminum thin film having a thickness of 2 μm or less, the transmittance is improved by about 10 times or more even for X-rays having a wavelength of 20 to 25 nm. .

As described above, in the present invention,
An aluminum thin film having a thickness of 0.1 μm or more and 2.5 μm or less is used as an X-ray incident window of an X-ray detector. Aluminum has a smaller linear absorption coefficient for X-rays having a wavelength of about 20 to 40 nm than an organic thin film (about 0.1 to 0.4 times that of polypropylene).
Since aluminum itself is conductive, a conductive coating is not required on the X-ray entrance window composed of an aluminum thin film.

Therefore, the X-ray detector of the present invention has an X-ray wavelength of about 20 to 40 nm as compared with a conventional X-ray detector using an organic thin film having a conductive coating as an X-ray entrance window. , The transmittance of the X-ray entrance window for the X-ray is improved, and the detection efficiency of the X-ray detector is improved.

The present invention is not limited to the above example. For example, in the above example, the support mesh is provided. However, if the mechanical strength of the aluminum thin film itself is sufficient due to the size of the X-ray incident window, the thickness of the aluminum thin film, and the degree of the pressure difference between the inside and outside of the X-ray detector, the support mesh is provided. No mesh is required.

The present invention can also be applied to Geiger-Muller counter tubes.

[Brief description of the drawings]

FIG. 1 is a view for explaining an electronic probe microanalyzer.

FIG. 2 is a diagram showing an example of the X-ray detector of the present invention.

FIG. 3 is a view showing an X-ray incident window of FIG. 2;

FIG. 4 is shown for explaining the thickness of the aluminum thin film of the present invention.

FIG. 5 is a view showing a conventional X-ray incident window.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gas flow proportional counter, 2 ... Housing, 3 ... Gas introduction duct, 4 ... Gas exhaust duct, 5 ... Housing hole,
6 pedestal, 7 X-ray entrance window, 8 window part, 9 pedestal fixing cap, 10 X-ray passage hole, 11 O-ring, 12 mesh, 13 aluminum thin film, 14 housing chamber, 15, 16 ... electric insulator, 17 ... core wire, 18, 19
... Pulse transmission line, 20 ... Capacitor, 21 ... Amplifier, 2
2: counting circuit, 23: ground line, 24: organic thin film, 2
5 ... mesh, 26 ... pedestal, 27 ... aluminum coating film

Claims (3)

[Claims] 1. An X-ray detector, wherein an X-ray incident window is constituted by an aluminum thin film. 2. The thickness of the aluminum thin film is 0.1 μm.
The X-ray detector according to claim 1, wherein the X-ray detector has a diameter of not less than m and not more than 2.5 µm. 3. The X-ray detector according to claim 1, wherein the aluminum thin film is attached to the entrance window base via a support mesh.