JP2003057355A - Semiconductor radiation detector for alpha-ray dust monitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector capable of realizing an α-ray dust monitor having excellent accuracy in discrimination of a nuclide of the α-ray dust and in calculation of its concentration, and having excellent stability. SOLUTION: A radiation sensitive domain 111a of a semiconductor radiation detection element 111 has a radiation entering part 1111, an airtight sealing part 1112 and a check part 1113, and a casing 15a and the airtightly sealed part 1112 are sealed airtightly by an O-ring 17 mounted on a ring groove 153 of the casing 15a. An optical pulse for function check from an LED 13 is allowed to enter the check part 1113 vertically by an optical fiber 14 and an optical path changing member 18 comprising a transparent resin and having the thickness of about 2 mm. An α-ray entrance window 151 of the casing 15a is covered by a PET film 16a having the thickness less than 1 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor radiation detector used in an α-ray dust monitor for measuring and monitoring α-rays emitted from dust contained in the environment.

[0002]

2. Description of the Related Art An α-ray dust monitor is a radiation measuring device for measuring and monitoring α-rays emitted from a unit volume of air in the environment to be measured. Then, the dust contained in the air is collected on the filter paper, and the energy of each α ray radiated from the dust is measured by the radiation detector, and it falls within the predetermined energy width within the predetermined time. A radiation measurement device that creates an energy spectrum using the number of detections as a histogram and calculates the nuclides of dust that emits α rays (hereinafter referred to as α ray dust) contained in the collected dust and its concentration from the energy spectrum. Is.

A radiation detector used in an α-ray dust monitor is a semiconductor radiation detector equipped with a semiconductor radiation detection element which can be compact and lightweight and can obtain necessary information with desired accuracy. Detectors are commonly used. FIG. 2 is a radiation detector for an α-ray dust monitor according to the related art using a semiconductor type radiation detection element (simply referred to as a radiation detection element in FIG. 2, hereinafter referred to as a radiation detection element) 11 (simply a radiation detector in FIG. 2). In the following description, a configuration of Example 1 will be abbreviated as a radiation detector),
(A) is a conceptual diagram showing the overall configuration, and (b) is a plan view of the radiation detecting element 11.

The radiation detector 1 comprises a PET film 16 covering a radiation detecting element 11, a pulse amplifier 12, an LED 13, an optical fiber 14, a housing 15 for housing them, and an α-ray entrance window 151 of the housing 15.
It consists of and. The radiation detection element 11 is formed by forming a pn junction or a heterojunction on one surface of a high resistivity single crystal silicon wafer, and applying a reverse bias to this junction to form a depletion layer on both sides of the junction. . In the case where the region where the depletion layer is formed is the radiation sensitive region 111 and is a pn junction type, the region where the pn junction is formed is this region, and in the case of a hetero junction type of amorphous silicon. The region of the electrode formed on the amorphous silicon is almost this region.

When α rays move through a substance (in the case of the radiation detecting element 11, silicon), a high-density electron-hole pair is generated in the movement path due to the interaction between the substance and α rays. When this electron-hole pair generation region is a high electric field region such as a depletion layer, the electron-hole pair is separated into electrons and holes by the high electric field, and holes are extracted to the negative electrode side. Then, the electrons are extracted to the positive electrode side. Since the extracted holes or electrons are charged particles, the number of extracted holes or electrons can be calculated by measuring the amount of charge extracted from the electrode, and the energy of α rays lost in the substance can be calculated. I understand. Since the thickness of the depletion layer of the radiation detecting element 11 is designed to be thicker than the range of the α ray to be measured, the amount of charge extracted from the electrode corresponds to the energy of the α ray incident on the depletion layer.

The charges extracted from the electrodes of the radiation detecting element 11 are input to the pulse amplifier 12 and converted into voltage pulses having a peak value proportional to the amount of charges, and the radiation detector 1
Is output to the main body of the α-ray dust monitor, its energy is measured, and an energy spectrum is created based on the measurement result. The radionuclide contained in the α-ray dust and its concentration are calculated from the energy spectrum.

The LED 13 and the optical fiber 14 are members for checking whether or not the radiation detector 1 is operating normally. The LED 13 emits light in response to a test pulse input from the outside, and the light pulse is guided to the optical fiber 14 and applied to the reflecting surface 152 provided on the outer periphery of the tip of the housing 15 in the direction indicated by the arrow. The reflected light is guided to the radiation-sensitive region 111 of the radiation detection element 11, and electron-hole pairs are generated in the irradiation portion of the light pulse as in the case where α rays are incident, and the depletion layer of the radiation-sensitive region 111 is generated. The charge corresponding to the electron-hole pair generated inside is output. If a predetermined output is obtained by the irradiation of this light pulse, it is judged that the radiation detector 1 is functioning normally.

In order to reliably guide the light pulse of the required light quantity to the radiation sensitive area 111, it is necessary that the light incident on the radiation sensitive area 111 is incident on the surface of the radiation detecting element 11 with a certain inclination. (Because the required amount of light pulse does not reach the radiation sensitive area 111 if it is close to parallel), the housing 15
It is necessary to separate the inner surface of the radiation detector and the surface of the radiation detection element 11 on the radiation sensitive region 111 side by about 10 mm.

In the PET film 16, the members such as the radiation detecting element 11 housed in the housing 15 directly contact the air to be measured and the surface is contaminated, and the characteristics of the radiation detector 1 are unstable. For the purpose of isolating the inside of the housing 15 from the air to be measured, the α-ray entrance window 15 of the housing 15
Installed over 1. Since the air to be measured is passed through the filter paper (not shown) arranged facing the α-ray incident window 151 of the housing 15 from the α-ray incident window 151 side, in order to secure a predetermined air flow rate, It is necessary that the distance between the front surface of the radiation detector 1 (the left side surface of the housing 15 in FIG. 2) and the filter paper is 5 mm or more. The thickness of the PET film 16 is several μm.

[0010]

[Alpha] -ray dust monitor,
As explained in the section "Prior art", since it is a radiation measurement device that measures the nuclide and its concentration of α-ray dust in the environment to be measured, it can reliably discriminate the nuclide and determine its concentration accurately. It is required to measure. However, α
Rays are radiation that have a very strong interaction with matter,
It consumes a lot of energy when passing through a substance. For example, when a 5 MeV α ray passes through the air in the standard state, energy is consumed at a rate of 0.8 MeV / cm. When passing through a dense material, the energy consumption rate increases almost in proportion to the density. Therefore,
Even an α-ray having a specific energy value radiated from a specific nuclide, which is an air layer and another substance layer (for example, PET film 16) passing through before reaching the radiation-sensitive region 111 of the radiation detection element 11. If the thickness changes, the energy value possessed when reaching the radiation sensitive region 111 will be different.

Α emitted from the dust collected on the filter paper
If all the rays are incident vertically on the radiation detecting element 11, the thickness of the air layer, etc. through which the α rays incident on the radiation detecting element 11 pass becomes constant, so the specific energy value emitted from the specific nuclide. Α-rays with are all detected with the same energy value. However, since the emitting direction of the emitted α-rays is completely random, the α-rays incident on the radiation detecting element 11 have various inclinations, and the larger the angle of inclination, the thinner the air layer or the like passing through. The thickness becomes thicker, the energy value lost during that time increases, and the energy value when entering the radiation detection element 11 decreases. For such a situation, take the energy value of the α ray detected on the horizontal axis,
The so-called energy spectrum, in which the vertical axis shows the frequency of α-ray detection for each fixed width of energy value, has a sharp peak for each nuclide at an energy value equivalent to vertical incidence, and has a peak toward the lower energy side. It becomes a sawtooth spectrum in the state of pulling. The thicker the air layer or the like passing through, the more energy is consumed even with the same inclination angle, so the peak of the energy spectrum becomes lower and the tail becomes longer.

In order to discriminate various nuclides and obtain an α-ray dust monitor capable of more accurately calculating the respective concentrations, it is necessary to reduce the overlap of the respective energy spectra corresponding to the respective nuclides. For this purpose, it is necessary to reduce the number of tails drawn on the low energy side of the obtained energy spectrum.

Further, PE as a separating film which covers the α-ray entrance window 151 of the housing 15 and separates the outside atmosphere from the inside of the housing
Since the T film 16 has a thickness of several .mu.m, it does not break under normal stable use conditions, but it may break under external force such as a sudden pressure change. If the PET film 16 is damaged, the surface of the radiation detecting element 11 on the side of the radiation sensitive portion 111, the lead wire, etc. are directly exposed to the air to be measured, and the characteristics of the radiation detector 1 become unstable. May become unmeasurable.

The object of the present invention is to reduce the tail portion of the obtained energy spectrum of each nuclide to the low energy side as much as possible, and to discriminate the nuclide of α-ray dust and calculate the concentration thereof. An object of the present invention is to provide a radiation detector which can realize an excellent α-ray dust monitor and is excellent in stability.

[0015]

In order to achieve the above object, the following three points are important points, as is clear from the explanation in the section "Problems to be solved by the invention". (1) The function as a radiation detector is stable, and
The radiation detection function can be checked reliably.

(2) The thickness of the material layer including the air layer existing between the filter paper surface for collecting dust and the radiation sensitive area of the radiation detecting element is reduced to a unit of the material existing there. Reduce the mass per area. (3) To reduce the component that is incident at an angle. Among these, in order to satisfy the condition of (3), a collimator has already been adopted, and the component of α rays incident beyond the tilt angle determined by the ratio of the thickness of the collimator to the aperture size is removed. .

The present invention was devised as a result of pursuing the above conditions (1) and (2), and the three main points are as follows. The first is a structure in which the outer peripheral portion of the radiation sensitive area which is most susceptible to the environment in the semiconductor type radiation detection element, the lead wire, and the pulse amplifier are housed in a completely hermetic atmosphere, and the PET film covering the α-ray incident window is used. Make the thickness thinner.

Second, in order to reduce the thickness of the air layer, a light guide means that can surely guide the check light pulse to the radiation sensitive area even in a narrow space is introduced. Part 3
The function check unit based on the light pulse is housed in the airtight atmosphere. Each invention will be described. According to the invention of claim 1, a radiation detecting element having a radiation sensitive region formed on one surface of a semiconductor, and a pulse amplifier for converting a charge signal generated by the radiation detecting element by α rays into a voltage pulse signal and outputting the voltage pulse signal. A light emitting means and a light guiding means for irradiating a radiation sensitive area with a check light pulse for checking the α-ray detection function, and a housing containing these members and having an α-ray incident window on the α-ray incident side. What is claimed is: 1. A radiation detector comprising: a body; and an isolation film that covers an α-ray entrance window of the housing and isolates an external atmosphere from the inside of the housing, the radiation detector including the radiation incident portion and the radiation incident area as the radiation sensitive region. A radiation detecting element having an airtight seal portion surrounding the portion and a check portion arranged outside the airtight seal portion and receiving the check light pulse emitted and propagated by the light emitting means and the light guide means; and the radiation incident portion. To A seal member for hermetically housing the other part of the radiation detecting element except the pulse amplifier, the light emitting means and the light guiding means in the housing, and the radiation detecting element in a space hermetically sealed by the seal member. And an optical path changing member having two or more reflecting surfaces as a light guide means for guiding the check light pulse from the light emitting means to the check part.

According to the present invention, the radiation sensitive region of the radiation detecting element has the radiation incident portion, the airtight sealing portion and the check portion, and the sealing member surely hermetically seals the airtight sealing portion of the radiation detecting element and the housing. Since it is sealed, the other parts of the radiation detecting element except the radiation incident part, the pulse amplifier, the light emitting means and the light guiding means are surely isolated from the atmosphere to be measured, which is the most important for ensuring the stability of the radiation detecting element. A stable radiation detection characteristic can be obtained without exposing the outer peripheral portion of the radiation sensitive region and the leads to the atmosphere of outside air containing humidity. Further, according to the optical path changing member having two or more reflecting surfaces, the check light pulse guided from the surface side of the radiation detecting element, which is not the radiation sensitive area, is reflected twice or more, whereby the radiation sensitive element is exposed. Since the light can be made to enter the check portion of the region almost vertically, the thickness of the optical path changing member may be any thickness required to guide the light beam (for example, φ1 mm) introduced from the optical fiber to the check portion. , The distance between the inner surface of the housing and the surface of the radiation detection element, which required about 10 mm in the prior art, can be greatly reduced, and the air existing between the filter paper surface and the radiation sensitive area of the radiation detection element can be reduced. The layer thickness can be significantly reduced.

According to a second aspect of the present invention, in the first aspect of the present invention, the optical path changing member is sandwiched between one end of the optical path changing member and the casing with the bottom side being the check portion side, and the other side of the bottom side. An optical path changing member made of a transparent plastic having a trapezoidal shape in which a tip of an optical fiber is arranged at an end, and oblique sides on both sides have an inclination of 45 degrees with respect to a base, and the isolation film is made of PET. The thickness is 0.4 μm to 1 μm.

An optical path changing member made of a trapezoidal transparent plastic, one end of which is sandwiched between the check portion and the housing, receives a check light pulse incident vertically on the bottom.
The light is reflected twice at the hypotenuse of 45 degrees so that it enters the check part vertically. Further, the isolation film covering the α-ray incident window of the housing is a portion where an airtight state is secured by the seal member, that is, a portion of the radiation detecting element excluding the radiation incident portion, a pulse amplifier, a light emitting means and a light guiding means, Does not need to be isolated from the atmosphere to be measured, only the radiation incident part needs to be isolated, so it is not always necessary to ensure a reliable isolated state, and when it is damaged, it must be replaced and attached to the surface of the radiation incident part. All you have to do is remove the dust. Therefore, it is possible to use a much thinner film as the isolation film than in the prior art, and a PET film of 0.4 μm to 1 μm can be used. The reason why the material is PET is that PET is a practical material that is thin and is easy to obtain a mechanically strong film.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a semiconductor type radiation detector for an .alpha.-ray dust monitor (hereinafter abbreviated as a radiation detector) according to the present invention will be described with reference to examples.
The same reference numerals are used for parts having the same functions as those of the conventional technology. FIG. 1 shows an embodiment 1a of a radiation detector according to the present invention.
And (a) is a conceptual diagram showing the overall configuration.
Is a plan view of the semiconductor type radiation detecting element (simply referred to as a radiation detecting element in FIG. 1, hereinafter abbreviated as a radiation detecting element) 11a used in this embodiment, and (c) is a portion showing an optical path of a check light pulse. FIG.

The radiation detector 1a is a radiation detection element 11a.
A pulse amplifier 12, an LED 13 as a light emitting means, an optical fiber 14 and an optical path changing member 18 as a light guiding means, a housing 15a for housing them, and a PET for covering the α-ray incident window 151 of the housing 15a. It comprises a film 16a and an O-ring 17 that hermetically seals the inside of the housing between a part of the radiation sensitive area 111 of the radiation detection element 11a and the inner surface of the housing 15a.

The radiation detecting element 11a has the same structure as that of the conventional radiation detecting element, and a pn junction or a hetero junction is formed on one surface of a high resistivity single crystal silicon wafer, and a reverse bias is applied to this junction. It is applied to form a depletion layer on both sides of the junction. In the case where the region where the depletion layer is formed is the radiation sensitive region 111a and the region is a pn junction type, the region where the pn junction is formed becomes the radiation sensitive region 111a, which is a heterojunction type made of amorphous silicon. In this case, the region of the electrode formed on the amorphous silicon becomes the radiation sensitive region 111a. This radiation sensitive area 111a
As shown in FIG. 1 (b), is the α-ray entrance window 15 of the housing 15a.
The radiation incident part 1111 in the central part for detecting the α ray incident from 1 and the airtight seal part in the outer peripheral part of the radiation incident part 1111 for being hermetically sealed by the O-ring 17.
1112, LED 13 to optical fiber 14 and optical path changing member 18
And a check unit 1113 for receiving a function check light pulse guided via the function check signal and emitting a function check signal. The check unit 1113 is arranged at the outermost part of the radiation sensitive area 111a, and its shape is, for example, a semicircle or an anti-elliptical shape.

The explanation of the principle of detecting the α rays by the radiation detecting element 11a is omitted since it is completely the same as the section of "Prior Art". LED 13, optical fiber 14 and optical path changing member 18
Is a member for checking whether or not the radiation detector 1a is operating normally.The difference from the prior art is that the reflecting surface 152 of the housing in the prior art is replaced by the optical path changing member 18. is there. The optical path changing member 18 is made of transparent plastic such as acrylic resin, and is a trapezoidal member having both oblique sides inclined by 45 degrees with respect to the bottom side. The LED 13 emits light in response to a test pulse input from the outside. The optical pulse is guided to the optical fiber 14 and is incident on one end of the bottom side of the optical path changing member 18, and the reflection surface having an inclination of 45 degrees on the bottom side.
It is bent upward at a right angle at 181 and further bent right at a right angle at a reflecting surface 182 having a 45 degree inclination at the bottom, and the radiation sensitive area 111a of the radiation detecting element 11a is detected from above the bottom of the optical path changing member 18. The electron-hole pair is generated in the check unit 1113, similarly to the case where the α-ray is incident on the check unit 1113. The arrow in FIG. 1C indicates the path of the optical pulse in the optical path changing member 18. If a predetermined output is obtained by this optical pulse, it is determined that the radiation detector 1a is functioning normally.

When the path of the optical pulse is bent by the optical path changing member 18 as in this embodiment, the optical pulse is obliquely incident on the radiation sensitive area as described in the section "Prior Art". In contrast to, the beam of the optical pulse guided to the optical fiber 14 and incident on the bottom of the bottom is bent upward at a right angle by the reflecting surface 181, and becomes a light beam parallel to the bottom.
The light is bent rightward at 182 and vertically incident on the check unit 1113. Therefore, the thickness of the optical path changing member 18 may be any thickness as long as it can propagate the light beam parallel to the bottom side, and
A thickness of 3 mm is sufficient to fulfill the required function. As a result, the distance between the outer surface of the housing 15a on the α-ray entrance window side and the surface of the radiation sensitive area 111a of the radiation detection element 11a can be significantly shortened as compared with the conventional technique. The optical path changing member 18 is fitted into the concave portion 154 engraved in the housing 15a, and the airtight seal portion 1112 of the radiation detecting element 11a and the housing 15a.
When a and a are hermetically sealed by the O-ring 17, they are fixed by being sandwiched between the radiation detection element 11a and the housing 15a.

The optical path changing member 18 may be made of a transparent material that transmits the check light pulse. In this embodiment, it is made of an acrylic resin which is easy to process and is inexpensive. As an example of dimensions, the bottom corresponding to the length is 14 mm,
The upper side is 10 mm, the thickness corresponding to the height of the trapezoid is 2 mm, and the width is 12
mm. The length and width may be determined according to the size of the radiation detection element 11a, the position of the check section 1113 on the radiation detection element 11a, the thickness of the optical fiber, the processing accuracy, the positioning accuracy, and the like.

In this embodiment, the optical path changing member 18 is shown in which the hypotenuse is inclined by 45 degrees with respect to the base. However, the inclination of the hypotenuse is larger than 45 degrees so that both the hypotenuse and the upper side are reflected. There is also a system optical path changing member. In the case of any optical path changing member, the check light pulse is sent to the check unit 1113.
It is most desirable to make the light incident perpendicularly to. O-ring 17
Has a thickness of about 1 mmφ, and the α-ray entrance window of the housing 15a
It is fitted into a ring groove 153 engraved on the outer periphery of 151 to be positioned, and hermetically seals the housing 15a and the airtight seal part 1112 of the radiation detection element 11a, and the radiation detection element 11a excluding the radiation incidence part 1111 is removed. Other parts and pulse amplifier 12 and L
The ED 13, the optical fiber 14, and the optical path changing means 18 are completely isolated from the atmosphere to be measured. Therefore, in the radiation detection element 11a, the outermost part of the radiation sensitive area 111a, which is the most important for ensuring stability, and the leads (not shown) are not exposed to the atmosphere of the measurement target including humidity and dust, and thus stable. Radiation detection characteristics can be obtained. Further, surface contamination of the function checking member such as the LED 13 can be avoided, and a reliable function check can be carried out. The size of the O-ring 17 is the α-ray incident window 151
Since it is usually formed with a diameter of 50 mm, it is about 55 mm.

The casing 15a is made of brass or aluminum and serves as a container for the radiation detecting element 11a, the pulse amplifier 12 and the like, and also serves as a shield box for preventing noise from entering from the outside. PET film 16a, in order to prevent the radiation incident portion 1111 of the radiation detection element 11a are contaminated with dust and the like contained in the atmosphere to be measured, the housing
It is attached so as to cover the α-ray incident window 151 of 15a. In the case of this embodiment, the radiation-sensitive region 11 that strongly affects the stability of the detection characteristic is provided by the airtight seal by the O-ring 17.
Since the outer peripheral portion of 1a, the lead wire, and the like are completely isolated from the atmosphere to be measured, this PET film 16a ensures that the inside of the α-ray incident window 151 of the housing 15a is isolated from the atmosphere to be measured. Not necessarily required. Therefore, the PET film 16
It is possible to make the thickness of a much thinner than that of the conventional PET film. In this embodiment, the PET film 16 having a thickness of 0.6 μm is used.
a has been adopted. With such a thin film, the amount of moisture permeation increases and the possibility of breakage increases, but under normal use conditions there is almost no breakage and there is no practical problem. When the PET film 16a is damaged due to a large pressure difference or the like, the PET film 16a may be replaced to remove the dust adhering to the radiation incident portion 1111 of the radiation detecting element 11a.

As is apparent from the above description, if the thickness of the optical path changing member 18 is 2 to 3 mm, the optical path changing member 18 can fulfill its function. Therefore, according to this embodiment, the optical path changing member 18 is used. Even if the thickness of the portion of the housing in which is fitted is 2 mm, the distance between the outer surface of the housing 15a on the α-ray entrance window side and the surface of the radiation sensitive area 111a of the radiation detection element 11a can be 5 mm or less. . On the other hand, it is difficult to make the distance between the filter paper surface for collecting dust and the housing 1a smaller than 5 mm in order to supply the required amount of air to the filter paper, as described in the section "Prior Art". Is. Therefore, in the prior art, it was difficult to narrower than 15 mm, the distance between the filter paper surface and the radiation sensitive area of the radiation detection element, in the case of this embodiment, as is clear from the above description. It can be shortened to 10 mm or less. In other words, the thickness of the air layer through which the α rays pass is ⅔ or less as compared with the prior art. In addition to this, as described above, P as the isolation film is used.
Since the thickness of the ET film can be reduced to a fraction of that of the conventional technique or less, according to this embodiment, it is possible to realize the α-ray dust monitor excellent in the accuracy of discriminating nuclides and calculating the concentration thereof. Moreover, a radiation detector having excellent stability can be provided.

If a collimator is installed in the α-ray entrance window 151, α-rays incident at an inclination greater than the inclination determined by the thickness of the collimator and the width of the opening are removed, so that the discrimination of nuclides and their concentrations can be eliminated. The accuracy of the calculation becomes better.
If the thickness of the collimator that can be mounted is less than or equal to the distance from the surface of the housing 15a on the α-ray incident side to the surface of the radiation incident portion 1111 of the radiation detection element 11a, the collimator can be installed without increasing the thickness of the air layer. Can be installed.

[0032]

According to the invention of claim 1, the radiation sensitive region of the radiation detecting element has a radiation incident portion, an airtight seal portion and a check portion, and the sealing member is a hermetic seal portion of the radiation detecting element and a casing. Since the body is reliably hermetically sealed, the other parts of the radiation detecting element except the radiation incident part, the pulse amplifier, the light emitting means and the light guiding means are reliably separated from the atmosphere to be measured, and the radiation detecting element is used. It is possible to obtain stable radiation detection characteristics without exposing the outer peripheral portion of the radiation sensitive region and the leads, which are most important for ensuring stability, to the atmosphere of outside air containing humidity. Further, according to the optical path changing member having two or more reflecting surfaces, the check light pulse guided from the surface side of the radiation detecting element, which is not the radiation sensitive area, is reflected twice or more, whereby the radiation sensitive element is exposed. Since the light can be made to enter the check portion of the region almost vertically, the thickness of the optical path changing member may be any thickness required to guide the light beam (for example, φ1 mm) introduced from the optical fiber to the check portion. , The distance between the inner surface of the housing and the surface of the radiation detection element, which required about 10 mm in the prior art, can be greatly reduced, and the air existing between the filter paper surface and the radiation sensitive area of the radiation detection element can be reduced. The layer thickness can be significantly reduced.

Therefore, according to the present invention, the complete airtight sealing structure by the sealing member ensures the excellent stability of the α-ray detecting function, and the drastic reduction of the thickness of the air layer enables the discrimination of nuclides and The accuracy of calculating the concentration can be improved. According to the invention of claim 2, the optical path changing member made of a trapezoidal transparent plastic, one end of which is sandwiched between the check portion and the housing, has a check light pulse vertically incident on the bottom side of 45 degrees. The light is reflected twice on the hypotenuse so that it is vertically incident on the check portion. Since the direction of the center of the light beam propagating from the hypotenuse to the hypotenuse of the optical path changing member is parallel to the bottom, the thickness required to pass most of the light beam can be reduced. Further, since this optical path changing member is made of resin and has a simple shape, it is easy and inexpensive to manufacture.
The use of such an optical path changing member makes it possible to reduce the distance between the radiation incident side surface of the housing of the radiation detector and the radiation sensitive area of the radiation detecting element to 5 mm or less.

The airtight seal structure in the housing according to the first aspect of the present invention makes it possible to use a much thinner film as the isolation film than in the prior art.
Since a PET film of m to 1 μm can be adopted, the consumption of α-ray energy by the isolation film is greatly reduced to a fraction of that of the prior art to 1/10 or less. Therefore, according to the present invention, it is possible to further improve the accuracy of discrimination of nuclides and calculation of their concentrations.

[Brief description of drawings]

1A and 1B show a configuration of an embodiment of a radiation detector according to the present invention, FIG. 1A is a conceptual diagram showing the overall configuration, FIG. 1B is a plan view of a radiation detection element, and FIG. 1C is an optical path of a check light pulse. Enlarged view showing

2A and 2B show a configuration of an example of a radiation detector according to a conventional technique, FIG. 2A is a conceptual diagram showing an overall configuration, and FIG. 2B is a plan view of a radiation detection element.

[Explanation of symbols]

1,1a radiation detector 11, 11a Radiation detector 111, 111a Radiation sensitive area 1111 Radiation incident part 1112 Airtight seal part 1113 Check department 12 pulse amplifier 13 LED 14 optical fiber 15, 15a enclosure 151 α-ray incident window 152 Reflective surface 153 Ring groove 154 Recess 16, 16a PET film 17 O-ring 18 Optical path changing member 181, 182 Reflective surface

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Claims (2)

[Claims] 1. A semiconductor type radiation detecting element having a radiation sensitive region formed on one surface of a semiconductor, and a pulse for converting a charge signal generated by an α ray into a voltage pulse signal and outputting the voltage pulse signal. An amplifier, a light emitting means and a light guiding means for irradiating a radiation sensitive area with a check light pulse for checking the α-ray detection function, and these members are housed and an α-ray incident window is provided on the α-ray incident side. A semiconductor radiation detector for an α-ray dust monitor, comprising: a housing having the housing, and an isolation film that covers an α-ray entrance window of the housing to separate an external atmosphere from the inside of the housing. As a sensitive area, it has a radiation entrance portion, an airtight seal portion surrounding the radiation entrance portion, and a check portion arranged outside the airtight seal portion and receiving the check light pulse emitted and propagated by the light emitting means and the light guiding means. A semiconductor radiation detecting element, a seal member for hermetically housing the other portion of the radiation detecting element excluding the radiation incident part, the pulse amplifier, the light emitting means and the light guiding means in the housing, and this sealing member. An optical fiber as a light guide means for guiding a check light pulse from the light emitting means to the check portion of the semiconductor type radiation detection element in the space hermetically sealed with, and an optical path changing member having two or more reflecting surfaces. The semiconductor radiation detector for an α-ray dust monitor, characterized by comprising: 2. The optical path changing member is sandwiched between one end of the optical path changing member with the check portion and the casing with the bottom side being the check portion side, and the other end of the bottom side is provided with the tip of the optical fiber.
An optical path changing member made of a transparent plastic having a trapezoidal shape in which the hypotenuses on both sides are inclined by 45 degrees with respect to the base, and the isolation film is made of PET and has a thickness of 0.4 μm.
The semiconductor type radiation detector for an α-ray dust monitor according to claim 1, wherein m to 1 μm.