JP2001274450A - Beta ray detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a β-ray detector which satisfies a prescribed directional characteristic in a prescribed incident angle range of β rays. SOLUTION: A radiation detecting element used for this β-ray detector has a heterojunction or p-n junction which is formed on the whole flat surface of the element on the incident side of βrays, and a depletion layer formed on the whole flat surface until the junction reaches the side face of the element. For example, grooves 17 are formed into a p-type silicon substrate 11a having a high resistivity, and an amorphous silicon film 12a is formed on the whole surface of the substrate 11a on the side of the grooves 17. In addition, an upper electrode 14a is formed on the amorphous silicon film 12a except the grooves 17, and a lower electrode 13a is formed on the other surface. The depths of the grooves 17 are made deeper that the thickness of the depletion layer required for obtaining the prescribed directional characteristic and the lower end 16 of the depletion layer reaches the surfaces of the grooves 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the measurement of personal exposure dose equivalent by β-ray in the field of radiation measurement.

[0002]

2. Description of the Related Art The dose measurement of β-rays in radiation measurement includes measurement in which a β-ray detector is almost directly opposed to an object to be measured, such as a dust monitor and a survey meter, and measurement of β-rays, such as a personal alarm dosimeter. Some measurements cannot determine the incoming direction. In the former case, strict specifications are not required for the directional dependence of the sensitivity of the β-ray detector (hereinafter, the directional dependence of the sensitivity ratio to the sensitivity at normal incidence is referred to as directional characteristics). In the latter case, strict directional characteristics specifications are required. Conventional standards require that the angle be within ± 30% in an angle range of up to 30 degrees with respect to the vertical direction.

Hereinafter, a β-ray detector of a personal alarm dosimeter according to the prior art will be described. FIG. 7 is a block diagram showing a configuration of a β-ray detector, and FIG. 8 is a cross-sectional view showing an example (heterojunction type) of a semiconductor detection element as a radiation detection element of a conventional β-ray detector. Yes, FIG.
It is sectional drawing which shows the structure of other examples (p ⁺ n junction type).

The β-ray detector comprises a β-ray detecting element 1 and a γ-ray
The compensation detection element 2 and the output of each of the two detection elements 1 and 2
Amplifying circuit 3 for amplifying the force current pulse;
Of the signal pulses that have exceeded the reference value
Counting circuit 4 that counts the number of
Count value n₁From the count value n on the γ-ray compensation detection element 2 side _Two
And the output of the subtraction circuit 5 (n₁-N
_Two) To calculate the dose equivalent value from
And a display unit (not shown) for displaying measured values.
Have been.

When β-rays enter a substance, the β-rays interact with atoms of the substance from the incident position to ionize the substance, and generate electron-hole pairs in a cloud form from the incident position, Depletes that energy. Therefore, β-rays incident on the radiation detection element always generate electron-hole pairs from the incident surface. This is completely different from the case of γ-rays. Since γ-rays have a much lower probability of interaction with a substance and have a high permeability in the substance, most of the γ-rays incident on the radiation detecting element are transmitted, and a part of the γ-rays is transmitted to the radiation detecting element. Interact and generate an electron-hole pair from the interacted position.

Therefore, when detecting β-rays by detecting electron-hole pairs generated by β-rays, a member that consumes the energy of β-rays cannot be provided at the entrance of the β-rays. Γ-ray interference, which is much stronger, cannot be avoided. In other words, the β-ray detector needs a γ-ray detection circuit for compensating for the γ-ray interference component in addition to the β-ray detection circuit, and the β-ray detector has the above configuration.

[0007] The β-ray detecting element 1 comprises a radiation detecting element and a thin protective sheet covering the surface thereof. As this protective sheet, for example, a Kapton sheet, which is a kind of organic polymer sheet having a thickness of 25 μm, is used.
It only consumes a little energy in the wire. The γ-ray compensation detection element 2 is composed of a radiation detection element, a shielding metal plate and a metal case covering the surface thereof. The shielding metal plate is, for example, a copper plate having a thickness of 1 mm, and is entirely housed in, for example, an aluminum case having a thickness of 1 mm. Therefore, β-rays of 1 MeV or less, which occupy most of the β-rays, are completely shielded, and the β-ray sensitivity is 1/1000 or less as compared with the case without the shielding metal plate and the metal case.

Each reference value set in the counting circuit 5 is set in order to remove noise generated from the β-ray detecting element 1 and the γ-ray compensating detecting element 2 and to accurately compensate for γ-ray components. Usually, it is set to about 100 keV. β
The electron-hole pair formed by a line spreads in a cloud shape with the range of the range from the point of incidence. The range of β-rays in silicon is about 50 μm with 100 keV energy, about 160 μm at 200 keV, and about 570 μm at 500 keV.
At 1 MeV, it is about 1,500 μm.

Β-ray detecting element 1 and γ-ray compensating detecting element 2
The radiation detection elements having the same structure and the same size are used. However, the presence or absence of the shielding metal plate causes a slight difference between the γ-ray detection sensitivity of the β-ray detection element 1 and the γ-ray detection sensitivity of the γ-ray compensation detection element 2. This difference is adjusted by slightly shifting the reference value of the counting circuit 4 on the γ-ray compensation detection element 2 side from the reference value on the β-ray detection element 1 side.

Here, the radiation detecting element will be described with reference to FIGS. The radiation detecting element shown in FIG. 8 is a heterojunction semiconductor detecting element 10, which is a heterojunction diode of single crystal silicon and amorphous silicon. This semiconductor detecting element 10 has a high resistivity p-type silicon substrate (p-type silicon in FIG. 8) 11 as a base material, and has a plasma CV on one surface (upper surface in FIG. 8).
D forms an n-type amorphous silicon film 12 having a thickness of about 1 μm and a high resistivity, and the other surface (the lower surface in FIG. 8).
Is an electrode made of an aluminum vapor-deposited film (lower electrode in FIG. 8) 13
On the surface of the amorphous silicon film 12, an upper electrode 14 made of an aluminum evaporated film having a thickness of 1 μm or less is formed. The region where the upper electrode 14 is formed is a region sensitive to β rays.

Both electrodes 13 of the above heterojunction diode
When a reverse bias voltage is applied to and 14, a depletion layer (not shown) is formed across the heterojunction. The spread of the formed depletion layer in the lateral direction is limited by the region where the upper electrode 14 is formed, and the spread in the thickness direction is determined by the applied voltage and the resistivity of the p-type silicon substrate 11. . Electron-hole pairs generated in the depletion layer by the incident β-rays are separated by the electric field of the depletion layer and become current pulses. Therefore, the formation region of the depletion layer is the sensitive portion of the heterojunction semiconductor detection element 10, the radiation sensitive portion is close to the surface on the amorphous silicon film 12 side, and the β-ray incident surface is the amorphous silicon film 12 Side.

The radiation detecting element shown in FIG. 9 is a p ⁺ n junction type semiconductor detecting element 20, which is a p ⁺ n junction type diode. This semiconductor detecting element 20 has an n-type silicon substrate (n-type silicon in FIG. 9) 21 as a base material, a thin p ⁺ layer 22 formed on one surface (upper surface in FIG. 9), and another surface ( the lower surface) in FIG. 9, electrodes (the lower electrode in FIG. 9) 23 made of aluminum vapor deposited film on the substantially entire surface is formed, p ⁺ layer
An upper electrode 24 made of an aluminum vapor-deposited film for wire bonding is formed on a part of 22, and a surface protection film 25 is formed on the entire upper surface except for the portion where the upper electrode 24 is formed. p ⁺
The reason why the aluminum electrode 24 is formed only on a part of the layer 22 is that p ⁺
Since the layer 22 also functions as an electrode, an aluminum deposited film is not required as an electrode, so that only an amount necessary for wire bonding may be formed.

When a reverse bias voltage is applied to both electrodes 23 and 24 of such a p ⁺ n junction type diode, p
^A depletion layer (not shown) is formed across the ⁺ n junction. The function of the depletion layer is exactly the same as that of the heterojunction diode, and a description thereof will be omitted. Note that, as a radiation detecting element, as in the case of a p ⁺ n junction type diode, n ⁺ p
Junction type diodes can also be used.

[0014]

In a β-ray detector of a personal alarm dosimeter, which has strict requirements for directional characteristics, according to the conventional required specification, as described above, 30 degrees to the vertical direction (hereinafter referred to as the vertical direction). It is required that the angle be within ± 30% in the angle range up to the angle of inclination. However, recently, it has been required to satisfy the IEC standard that requires the angle to be within ± 30% in an angle range up to a tilt angle of 60 degrees.

The directional characteristics indicated by thick lines in FIG. 10 are examples of directional characteristics measured by a conventional β-ray detector. These radiation detecting elements are of a heterojunction type, have a chip size of 3 mm × 3 mm, an upper electrode of 1.5 mm × 1.5 mm, and a thickness of a depletion layer of about 200 μm. As can be seen from FIG. 10, this β-ray detector was able to satisfy ± 30% with a margin when the tilt range was within 30 degrees, but was satisfied within ± 30% when the tilt range was within 60 degrees. It has a tilt angle range that cannot be achieved.

An object of the present invention is to provide a β-ray detector that satisfies a predetermined directional characteristic in a predetermined β-ray incident tilt range, and at least ± 30 in a β-ray incident tilt range up to a tilt angle of 60 degrees. An object of the present invention is to provide a β-ray detector that satisfies the directional characteristic of within%.

[0017]

As described in the background of the invention, when .beta.-rays are incident on a semiconductor detecting element, the .beta.-rays generate electron-hole pairs from the incident position and consume their energy. . Therefore, if the energy of β-rays falls below the reference value of the counting circuit before reaching the depletion layer,
Even if the β ray reaches the depletion layer, it is not counted.

Since the heterojunction or the pn junction is formed close to the surface, β-rays having an energy equal to or higher than a reference value incident on the heterojunction or the pn junction are almost equal thereto.
100% is detected (this is referred to as direct incidence). However, the β-rays incident on a position distant from the junction have an energy above the reference value when they reach the depletion layer.
Only lines are detected (this is called indirect incidence).

When the β-rays are perpendicularly incident on the surface of the semiconductor detection element, most of the detected β-rays are directly incident, and the sensitivity is determined by the junction area. On the other hand, in the case of β-rays which are incident on the semiconductor detecting element surface at an angle of inclination θ, the direct incidence is cos θ times that of normal incidence and decreases as the angle of inclination θ increases. The indirect incident component corresponds to the case where β-rays enter from the side surface of the depletion layer, and relates to the thickness of the depletion layer, the inclination θ, and the energy distribution of β-rays, and cannot be easily estimated.

FIG. 11 is an explanatory diagram showing the above-mentioned situation in the case of inclination angles of 30 degrees and 60 degrees. In the figure, the length of one side of the junction is L, and the thickness of the depletion layer is D. In the case of the inclination angle of 30 degrees, the direct incidence is 86.6% of that in the case of the vertical incidence, so that there is no problem in the directional characteristics. However, in the case of a tilt angle of 60 degrees, the amount of direct incidence is reduced to 50% of that in the case of normal incidence, so that this component alone cannot satisfy the specification of the directional characteristics within ± 30%.
This situation is shown in the directional characteristics of the conventional example shown in FIG. The value of -44% at a tilt angle of 60 degrees means that the contribution of the indirect incidence is about 6%. That is, 0.
Part of the β-rays incident on the portion corresponding to 866D was counted.

FIG. 12 shows the sensitivity calculated when all the β-rays incident on the side surface of the depletion layer are effectively detected, that is, there is no substance that consumes the energy of the β-rays outside the depletion layer. It is a diagram showing the result of having performed. The horizontal axis is the ratio D / L of the thickness D of the depletion layer to the length L of one side of the junction, and the vertical axis is the sensitivity ratio to the vertical incidence sensitivity. FIG.
Using an example, the sensitivity ratio for a tilt angle of 60 degrees is: And cos θ + sin θD / L (2) for the inclination angle θ.

Therefore, in order to obtain a directional characteristic within ± 30% at an inclination angle of 60 degrees, 0.7 ≦ 0.5 + 0.866 D / L ≦ 1.3, and the lower limit of D / L is 0.233. If L = 1.5 mm, D ≧ 0.35 mm, and the value of D can be sufficiently realized by increasing the applied voltage and selecting the resistivity of the crystalline silicon substrate.

The semiconductor detecting element corresponding to the solid line in FIG.
Since D = 0.2 mm and L = 1.5 mm, when the directional characteristics are calculated by equation (2), the results are as shown by the dotted line in FIG. Figure
Comparing the bold line of 10 with the dotted line, at a tilt angle of 60 degrees,
It can be seen that about half of the β rays incident on the portion corresponding to 0.866 D contribute as indirect incident components. Therefore, if the side area of the depletion layer is increased while the junction area is kept the same, that is, if the peripheral length of the junction is increased, the amount of indirect incident light can be increased. This is shown in FIG.
Is equivalent to increasing the D / L in.

Based on the above considerations, the present invention uses the following two means to improve the directional characteristics. 1) Be able to make β-rays incident on the side of the depletion layer with little energy consumption. That is, the size of the heterojunction or pn junction is made substantially the same as the size of the radiation detection element, and the depletion layer reaches the side surface or the vicinity of the side surface of the radiation detection element.

2) To increase the ratio of indirect incident light, the side surface area that can contribute to indirect incident light is increased. That is, the shape of the hetero junction or the pn junction is elongated, and the perimeter for the same junction area is increased. The inventions of claims 1 to 4 are inventions by means of 1), and the inventions of claims 5 and 6 are inventions of means of 2).

In the first aspect of the present invention, a semiconductor radiation detecting element which detects radiation by a depletion layer formed by a reverse bias applied to a hetero junction or a pn junction detects β rays and γ rays. A gamma ray detecting means for detecting a gamma ray with a semiconductor radiation detecting element similar to the above, and converting the gamma ray component of the output of the
In a β-ray detector that measures the dose equivalent of β-ray by compensating with the output of the line detection means, the thickness of the depletion layer is set according to a predetermined directional characteristic, and the depletion layer is formed on a side surface of the semiconductor radiation detecting element. Reached or close to surface.

Since the depletion layer reaches or is close to the side surface of the semiconductor radiation detecting element, β-rays incident on the side surface can reach the depletion layer with little consumption of its energy. In addition, since the thickness of the depletion layer is set according to the predetermined directional characteristics, the predetermined directional characteristics can be secured. In the invention of claim 1, the semiconductor radiation detecting element is a heterojunction type of single crystal silicon and amorphous silicon, and the amorphous silicon has at least one of a plane on the radiation incident side of single crystal silicon and a side surface connected to this plane. Electrodes are formed on the entire surface of the amorphous silicon formed on the plane on the radiation incident side, which is formed on the portion where the depletion layer is formed (the invention of claim 2).

Since amorphous silicon is formed on the surface of the depletion layer forming portion, a stable diode having a small leakage current can be obtained. Since electrodes are formed on the entire surface of the plane on the radiation incident side, A depletion layer is formed up to the side surface. Further, in the first aspect of the present invention, the semiconductor radiation detecting element is a pn junction type made of single crystal silicon, and the pn junction is formed close to a plane on the radiation incident side of the single crystal silicon, and the pn junction is formed. Has reached the side surface of the single crystal silicon, and a surface protection film is formed on at least the surface of the surface of the single crystal silicon where the depletion layer is formed. invention).

Since a surface protection film is formed on the surface of the portion where the depletion layer is formed, a stable diode with small leakage current can be obtained, and the pn junction reaches the side surface of the single crystal silicon. Therefore, a depletion layer is formed up to the side surface. In any one of the first to third aspects of the present invention, the shape of the plane on the radiation incident side of the semiconductor radiation detecting element is a square, and the thickness of the depletion layer is from 23% of the length of one side of the square. It is 65% (the invention of claim 4).

As the shape of the semiconductor radiation detecting element, a rectangle or a square is the most easily manufactured shape, and among them, a square has the most excellent directional characteristics. To obtain a directional characteristic within ± 30% at an inclination of 60 degrees, (1)
From the formula, the lower limit of D / L is 0.23 and the upper limit is 0.92. However, since the upper limit is larger when the light is incident in the diagonal direction of the square, it is appropriate to set the upper limit obtained by dividing the upper limit obtained from Expression (1) by the square root of 2 as the upper limit. , D / L is 0.65.

According to a fifth aspect of the present invention, a semiconductor radiation detecting element for detecting radiation by a depletion layer formed by a reverse bias applied to a hetero junction or a pn junction detects β rays and γ rays. A gamma ray detecting means for detecting a gamma ray with a semiconductor radiation detecting element similar to the above, and converting the gamma ray component of the output of the
In a β-ray detector that measures the dose equivalent of β-rays by compensating with the output of the line detection means, the shape of the heterojunction or pn junction has a central connection portion and a radial or four-sided dendritic shape from this connection portion. It has a shape consisting of a protruding branch.

If the joining shape is a shape having a branch portion, even if the joining area is the same, the peripheral length thereof becomes longer, and the side surface area that can contribute to the indirect incidence increases. In the invention according to claim 5, the area of the branch portion is larger than the area of the connection portion, and the width of the branch portion is 0.2 mm to 0.05 mm (the invention of claim 6). According to the prototype results of the inventor, the area of the branch portion is the same as the area of the connection portion, and when the width of the branch portion is 0.2 mm, at a tilt angle of 60 degrees, the sensitivity is normal incidence. It was just 70%. Therefore, in order to obtain -30% or less at a tilt angle of 60 degrees, if the width of the branch is 0.2 mm, the area of the branch should be larger than the area of the connection. If the area of the connection portion is the same as the area of the connection portion, the width of the branch portion may be set to 0.2 mm or less. The lower limit value of 0.05 mm of the width of the branch portion is the same value as the range of the β-ray corresponding to the reference value of 100 keV of the counting circuit described in the section of the related art, and a signal exceeding the reference value is obtained. This width is necessary for this.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a β-ray detector according to the present invention will be described using an example. Parts having the same functions as those of the prior art are denoted by the same reference numerals. The configuration of the β-ray detector is the same as the configuration in the related art shown in FIG. 7, and the configurations of the β-ray detection element and the detection element for γ-ray compensation are also the same as those in the conventional technique. The semiconductor detection element used for the β-ray detection element and the γ-ray compensation detection element and the directional characteristics of the β-ray detector using the semiconductor detection element will be described.

[First Embodiment] FIG. 1 is a sectional view showing the structure of a first embodiment of a semiconductor detecting element of a β-ray detector according to the present invention. FIG. FIG. 4 is a diagram showing directional characteristics of a β-ray detector using an element. The semiconductor detection element 10a of this embodiment is a heterojunction semiconductor detection element, and is a heterojunction diode of single crystal silicon and amorphous silicon. This semiconductor detecting element 10a is formed with a high-resistivity p-type silicon substrate (p-type silicon in FIG. 1) 11a having a groove 17 slightly deeper than the thickness of a depletion layer formed on one side as a base material. An n-type high-resistivity amorphous silicon film 12a having a thickness of about 1 μm is formed on the surface on the side including the inside of the groove 17 by plasma CVD, and an electrode (aluminum-deposited film) is formed on the other surface. A lower electrode 13a is formed in FIG. 1, and an upper electrode 14a made of an aluminum vapor-deposited film having a thickness of 1 μm or less is formed on the amorphous silicon film 12a other than the groove 17. The above structure is formed in a wafer state, and this wafer is cut at the bottom of the groove 17 to become individual elements.

The above-mentioned grooved p-type silicon substrate 11a is formed by processing a groove 17 in a wafer with a dicer, and then etching with a mixed acid solution of fluorinic acid or the like to remove and clean a processing strain layer in the groove processed portion. It is produced. When a reverse bias voltage is applied to both electrodes 13a and 14a of the above heterojunction diode, a depletion layer is formed with the heterojunction sandwiched therebetween. The formed depletion layer has a lower end as shown in FIG.
The groove 16 does not reach the bottom of the groove 17, but reaches the side of the groove 17 because the upper electrode 14a is formed on the entire upper surface. The lower end 16 of the depletion layer is controlled by the resistivity of the p-type silicon substrate and the applied voltage.

Such a heterojunction type semiconductor detecting element 10
When β-rays are incident on a, the depletion layer is formed up to the side surface. Therefore, as described in the section “Means for Solving the Problems”, the β-rays incident on the side surface have the same sensitivity as the direct incidence. To contribute. FIG. 4 shows the directional characteristics of a β-ray detector using the semiconductor detecting element 10a of this embodiment, which was prototyped by setting the upper electrode 14a to 1.0 mm × 1.0 mm and setting the thickness of the depletion layer to 300 μm. FIG. Even at a tilt angle of 60 degrees, the sensitivity ratio with respect to the vertical incidence sensitivity is 76%, which sufficiently satisfies the directional characteristics within ± 30%.

[Second Embodiment] FIG. 2 shows a semiconductor device according to the present invention.
FIG. 6 is a cross-sectional view illustrating a structure of a body detection element according to a second embodiment.
The semiconductor detection element 20a of this embodiment has p⁺n-junction semiconductor
Body detection element, p ⁺It is an n-junction type diode.
This semiconductor detecting element 20a has a thickness on one side greater than the thickness of the depletion layer.
High resistivity n-type silicon substrate with deep groove 27 formed
(In FIG. 2, n-type silicon) 21a as a base material and grooves 27 as
The surface except for the groove 27 on the formed side has a thin p⁺Layer 22a is formed
And p on the side where the groove 27 is formed⁺The surface containing layer 22a
A surface protective film 25a is formed, and the other surface is formed from an aluminum vapor-deposited film.
(A lower electrode in FIG. 2) 23a is formed, and p⁺Tier 2
Part of the surface protection film 25a on 2a is removed, and
Upper electrode made of aluminum vapor-deposited film for ear bonding
A pole 24a is formed. The above structure is formed in wafer state
The wafer is cut at the bottom of the groove 27 and
Become a child.

P⁺The upper electrode 24a is formed only on a part of the layer 22a.
What is created is p⁺Since the layer 22a also functions as an electrode,
Since an aluminum deposition film as an electrode is unnecessary, a wire bond
This is because it is only necessary to form an amount necessary for the fining. Up
Note p⁺The layer 22a, the groove 27 and the surface protective film 25a are, for example,
P on one side of the wafer ⁺After forming the layer 22a, use a dicer
The groove 27 was machined to remove and clean the strained layer in the machined area.
Etching with a mixed acid solution such as hydrofluoric-nitric acid
Silicon oxide film or silicon nitride film by plasma CVD
And the like to form a surface protective film 25a.
You.

In the p ⁺ n junction type semiconductor detector 20a, the hetero junction type semiconductor detector 10 of the first embodiment is also used.
Similarly to the case of the first embodiment, since the formed depletion layer reaches the side surface of the groove 27, the directional characteristics of the β-ray detector using the p ⁺ n-junction type semiconductor detecting element 20a are exactly the same as those of the first embodiment. Can be obtained. In addition, p ⁺ n
Similar to the junction type diode, an n ⁺ p junction type diode can be used.

[Third Embodiment] FIG. 3 is a sectional view showing the structure of a third embodiment of the semiconductor detecting element of the present invention.
In the case of the first embodiment or the second embodiment, the size of the semiconductor detecting element is limited by the limit of the thickness of the depletion layer that can be formed, and the obtained sensitivity is limited. It is self-evident that a plurality of semiconductor detection elements may be used when sensitivity higher than this limit is required, but as the number increases, the number of assembling steps increases and the cost increases. This embodiment is to provide a semiconductor detecting element having a sensitivity higher than the above-mentioned limit with a small increase in cost.

In this embodiment, one semiconductor detecting element is used.
First, a semiconductor detection element corresponding to the first embodiment is used as a unit.
It is made up of multiple units. Between adjacent units
Is formed with a groove 17a, and the width W of the groove 17a is
Is the maximum tilt angle required for _maxAnd the thickness of the depletion layer
If D, W ≧ D tanθ_maxIs set to this
The groove width W is such that an adjacent unit is located on the side of the depletion layer of the adjacent unit.
From the conditions to not block the β-ray incident from
Is set. Θ shown in FIG._max= 60 degrees, the first
In the case of the semiconductor detection element example (D = 300 μm) shown in the embodiment,
In this case, W ≧ 0.52 mm, which is one side of the upper electrode 14a.
A groove 17a of a little more than a half of 1 mm is formed.

By forming the groove 17a that satisfies this condition, it is possible to obtain exactly the same directional characteristics as the individual units, and to handle them as one part in the assembly process. Although this embodiment is a case of a hetero-junction type semiconductor detecting element, the present invention can be applied to a pn junction type semiconductor element in exactly the same manner, and the effect is exactly the same.

[Fourth Embodiment] FIG. 5 is a plan view showing a fourth embodiment of the semiconductor detecting element according to the present invention.
FIG. 3 is a diagram showing directional characteristics of a β-ray detector using the semiconductor detection element of this embodiment. In this embodiment, a predetermined directional characteristic is obtained depending on the shape of the upper electrode.

The semiconductor detecting element of this embodiment is a heterojunction semiconductor detecting element 10c, and its upper electrode 14b is
It is composed of a circular connecting portion 141 at the center and branch portions 142 extending radially from the connecting portion 141 in eight directions. By forming the branch portions 142, the directional characteristics are greatly improved as compared with the case of a square upper electrode having the same area. This is because the peripheral length of the electrode is increased by forming the branch portion 142, and the amount of indirect incidence is increased.

The chip size (3 mm × 3 mm) and the electrode area (1.5 mm × 1.times.) Of the conventional example having the directional characteristics shown by the thick line in FIG.
5 mm), as the upper electrode 14b, as the upper electrode 14b, a connecting portion 141 of 1.1 mmφ (area is 0.95 mm ² ) and a branch portion 142 extending in eight directions with a width of 0.2 mm and within 0.2 mm × 2.2 mm (area is 1.24mm
² ) A heterojunction type semiconductor detection element 10c formed with the above was prototyped, and the thickness of the depletion layer was set to 200 μm using this.
The directional characteristics were measured with a line detector, and the results shown in FIG. 6 were obtained. It satisfies the directional characteristics within ± 30% at a tilt angle of 60 degrees.

The width of the branch 142 is set to 0.2 mm, and the connection 141
When the prototype was made with the same area as the area of the branch portion 142, the inclination was exactly -30% at a tilt angle of 60 degrees. Also,
If the width of the branch 142 is reduced, the perimeter becomes longer,
Directional characteristics are improved. However, when the width of the branch 142 becomes less than the range (about 50 μm) corresponding to 100 keV, which is the reference value of the counting circuit, the incident β-rays fall within the depletion layer of the branch 142 by 10%.
Branches 142 having a width of less than 50 μm are not suitable because they are more likely to exit the depletion layer before generating electron-hole pairs equivalent to 0 keV.

When the area of the detection element is increased in order to obtain higher sensitivity, it is effective to branch the branch into a portion that extends radially and has a larger interval. In this embodiment, a heterojunction type semiconductor detector is used.
In the case of a junction type semiconductor detection element, the same electrode shape is exactly the same.

[0048]

According to the first aspect of the present invention, a semiconductor radiation detecting element which detects radiation by a depletion layer formed by a reverse bias applied to a hetero junction or a pn junction detects β rays and γ rays. Γ-ray detecting means for detecting γ-rays with the same semiconductor radiation detecting element as described above, and the γ-ray component of the output of the β-
In a β-ray detector that measures the dose equivalent of β-ray by compensating with the output of the line detection means, the thickness of the depletion layer is set according to a predetermined directional characteristic, and the depletion layer is formed on a side surface of the semiconductor radiation detecting element. Since the light reaches or is close to the surface, the β-rays incident on the side surface can reach the depletion layer with little consumption of its energy, and a predetermined directional characteristic can be secured. Therefore, it is possible to provide a β-ray detector that satisfies a predetermined directional characteristic in a predetermined inclination range.

According to the first aspect of the present invention, the semiconductor radiation detecting element is a heterojunction type of single crystal silicon and amorphous silicon, and the amorphous silicon is composed of a plane on the radiation incident side of crystalline silicon and a side surface connected to this plane. Since the electrodes are formed on at least the portion where the depletion layer is formed, and the electrodes are formed on the entire surface of the amorphous silicon formed on the plane on the radiation incident side, a stable diode with low leakage current can be obtained. The depletion layer is formed up to the side surface (the invention of claim 2).

Further, according to the first aspect of the present invention, the semiconductor radiation detecting element is a pn junction type made of single crystal silicon, and the pn junction is formed on the entire surface of the crystalline silicon in proximity to the radiation incident side plane, The end of the pn junction reaches the side surface of the crystalline silicon, and at least the surface of the portion of the single crystal silicon where the depletion layer is formed has:
Since the surface protection film is formed, a stable diode having a small leakage current can be obtained, and the depletion layer is formed up to the side surface of the crystalline silicon (the invention of claim 3).

In any one of the first to third aspects of the present invention, the shape of the plane on the radiation incident side of the semiconductor radiation detecting element is a square, and the thickness of the depletion layer is the length of one side of the square. 23% to 65%. As the shape of the semiconductor radiation detecting element, a rectangle or a square is the most easily manufactured shape, and among them, a square has the most excellent directional characteristics. In order to obtain a directional characteristic within ± 30% at a tilt angle of 60 degrees, the lower limit value of D / L is 0.23 and the upper limit value is 0.92 from equation (1). However, regarding the upper limit,
Since it is larger when the light is incident in the diagonal direction of the square, it is appropriate to set the upper limit obtained by dividing the upper limit obtained from Expression (1) by the square root of 2, as the upper limit, and the upper limit of D / L Is
0.65. Therefore, it is possible to provide a β-ray detector that satisfies the directional characteristics within ± 30% in a tilt angle range up to a tilt angle of 60 degrees (the invention of claim 4).

According to the fifth aspect of the present invention, a semiconductor radiation detecting element for detecting radiation by a depletion layer formed by a reverse bias applied to a heterojunction or a pn junction has β
Β-ray / γ-ray detecting means for detecting rays and γ-rays, and γ-ray detecting means for detecting γ-rays with the same semiconductor radiation detecting element as described above, and the γ-ray component of the output of the β-ray / γ-ray detecting means Is compensated by the output of the γ-ray detecting means to measure the dose equivalent of β-ray
In the line detector, the shape of the heterojunction or pn junction is a shape including a central connecting portion and a branch portion radially or quadrilaterally protruding from this connecting portion.

When the shape of the joint has a branch portion, the peripheral length of the joint is increased even if the joint area is the same, and the side surface area that can contribute to the indirect incidence is increased. Therefore, it is possible to provide a β-ray detector that satisfies a predetermined directional characteristic in a predetermined inclination range. In the invention of claim 5, the area of the branch portion is larger than the area of the connection portion,
The width of the branch is 0.2 mm to 0.05 mm. According to the prototype results of the inventor, the area of the branch portion is the same as the area of the connection portion, and when the width of the branch portion is 0.2 mm, at a tilt angle of 60 degrees, the sensitivity is normal incidence. 70%. Therefore, in order to obtain within ± 30% at a tilt angle of 60 degrees,
When the width of the branch portion is 0.2 mm, the area of the branch portion may be equal to or larger than the area of the connection portion. May be set to 0.2 mm or less. The lower limit value of 0.05 mm of the width of the branch portion is the same value as the range of the β-ray corresponding to the reference value of 100 keV of the counting circuit described in the section of the related art, and a signal exceeding the reference value is obtained. In order to achieve this, the width is required (the invention of claim 6).

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a first embodiment of a semiconductor detecting element of a β-ray detector according to the present invention.

FIG. 2 is a sectional view showing the structure of a second embodiment of the semiconductor detecting element of the present invention;

FIG. 3 is a sectional view showing the structure of a third embodiment of the semiconductor detecting element of the present invention;

FIG. 4 is a diagram showing directional characteristics of a β-ray detector using the semiconductor detection element of the first embodiment.

FIG. 5 is a plan view showing a fourth embodiment of the semiconductor detecting element according to the present invention;

FIG. 6 is a diagram showing directional characteristics of a β-ray detector using a semiconductor detection element according to a fourth embodiment.

FIG. 7 is a block diagram illustrating a configuration of a β-ray detector.

FIG. 8 is a cross-sectional view showing the structure of an example of a semiconductor detection element of a β-ray detector according to the related art.

FIG. 9 is a cross-sectional view showing the structure of another example of a conventional semiconductor detecting element.

FIG. 10 is a diagram showing an example of a directional characteristic of a conventional β-ray detector.

FIG. 11 is an explanatory diagram for explaining a problem of the related art.

FIG. 12 is a diagram showing a calculation result by equation (2).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 beta-ray detection element 2 gamma-ray compensation detection element 3 amplifier circuit 4 counting circuit 5 subtraction circuit 10, 10a, 10b, 10c heterojunction semiconductor detection element 11, 11a p-type silicon 12, 12a amorphous silicon 13, 13a lower electrode 14, 14a, 14b Upper electrode 141 Connection part 142 Branch part 16 Lower end of depletion layer 17, 17a Groove 20, 20a p ⁺ n junction type semiconductor detector 21, 21a n-type silicon 22, 22a p ⁺ layer 23, 23a Lower part Electrode 24, 24a Upper electrode 25, 25a Surface protective film 26 Lower edge of depletion layer 27 Groove

Claims (6)

[Claims] 1. A β-ray / γ-ray detecting means for detecting β-rays and γ-rays by a semiconductor radiation detecting element for detecting radiation by a depletion layer formed by a reverse bias applied to a hetero junction or a pn junction; Γ-ray detecting means for detecting γ-rays with a similar semiconductor radiation detecting element, and compensating for the γ-ray component of the output of the β-ray / γ-ray detecting means with the output of the γ-ray detecting means, thereby obtaining the dose equivalent of the β-ray. In the β-ray detector to be measured, the thickness of the depletion layer is set according to a predetermined directional characteristic, and the depletion layer reaches or approaches the side surface of the semiconductor radiation detecting element. Detector. 2. A semiconductor radiation detecting element comprising a heterojunction type of single crystal silicon and amorphous silicon, wherein the amorphous silicon has at least a depletion layer in a plane on the radiation incident side of the single crystal silicon and a side surface connected to the plane. 2. The β-ray detector according to claim 1, wherein an electrode is formed on the entire surface of the amorphous silicon formed on a plane on the radiation incident side, wherein the β-ray detector is formed on a portion where is formed. 3. The semiconductor radiation detecting element is of a pn junction type made of single crystal silicon, wherein the pn junction is formed near the entire surface of the single crystal silicon on the radiation incident side, and an end of the pn junction is formed. The surface protection film is formed on a side surface of the single crystal silicon, and a surface protection film is formed on at least a surface of a portion of the surface of the single crystal silicon where a depletion layer is formed. The described β-ray detector. 4. The semiconductor radiation detecting element has a square planar shape on the radiation incident side, and the thickness of the depletion layer is 23% to 59% of the length of one side of the square.
The β-ray detector according to any one of claims 1 to 3, wherein 5. A β-ray / γ-ray detecting means for detecting β-rays and γ-rays by a semiconductor radiation detecting element for detecting radiation by a depletion layer formed by a reverse bias applied to a hetero junction or a pn junction; Γ-ray detecting means for detecting γ-rays with a similar semiconductor radiation detecting element, and compensating for the γ-ray component of the output of the β-ray / γ-ray detecting means with the output of the γ-ray detecting means, thereby obtaining the dose equivalent of the β-ray. In the β-ray detector to be measured, the shape of the heterojunction or pn junction is
A β-ray detector characterized in that the β-ray detector has a shape comprising a branch portion radially or quadrilaterally protruding from this connection portion. 6. The β-ray detector according to claim 5, wherein the area of the branch is larger than the area of the connection, and the width of the branch is 0.2 mm to 0.05 mm.