JP3644306B2 - Radiation detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation detector for measuring a dose or dose equivalent of γ rays, and particularly to reduce a difference in detection sensitivity over a wide range of energy.
[0002]
[Prior art]
When measuring γ-ray dose or dose equivalent at nuclear power plants, accelerator facilities, etc., photon energy vs. dose sensitivity dependence or photon energy vs. dose equivalent sensitivity dependence over a wide energy range from several tens of kev to several MeV There is a need for radiation detectors with good properties (hereinafter abbreviated as photon energy characteristics).
[0003]
Therefore, the ionization chamber is also used as a detector to measure gamma ray dose or dose equivalent because it has good photon energy characteristics and high sensitivity by increasing the volume. There were many things. However, this ionization chamber has responded to the recent miniaturization needs by increasing the internal gas pressure. However, there is a technical limit, and the ion chamber has a small size instead of the ionization chamber, that is, sensitivity per unit volume. A high radiation detector was sought.
[0004]
Therefore, among radiation detectors, CdTe as a compound semiconductor has a large atomic number of 48-52 and stable temperature characteristics up to about 50 ° C., so it is expected to be a small radiation detector. ing. However, CdTe has a large dependence of sensitivity on photon energy (sensitivity decreases as energy increases), and cannot be used covering a wide range of photon energies.
[0005]
As an improvement example that covers the wide range of photon energy characteristics, one described in Japanese Patent Publication No. 6-27814 has been proposed. FIG. 9 is a diagram showing the structure of a conventional radiation detector. In the figure, 1 is a semiconductor detector, 2 is a holding plate for holding the semiconductor detector 1, 3 is a radiation absorption filter provided in a dome shape so as to cover the semiconductor detector 1 in the radiation incident direction, and 4 is radiation. It is a pore formed in the absorption filter 3.
[0006]
FIG. 10 is a cross-sectional view showing the detailed structure of the semiconductor detector shown in FIG. In the figure, 5 is a CdTe semiconductor, 6 is a negative electrode formed on one surface of the CdTe semiconductor 5, and 7 is a positive electrode formed on the other surface of the CdTe semiconductor 5.
[0007]
The radiation detection method of the conventional radiation detector comprised as mentioned above is demonstrated. First, the semiconductor detector 1 is attached to the holding plate 2 while being electrically insulated, and is biased with a DC voltage. When radiation is incident on the semiconductor detector 1 and its energy is absorbed, electrons and holes in the shell are generated in the semiconductor detector 1 and are collected in the respective electrodes 7 and 6 and are pulsed. Current flows, and radiation is detected by detecting this current.
[0008]
In FIG. 11, the thickness of the semiconductor detector 1 is the same, lead is used as the material for the radiation absorbing filter 3, the thickness (h _{1 to} h ₄ is set, and the relationship of the thickness is h ₁ > h ₂ > h ₃ > The photon energy characteristic when h ₄ is used as a parameter is shown. By selecting the thickness of the radiation absorbing filter 3 as, for example, h ₂ , good photon energy characteristics are obtained from 80 keV to 1 MeV. The characteristics of the low energy region are improved by providing a large number of pores 4 in the radiation absorption filter 3.
[0009]
[Problems to be solved by the invention]
The conventional radiation detector is configured as described above, and the characteristics in the energy range of 80 keV to 1 MeV are good, but the photon energy characteristics cannot be improved for the energy range of 1 MeV or more. Therefore, there is a problem that it is not possible to cope with detection of an energy range from several tens of keV to several MeV, which is required in nuclear power plants, accelerator utilization facilities, and the like with a constant sensitivity. This is apparent from the fact that the detection sensitivity varies greatly in the energy range of 80 keV to 6.5 MeV as shown in FIG.
[0010]
The present invention has been made to solve the above-described problems, and an object thereof is to provide a radiation detector capable of reducing a difference in detection sensitivity over a wide range from low energy to high energy.
[0011]
[Means for Solving the Problems]
Engaging Ru Radiation detector in this invention is a radiation detector that uses a semiconductor capable of detecting radiation as a detection object, a plurality comprises a sensing body desired thickness different area of the radiation entrance surface is set The detectors each have a detector with a small area of the radiation incident surface placed above the radiation incident surface of the detector having a large area of the radiation incident surface. A radiation detector in which the thickness of each of the radiation absorption filters is set so that the radiation absorption filter of the radiation absorption filter that covers the radiation incident surface of the detection body is smaller as the detection body located in the upper stage includes the radiation absorption filter that covers the radiation detector. And when all the detection bodies are surrounded by the electromagnetic shield, the potentials on the upper surface side of the detection body at the uppermost position and the lower surface side of the detection body at the lowermost position are set to zero potential .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
Embodiments of the present invention will be described below. 1 is a cross-sectional view showing a configuration of a radiation detector according to Embodiment 1 of the present invention. In the figure, reference numerals 8 and 9 denote first and second detectors made of semiconductors capable of detecting radiation, for example, CdTe. The radiation incident surfaces of the first detectors 8 are different in area of the radiation incident surface. Is smaller than the area of the radiation incident surface of the second detector 9, and the first detector 8 is placed on the radiation incident surface of the second detector 9. 10, 11, 12, and 13 are electrodes formed on the respective surfaces of the detection bodies 8 and 9, and are either positive electrodes or negative electrodes.
[0016]
Reference numerals 14 and 15 denote first and second radiation absorption filters formed so as to cover the radiation incident surfaces of the respective detectors 8 and 9, and the amount of radiation absorbed by the first radiation absorption filter 14 is the second radiation. It is smaller than the amount of radiation absorbed by the absorption filter 15. Reference numeral 16 denotes an insulating film formed between the first detection body 8 and the second radiation absorption filter 15 for electrically insulating the detection bodies 8 and 9.
[0017]
Next, the principle of radiation detection in the radiation detector according to the first embodiment configured as described above is the same as that in the conventional case, and is therefore omitted. Here, in order to obtain good photon energy characteristics of the radiation detector, the area distribution of the radiation incident surface between the first detector 8 and the second detector 9 will be described. First, a specification sensitivity η per unit area as a radiation detector is determined from sensitivity and dimensions required for the radiation detector.
[0018]
Next, a required energy range, for example, 80 keV to 6.5 MeV, is divided into a plurality of regions. Here, for example, 80 keV to 200 keV is set as a low energy region, and 200 keV to 6.5 MeV is set as a high energy region. Since the sensitivity in the high energy region at this time is almost determined by the sensitivity of the detection body, first, the thickness of the detection body is determined.
[0019]
Therefore, the relative sensitivity per unit area of the detection body with respect to each photon energy is obtained using the thickness of the detection body as a parameter. Graph A in FIG. 2 shows relative sensitivities when the thicknesses of the detection bodies are set to a ₁ , a ₂ , and a ₃ (thickness relationships are a ₁ > a ₂ > a ₃ ), respectively.
[0020]
The thickness of the detection body is determined to be, for example, the thickness a ₁ so that the photon energy characteristic satisfies the allowable range over the entire high energy region. Then, the relative sensitivity η ₂ at the center energy of the high energy region of thickness a ₁ (here, 3 MeV between the centers of 200 keV to 6.5 MeV) is read from a ₁ of graph A in FIG. .
[0021]
Next, when the thickness of the first radiation absorption filter 14 with respect to the thickness a _{1 of the} detection body determined as described above is used as a parameter, per unit area of the first detection body for each photon energy. Find the relative sensitivity. Graph B in FIG. 2 shows b ₁ , b ₂ , b ₃ , and b ₄ as the thickness of the first radiation absorbing filter 14 (thickness relationship is b ₁ > b ₂ > b ₃ > b ₄ ). The relative sensitivity when set to.
[0022]
The thickness of the first radiation absorption filter 14 is determined to be, for example, the thickness b ₂ so that the photon energy characteristic satisfies the allowable range over the entire low energy region. Then, the relative sensitivity η ₁ of the center energy (here, for example, 150 keV between the centers of 80 keV to 200 keV) of this thickness b ₂ is read from b ₂ of the graph B in FIG.
[0023]
Next, the thickness of the second radiation absorbing filter 15 that covers the second detector 9 is such that the thickness of the second energy absorbing filter 15 does not substantially detect the low energy region, and the photon energy characteristics over the entire high energy region. The thickness is determined to satisfy the allowable range.
[0024]
Therefore, when the thickness of the second radiation absorbing filter 15 with respect to the thickness a _{1 of} the second detector 9 determined as described above is used as a parameter, the second detector 9 with respect to each photon energy. Find the relative sensitivity per unit area. Graph C in FIG. 2 shows relative values when the thickness of the second radiation absorbing filter 15 is set to c ₁ , c ₂ , and c ₃ (thickness relationships are c ₁ > c ₂ > c ₃ ), respectively. Indicates sensitivity. Here, the thickness of the second radiation absorbing filter 15 is determined, for example, the thickness c _2. Then, the relative sensitivity η ₃ of the central energy (here, for example, ₃ MeV) in the high energy region of the thickness c ₂ is read from c ₂ of the graph C in FIG.
[0025]
By setting in this way, the detection of the low energy region is detected with the relative sensitivity η ₁ in the area S ₁ of the radiation incident surface of the first detector 8. Then, the detection of high-energy regions, generally, in relative sensitivity eta ₃ at the area S ₀ of the radiation incident surface of the second detection body 9, the relative in radiation entrance surface area S ₁ of the first detection member 8 Radiation is detected with sensitivity η ₂ .
[0026]
Then, the area S ₁ of the radiation incident surface of the first detector 8 and the area S ₀ of the radiation incident surface of the second detector 9 are adjusted so that the sensitivities of the radiation detectors in the low energy region and the high energy region are aligned. The detection sensitivity per unit area of the radiation detector is made equal to the specification sensitivity η. When each area is weighted and combined as shown in FIG. 3, it can be confirmed that the sensitivity difference from the low energy region to the high energy region is within about ± 20%.
[0027]
The radiation detector according to the first embodiment configured as described above includes a first detector having a small area of the radiation incident surface above the radiation incident surface of the second detector 9 having a large area of the radiation incident surface. The amount of radiation absorbed by the first radiation absorbing filter 14 of the first detector 8 placed on the upper stage is equal to the amount of radiation absorbed by the second radiation absorbing filter 15 of the second detector 9. Since it is set smaller, a low energy region to a high energy region can be detected with uniform sensitivity.
[0028]
In the first embodiment, the electrodes 10, 11, 12, and 13 are provided on both surfaces of the detectors 8 and 9 to detect radiation, but the present invention is not limited to this. For example, as shown in FIG. 4, a conductive member 17 is provided between the first detector 8 and the second radiation absorption filter 15, and the first detector 8 and the second detector 9 are electrically connected. Connect to. Then, the electrode on the side sandwiched between the first detection body 8 and the second detection body 9, for example, the electrode 12 is shared as plus or minus.
[0029]
Further, the electrode 10 on the upper surface of the first detection body 8 and the electrode 13 on the lower surface of the second detection body 9 are set as negative or positive electrodes on the same side, and are connected by a connection line. In this way, it is possible to reduce the number of connection lines as well as to achieve the same effect as in the first embodiment, and to simplify the configuration.
[0030]
In the first embodiment, the sensitivity is set in the first and second detectors 8 and 9 with the target energy region divided into the low energy region and the high energy region. However, the present invention is not limited to this. If three target bodies are provided, the target energy region is divided into three parts, and radiation absorbing filters and detectors corresponding to the respective energy areas are provided, for example, as shown in FIG. The uniformity of sensitivity in the middle part of the energy range can be improved, and the overall sensitivity is further flattened.
[0031]
Embodiment 2. FIG.
In the first embodiment, the case where the electromagnetic shield is particularly provided is not described. However, in the second embodiment, the case where the electromagnetic shield is provided is described. FIG. 6 is a cross-sectional view showing the configuration of the radiation detector according to the second embodiment. In the figure, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. Reference numeral 18 denotes an electromagnetic shield that covers all the detection bodies 8 and 9.
[0032]
Reference numerals 19 and 20 denote minus electrodes formed on the surfaces of the respective detection bodies 8 and 9 on the side close to the electromagnetic shield 18. By forming in this way, the upper surface side of the first detection body 8 at the uppermost position. In addition, the potential on the lower surface side of the second detection body 9 at the lowermost position can be set to 0 potential. 21 is a positive electrode formed on the surface of the second detector 9 opposite to the negative electrode 20, 22 is a conductive member formed so as to contact the positive electrode 21, and the positive electrode 21 side is electrically connected. It is for securely holding on the positive side.
[0033]
The radiation detector according to the second embodiment configured as described above uses an electromagnetic shield 18 to prevent external noise intrusion. At this time, since the minus electrodes 19 and 20 of the detection bodies 8 and 9 on the side close to the electromagnetic shield 18 are set to 0 electrodes, the electromagnetic shield 18, the first radiation absorption filter 14, and the second detection body. Therefore, the stray capacitance between the electromagnetic shield 18 and the portion inside the electromagnetic shield 18 is minimized and becomes electrically stable. Therefore, reliable noise resistance can be obtained. In addition, the electrode shield 18 can also serve as the first radiation absorption filter 14 and can simplify the configuration.
[0034]
In each of the embodiments described above, an example in which CdTe is used as each of the detectors 8 and 9 has been described. However, the present invention is not limited to this, and CdZnTe as a semiconductor capable of detecting radiation is used. A detector may be formed. As shown in FIG. 7, the sensitivity of CdTe begins to decrease at a temperature of about 50 ° C. or higher, and the temperature characteristic that is practically required is ± 10% up to about 60 ° C.
[0035]
However, CdZnTe can be used up to about 100 ° C., and can be used even in a high temperature environment. Therefore, for example, it is suitable for the use of a radiation detector or the like that is installed close to a place where there is a possibility that the temperature of the measurement target may become high during an accident, such as an exhaust gas monitor for accidents.
[0036]
Further, in each of the above-described embodiments, the example in which the respective detection bodies 8 and 9 are formed only in one direction plane is shown, but the present invention is not limited to this. For example, as shown in FIG. Each of the detectors 8 and 9 may be provided on a plurality of surfaces of the structure, and each of the radiation absorbing filters 14 and 15 (not shown) may be provided. The detection area can be expanded as compared with the case of forming in the above.
[0037]
【The invention's effect】
As described above, a plurality according to this inventions, in the radiation detector using the semiconductor capable of detecting radiation as a sensing element, the sensing element which is the area of the radiation entrance surface different desired thickness is set Each detector is mounted on the upper side of the radiation incident surface of the detector having a larger area of the radiation incident surface, and the radiation incident surface side of each detector is placed on the radiation incident surface side of the detector. Radiation detection in which the thickness of each of the radiation absorption filters is set so that the radiation absorption filter includes a radiation absorption filter that covers each of the radiation detectors and the radiation absorption filter that covers the radiation incident surface of the detection object is smaller in the upper detection body. a vessel, when enclosing all the sensing elements in electromagnetic shielding, since the lower surface side of the potential of the detection of the upper surface side and the lowermost position of the detection of the uppermost position is set to zero potential, wide It is possible to provide a radiation detector capable of detecting and uniform sensitivity in energy region.
In addition, it is possible to provide a radiation detector that is electrically stable and can obtain reliable noise resistance.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the configuration of a radiation detector according to Embodiment 1 of the present invention.
FIG. 2 is a diagram showing the relationship between photon energy and relative sensitivity when the thicknesses of the radiation absorption filter and detector for forming the radiation detector shown in FIG. 1 are used as parameters, respectively.
FIG. 3 is a diagram showing a relationship between photon energy and relative sensitivity of the radiation detector shown in FIG. 1;
FIG. 4 is a cross-sectional view showing the configuration of the radiation detector according to the first embodiment of the present invention.
FIG. 5 is a diagram showing the relationship between photon energy and relative sensitivity of the radiation detector according to Embodiment 1 of the present invention;
FIG. 6 is a cross-sectional view showing a configuration of a radiation detector according to Embodiment 2 of the present invention.
FIG. 7 is a diagram showing the relationship between the temperature and relative sensitivity of each substance in the detector of the radiation detector according to the second embodiment of the present invention.
FIG. 8 is a diagram showing a configuration of a radiation detector according to a second embodiment of the present invention.
FIG. 9 is a cross-sectional view showing a configuration of a conventional radiation detector.
10 is a cross-sectional view showing a configuration of a detector of the radiation detector shown in FIG.
11 is a diagram showing the relationship between photon energy and relative sensitivity when the thickness of the radiation absorption filter for forming the radiation detector shown in FIG. 9 is used as a parameter.
[Explanation of symbols]
8 1st detection body, 9 2nd detection body 10, 11, 12, 13 electrode,
14 1st radiation absorption filter, 15 2nd radiation absorption filter,
16 Insulating film, 17, 22 Conductive member, 18 Electromagnetic shield,
19, 20 Negative electrode, 21 Positive electrode, 23 Regular hexahedral structure.

Claims (1)

In a radiation detector using a semiconductor capable of detecting radiation as a sensing element, the radiation detector includes a plurality of sensing elements having different radiation incident areas and having a desired thickness. A detector with a small area of the radiation incident surface is placed on the upper part of the radiation incident surface of the detector with a large area, and is provided with a radiation absorption filter that covers the radiation incident surface side of each of the detectors, and is located in the upper stage. A radiation detector in which the thickness of each of the radiation absorption filters is set so that the radiation absorption amount of the radiation absorption filter covering the radiation incident surface of the detection body is smaller as the detection body is, and all the detection bodies are electromagnetic shields. , The radiation detector is characterized in that the potential on the upper surface side of the detection body at the uppermost position and the lower surface side of the detection body at the lowermost position is set to 0 potential .

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