JP2016020832A - Radiation detector and radiation monitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-weight, compact radiation detector capable of quickly locating radioactive substances in a widely contaminated area, and to provide a radiation monitor having the same.SOLUTION: A radiation detector includes: a sensor unit 10 having front-stage sensor elements 13 that detect a partial Compton scattered electron energy value, and rear-stage sensor elements 14 that detect a residual Compton scattered electron energy value; and a signal processing unit 20 that obtains a Compton scattered electron energy value by adding the partial Compton scattered electron energy value and the residual Compton scattered electron energy value and computes an incident angle. A radiation monitor having such radiation detector 1 is also disclosed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radiation detector that performs monitoring in an environment where a large number of γ rays are incident from a wide area, and a radiation monitor equipped with the radiation detector.

  When a large amount of radioactive material is dissipated into the environment and pollution occurs in a wide area, decontamination is performed in order to reduce the dose in the human living space. Decontamination is removal or shielding (covering with a shielding object) of a radioactive substance or a substance to which a radioactive substance is attached, and removing contamination. In proceeding with such decontamination work, there is a demand to monitor radiation over a wide area.

  By this monitoring, radioactive substances accumulate and the location (hot spot) with a high dose rate is determined. The efficiency of the decontamination work can be increased by preferentially decontaminating the part and confirming the effect after the decontamination work. However, conventionally, there has been no monitor for monitoring radiation in a wide area as described above and determining a portion with a high dose rate.

  There is a Compton camera that detects the position of a radioactive substance at a wide angle. If the prior art of this Compton camera is given, there are those used in nuclear medicine, although the industrial fields are different. For example, what is disclosed in Patent Document 1 is known.

  The apparatus described in Patent Document 1 includes a Compton camera having a front-stage detector that detects information of charged particles generated by Compton scattering in gas and a rear-stage detector that detects information of scattered photons. It is configured by stacking a plurality of upstream detectors with different types of gas.

JP 2008-232971 A

  This Compton camera is used in nuclear medicine examinations. Nuclear medicine tests diagnose a disease using a radiopharmaceutical containing a very small amount of radioactive material. This small amount of radiopharmaceutical is put into the body by injection or the like, the radioactive substance is concentrated in a specific organ (bone, tumor, etc.), the radiation emitted from it is measured from outside the body with a Compton camera, and the distribution is imaged to form an organ. Check the function (function). Such a Compton camera for nuclear medicine examination detects one place where radiation is emitted from a very small amount of radioactive material, and it is easy to identify this place.

  However, in the monitoring when contamination occurs in a wide area, it is assumed that many radiations are incident from multiple directions at the same time, so it is not easy to specify the position and angle, and the conventional Compton camera is used for monitoring the contaminated environment. Cannot simply be applied. There was a request to be able to monitor in the wide area when pollution caused by the dissipation of radioactive material occurred.

  Furthermore, monitoring when contamination occurs in a wide area does not allow accurate inspection over a sufficient amount of time as in nuclear medicine inspection applications. There was a request to be able to perform quick monitoring because it affects decontamination efficiency.

  And there was a request to make it a lightweight and compact device. For example, a sodium iodide crystal detector equipped with a perforated lead shielding collimator is known as a conventional radiation detector, but it is large in size and heavy. There was a request to make the radiation detector smaller and lighter.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a lightweight and small radiation detector that quickly locates a radioactive substance in a contaminated area in a wide area, and this radiation. The object is to provide a radiation monitor equipped with a detector.

The invention according to claim 1 of the present invention is
A pre-stage sensor element for detecting a partially Compton scattered electron energy value, which is a partial energy of Compton scattered electrons, by making a γ-ray radiated from a radioactive material incident to generate a Compton scattering phenomenon;
A rear sensor element that is arranged to face the front sensor element and detects a residual Compton scattered electron energy value, which is the remaining energy of the Compton scattered electrons scattered by the Compton scattering phenomenon in the front sensor element;
A radiation detector comprising:

The invention according to claim 2 of the present invention is
The radiation detector according to claim 1.
The latter sensor element is a radiation detector characterized in that the detection efficiency for Compton scattered electrons is nearly 100%, and the detection efficiency for Compton scattered γ rays is 1% or less.

The invention according to claim 3 of the present invention is
The radiation detector according to claim 1 or 2,
The radiation detector is characterized in that a dead layer having a predetermined thickness is provided between the front sensor element and the rear sensor element.

The invention according to claim 4 of the present invention is
In the radiation detector as described in any one of Claims 1-3,
It is set as the radiation detector characterized by providing the resin collimator which covers the circumference | surroundings of the said front | former stage sensor element and the said back | latter stage sensor element.

The invention according to claim 5 of the present invention is
In the radiation detector as described in any one of Claims 1-4,
The front sensor elements are arranged in a matrix of n × n,
The rear sensor elements are arranged in an n × n matrix to form a rear sensor unit,
A radiation detector is characterized in that the front sensor unit and the rear sensor unit are opposed to each other.

The invention according to claim 6 of the present invention is
In the radiation detector as described in any one of Claims 1-5,
The signal processing unit includes a signal processing unit to which detection signals from the front sensor element and the rear sensor element are input.
Detection data selection means for selecting detection data relating to detection signals output simultaneously from the front sensor element and the rear sensor element;
Compton scattered electron energy value detection for obtaining the Compton scattered electron energy value by adding the detected data of the partially Compton scattered electron energy value from the former sensor element and the detected data of the residual Compton scattered electron energy value from the latter sensor element. Means,
A radiation detector that functions as a position specifying unit that calculates an incident angle of γ rays from pre-registered γ ray energy values and Compton scattered electron energy values.

The invention according to claim 7 of the present invention provides
The radiation detector according to claim 6.
The position specifying means of the signal processing unit is:
Compton scattered γ-ray energy value calculating means for calculating a Compton scattered γ-ray energy value from a pre-registered γ-ray energy value and Compton scattered electron energy value;
Compton scattering γ-ray scattering angle calculating means for calculating a Compton scattering γ-ray scattering angle from a pre-registered γ-ray energy value and Compton scattering γ-ray energy value;
It functions as a Compton scattering electron scattering angle calculation means for calculating the Compton scattering electron scattering angle from the Compton scattering γ ray scattering angle,
The radiation detector is characterized by acquiring the Compton scattered electron scattering angle as an incident angle.

The invention according to claim 8 of the present invention is
The radiation detector according to claim 6.
The signal processing unit includes a database that registers a Compton scattered electron scattering angle in association with a Compton scattered electron energy value,
The position specifying means of the signal processing unit is:
Functions as a database reference means for reading the Compton scattered electron scattering angle corresponding to the detected Compton scattered electron energy value,
The radiation detector is characterized by acquiring the Compton scattered electron scattering angle as an incident angle.

The invention according to claim 9 of the present invention is
A moving object,
The radiation detector according to any one of claims 1 to 8, which is attached to the lower side of the movable body so that the front-stage sensor element faces downward.
With
A radiation monitor is characterized in that a moving body is positioned above a detection target location, and the radiation detector detects radiation at a detection target location below.

  According to the present invention, it is possible to provide a light and small radiation detector that quickly locates a radioactive substance in a contaminated area in a wide area, and a radiation monitor equipped with this radiation detector.

It is a block block diagram of the radiation detector of the form for implementing this invention. 2A and 2B are explanatory views of the sensor unit, in which FIG. 2A is a perspective view with the rear sensor unit removed, and FIG. 2B is a perspective view of a normal sensor unit. It is a block block diagram explaining the internal structure of a signal processing part. It is explanatory drawing of the radiation detection principle of the radiation detector of this invention. It is a table | surface which shows the relationship between an energy value and a scattering angle. It is a characteristic view which shows the relationship between an energy value and a scattering angle. It is a figure which shows the specific example of an energy value and a scattering angle, FIG. 7 (a) is a figure which shows the example whose incident angle is 0 degree, FIG.7 (b) is a figure which shows the example whose incident angle is 31.9 degrees. It is. It is a figure which shows the specific example of an energy value and a scattering angle, FIG.8 (a) is a figure which shows the example whose incident angle is 46.4 degrees, FIG.8 (b) is an example whose incident angle is 58.4 degrees. FIG. It is a flowchart explaining the signal processing by a signal processing part. It is a flowchart explaining the other signal processing by a signal processing part. It is a block block diagram of the principal part of the radiation detector of the other form for implementing this invention. It is explanatory drawing of the radiation monitor of the form for implementing this invention.

  Next, a radiation detector and a radiation monitor according to an embodiment for carrying out the present invention will be described below with reference to the drawings. First, the radiation detector will be described. As shown in FIG. 1, the radiation detector 1 includes a sensor unit 10, and further includes a signal processing unit 20 that processes a detection signal of the sensor unit 10.

  Specifically, as shown in FIGS. 1 and 2, the sensor unit 10 includes a front sensor unit 11 and a rear sensor unit 12. In the front sensor unit 11, the front sensor elements 13 are arranged in a matrix as shown in FIG. 2A, and in the rear sensor unit 12, the rear sensor in a matrix as shown in FIG. 2B. Element 14 is arranged. One front sensor element 13 and the rear sensor element 14 immediately above form one set of sensors.

  The pre-stage sensor element 13 is a semiconductor-type radiation detection element using silicon, which is a light element, and generates a depletion layer by applying a reverse bias to a semiconductor having a diode structure. Compton scattered electrons generated by the Compton scattering reaction at the time of collision with the electron collect electrons of electron-hole pairs generated when passing through this depletion layer, thereby obtaining one pulse for one radiation. The magnitude of this pulse is proportional to the distance through which the Compton scattered electrons pass, but the Compton scattered electrons have such a large energy as to jump out toward the rear sensor element 14, and the front sensor element 13 has one of the Compton scattered electrons. The partial Compton scattered electron energy value, which is the energy of the part, is detected. In the former sensor element 13, incident γ rays need to collide with static electrons to cause a Compton scattering reaction, but silicon is also advantageous in this respect because it tends to cause a Compton scattering reaction.

  The post-stage sensor element 14 is also a semiconductor radiation detection element using silicon, which is a light element, and a depletion layer is generated by applying a reverse bias to a semiconductor having a diode structure, and is incident from the pre-stage sensor element 13. Compton scattered electrons collect electrons of electron-hole pairs generated when passing through this depletion layer, thereby obtaining one pulse for one radiation. The rear sensor element 14 detects a residual Compton scattered electron energy value that is the remaining energy of the Compton scattered electrons scattered by the Compton scattering phenomenon in the front sensor element 13. Silicon has a detection efficiency of nearly 100% with respect to Compton scattered electrons, and has a detection efficiency of 1% or less with respect to Compton scattered γ-rays, which is noise. In particular, Compton scattered electrons are detected, but silicon having a thin sensitive layer is employed to make it difficult to detect Compton scattered γ rays. Thereby, the S / N ratio can be increased.

  Further, a gap (insensitive layer) is provided between the front sensor element 13 and the rear sensor element 14. The presence of the insensitive layer prevents electrons having a low energy level such as noise from reaching the detection efficiency for Compton scattered electrons caused by γ rays from the radioactive material to be detected. As the width (thickness) of such a void (insensitive layer), at least a width that can detect Compton scattered electrons due to γ rays of a nuclide to be measured (Cs137 in this embodiment) is adopted.

  The front-stage sensor unit 11 and the rear-stage sensor unit 12 are 5 × 5 matrices as shown in FIGS. 2A and 2B, but are not limited to this, and the n × n matrix and can do. For example, in the front-stage sensor unit 11 and the rear-stage sensor unit 12, the front sensor element 13 and the rear sensor element 14 each having a square of 10 mm can be arranged at 10 × 10 so that the square is about 100 mm. In the sensor unit 10, γ rays are incident on the lower front sensor unit 11. All of the front-stage sensor element 13 and the rear-stage sensor element 14 are connected to the signal processing unit 20, respectively.

  As shown in FIG. 3, the signal processing unit 20 includes a front processing unit 21 connected to the front sensor element 13, a front processing unit 22 connected to the rear sensor element 14, and a CPU 23 connected to the front processing units 21 and 22. The data storage unit 24 and the data communication unit 25 connected to the CPU 23 are provided. Although not shown in FIG. 3, the pre-stage processing unit 21 includes the same number of n × n (5 × 5 in the present embodiment) pre-stage sensor elements 13. Further, the pre-stage processing unit 22 includes the same number as n × n (in this embodiment, 5 × 5) rear-stage sensor elements 14.

The pre-stage processing units 21 and 22 have a function of adjusting detection signals from the pre-stage sensor element 13 and the post-stage sensor element 14, and an amplifier that adjusts the wave height for input to the CPU 23 or a detection signal as digital detection data. An AD converter for conversion is installed. The pre-processing units 21 and 22 may be configured to be built in the CPU 23.
For example, the CPU 23 generates result data on the energy value, the address that identifies the sensor from which the input detection data is emitted, the detection time, and the incident angle of radiation. The result data will be described later.

  The data storage unit 24 is a hard disk or USB memory that stores result data output from the CPU 23. Pre-registered data (γ-ray energy value), data obtained by measurement (Compton scattered electron energy value, address for specifying sensor position, detection time, etc.) and data calculated by calculation (incidence of γ-rays) Angle etc.) is stored as result data and used for offline processing on the ground.

  The data communication unit 25 converts the signal including the result data output from the CPU 23 into a radio wave suitable for air transmission such as by modulating the signal into a predetermined method, and transmits the radio wave via a transmission antenna (not shown). In this case, data including a γ-ray energy value, a Compton scattered electron energy value, an address specifying the detected sensor position, a detection time, an incident angle of γ-rays, etc. is generated and output by communication, and the analysis is performed elsewhere. And so on.

  Note that the radiation detector 1 is assumed to be used in a high-dose radiation region of 1 Sv to several tens of Sv. Electronic circuits included in the pre-processing units 21 and 22 such as preamplifiers, linear amplifiers, and comparators, the CPU 23, the data storage unit 24, and the data communication unit 25 are affected by malfunction of the circuit and deterioration of electronic components in the high-dose radiation region. Is concerned. Therefore, radiation countermeasures are taken so as not to be affected by high-dose radiation. The configuration of the radiation detector 1 is as described above.

  Next, the principle of radiation detection by the radiation detector 1 of the present invention will be described. This radiation detector 1 identifies the incident direction from the track and energy value of Compton scattered electrons generated by Compton scattering that occurs when γ rays are incident, and identifies the direction or position where the radioactive substance that becomes the γ ray source exists. To do. In Compton scattering, Compton scattered γ rays and Compton scattered electrons are generated, and both have angle information. A conventional Compton camera uses Compton scattered γ rays, but the present invention is different in that Compton scattered electrons are used.

  The pre-stage sensor element 13 is arranged facing the γ-ray generation source, as is apparent from FIG. Specifically, the front sensor element 13 is disposed facing downward. When γ-rays having a γ-ray energy value hν are incident on the upstream sensor element 13, they collide with static electrons in the upstream sensor element 13 with a predetermined probability (for example, 1%), and lose a part of the energy value to change the flight direction. Compton scattering is caused to generate Compton scattered γ rays having a Compton scattered γ ray energy value hν ′ and Compton scattered electrons having a Compton scattered electron energy value T. At the same time, the pre-stage sensor element 13 generates an electric signal pulse having a wave height proportional to the partial Compton scattered electron energy value, which is a partial energy of the Compton scattered electrons scattered by the Compton scattered phenomenon when γ rays are incident. To do.

  The rear sensor element 14 is disposed so as to face the front sensor element 13 and detects Compton scattered electrons emitted from the front sensor element 13. Then, when Compton scattered electrons are incident, an electric signal pulse having a wave height proportional to the remaining Compton scattered electron energy value, which is the remaining energy, is generated. Thus, when detected by the set of the rear sensor element 14 and the front sensor element 13 at the same time, the Compton scattered electrons are considered to be tracks that jump immediately above.

  The energy value is discriminated by measuring only the high energy value component that passes through the gap (insensitive layer) between the front sensor element 13 and the rear sensor element 14. As a result, γ rays incident at a constant incident angle with a high energy value are detected.

Here, when the γ-ray energy value hν of the γ-rays emitted from the radioactive substance, the Compton scattered γ-ray energy value hν ′, the Compton scattered electron energy value T, and the static energy value m ₀ c ^{2 of} the static electrons, The following equation holds from the law of value storage.

Here, regarding γ rays, it is assumed that γ rays are emitted from the radioactive substance Cs137, and the γ ray energy value hν of γ rays is registered in advance as a known value of 0.662 MeV. The Compton scattered electron energy value T is a total value of the partially Compton scattered electron energy value detected by the former sensor element 13 and the Compton scattered electron energy value detected by the latter sensor element 14. The static energy value m ₀ c ² of static electrons is registered as a constant. Therefore, the Compton scattered γ-ray energy value hν ′ can be calculated.

When the Compton scattered γ-ray scattering angle θ and the constant α (= hν / m ₀ c ² ), the following Klein-Nishina equation is established.

  Thereby, the Compton scattered γ-ray scattering angle θ is calculated. Further, the following equation is established when the Compton scattered electron scattering angle φ is used.

  In this way, the Compton scattered electron scattering angle φ is calculated. As is clear from FIG. 4, the Compton scattered electron scattering angle φ coincides with the incident angle when the γ-rays are incident on the front sensor element 13. That is, it is inferred that γ rays are incident from a radioactive substance on the ellipse in FIG. 4 (when viewed from above, a perfect circle). The incident direction of γ rays can be calculated and discriminated in a cone shape from the track of Compton scattered electrons (considered to fly directly above by detection by the upper and lower sensor elements) and the Compton scattered electron scattering direction φ.

  Probably, Compton scattered γ-rays may reach the upper rear sensor element 14 in this case, but in this case, the Compton scattered γ-rays are substantially transmitted through the rear sensor element 14, and thus the detection efficiency of Compton scattered γ-rays is increased. Is 1% or less, and even if detected, it is processed as noise.

Subsequently, the relationship among the Compton scattered γ-ray scattering angle θ, the Compton scattered γ-ray energy value hν ′, the Compton scattered electron energy value T, and the Compton scattered electron scattering angle φ is specifically shown in FIGS. Shown by value. Here, it is assumed that γ rays are emitted from the radioactive substance Cs137, and the γ ray energy value hν is 0.662 MeV. The constant α is equal to hν / m ₀ c ² = 0.662 / 0.511 = 1.295. As shown in FIGS. 5 and 6, if the Compton scattered electron energy value T is known, the Compton scattered electron scattering angle φ is determined on a one-to-one basis.

  As shown in FIG. 7A, when γ rays enter the front sensor element 13 from directly below, the Compton scattered electron scattering angle φ is 0 °, and the Compton scattered electron energy value T detected by the rear sensor element 14 is 0. .478 and the maximum value.

  As shown in FIG. 7B, when γ rays are incident on the front sensor element 13 at an incident angle of 31.9 °, the Compton scattered electron scattering angle φ is also 31.9 °, which is detected by the rear sensor element 14. Compton scattered electron energy value T to be as small as 0.305.

  As shown in FIG. 8A, when γ rays are incident on the front sensor element 13 at an incident angle of 46.4 °, the Compton scattered electron scattering angle φ is also 46.4 °, which is detected by the rear sensor element 14. Compton scattered electron energy value T to be further reduced to 0.182.

  As shown in FIG. 8B, when γ rays are incident on the front sensor element 13 at an incident angle of 58.4 °, the Compton scattered electron scattering angle φ is 58.4 °, and the rear sensor element 14 detects it. Compton scattered electron energy value T to be further reduced to 0.098.

  In the radiation detector 1, by selecting a case where the Compton scattered electron energy value T detected by both the front-stage sensor element 13 and the rear-stage sensor element 14 is equal to or greater than a predetermined value, γ rays within a certain incident angle range are selected. Only the detection target. For example, it can be detected only when the Compton scattered electron energy value T is 0.305 or more, and only γ rays having an incident angle of 0 ° or more and 30 ° or less can be detected.

  Thereby, it is possible to select only the γ-rays immediately below the radiation detector 1, select the state of the specific location, and detect with high accuracy. For example, the Compton camera of the prior art dealt with the incident direction of γ rays incident from all directions, but the radiation detector 1 of the present invention makes it possible to detect at high speed by narrowing the detection target. However, the detection capability is also improved. The detection principle is like this.

  Next, the detection process by the signal processing unit 20 will be described with reference to the flowchart of FIG. This process is for explaining detection by a pair of the front sensor element 13 and the rear sensor element 14 that are vertically opposed to each other. Done.

  When the detection data related to the detection signal is input from the front-stage sensor element 13 and the rear-stage sensor element 14 via the front-stage processing sections 21 and 22, the signal processing section 20 is simultaneously received from the front-stage sensor element 13 and the rear-stage sensor element 14. It functions as detection data selection means for selecting only the detection data at the time of output (step S1 in FIG. 9).

  In Compton scattering, the emission of Compton scattered electrons due to the incidence of γ rays on the front sensor element 13 and the incidence of Compton scattered electrons on the rear sensor element 14 are substantially simultaneous. Therefore, by selecting only the detection data related to the detection signals simultaneously detected by the front sensor element 13 and the rear sensor element 14 that form a pair at the top and bottom, the Compton scattered electrons whose tracks are only directly above are selected, and the others are regarded as noise. Remove. At this time, an address notifying which position on the matrix the set of the rear sensor element 13 and the rear sensor element 14 is included is included as position data. The detection time is also included as data.

  Subsequently, the signal processing unit 20 acquires the Compton scattered electron energy value T from the detection data of the partial Compton scattered electron energy value from the front sensor element 13 and the residual Compton scattered electron energy value from the rear sensor element 14. It functions as an energy value detection means (step S2 in FIG. 9). The wave height of the detection data is proportional to the energy value, and an energy value corresponding to the wave height is acquired. The Compton scattered electron energy value T is a total value of the partial Compton scattered electron energy value detected by the front sensor element 13 and the residual Compton scattered electron energy value detected by the rear sensor element 14.

Subsequently, the signal processing unit 20 calculates the Compton scattered γ-ray energy value hν ′ from the γ-ray energy value hν previously registered in the data storage unit 24 and the detected Compton scattered electron energy value T. It functions as an energy value calculation means (step S3 in FIG. 9). The Compton scattered γ-ray energy value hν ′ is calculated from Equation 1 above. Note that m ₀ c ² is also registered in the data storage unit 24.

  Subsequently, the signal processing unit 20 calculates the Compton scattered γ-ray scattering angle θ from the γ-ray energy value hν registered in advance in the data storage unit 24 and the calculated Compton scattered γ-ray energy value hν ′. It functions as a line scattering angle calculation means (step S4 in FIG. 9). The Compton scattered γ-ray scattering angle θ is calculated from Equation 2 above. Α is also registered in the data storage unit 24.

  Subsequently, the signal processing unit 20 functions as a Compton scattered electron scattering angle calculation unit that calculates the Compton scattered electron scattering angle φ from the calculated Compton scattered γ-ray scattering angle θ (step S5 in FIG. 9). The Compton scattered electron scattering angle φ is calculated from the above equation (3).

  Subsequently, the signal processing unit 20 functions as a result data generation unit that generates the result data by using the calculated Compton scattered electron scattering angle φ as the incident angle of γ rays (step S6 in FIG. 9). The result data is calculated by, for example, pre-registered data (γ-ray energy value), data obtained by measurement (Compton scattered electron energy value, address for specifying the position of the sensor, detection time, etc.) or calculation. Data (incidence angle of γ rays, etc.) and the like are generated as result data.

  Further, the input γ rays may be counted to calculate the dose and include it in the result data. Furthermore, position-specific dose rate data in which the address for specifying the position, the detection time, and the count value are associated may be included in the result data. Realize on-site monitoring where measurement is performed by calculating dose rates by location. The content of the result data is appropriately selected according to the actual situation.

  The signal processing unit 20 functions as an output unit that outputs the result data (step S7 in FIG. 9). As shown in FIG. 3, the result data may be registered in the data storage unit 24, or the result data may be output to the data communication unit 25 and transmitted to other locations by communication. Further, registration and communication may be performed by outputting to both the data storage unit 24 and the data communication unit 25. The radiation detector 1 is like this.

  Next, another form of the radiation detector 1 will be described. In this embodiment, the configuration is the same as that of the radiation detector 1 described with reference to FIGS. 1 to 8, but instead of the algorithm of the flowchart of FIG. 9, an algorithm that realizes high-speed processing as shown in FIG. 10 is adopted. Is different. Further, the signal processing unit 20 registers data as shown in FIG. 5, and in particular, associates the Compton scattered electron scattering angle φ with one-to-one correspondence in association with the Compton scattered electron energy value T. The difference is that a database is provided. If the Compton scattered electron energy value T (for example, 0.444 MeV in FIG. 5) is determined in this database, the corresponding Compton scattered electron scattering angle φ (for example, 12.8 ° in FIG. 5) is determined. .

Next, signal processing in this embodiment will be described with reference to FIG.
When the detection data related to the detection signal is input from the front-stage sensor element 13 and the rear-stage sensor element 14 via the front-stage processing sections 21 and 22, the signal processing section 20 It functions as detection data selection means for selecting only the detection data at the time of output (step S11 in FIG. 10).

  In Compton scattering, the emission of Compton scattered electrons due to the incidence of γ rays on the front sensor element 13 and the incidence of Compton scattered electrons on the rear sensor element 14 are substantially simultaneous. Therefore, by selecting only the detection data related to the detection signals simultaneously detected by the front sensor element 13 and the rear sensor element 14 that form a pair at the top and bottom, the Compton scattered electrons whose tracks are only directly above are selected, and the others are regarded as noise. Remove. At this time, an address notifying which position on the matrix the set of the rear sensor element 13 and the rear sensor element 14 is included is included as position data. The detection time is also included as data.

  Subsequently, the signal processing unit 20 acquires the Compton scattered electron energy value T from the detection data of the partial Compton scattered electron energy value from the front sensor element 13 and the residual Compton scattered electron energy value from the rear sensor element 14. It functions as an energy value detection means (step S12 in FIG. 10). The wave height of the detection data is proportional to the energy value, and an energy value corresponding to the wave height is acquired. The Compton scattered electron energy value T is a total value of the partial Compton scattered electron energy value detected by the front sensor element 13 and the residual Compton scattered electron energy value detected by the rear sensor element 14.

  Subsequently, the signal processing unit 20 functions as a database reference unit that reads the Compton scattered electron scattering angle φ corresponding to the detected Compton scattered electron energy value T from the database (step S13 in FIG. 10). Thus, the Compton scattered electron scattering angle φ is calculated.

  Subsequently, the signal processing unit 20 functions as a result data generating unit that generates the result data by using the calculated Compton scattered electron scattering angle φ as the incident angle of γ rays (step S14 in FIG. 10). The result data is calculated by, for example, pre-registered data (γ-ray energy value), data obtained by measurement (Compton scattered electron energy value, address for specifying the position of the sensor, detection time, etc.) or calculation. Data (incidence angle of γ rays, etc.) and the like are generated as result data.

  Alternatively, the input γ rays may be counted, and the dose may be calculated from the count value and included in the result data. Furthermore, position-specific dose rate data in which the address for specifying the position, the detection time, and the count value are associated may be included in the result data. Realize on-site monitoring where measurement is performed by calculating dose rates by location. The content of the result data is appropriately selected according to the actual situation.

  The signal processing unit 20 functions as an output unit that outputs the result data (step S15 in FIG. 10). As shown in FIG. 3, the result data may be registered in the data storage unit 24, or the result data may be output to the data communication unit 25 and transmitted to another location by communication. Further, registration and communication may be performed by outputting to both the data storage unit 24 and the data communication unit 25. The radiation detector 1 is like this.

  In such a radiation detector 1, since the time-consuming calculations such as Equations 1 to 3 above are omitted, the processing time can be increased by simplifying the algorithm. In particular, as is apparent from processing for a large number of sensors of n × n, the calculation load can be reduced.

Next, another form of radiation detector will be described. FIG. 11 is a block configuration diagram of another form of radiation detector.
In the sensor part 10, in addition to the structure demonstrated previously, the lightweight resin collimator 15 is arrange | positioned. The resin collimator 15 limits the Compton scattered electron scattering angle to within about ± 30 °, for example. Since the track of Compton scattered electrons is limited (for example, within ± 30 °), the incident angle can be calculated more accurately from the energy value. Further, by limiting the tracks, the calculation load can be reduced. Such a resin collimator 15 may be applied in each form described above with reference to FIGS.

  The signal processing unit 20 is connected to the amplifier 26 connected to the front sensor element 13, the amplifier 27 connected to the rear sensor element 14, the analog adder 28 connected to both amplifiers 26, 27, and the analog adder 28. SCA (single channel analyzer) 29, CPU 23 connected to n × n SCA 29 equal to the number of sensors, data storage unit 24, and data communication unit 25.

  For example, a partial Compton scattered electron energy value, which is a part of energy of Compton scattered electrons that are scattered by the Compton scattering phenomenon when γ-rays are incident on the front sensor element 13, is acquired, and the Compton scattering is transmitted to the rear sensor element 14 almost simultaneously. It is assumed that the residual Compton scattered electron energy value, which is the energy remaining after the electrons are incident, is acquired. The analog adder 28 adds the output from the rear sensor element 14 when the output from the front sensor element 13 is obtained. The analog adder 28 adjusts the wave height and outputs it. The analog adder 28 outputs a Compton scattered electron energy value T obtained by adding the partially Compton scattered electron energy value and the remaining Compton scattered electron energy value to the SCA 29.

  The SCA 29 identifies 0.478 to 0.305 [MeV] representing the Compton scattered electron energy value T within ± 30 ° from the input value, and outputs each count value. The CPU 23 detects how many times the γ-rays are input to a certain pre-stage sensor element 13 at a predetermined angle. Then, the data is stored in the data storage unit 24 or is output to another management apparatus via the data communication unit 25. These data identify how much radiation has been output from which part. Such a radiation monitor may be used. In this embodiment, since data to be processed is thinned out by the amplifiers 26 and 27 and the analog adder 28 which are analog circuits, the processing of the CPU 23 is reduced, which contributes to further speedup.

  In the radiation detector 1 described above, a partial Compton scattered electron energy value, which is a partial energy of Compton scattered electrons that are scattered by the Compton scattering phenomenon when γ-rays are incident on the front sensor element 13, is obtained. At the same time, it is assumed that the residual Compton scattered electron energy value, which is the energy remaining after the Compton scattered electrons are incident on the rear sensor element 14, is acquired. At this time, the dose may be calculated by counting as γ rays. Moreover, it is good also considering the dose rate data classified by position which matched the address which identifies a position, detection time, and a count value as result data. Realize on-site monitoring where measurement is performed by calculating dose rates by location.

  Next, the radiation monitor 2 on which the radiation detector 1 is mounted will be described. As shown in FIG. 12, the radiation monitor 2 includes a sensor unit 10 and a signal processing unit 20 of the radiation detector 1, and a radio control helicopter 30 which is a specific example of a moving object. For example, the sensor unit 10 is attached to the lower side of the radio control helicopter 30 and the signal processing unit 20 is attached to the inside.

  The radiation detector 1 has a weight of about 2 to 3 kg, for example, and is a weight that can be mounted on the radio control helicopter 30. This is because a lightweight silicon sensor is employed in place of the conventional scintillator or lead collimator.

  The radio control helicopter 30 is assumed to fly in a place where radioactive materials are dissipated. As shown in FIG. 12, the height from the ground to the radio controlled helicopter 30 which is a moving body is h, and the γ-ray with the incident angle φ is on a circle with a radius L = h · tan φ. And by acquiring a large number of data, it is possible to specify how much radioactive material is present in which part. In particular, since the moving body is located at a high location, the radiation monitor 2 can monitor a wide location even if the detectable angle of the radiation detector 1 is narrow. In addition, by moving the radio control helicopter 30, monitoring in a wide range is realized in a short time. The radiation monitor 2 is like this.

  In addition, although this embodiment demonstrated especially the form attached to a radio control helicopter, of course, it is not limited to such a form, For example, you may attach to a normal helicopter and an airplane. Further, the vehicle may be used by being attached to a bucket, crane, or ladder of an aerial work vehicle such as a bucket car, a crane car, or a ladder car. The radiation monitor 2 can be configured using a movable body that can move upward. The present invention can also be applied to such a radiation monitor.

  The radiation detector 1 and the radiation monitor 2 of the present invention have been described above. In the present embodiment, the description has been made assuming that radioactive cesium 137 having a long half-life is measured. However, other nuclides such as radioactive cesium 134 with a short half-life can also be detected. It is also possible to deal with 662 keV γ rays derived from radioactive cesium 137 and 605 keV and 796 keV γ rays derived from radioactive cesium 134. This can be dealt with by presetting the algorithm and database of the CPU 23 for these nuclides.

The present invention has the following advantages.
Conventionally, Compton scattered γ-rays are measured, and a large sensor is used in order to obtain detection efficiency of Compton scattered γ-rays. However, in the present invention, it is possible to reduce the weight and size by measuring Compton scattered electrons.

  In addition, as in the present invention, the front sensor element 13 and the rear sensor element 14 are arranged in two upper and lower layers, thereby realizing track identification and position detection.

  In addition, since the radiation monitor 2 detects only radioactive substances emitted from directly below, only the contamination status of the lower part of the moving body is monitored, so that the contamination status can be grasped reliably. it can.

  The radiation monitor of the present invention is capable of quickly identifying, for example, a region where high-dose radiation is concentrated and emitted in an area where radioactive materials are dissipated in a wide area, and is used for decontamination in a wide area. It is suitable for.

1: Radiation detector 2: Radiation monitor 10: Sensor unit 11: Pre-stage sensor unit 12: Sub-stage sensor unit 13: Pre-stage sensor element 14: Sub-stage sensor element 20: Signal processing units 21, 22: Pre-stage processing unit 23: CPU
24: Data storage unit 25: Data communication unit 26, 27: Amplifier 28: Analog adder 29: SCA
30: Radio control helicopter

Claims (9)

A pre-stage sensor element for detecting a partially Compton scattered electron energy value, which is a partial energy of Compton scattered electrons, by making a γ-ray radiated from a radioactive material incident to generate a Compton scattering phenomenon;
A rear sensor element that is arranged to face the front sensor element and detects a residual Compton scattered electron energy value, which is the remaining energy of the Compton scattered electrons scattered by the Compton scattering phenomenon in the front sensor element;
A radiation detector comprising: The radiation detector according to claim 1.
2. The radiation detector according to claim 1, wherein the latter sensor element is a Si sensor having a detection efficiency for Compton scattered electrons of nearly 100% and a detection efficiency for Compton scattered γ rays of 1% or less. The radiation detector according to claim 1 or 2,
A radiation detector, wherein a dead layer having a predetermined thickness is provided between the front sensor element and the rear sensor element. In the radiation detector as described in any one of Claims 1-3,
A radiation detector comprising a resin collimator that covers the periphery of the front sensor element and the rear sensor element. In the radiation detector as described in any one of Claims 1-4,
The front sensor elements are arranged in a matrix of n × n,
The rear sensor elements are arranged in an n × n matrix to form a rear sensor unit,
A radiation detector, characterized in that a front sensor part and a rear sensor part are opposed to each other. In the radiation detector as described in any one of Claims 1-5,
The signal processing unit includes a signal processing unit to which detection signals from the front sensor element and the rear sensor element are input.
Detection data selection means for selecting detection data relating to detection signals output simultaneously from the front sensor element and the rear sensor element;
Compton scattered electron energy value detection for obtaining the Compton scattered electron energy value by adding the detected data of the partially Compton scattered electron energy value from the former sensor element and the detected data of the residual Compton scattered electron energy value from the latter sensor element. Means,
A radiation detector that functions as a position specifying means for calculating an incident angle of γ-rays from pre-registered γ-ray energy values and Compton scattered electron energy values. The radiation detector according to claim 6.
The position specifying means of the signal processing unit is:
Compton scattered γ-ray energy value calculating means for calculating a Compton scattered γ-ray energy value from a pre-registered γ-ray energy value and Compton scattered electron energy value;
Compton scattering γ-ray scattering angle calculating means for calculating a Compton scattering γ-ray scattering angle from a pre-registered γ-ray energy value and Compton scattering γ-ray energy value;
It functions as a Compton scattering electron scattering angle calculation means for calculating the Compton scattering electron scattering angle from the Compton scattering γ ray scattering angle,
A radiation detector characterized in that the Compton scattered electron scattering angle is obtained as an incident angle. The radiation detector according to claim 6.
The signal processing unit includes a database that registers a Compton scattered electron scattering angle in association with a Compton scattered electron energy value,
The position specifying means of the signal processing unit is:
Functions as a database reference means for reading the Compton scattered electron scattering angle corresponding to the detected Compton scattered electron energy value,
A radiation detector characterized in that the Compton scattered electron scattering angle is obtained as an incident angle. A moving object,
The radiation detector according to any one of claims 1 to 8, which is attached to the lower side of the movable body so that the front-stage sensor element faces downward.
With
A radiation monitor, wherein a moving body is positioned above a detection target location, and the radiation detector detects radiation at a detection target location below.

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