JP2004170125A - Radiation measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine a direction along which radiation comes without requiring a rotary mechanism. <P>SOLUTION: A detection part 10 comprises three detection units 14, 16, and 18. The detection units 14 and 16 are detection units of a direction dependent type, and their directions are shifted by 90° from one another. In a standardizing part 50, a standardized discrete value is found by dividing a discrete value obtained by the detection unit 14 by a discrete value obtained by the detection unit 18. Likewise, in the standardizing part 50, a standardized discrete value is found by dividing a discrete value obtained by the detection unit 16 by a discrete value obtained by the detection unit 18. A coming direction determining part 54 determines a coming direction by referring to a response table 56 from the standardized two discrete values. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a radiation measurement apparatus, and more particularly to an azimuth detection type radiation measurement apparatus capable of detecting a radiation azimuth.
[0002]
[Prior art]
The azimuth detection type radiation detection apparatus is installed inside or outside the radiation handling facility (site of the radiation handling facility or at a monitoring point), and specifies a flight direction of radiation. For example, such a function may be incorporated in a radiation measurement device such as a survey meter or a monitoring post. Conventionally, a collimator for narrowing the detection field of view and providing sensitivity only in a specific direction is attached to a radiation detector, and a unit including the radiation detector and the collimator is automatically (or artificially) placed on a horizontal plane. By rotating the radiation and specifying a peak in the intensity distribution (dose rate distribution, count rate distribution, etc.) of the radiation obtained at that time, the arrival direction of the radiation is specified as the direction in which the peak exists.
[0003]
[Problems to be solved by the invention]
However, since the collimator has a form that covers almost the entire radiation detector, the weight is large, and the radiation detector itself is also subject to rotational driving, so that a large drive is required to rotate the above-described unit. A rotating mechanism that generates a force is required.
[0004]
An object of the present invention is to make it possible to specify a radiation azimuth without requiring a rotation mechanism. It is another object of the present invention to provide a new structure of the radiation detection unit.
[0005]
[Means for Solving the Problems]
The present invention includes at least one azimuth-dependent radiation detection unit having different sensitivities depending on azimuths, a detection unit including a plurality of radiation detection units, and a radiation azimuth from radiation values detected by the plurality of radiation detection units. And a calculation unit for specifying
[0006]
According to the above configuration, for example, a detection value is obtained from a plurality of detection values obtained by a plurality of radiation detection units by utilizing a fact that a detection value obtained by at least one azimuth-dependent radiation detection unit changes according to a radiation azimuth. The azimuth of the radiation is specified based on the mutual ratio. Here, the detection value may be a dose rate or a count rate.
[0007]
The detection unit may include a plurality of direction-dependent radiation detection units, or may include a direction-dependent radiation detection unit and a normal radiation detection unit having uniform sensitivity over all directions. Good. The azimuth detection range is desirably all directions (360 degrees), but may be limited to a specific range (for example, 180 degrees). For example, if the above configuration is incorporated in a monitoring post that measures environmental radiation, it is possible to easily identify, for example, the direction in which a radiation abnormality has occurred.
[0008]
Preferably, the azimuth-dependent radiation detection unit includes a radiation detector having uniform sensitivity characteristics in all directions, and a shielding member provided around the radiation detector and having a different degree of shielding depending on the direction. Including. Preferably, the width of the shielding member in the vertical direction gradually changes along the circumferential direction around the radiation detector. Preferably, the shielding member is provided all over the circumferential direction. Preferably, the shielding member is provided over a part of the circumferential direction.
[0009]
Preferably, the plurality of radiation detection units are arranged vertically. According to this configuration, mutual interference between the radiation detection units on the detection surface can be eliminated.
[0010]
Preferably, the detection unit has a first radiation detection unit as the azimuth-dependent radiation detection unit, and an azimuth-dependent sensitivity characteristic different from the azimuth-dependent sensitivity characteristic of the first radiation detection unit. A second radiation detection unit as a dependent radiation detection unit. The azimuth sensitivity characteristic corresponds to the response characteristic in the horizontal direction.
[0011]
Preferably, the first radiation detection unit and the second radiation detection unit have the same structure, and their directions are shifted from each other by a predetermined rotation angle. Preferably, the detection unit further includes a third radiation detection unit having uniform sensitivity in all directions.
[0012]
Preferably, the arithmetic unit includes a ratio of a detection value of the first radiation detection unit to a detection value of the third radiation detection unit, and a detection value of the second radiation detection unit with respect to a detection value of the third radiation detection unit. And the radiation azimuth based on the ratio. According to this configuration, the detection values of the first and second radiation detection units are standardized (after calculating the ratio) on the basis of the detection values of the third radiation detection unit, and then they are standardized. The flying direction is specified from the combination of the values.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 shows a preferred embodiment of the radiation measuring apparatus according to the present invention, and FIG. 1 is a conceptual diagram showing the entire configuration.
[0015]
This radiation measuring device is incorporated in, for example, a monitoring post that measures environmental radiation. Of course, this radiation measuring apparatus can be used for an area monitor used in a radiation handling facility, for example.
[0016]
The radiation measurement device shown in FIG. 1 is roughly composed of a detection unit 10 and a processing unit 12. The detection unit 10 includes three detection units 14, 16, and 18 in the present embodiment.
[0017]
The detection unit 14 and the detection unit 16 are azimuth-dependent detection units having different sensitivities depending on the azimuth. However, the detection unit 14 and the detection unit 16 differ from each other by 90 degrees in reference orientation (that is, orientation) (see FIG. 1). That is, the pattern of the sensitivity characteristics over the entire circumference in the horizontal direction is the same in the detection unit 14 and the detection unit 16, but the peak points or dip points of such sensitivity characteristics are shifted from each other by 90 degrees.
[0018]
On the other hand, the detection unit 18 is a detection unit having uniform sensitivity in all directions in the horizontal direction.
[0019]
This will be described more specifically below. Here, since the detection unit 16 has the same configuration as the detection unit 14, the detection unit 14 will be described as a representative.
[0020]
The detection unit 14 is roughly composed of a scintillator 20, a photomultiplier tube 24, and a direction-dependent collimator 22. The scintillator 20 is, for example, a NaI type scintillator, and has a cylindrical shape in the present embodiment as illustrated. As is well known, the scintillator 20 functions as a radiation detector, and when radiation is incident, photons are generated there.
[0021]
The photomultiplier tube 24 receives the photons generated as described above by a light receiving surface, and converts the photons into an electric signal (electric pulse) by the received light. Here, a plurality of photomultiplier tubes 24 may be provided for one scintillator 20, and so-called simultaneous counting may be performed. Further, a light guide may be provided between the scintillator 20 and the photomultiplier tube 24 as needed. The photomultiplier tube 24 has a built-in preamplifier in this embodiment.
[0022]
As described above, since the scintillator 20 has a cylindrical shape, the scintillator 20 has uniform sensitivity in all directions in the horizontal direction. However, since the collimator 22 is wound along the outer surface of the scintillator 20 as shown in FIG. 1, the detection unit 10 has the azimuth-dependent sensitivity characteristic as described above. As described later, the collimator 22 has a shape in which the thickness in the vertical direction is increased stepwise in a clockwise direction from a certain direction. Therefore, a discontinuous vertical plane occurs at the start point of the thickness. The position of the vertical plane differs by 90 degrees between the detection unit 14 and the detection unit 16 as shown in FIG. Incidentally, in FIG. 1, the specific direction is set to 0 degree for convenience of explanation. The angle is positive in the counterclockwise direction when viewed from above.
[0023]
The detection unit 18 is constituted by a scintillator 32 and a photomultiplier tube 34 as shown. The scintillator 32 has the same configuration as the above-described scintillator 20, and the photomultiplier tube 34 has the same configuration as the above-described photomultiplier tube 24. Therefore, the detection unit 18 is different from the detection units 14 and 16 in that no collimator is provided.
[0024]
As shown in FIG. 1, the three detection units 14, 16, 18 are vertically aligned, that is, when they are arranged in the horizontal direction, interference on the mutual detection surfaces is prevented.
[0025]
Next, the processing unit 12 will be described. The processing unit 12 has processing circuits 36, 38, and 40 provided for each of the detection units 14, 16, and 18. Since the processing circuits 36, 38, and 40 have the same configuration as each other, the contents of the processing circuit 36 will be described here as a representative.
[0026]
The pulse output from the photomultiplier tube 24 is amplified by the amplifier 40, and the amplified pulse is input to the discriminator 42. The discriminator 42 performs a peak discrimination process, and outputs a pulse having a certain peak value or more. The pulse is input to the rate meter 44.
[0027]
The rate meter 44 is a circuit that obtains a counting rate by counting input pulses. Of course, the dose rate may be calculated instead of the count rate. Here, the background counting rate measured in advance is stored in the memory 46. Then, in the subtracter 48, the value stored in the memory 46 is subtracted from the current output value of the rate meter 44, that is, the background count rate is subtracted from the current count rate. As a result, data representing the net count rate is output to the normalization unit 50.
[0028]
As shown in FIG. 1, in this embodiment, two normalization units 50 and 52 are provided. Here, the data of the net count rate obtained by the processing circuit 36 and the data of the net count rate obtained by the processing circuit 40 are input to the normalization unit 50. Here, the net count rate obtained by the processing circuit 40 is a standard for standardization. That is, the count rate is a reference.
[0029]
The data of the net count rate obtained by the processing circuit 38 is input to the normalization unit 52. Further, the data of the net count rate obtained by the processing circuit 40 as described above is input.
[0030]
Then, the normalizing unit 50 normalizes the count rate by dividing the net count rate obtained by the processing circuit 36 by the net count rate obtained by the processing circuit 40. That is, the calculation of the ratio is executed. Similarly, the normalizing unit 52 performs normalization by dividing the net count rate obtained by the processing circuit 38 by the net count rate obtained by the processing circuit 40, that is, obtains a ratio between them. Then, data representing the ratios obtained by the normalization unit 50 and the standardization unit 52 are input to the flying direction determination unit 54. The flying direction determining unit 54 determines the flying direction of the radiation from a combination of these two ratios based on the principle described later. In this case, the response table 56 is referred. This response table 56 stores response characteristics as described later with reference to FIG. 6 or FIG. The flying direction determined by the flying direction determination unit 54 is displayed on the display unit 58 as angle information.
[0031]
Incidentally, the flight direction determination unit 54 calculates two angles that are candidates for the flight direction from the ratio obtained by the normalization unit 50, and similarly calculates the flight direction from the ratio obtained by the standardization unit 52. By determining two candidate angles and comparing the two angle pairs with each other, specifically, by specifying a matching angle between the two angle pairs, the flying direction may be determined. Good.
[0032]
Note that the background count value stored in the memory 46 may be obtained in advance at a time when the system can be considered to be normal or a normal time, for example, under the control of a control unit (not shown). The normal state may be automatically determined based on the magnitude of the count rate measured by the detection unit, and the count value obtained at that time may be used as the background count value.
[0033]
FIG. 2 is an enlarged view of the detection unit 14 shown in FIG. As described above, the detection unit 10 includes the scintillator 20, the photomultiplier tube 24, and the azimuth-dependent collimator 22. Here, the level on the lower surface 22D side of the collimator 22 is represented by H1, and the level at the highest point is represented by H2. Incidentally, H1 corresponds to the level of the lower surface of the scintillator 20, and H2 corresponds to the level of the upper surface of the scintillator 20. That is, the vertical thickness of the collimator 22 is gradually increased from substantially 0 to the thickness of the scintillator 20.
[0034]
Focusing on the collimator 22, the thickness in the vertical direction is gradually increased from the thinner one end 22A, and the thickest other end 22B is finally formed. Moreover, the collimator 22 is wound along the outer surface of the scintillator 20, and a vertical surface 22C is formed at the other end 22B. The lower surface 22D of the collimator 22 forms a ring-shaped horizontal surface, and the upper surface 22E of the collimator 22 forms an inclined surface such as a spiral slope.
[0035]
FIG. 3 shows a state where the collimator 22 is expanded. The horizontal axis indicates the angle, and the vertical axis indicates the vertical thickness (height) of the scintillator made of lead. As shown, the thickness is continuously increased from H1 to H2. The change range is 360 degrees. Reference numeral 200 represents the existence range of the collimator 22, and reference numeral 202 represents the area of the outer surface of the scintillator 20 that is not hidden by the collimator 22. FIG. 4 shows the vertical thickness of the collimator 22 at each angle in different expressions. The numerical value attached to the circumference is an angle (azimuth), and the numerical value attached in the radial direction indicates the vertical thickness (arbitrary unit).
[0036]
FIG. 5 shows the response characteristics of the detection unit shown in FIG. 2 over all directions. Numerical values on the circumference indicate angles. The radial direction indicates a response (arbitrary unit). Since the collimator 22 has a special form as described above, for example, when the detection unit 14 is fixed and the radiation source is rotated around the detection unit 14, a response characteristic as shown in FIG. 5 is obtained. As shown in the response characteristics, when a certain standardized counting rate is obtained, two azimuths are basically specified thereby. However, in the present embodiment, as shown in FIG. 1, two detection units 14 and 16 having directions different from each other by 90 degrees are used, so even if such two angles are specified, one of them is determined. Angle can be selected. This will be described with reference to FIG.
[0037]
In FIG. 6, the horizontal axis shows the angle, and the vertical axis shows the response (the response of the detection unit 18 is "1"). Here, 300A indicates the response characteristic of the detection unit 14 illustrated in FIG. 1, and 300B indicates the response characteristic of the detection unit 16 illustrated in FIG. Due to the fact that the detection units 14 and 16 are 90 degrees different from each other, their characteristics are shifted by 90 degrees. Assuming such response characteristics, when two ratios, that is, values corresponding to the standardized response, are obtained by the standardization units 50 and 52, it is possible to specify one azimuth from the two values. . The specified direction is the flying direction. Incidentally, in the case where the radiation azimuth is limited to, for example, a predetermined angle range, the detection unit 10 can be configured by the detection unit 14 and the detection unit 18.
[0038]
FIG. 7 shows another embodiment of the azimuth-dependent detection unit. Here, the same components as those described above are denoted by the same reference numerals, and description thereof will be omitted. Here, the collimator 70 has an azimuth-dependent characteristic similarly to the above-described collimator 22 and the like. However, in the embodiment shown in FIG. 6, the collimator 70 is provided only over a range of 180 degrees. , The thickness in the vertical direction is continuously increased from 0 to the maximum. That is, the thickness of the collimator 70 is increased from H1 corresponding to the level of the lower surface of the scintillator 20 to H2 corresponding to the level of the upper surface of the scintillator 20.
[0039]
FIG. 8 shows the vertical thickness when the collimator 70 is deployed. The horizontal axis indicates the angle, and the vertical axis indicates the vertical thickness (height) of the collimator 70 made of lead. As shown, the thickness in the vertical direction is continuously varied over a range of 180 degrees. Here, reference numeral 204 denotes a range covered by the scintillator 70, and reference numeral 206 denotes an exposed range that is not covered by the scintillator 70. FIG. 9 shows the vertical thickness of the collimator 70 at each angle in different expressions. The numerical value attached to the circumference is an angle, and the numerical value attached in the radial direction indicates the vertical thickness (arbitrary unit).
[0040]
Therefore, the detection unit shown in FIG. 7 may be used instead of the detection unit 14 shown in FIG. 1, and the detection unit shown in FIG. 7 may be used instead of the detection unit 16 shown in FIG. Good. However, even in this case, it is necessary to make the directions of the detection units differ from each other by 90 degrees or another predetermined angle.
[0041]
FIG. 10 shows response characteristics of the detection unit shown in FIG. 7 over all directions.
[0042]
FIG. 11 shows response characteristics in the embodiment using the detection unit shown in FIG. 7 (response of the detection unit 18 is "1"). 302A shows the response characteristic of one (upper) detection unit, and 302B shows the response characteristic of the other (middle). Since the two response characteristics are out of phase with each other as shown in FIG. 6, a detection value, that is, a count value is obtained by using each detection unit, and is normalized by the count value by the detection unit 18. The flying direction can be easily determined from the ratio of the two standardized count values.
[0043]
In the above embodiment, for example, X-rays and γ-rays are measured, but other radiation (eg, neutrons) may be measured. When measuring neutrons, it is desirable to separately provide a moderator and other components necessary for detecting neutrons. In the above-described embodiments, the thickness of the azimuth-dependent collimator is continuously increased in a proportional relationship. However, the collimator may have a non-linear inclination.
[0044]
【The invention's effect】
As described above, according to the present invention, it is possible to specify the radiation azimuth without requiring a rotation mechanism.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an overall configuration of a radiation measuring apparatus according to the present invention.
FIG. 2 is an enlarged view of the detection unit shown in FIG.
FIG. 3 is a view showing a state where the collimator shown in FIG. 1 is developed.
FIG. 4 is a diagram showing a change in thickness in the vertical direction of the collimator shown in FIG. 1;
FIG. 5 is a diagram showing sensitivity characteristics in the horizontal direction of the detection unit shown in FIG.
FIG. 6 is a diagram showing a relationship between an angle and a response for the detection unit shown in FIG. 1;
FIG. 7 is an enlarged view of a detection unit according to another embodiment.
8 is a view showing a state where the collimator shown in FIG. 7 is developed.
9 is a diagram showing a change in thickness in the vertical direction of the collimator shown in FIG. 7;
10 is a diagram showing sensitivity characteristics in the horizontal direction of the detection unit shown in FIG. 7;
11 is a diagram illustrating a relationship between an angle and a response for the detection unit illustrated in FIG. 7;
[Explanation of symbols]
10 detection unit, 12 processing unit, 14, 16, 18 detection unit, 20, 32 scintillator, 24, 34 photomultiplier tube, 22, 28 direction-dependent collimator, 36, 38, 40 processing circuit, 50, 52 standardization Section, 54 Flight direction determination section.

Claims (10)

A detection unit including at least one direction-dependent radiation detection unit having different sensitivities depending on the direction, and a detection unit including a plurality of radiation detection units;
An arithmetic unit that specifies the direction of arrival of radiation from the detection values by the plurality of radiation detection units,
A radiation measurement device comprising: The device of claim 1,
The azimuth-dependent radiation detection unit,
A radiation detector having uniform sensitivity characteristics in all directions;
A shielding member provided around the radiation detector and having a different degree of shielding depending on the direction,
A radiation measurement device comprising: The device according to claim 2,
The radiation measuring apparatus according to claim 1, wherein a vertical width of the shielding member gradually changes along a circumferential direction around the radiation detector. The device according to claim 3,
The radiation measuring apparatus, wherein the shielding member is provided over the entire circumference. The device according to claim 4,
The radiation measuring device, wherein the shielding member is provided over a part of the circumferential direction. The device of claim 1,
The radiation measurement device according to claim 1, wherein the plurality of radiation detection units are arranged in a vertical direction. The device of claim 1,
The detection unit,
A first radiation detection unit as the direction-dependent radiation detection unit,
A second radiation detection unit having an azimuth sensitivity characteristic different from the azimuth sensitivity characteristic of the first radiation detection unit, and a second radiation detection unit as the azimuth-dependent radiation detection unit;
A radiation measurement device comprising: The device according to claim 7,
The radiation measurement apparatus, wherein the first radiation detection unit and the second radiation detection unit have the same structure as each other, and their directions are shifted from each other by a predetermined rotation angle. The device according to claim 7,
The radiation measurement apparatus according to claim 1, wherein the detection unit further includes a third radiation detection unit having uniform sensitivity in all directions. The device according to claim 9,
The arithmetic unit is configured to calculate a ratio of a detection value of the first radiation detection unit to a detection value of the third radiation detection unit, and a ratio of a detection value of the second radiation detection unit to a detection value of the third radiation detection unit. A radiation measurement apparatus for identifying the direction of arrival of radiation based on the following.

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