JP2016183870A - Radioactivity measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radioactivity measurement device capable of accurately measuring a radioactivity intensity even when a radioactivity distribution is not uniform in a measured sample.SOLUTION: A radioactivity measurement device 10 has: a pair of radiation detectors 11, 12 for detecting radiation emitted from a measured sample 110 and outputting signal pulses; pulse counting parts 41, 42 for respectively counting signal pulses output by the radiation detectors 11, 12 and outputting pulse counting values; and a calculation device 70 configured to calculate a position of the center of gravity G and a radioactivity intensity A in a radioactivity distribution on a straight line linking between sensitive parts 11a, 11b of the radiation detectors 11, 12 by using a comparison of pulse counting values output by the pulse counting parts 41, 42 per unit time and a distance of a passage of the straight line through the measured sample 110.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radioactivity measuring apparatus that measures the radioactivity intensity of a sample to be measured.

  A conventional radioactivity measurement apparatus includes a radiation detector that detects radiation emitted from radionuclides contained in a sample to be measured, and a radioactivity intensity of the sample to be measured (nuclear decay rate) by processing the output of the radiation detector. ) Is provided.

  For example, the calculation device of the radioactivity measurement apparatus disclosed in Patent Document 1 obtains the scattered radiation intensity and direct line intensity of radiation based on the energy spectrum obtained by processing the output of the radiation detector, and uses these to calculate the radiation intensity. The density value of the measurement sample is calculated. Then, the radiation attenuation amount is calculated using the density value, and the radioactivity intensity is calculated using the radiation attenuation amount and the like.

JP 2001-264493 A (FIG. 4)

However, the calculation method of the radioactivity intensity disclosed in Patent Document 1 is performed on the premise that the radioactivity distribution is uniform in the sample to be measured. Accordingly, there is a problem that the radioactivity intensity cannot be calculated with high accuracy when the radioactivity distribution in the sample is not uniform and is unevenly distributed, for example, at a specific location.

  The present invention has been made to solve the above-described problems, and is a radioactivity measurement capable of measuring the radioactivity intensity with high accuracy even when the radioactivity distribution is not uniform within the sample to be measured. The object is to obtain a device.

In order to achieve the above object, a radioactivity measurement apparatus according to the present invention comprises:
A pair of radiation detectors for detecting radiation emitted from the sample to be measured and outputting signal pulses;
A pulse counting unit that counts the number of signal pulses respectively output by a pair of radiation detectors and outputs a pulse count value;
Radioactivity distribution on a straight line using the ratio of the pulse count value output per unit time by the pulse counter and the distance that the straight line connecting the sensitive parts of the pair of radiation detectors passes through the sample to be measured And a computing device configured to calculate the position of the center of gravity and the radioactivity intensity.

  According to the present invention, since the gravity center position of the radiation distribution on the straight line connecting the sensitive parts of the pair of radiation detectors is calculated, the distance between the calculated gravity center position and the radiation detector can be obtained. In addition, since the amount of radiation emitted from the center of gravity is attenuated by the sample to be measured, it is possible to measure the radioactivity intensity with high accuracy even when the radioactivity distribution is not uniform within the sample to be measured. It becomes possible.

It is a block diagram which shows the radioactivity measuring apparatus by Embodiment 1 of this invention. It is a figure which shows the radioactive distribution on the straight line which connects the sensitive part of a pair of detection element. It is a graph which shows the example of the change of the count value according to the position of the radiation source in a to-be-measured sample. It is a graph which shows ratio of the count value of FIG. It is a block diagram which shows the radioactivity measuring apparatus by Embodiment 2 of this invention. It is a perspective view which shows a part of radioactivity measuring apparatus by Embodiment 3 of this invention. It is a top view which shows a part of radioactivity measuring apparatus by Embodiment 3 of this invention. It is a block diagram which shows the radioactivity measuring apparatus by Embodiment 4 of this invention. It is a figure which shows the radioactivity measuring method in case a to-be-measured sample is not circular.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or similar components are denoted by the same reference numerals.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a radioactivity measurement apparatus 100 according to Embodiment 1 of the present invention.
The radioactivity measurement apparatus 100 includes a pair of detection elements 11 and 12, amplifiers 21 and 22, energy discriminators 31 and 32, pulse counting circuits 41 and 42, a density measurement unit 50, a dimension measurement unit 60, And an arithmetic unit 70.

  The radioactivity measurement apparatus 100 is configured to measure the radioactivity intensity of the sample 110 to be measured. The sample 110 to be measured is arranged in a container 120 having a specific shape. In the embodiment, the container 120 has a circular shape in a plan view (or a cross-sectional shape). The sample to be measured 110 may be a fluid or powder filled in the container 120. The container 120 may be a marinade container having a recess formed on the bottom surface. Note that the sample to be measured 110 may be a solid, and in this case, the container 120 is not necessarily required.

  The detection elements 11 and 12 are arranged on the outside of the sample 110 to be measured (or on the container 120) and facing the vicinity. The detection elements 11 and 12 can be regarded as the same. The detection elements 11 and 12 are configured to detect radiation such as gamma rays and characteristic X-rays by the sensitive portions 11a and 12a having sensitivity to radiation. In the embodiment, a straight line 1000 (one-dot chain line in FIG. 1) connecting the sensitive parts 11a and 12a passes through the center O of the circle.

  The detection elements 11 and 12 may be configured to detect radiation having low energy, for example, energy of 100 keV or less (or about 100 keV or less). As the detection elements 11 and 12, a semiconductor detector having silicon, germanium or the like as the sensitive parts 11a and 12a, or a scintillator having sodium iodide, cesium iodide or the like as the sensitive parts 11a and 12a may be used. Good. The detection elements 11 and 12 may be connected to a high-voltage DC power source for applying an operating voltage thereto.

  The amplifiers 21 and 22 are connected to the detection elements 11 and 12, respectively, and are configured to amplify electric charges generated when radiation enters the sensitive portions 11 a and 12 a of the detection elements 11 and 12. As the amplifiers 21 and 22, a combination of a preamplifier and a waveform shaping amplifier may be used when the detection elements 11 and 12 are semiconductor detectors, and photomultiplier when the detection elements 11 and 12 are scintillators. A tube may be used.

  When the detection elements 11 and 12 are semiconductor detectors, when radiation is incident on the sensitive portions 11a and 12a, electric charges are generated and output as signal pulses. In this case, the detection elements 11 and 12 correspond to “radiation detectors” that detect radiation and output signal pulses. When the detection elements 11 and 12 are scintillators, scintillation light is generated when radiation enters the sensitive portions 11a and 12a, which are photoelectrically converted and amplified by the photomultiplier tubes that are the amplifiers 21 and 22 and output as signal pulses. Is done. In this case, the combination of the detection elements 11 and 12 and the amplifiers 21 and 22 corresponds to a “radiation detector”. The height (wave height) of the voltage pulse output from the radiation detector is proportional to the energy applied to the sensitive portions 11a and 12a of the detection elements 11 and 12.

  The radiation detector including the detection elements 11 and 12 is covered with a shield made of lead or the like so as to shield the background from the surrounding environment. The shield may have a thickness that allows radiation with energy greater than 100 keV to be transmitted and radiation with energy less than or equal to 100 keV to interact and be absorbed.

  The energy discriminators (wave height discriminators) 31 and 32 are connected to the amplifiers 21 and 22, respectively, and are configured to discriminate only signal pulses having appropriate heights among the signal pulses output from the amplifiers 21 and 22. Has been. Specifically, the energy discriminators 31 and 32 pass only signal pulses corresponding to a specific energy region of the sample 110 to be measured (for example, an energy region of radiation emitted from the radionuclide of the sample 110 to be measured), A signal pulse corresponding to other energy is removed.

  In the first embodiment, the energy discriminators 31 and 32 are not indispensable components. However, the energy discriminators 31 and 32 pass only a signal pulse corresponding to a specific energy region of radiation, thereby causing noise such as background. Can be removed efficiently, and measurement can be performed with high accuracy.

  The pulse counting circuits (pulse counting units) 41 and 42 are connected to the energy discriminators 31 and 32, respectively, and count the number of signal pulses discriminated by the energy discriminators 31 and 32 for a certain measurement time. The counter is configured to output a count value. As the pulse counting circuits 41 and 42, a multichannel analyzer, a scaler, or a counter may be used.

  The density measuring unit 50 is configured to measure the density obtained from the volume and mass of the sample 110 to be measured. The density measuring unit 50 may include a container having a constant volume and a mass meter. The density measuring unit 50 transmits information on the density measured in advance to the arithmetic device 70. When the density of the sample 110 to be measured is previously measured by another method, the density measurement unit 50 is not provided, and the operator inputs the density directly to the input unit provided in the arithmetic unit 70. May be.

  The dimension measuring unit 60 is configured to measure the distance d through which the straight line 1000 connecting the sensitive parts 11a and 12a of the detection elements 11 and 12 passes through the sample 110 to be measured (in plan view). When the sample 110 to be measured is filled in the cylindrical container 120, the dimension measuring unit 60 is a memory that stores the inner diameter of the container 120. When the shape of the sample 110 to be measured changes, an apparatus that can measure the dimensions of the sample 110 to be measured using an image input device, a displacement sensor, or the like can be used as the dimension measuring unit 60. The dimension measuring unit 60 transmits information on the dimension (distance d) measured in advance to the arithmetic device 70. When the dimension of the sample 110 to be measured is measured in advance by another method, the dimension measurement unit 60 is not provided, and the operator directly inputs the dimension to the input unit provided in the arithmetic unit 70. May be.

  The arithmetic device 70 is connected to the pulse counting circuits 41 and 42, the density measuring unit 50 and the dimension measuring unit 60. The arithmetic device 70 includes a CPU (Central Processing Unit), a memory, and the like. The measurement results of the density measuring unit 50 and the dimension measuring unit 60 are stored in the memory of the arithmetic device 70. The arithmetic device 70 may have an input unit for an operator to input as described above.

In the first embodiment, the arithmetic device 70 is configured to execute the following steps S0 and S1 according to a program stored in a memory. Note that step S0 is also performed in the second to fourth embodiments.
(S0) Based on the density of the sample to be measured 110 output from the density measuring unit 50, the linear attenuation coefficient λ of the sample to be measured 110 is calculated.
(S1) The ratio C ₁ / C _{2 of the} number of pulses (pulse counting rate) C ₁ and C ₂ output per unit time by the pulse counting circuits 41 and 42 and the distance d output from the dimension measuring unit 60 are used. Then, the gravity center position (hereinafter referred to as the radiation gravity center G) and the radiation intensity A of the radiation distribution 1100 (see FIG. 2) on the straight line 1000 connecting the sensitive parts 11a and 12a are calculated.

  Next, step S1 will be described in detail.

In the following description, as shown in FIG. 1, the distance from the sensitive portion 11a of the detection element 11 to the radioactive centroid G is x ₁ , and the distance from the sensitive portion 12a of the detection element 12 to the radioactive centroid G is x ₂ . Further, the emission rate per destruction of the radiation emitted from the radionuclide of the sample 110 to be measured is r, the detection efficiency (of the solid angle when the sensitive parts 12a and 12b are viewed from the radioactivity center G of the total solid angle. The ratio of corners) is k ₁ and k ₂ .

  The linear attenuation coefficient λ is determined from the energy of radiation emitted from the sample 110 to be measured, the material and density of the sample. Specifically, the linear attenuation coefficient λ can be obtained by multiplying the mass attenuation coefficient by the density of the measured sample 110 measured by the density measuring unit 50. For example, “Isotope Handbook” (edited by the Japan Isotope Association, 1984) has mass attenuation coefficients of various substances with respect to energy of X-rays and gamma rays. Moreover, the release rate r per destruction is a value specific to the nuclide of the sample 110 to be measured, and can be obtained from documents relating to isotopes such as “Isotope Notebook 11th Edition” (edited by Japan Isotope Association, 2011). For example, in the characteristic X-ray of 32.1 keV emitted from cesium 137, the emission rate r per destruction is 5.8%.

Here, the radioactivity intensity A when the radiation having the radioactivity intensity A ₀ travels the distance x through the sample having the linear attenuation coefficient λ is expressed by the following equation (1).
A = A ₀ · exp (−λ · x) (1)

In general, the counting rate is represented by the product of detection efficiency, radiation emission rate, and radioactivity intensity. Therefore, the count rates C ₁ and C ₂ are expressed by the following formulas (2) and (3).
C ₁ = k ₁ · r · A · exp (−λ · x ₁ ) (2)
C ₂ = k ₂ · r · A · exp (−λ · x ₂ ) (3)

When the areas where the sensitive parts 11a and 12a are viewed from the radioactive center of gravity G are S ₁ and S ₂ , respectively, the detection efficiencies k ₁ and k ₂ are expressed by the following equations (4) and (5).
k ₁ = S ₁ / (4π · x ₁ ² ) (4)
k ₂ = S ₂ / (4π · x ₂ ² ) (5)

When the equations (2) and (3) are rewritten using the equations (4) and (5), the following equations (6) and (7) are obtained.
C ₁ = {S ₁ / (4π · x ₁ ² )} · r · A · exp (−λ · x ₁ ) (6)
C ₂ = {S ₂ / (4π · x ₂ ² )} · r · A · exp (−λ · x ₂ ) (7)

From the equations (6) and (7), the ratio C ₁ / C ₂ of the count rates corresponding to the detection elements 11 and 12 is expressed by the following equation (8).
_{C 1 / C 2 = {S} 1 · exp (-λ · x 1) / (x 1 2)} / {S 2 · exp (-λ · x 2) / (x 2 2)} ... (8)

When the detection elements 11 and 12 can be regarded as the same, the areas S ₁ and S ₂ are equal. At this time, the equation (8) is expressed by the following equations (9) and (10).
C ₁ / C ₂ = {x ₂ ² / x ₁ ² } · exp {−λ · (x ₁ −x ₂ )} (9)
x ₁ + x ₂ = d (10)

By solving the simultaneous equations (9) and (10) for the two unknowns (x ₁ , x ₂ ), x ₁ and x ₂ can be obtained, that is, the barycentric position G of the radioactivity distribution 1100 can be obtained.

On the other hand, when x ₁ and x ₂ are obtained, the radioactivity intensity A represented by the following formula (11) can be obtained from the formula (6) or the formula (7).
A = {4π · x ₁ ² · C ₁ } / {S ₁ · r · exp (−λ · x ₁ )} (11)

  As described above, according to the first embodiment, the gravity center position G of the radiation distribution 1100 on the straight line 1000 connecting the sensitive portions 11a and 12a of the pair of detection elements 11 and 12 is calculated. By adjusting the sample 110 to be measured, the radioactivity intensity A can be measured with high accuracy even when the radioactivity distribution is not uniform in the sample 110 to be measured.

In general, when measuring radiation of low energy (for example, 100 keV or less), the self-shielding effect in which the radiation is absorbed and attenuated by the constituent material of the sample to be measured appears remarkably, and the measurement accuracy decreases. A correction method is appropriately implemented. On the other hand, the large self-shielding effect in the first embodiment is that the ratio C ₁ / C ₂ of the count rate corresponding to the output of the detection elements 11 and 12 is relative to the displacement (from the center O of the circle) of the radioactivity center G. It means a big change. That is, since the sensitivity in obtaining the radioactivity center of gravity G increases, the radioactivity intensity A can be obtained with higher accuracy.

FIG. 3 is a graph showing an example of changes in the count value according to the position of the radiation source in the sample 110 to be measured. The horizontal axis of the graph represents the distance x ₁ from the detection element 11 to the radiation center of gravity G, the vertical axis shows a scale of common logarithm of the count value.
The sample 110 to be measured is water (density 1 g / cm ³ ) enclosed in a cylindrical container 120, and the sample 110 to be measured includes cesium 137 that emits characteristic X-rays of 32.1 keV. And The diameter d of the circle of the container 120 is 10 cm, and the measurement time is 10 minutes. Since the count value is obtained by multiplying the count rate by time, c ₁ = C ₁ × 600 (seconds) and c ₂ = C ₂ × 600 (seconds). It can be seen from FIG. 3 that both the count values c ₁ and c ₂ change greatly depending on the position of the radiation source.

FIG. 4 is a graph showing the count value ratio c ₁ / c ₂ of FIG.
It can be seen that the ratio c ₁ / c ₂ of the count value changes by about 6 orders of magnitude depending on the position of the radiation source. That is, since the change of the ratio c ₁ / c ₂ of the count value with respect to the change of the position of the radiation source is large, the position of the radiation source (position of the radiation gravity center G) can be obtained with high accuracy. As a result, the radioactivity intensity A can be determined with higher accuracy.

  Furthermore, when measuring low energy radiation, the thickness of the shield can be reduced. Thereby, the radioactivity measuring apparatus 100 can be reduced in weight and cost can be reduced.

  For example, consider an example in which cesium 137 is included in the sample 110 to be measured as a radionuclide. Cesium 137 emits characteristic X-rays with energy of 32.1 keV or 36.5 keV in addition to gamma rays with energy of 662 keV. When measuring 662 keV gamma rays, the background radiation from the surrounding environment must also reduce gamma rays near 662 keV. Therefore, the shield needs to be thick enough and is therefore heavy. For example, the thickness of lead necessary for attenuating the intensity of 662 keV gamma rays to 1/100 is about 3 cm to 4 cm. Accordingly, assuming that the entire radiation detector is surrounded by this shield, typically the shield alone will weigh at least 100 kg.

  On the other hand, when the characteristic X-ray of 32.1 keV emitted from cesium 137 is used as a measurement object, the lead thickness required to attenuate the intensity to 1/100 is 0.5 mm or less. That is, since sufficient shielding is possible only with a housing having a thickness of several millimeters, an additional shielding body is not required, and the weight can be significantly reduced. Thereby, the radioactivity measuring apparatus 100 can be reduced in weight and cost can be reduced.

  Since 662 keV gamma rays are also incident on the detection elements 11 and 12, this may be a background factor. In the first embodiment, the thicknesses of the detection elements 11 and 12 are set to such a size that the radiation with energy exceeding 100 keV is transmitted and the radiation with energy of 100 keV or less causes high interaction and is absorbed. 662 keV gamma rays are hardly transmitted and detected, but 32 keV characteristic X-rays are detected. Thereby, since only 32 keV can be measured selectively, high measurement accuracy can be secured.

Embodiment 2. FIG.
FIG. 5 is a block diagram showing a radioactivity measurement apparatus 200 according to Embodiment 2 of the present invention.
The radioactivity measurement apparatus 200 includes a rotation mechanism 80 that rotates the sample 110 to be measured, and a rotation angle detector 90 that detects the rotation angle. The other configuration of the radioactivity measurement apparatus 200 is the same as that of the radioactivity measurement apparatus 100 according to the first embodiment, and in the description and drawings, the same reference numerals as those used in the first embodiment are given and the description is omitted.

  The rotating mechanism 80 includes a rotating table 81 on which the sample 110 to be measured is placed, and a motor (output shaft) 82 attached to the rotating table 81. The output shaft of the motor 82 is attached to the center O of the circle, that is, the center O of the circle becomes the center of rotation. The arithmetic unit 70 transmits a control signal to a power source (not shown) to drive the motor 82. The motor 82 may be a stepping motor. The rotation angle detection unit 90 may be a rotary encoder that detects the rotation angle of the motor 82. In addition, a servo motor incorporating the functions of the motor 82 and the rotation angle detection unit 90 and incorporating an encoder may be provided.

In the second embodiment, the arithmetic device 70 is configured to execute the following steps S1 to S5 according to a program stored in a memory.
(S1) The count rates C ₁ and C ₂ output at a rotation angle of 0 degree are stored in the memory.
(S2) on the basis of the equation (1) described in Embodiment 1 in the formula (11), to calculate the radioactivity centroid _{G 1} and the radioactivity intensity _{A 1} on the straight line 1000 connecting the detection elements 11 and 12, the memory Store.
(S3) The detection rate is detected by the detection elements 11 and 12 while the measured sample 110 is rotated by a predetermined angle with respect to the detection elements 11 and 12 by the motor 82, and the count rate C ₁ corresponding to the output of the detection elements 11 and 12 , C ₂ are stored in the memory of the arithmetic unit 70.
(S4) the radioactivity centroid _{G 2} and the radioactivity intensity _{A 2} was calculated on the straight line 1000 connecting the detection elements 11 and 12, and stored in memory.
(S5) Steps S2 to S4 are repeated n times until the rotation angle of the sample 110 to be measured reaches 360 degrees or more.

By associating the rotation angle of the sample 110 to be measured detected by the rotation angle detector 90 with the outputs of the detection elements 11 and 12 (finally, the outputs of the pulse counting circuits 41 and 42), in response, the radioactivity centroid _G 1 on the straight line _{1000, G} 2 _..., G _n and the radioactivity intensity _{a 1,} a 2 ..., data _{a n} is obtained. Radioactivity center of gravity G _1, G 2 _..., in order to determine the radioactivity center of gravity G by using the data of G _n, for example, be considered the following two methods.
(Method 1) radioactivity intensity _{A 1,} A 2 ..., radioactivity centroid _G i corresponding to the maximum value of _{A n} (i is an integer from 1 to n) is assumed to be the radiation center of gravity G.
(Method 2) The position calculated by the following equation (12) is defined as the radioactive gravity center G.

  According to the second embodiment, the radioactivity gravity center G can be obtained more accurately than in the first embodiment by performing measurement over the entire sample 110 to be measured. In addition, the radioactivity gravity center G can be calculated | required correctly, so that the step of a rotation angle is made small in step S3.

  In the second embodiment, a rotation mechanism for rotating the sample to be measured 110 is provided. However, if the sample to be measured 110 and the detection elements 11 and 12 rotate relatively, measurement can be performed over the entire sample to be measured 110. Therefore, a rotation mechanism that fixes the sample 110 to be measured and rotates the detection elements 11 and 12 may be provided.

Embodiment 3 FIG.
FIG. 6 is a perspective view showing a part of radioactivity measuring apparatus 300 according to Embodiment 3 of the present invention. FIG. 7 is a plan view showing a part of the radioactivity measurement apparatus 300. 6 and 7, the circuit configurations after the amplifiers 21 and 22 are not shown.
In the radioactivity measurement apparatus 300, a plurality of pairs of detection elements 11 and 12 are arranged over the entire periphery of the sample 110 to be measured. Other configurations of the radioactivity measurement apparatus 300 are the same as those of the radioactivity measurement apparatus 100 according to the first embodiment. As shown in FIG. 7, a straight line 1000 connecting each pair of detection elements 11 and 12 (sensitive parts) passes through the center O of the sample 110 to be measured.

In the third embodiment, the computing device 70 is configured to execute the following steps according to a program stored in the memory. That is, based on the formulas (1) to (11) described in the first embodiment, the radioactivity centroids G ₁ , G ₂ ... G _m and the radioactivity on the straight line 1000 connecting the pair of detection elements 11, 12. Intensities A ₁ , A ₂ ..., _Am are calculated and stored in the memory. Note that m is equal to half the number of detection elements.

  According to the third embodiment, as in the second embodiment, the radioactivity gravity center G can be accurately obtained by performing measurement over the entire sample to be measured 110. In particular, according to the third embodiment, it is not necessary to perform measurement a plurality of times while rotating the sample 110 to be measured as in the second embodiment, and the measurement can be performed simultaneously on all the detection elements 11 and 12. Measurement time can be greatly reduced. In addition, the radioactivity gravity center G can be calculated | required correctly, so that the number of the detection elements 11 and 12 arrange | positioned increases.

Embodiment 4 FIG.
FIG. 8 is a block diagram showing a radioactivity measurement apparatus 400 according to Embodiment 4 of the present invention.
In the first to third embodiments, radiation is detected using a pair or a plurality of pairs of detection elements. In the radioactivity measurement apparatus 400, a pair of detection elements is substituted by one detection element 11. The radioactivity measuring apparatus 400 includes one amplifier, one energy discriminator, and one pulse counting circuit corresponding to the single detection element. The radioactivity measurement apparatus 400 includes a rotation mechanism 80 and a rotation angle detection unit 90 as in the radioactivity measurement apparatus 200 according to the second embodiment.

In the fourth embodiment, the arithmetic device 70 is configured to execute the following steps S1 to S3 according to a program stored in a memory.
(S1) stores the value of the count rate C ₁ outputted by the rotation angle of 0 degrees in the memory.
(S2) performs the detection by the detection element 11 in a state in which the sample 110 is rotated by 180 degrees with respect to the detection element 11 by the motor 82 again, the arithmetic unit 70 the value of the count rate D ₁ corresponding to the output memory To store. As shown in FIG. 8, the distance to the sensitive portion 11a of the detecting element 11 from radioactivity centroid G _D of the measurement sample 110 after rotation is equal to x _2, thus the counting rate D ₁ is measured in the first embodiment It was equal to the count rate _{C 2.}
(S3) Therefore, based on the equations (1) to (11) described in the first embodiment, the activity gravity center G and the activity on the straight line 1000 connecting the sensitive part 11a and the center O (rotation center) of the circle. The intensity A is calculated and stored in the memory.

  According to the fourth embodiment, since the gravity center position G of the radioactivity distribution 1100 on the straight line 1000 connecting the sensitive part 11a and the center O (rotation center) of the circle is calculated, the radioactivity intensity is the same as in the first embodiment. A can be measured with high accuracy. In particular, according to the fourth embodiment, the detection device, the amplifier, the energy discriminator, and the pulse counting circuit are not required one by one as compared with the first embodiment, so that the cost of the entire apparatus can be greatly reduced. .

  As described in the second embodiment, instead of the rotation mechanism that rotates the sample 110 to be measured, a rotation mechanism that fixes the sample 110 to be measured and rotates the detection element 11 may be provided.

  While the present invention has been described with reference to the above embodiment, the present invention is not limited to the above embodiment. In addition, various modifications and improvements may be added to the above-described embodiment, and thus there are various modifications in the above-described embodiment.

For example, in the above embodiment, the straight line 1000 connecting the sensitive portions 11a and 11b of the pair of detection elements 11 and 12 passes through the center O of the circle, but even if it does not pass through the center O of the circle. If the value of x ₁ + x ₂ is known corresponding to equation (10), equation (9) can be solved to calculate the activity gravity center G and activity intensity A.

In the above-described embodiment, an example in which the sample 110 to be measured is circular in plan view (or a cross-sectional shape) has been described. However, even when the sample 110 is not circular, the shape of the sample 110 to be measured (or the container 120) If the positional relationship between the sample 110 to be measured and the detection elements 11 and 12 is known (or by measuring the shape and the positional relationship in advance), the dimension (distance d) can be obtained. The center of gravity G and the intensity A can be calculated. For example, as shown in FIG. 9, when the sample 110 to be measured is square in plan view, the dimensions change as the distances d ₁ to d ₅ according to the positions where the detection elements 11 and 12 are arranged.

  DESCRIPTION OF SYMBOLS 11,12 Detection element, 21,22 Amplifier, 31,32 Energy discriminator, 41,42 Pulse counting circuit, 50 Density measurement part, 60 Dimension measurement part, 70 Arithmetic unit, 80 Rotation mechanism, 90 Rotation angle detection part, 100 , 200, 300, 400 Radioactivity measuring device, 110 sample to be measured, 120 container

Claims (9)

A pair of radiation detectors for detecting radiation emitted from the sample to be measured and outputting signal pulses;
A pulse counter for counting the number of signal pulses output by the pair of radiation detectors and outputting a pulse count value;
Using the ratio of the pulse count value output per unit time by the pulse counter and the distance through which the straight line connecting the sensitive parts of the pair of radiation detectors passes through the sample to be measured, A radioactivity measuring apparatus comprising: a center of gravity position of a radioactivity distribution of the radioactivity and an arithmetic unit configured to calculate the radioactivity intensity. A rotation mechanism that relatively rotates the sample to be measured and the pair of radiation detectors;
The arithmetic unit is configured to calculate the gravity center position and the radioactivity intensity of the radioactivity distribution on the straight line a plurality of times according to a plurality of relative rotation angles,
The radioactivity measurement apparatus according to claim 1. Comprising a plurality of pairs of said radiation detectors;
The arithmetic unit is configured to calculate a gravity center position and a radioactivity intensity of a radioactivity distribution on a straight line respectively connecting the sensitive parts of the plurality of pairs of radiation detectors,
The radioactivity measurement apparatus according to claim 1. A radiation detector that detects radiation emitted from the sample to be measured and outputs a signal pulse;
A rotation mechanism for rotating the sample to be measured with respect to the radiation detector;
A pulse counter for counting the number of signal pulses output by the radiation detector and outputting a pulse count value;
A ratio of first and second pulse count values output per unit time by the pulse counter when the sensitive part of the radiation detector is in the first and second positions with respect to the sample to be measured; Using the distance that the straight line connecting the sensitive part of the radiation detector and the rotation center of the sample to be measured passes through the sample to be measured, the position of the center of gravity and the radioactivity intensity of the radioactivity distribution on the straight line are calculated. A radioactivity measuring apparatus comprising: an arithmetic unit configured to perform the above-described operation. An energy discriminator is provided that removes signal pulses other than signal pulses corresponding to a specific energy region among signal pulses output by the detection element,
The radioactivity measurement apparatus according to any one of claims 1 to 4. The arithmetic unit is configured to calculate a linear attenuation coefficient of the sample to be measured based on the density of the sample to be measured.
The radioactivity measurement apparatus according to any one of claims 1 to 5. A density measuring unit that measures the density of the sample to be measured and a dimension measuring unit that measures a distance that the straight line passes through the sample to be measured are provided.
The radioactivity measurement apparatus according to any one of claims 1 to 6. The radiation detector is configured to detect radiation having energy of 100 keV or less,
The radioactivity measuring apparatus according to any one of claims 1 to 7.   9. The radioactivity measuring apparatus according to claim 8, wherein the radiation detector has a thickness that allows the radiation with energy exceeding 100 keV to pass through and absorbs radiation with energy less than 100 keV.

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