JP5988890B2 - Radioactivity analyzer and radioactivity analysis method - Google Patents

Description

  The present invention relates to a radioactivity analyzer and a radioactivity analysis method capable of measuring the radioactivity or radioactivity concentration of an object to be measured at high speed and with high accuracy.

  A radioactivity analyzer that analyzes and quantifies radioactive substances contained in food, water, soil, etc. detects radiation from the object to be measured, and measures its energy and intensity. In other words, the radioactivity analyzer performs analysis and quantification by measuring the intensity of radiation having energy emitted by the measurement target nuclide. As a method for measuring the energy and intensity of radiation at high speed and with high accuracy, inverse problem calculation using a response function of a detector can be applied.

  For example, in order to obtain a photon energy spectrum from a measured pulse wave height distribution, there is a conventional technique in which unfolding is performed using a response distribution matrix, and the intensity of photon energy is measured to quantify radioactive substances (see, for example, Patent Document 1). ).

  In order to perform unfolding with high accuracy, it is necessary to select an optimal response function. For example, there is a method of correcting blurring of a radiographic image by unfolding (see, for example, Patent Document 2). In this method, when blurring of a radiographic image is corrected by inverse problem calculation, there are a plurality of response functions used for inverse problem calculation with respect to the energy of the radiation, and an optimal response function is selected for each energy.

Special table 2008-54579 JP 2006-234727 A

However, the prior art has the following problems.
In the technique as disclosed in Patent Document 1, an object to be measured having a certain shape and density is arranged at a predetermined measurement location, and a response that a detector fixed at the certain location shows. Is obtained in advance by simulation or the like.

  Measurement results obtained by the detector when the energy of radiation is changed to various values are stored in the database in advance as a response function (response distribution matrix). Then, an inverse problem calculation using a response distribution matrix stored in the database is performed on the result of actually measuring the measurement object, thereby obtaining the energy and intensity of incident radiation.

  However, the response distribution matrix is created assuming the shape / density and geometrical arrangement of the object to be measured. Therefore, when the shape and density of the object to be measured are different from those assumed, there is a problem that it cannot be solved accurately. That is, when the shape and density of the object to be detected change variously, the accuracy of the energy spectrum obtained by unfolding (inverse problem calculation) decreases, and as a result, the quantitative accuracy of the radioactive material of the measurement nuclide It was a problem that remarkably decreased.

  Patent Document 2 discloses a method for selecting an optimal response function for each energy and solving an inverse problem calculation. However, the inverse problem cannot be accurately solved only by selecting the response function based on the energy information, and thus cannot be applied to the analysis and quantification of radioactivity.

  The present invention has been made to solve the above-described problems. Even when the shape and density of the object to be detected are different, the radioactivity or radioactivity concentration of the object to be measured can be increased at high speed and high. An object of the present invention is to obtain a radioactivity analyzer and a radioactivity analysis method capable of measuring with high accuracy.

The radioactivity analyzer according to the present invention uses, as a detector response function, an input / output relationship between an energy spectrum of radiation radiated from an object to be measured and a pulse wave height distribution measured by a detector according to the energy spectrum in advance. By performing inverse problem calculation using the database to store, the response function selection unit that extracts the detector response function from the database, the detector response function extracted by the response function selection unit and the measured pulse wave height distribution, A radioactivity analyzer that includes an inverse problem calculation unit that obtains an energy spectrum of radiation and analyzes and quantifies a radionuclide contained in the object to be measured. a plurality of detector response function according to the parameter information including the shape is stored in advance, Pas measured by a detector Based on the scan-height distribution, and a parameter determining unit for calculating a parameter information about the shape of the object to be measured, are embedded in the measuring table to be measured object is placed, toward the detector, the object to be measured One or more live zero radiation sources that radiate radiation having different energies from different from the measurement target nuclide, and the parameter determination unit is radiated from the one or more live zero radiation sources, Based on the respective pulse height distributions measured by the detector according to the energy of the radiation incident on the detector in the absence of light and the energy of the radiation that has passed through the object to be measured and incident on the detector, calculating the thickness of the measurement object as a shape included in the parameter information, the response function selecting section, corresponding to the pulse-height distribution measured by the detector parameter determination unit The detector response function according to the calculated parameter information and extracts from the database.

In addition, the radioactivity analysis method according to the present invention provides an input / output relationship between an energy spectrum of radiation radiated from an object to be measured and a pulse wave height distribution measured by a detector according to the energy spectrum. As a pre-stored database, the detector response function is extracted from the database, and by performing inverse problem calculation using the extracted detector response function and the measured pulse wave height distribution, the radiation energy spectrum is obtained, A radioactivity analysis method applied to a radioactivity analyzer that analyzes and quantifies a radionuclide contained in an object to be measured, the parameter including the shape of the object to be measured as a detector response function with respect to a database A step of storing a plurality of detector response functions corresponding to information in advance, and a pulse measured by the detector Based on the high distribution, parameter determining step and, according to the parameter information that is calculated corresponding to the pulse-height distribution measured by the detector in the parameter decision step detector for calculating a parameter information about the shape of the measurement object The response function selection step for extracting the response function from the database, and the inverse response calculation using the detector response function extracted in the response function selection step and the pulse wave height distribution measured by the detector, thereby calculating the incident radiation. An inverse problem calculation step for obtaining an energy spectrum and analyzing / quantifying the radionuclide contained in the object to be measured , and the parameter determining step is embedded in a measurement table on which the object to be measured is placed, Toward the target object and radiate radiation with energy different from that of the measurement target nuclide. Depending on the energy of the radiation emitted from one or more live zero sources and incident on the detector without the object to be measured, and the energy of the radiation incident on the detector after passing through the object to be measured based on the respective pulse height distribution measured by the detector Te, a shall be calculated as shapes included the thickness of the measurement object in the parameter information.

  According to the present invention, an object to be detected is selected by selecting an optimum detector response function using at least one of the density, shape, center of gravity of the object to be measured, and the distance to the detector as parameter information. Even if the shape and density of the radio waves are different, it is possible to obtain a radioactivity analyzer and a radioactivity analysis method capable of measuring the radioactivity or radioactivity concentration of the measurement object at high speed and with high accuracy.

It is a block diagram which shows the radioactivity analyzer by Embodiment 1 of this invention. It is a figure which shows the example of the measured pulse wave height distribution by Embodiment 1 of this invention. It is a figure which shows the example of the source spectrum calculated | required by unfolding the measured pulse wave height distribution by Embodiment 1 of this invention. It is a figure which shows the example of pulse wave height distribution measured when there is no to-be-measured target object by Embodiment 1 of this invention. It is a figure which shows the example of pulse wave height distribution measured when there exists a to-be-measured object by Embodiment 1 of this invention. It is explanatory drawing which showed typically the calculation method of the thickness and density of the mixture which consists of two types of pure substances by Embodiment 1 of this invention. It is an example of the source spectrum calculated | required by unfolding the measured pulse wave height distribution by Embodiment 1 of this invention. It is a block diagram which shows the radioactivity analyzer by Embodiment 2 of this invention.

  Hereinafter, preferred embodiments of the radioactivity analyzer and radioactivity analysis method of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a radioactivity analyzer according to Embodiment 1 of the present invention. A measurement object 1 (density: ρ, thickness: t) that may contain a radioactive substance is placed on a measurement table 2. In addition, a radiation detector 3 such as a NaI scintillation detector is disposed above the object 1 to be measured.

  In addition, a reference live zero source A (12A) and a live zero source B (12B) are embedded in the measurement table 2. Here, the live zero radiation source is provided for confirming the soundness of the detector, and is always fixedly disposed in the vicinity of the detector 3 and radiated from the live zero radiation source. By measuring the intense radiation with the detector 3, a constant instruction value is output, and it can be confirmed whether the detector 3 is operating normally.

  As the live zero source, a nuclide other than the measurement target nuclide of the object 1 to be measured is selected, and an appropriate type and number of live zero sources are determined so that a plurality of energies are generated. For example, when the measurement target nuclide of the object 1 to be measured is Cs-137, the live zero source selects a nuclide that emits radiation with energy different from that of the measurement target nuclide, such as Am-241 or Co-60. .

  With this arrangement, when the object 1 to be measured is placed on the measurement table 2, the radiation emitted from the live zero source A (12A) and the live zero source B (12B) is the object 1 to be measured. Then, the light enters the radiation detector 3.

  FIG. 1 shows an embodiment of the present invention provided with live zero source 12A, 12B. First, the operation when there is no conventional live zero source will be described. This measurement technique uses an inverse problem solution (unfolding) technique that measures the radioactivity or radioactivity concentration of a radioactive substance at high speed. Assuming that the measurement object 1 contains a radioactive substance that emits gamma rays of energy E3, first, gamma rays of energy E3 enter the radiation detector 3.

  The γ-rays interact with the sensitive part of the radiation detector 3 and give all or part of the energy of the radiation to the sensitive part of the radiation detector 3. As a result, the radiation detector 3 outputs a voltage pulse having a height proportional to the energy applied to the sensitive part. The voltage pulse is amplified by the amplifier 4 and the pulse height is analyzed by a multi-wave height analyzer (multi-channel analyzer) 5. The multiple wave height analyzer 5 measures the pulse height distribution of the pulse.

  FIG. 2 is a diagram showing an example of a measured pulse wave height distribution according to the first embodiment of the present invention. As shown in FIG. 2, a peak is observed at a location corresponding to the energy E3 emitted from the radioactive substance. Here, the peak height, that is, the pulse count, is a certain value determined from the radioactivity and properties of the radioactive substance, the positional relationship with the detector, and the detection efficiency of the detector.

  In FIG. 2, counts are also observed at locations other than the energy E <b> 3, but this is due to Compton scattering in which only a part of the radiation energy is absorbed by the detection unit. In normal measurement, in order to quantify the nuclide that emits energy E3, it is obtained from the count of only the peak portion of energy E3, and the count of the Compton continuous portion other than the peak cannot identify the incident γ-ray energy. exclude.

  Accordingly, since only a part of the radiation detector 3 that has caused an interaction is counted, detection efficiency is insufficient, and extra measurement time is required. Therefore, in the present invention, all events including Compton scattering are counted by the method described below.

The height of the energy peak of the wave height distribution measured by the multi-wave height analyzer 5 and the shape of the Compton continuous part are determined by the position / shape of the radioactive material and the characteristics of the detector. These response characteristics are the detector response function and be called. When the source spectrum is S, the pulse wave height distribution is M, and the detector response function is R, the following equation (1) is established.
M = RS (1)

Here, by using the inverse function R ⁻¹ of the detector response function, the source spectrum S can be obtained from the measured wave height distribution M using the following equation (2).
S = R ⁻¹ M (2)

  This process is called inverse problem calculation (unfolding). In the inverse problem calculation, it corresponds to returning the measured wave height distribution M to the source spectrum S. Therefore, not only the peak portion of the measured wave height distribution M but also the Compton continuous portion is counted. Become.

  Accordingly, the number of pulses that can be substantially counted is increased as compared with the case where unfolding is not performed, so that the detection efficiency can be improved. The above process is performed by the inverse problem calculation unit 6 using the response function database 11 of FIG. 1, and the result is displayed on the display unit 7.

  FIG. 3 is a diagram showing an example of a source spectrum obtained by unfolding the measured pulse wave height distribution according to the first embodiment of the present invention. More specifically, an example of the source spectrum S obtained by unfolding the wave height distribution of FIG. 2 based on the above equation (2) is shown. The peak (line spectrum) shown at the energy E3 in FIG. 3 is a value including the count of the Compton continuous part other than the count of the energy peak E3 in FIG.

  By the way, the values stored in the detector response function R used in this calculation are the dimensional shape / composition / density / center of gravity of the object 1 to be measured, the positional relationship (distance) with the detector, the detector dimensional shape / material. Of course, if the arrangement and materials of the peripheral members are different, it will change. Therefore, in order to obtain an accurate inverse problem calculation result, it is necessary to use an accurate response function.

  The dimensional shape / material of the detector and the arrangement / material of the peripheral members are usually fixed and do not change. Therefore, the dimension / shape / composition / density / center of gravity of the object 1 to be measured and the distance to the detector are the elements that determine the optimum response function, and these elements will be referred to as parameter information in the present application. A method for selecting a response function based on parameter information will be described below.

  In order to select an optimal detector response function, first, the shape and density of the measurement object 1 are obtained by the following method. The measurement object 1 is often a mixture of two or more substances. For example, in the case of a food containing a lot of water, it can be regarded as a mixture consisting of approximately two substances, water and air.

  Further, in the case of a food containing almost no water, although it depends on the type of food, it can be considered as a mixture of cellulose and air, which is a representative fibrous material, for example. The composition ratio of the mixture, that is, the mixing ratio and density are not necessarily the same depending on individual samples, and may vary greatly.

  Next, the operation will be described. In FIG. 1, first, when there is no object 1 to be measured, γ rays emitted from the live zero source A (12A) and the live zero source B (12B) are directly incident on the radiation detector 3. As a result, the radiation detector 3 detects γ-rays, generates a voltage pulse, the amplifier 4 amplifies the pulse, and the multi-wave height analyzer (multi-channel analyzer) 5 analyzes the pulse wave height.

  FIG. 4 is a diagram showing an example of a pulse wave height distribution measured when there is no measurement object 1 according to the first embodiment of the present invention. The energy of the radiation emitted from the live zero source A (12A) and the live zero source B (12B) is E1 and E2, respectively. In this case, peaks are observed at locations corresponding to the energy E1 and E2, and the peak height, that is, the pulse count, is determined from the radioactivity of the live zero source, the detector arrangement, and the detection efficiency of the detector. Value.

  In addition, counts are also observed at locations other than the energy E1 and E2, but this is due to Compton scattering, etc. in which only a part of the energy of radiation is absorbed by the detection unit. In FIG. 4, the height of the peak corresponding to the energy E1 is shown as a, the height of the peak corresponding to the energy E2 is shown as b, and the continuous part due to Compton scattering also shows the count value.

  Next, the operation when measuring a sample, that is, when the object 1 to be measured is present will be described. In FIG. 1, γ rays emitted from the live zero source A (12 A) and the live zero source B (12 B) pass through the measurement object 1 and enter the radiation detector 3. As a result, the radiation detector 3 detects γ-rays to generate a voltage pulse, the amplifier 4 amplifies the pulse, and the multi-wave height analyzer (multi-channel analyzer) 5 analyzes the pulse wave height.

  FIG. 5 is a diagram showing an example of a pulse wave height distribution measured when there is an object to be measured 1 according to Embodiment 1 of the present invention. In addition to the radiation energies E1 and E2 emitted from the live zero radiation source A (12A) and the live zero radiation source B (12B), a peak is observed at a position corresponding to the energy E3 of the measurement nuclide. The height of the peak, that is, the number of pulses counted, is a certain value determined from the radioactivity of the radioactive substance contained in the live zero source and the object 1 to be measured, the detector arrangement, and the detection efficiency of the detector.

  In addition, counts are also observed at locations other than the energy E1, E2, and E3, which corresponds to Compton scattering in which only a part of the energy of radiation is absorbed by the detection unit. Here, the peak height a ′ corresponding to the energy E <b> 1 in FIG. 5 is lower than the height a when the object 1 to be measured is not present. This is because the gamma rays of energy E1 are attenuated when passing through the measurement object 1.

Similarly, the peak height b ′ corresponding to the energy E2 is lower than the height b when there is no object 1 to be measured. This is also because the gamma rays of energy E2 are attenuated when passing through the measurement object 1. This attenuation ratio is determined by the energy of γ rays, the material, density, and thickness of the object 1 to be measured. Generally, when the linear attenuation coefficient determined by the material of the object 1 to be measured and the energy of γ-ray is μ and the thickness of the object 1 to be measured is t, it corresponds to exp (−μt) times before attenuation. .

  As described above, two types of measurement data are obtained when the object 1 to be measured is present and when it is not present. Using these two types of measurement data, the object thickness / density determination unit 8 in FIG. 1 obtains the effective density and thickness of the object 1 to be measured. Below, the example of the determination method of the thickness and density of the to-be-measured object 1 is described.

FIG. 6 is an explanatory view schematically showing a method for calculating the thickness and density of a mixture composed of two kinds of pure substances according to Embodiment 1 of the present invention. When the object 1 to be measured is a mixture of the pure substance 1 and the pure substance 2, the density of the pure substance 1 is ρ1, the thickness of the pure substance 1 alone is t1, the density of the pure substance 2 is ρ2, and only the pure substance 2 is Let thickness be t2. If the transmittance when the γ-rays of energy E1 are transmitted through the mixture (thickness: t1 + t2) is P, the transmittance P is given by the following equation (3).
exp {−μ1 (E1) t1−μ2 (E1) t2} = P (3)

Similarly, when the transmittance when the γ-rays of energy E2 are transmitted through the mixture (thickness: t1 + t2) is Q, the transmittance Q is given by the following equation (4).
exp {−μ1 (E2) t1−μ2 (E2) t2} = Q (4)

  Where μ1 (E1) is the linear attenuation coefficient for the γ-ray energy E1 of the substance 1, μ1 (E2) is the linear attenuation coefficient for the γ-ray energy E2 of the substance 1, and μ2 (E1) is the γ-ray energy of the substance 2 A linear attenuation coefficient with respect to E1, μ2 (E2) is a linear attenuation coefficient with respect to the γ-ray energy E2 of the substance 2.

  Since the transmittance P and the transmittance Q are obtained from the count value of the energy peak (a ′ / a for energy E1 and b ′ / b for energy E2), the above equations (3) and (4 ) Are only t1 and t2. Therefore, both t1 and t2 can be obtained from the simultaneous equations of the above equations (3) and (4).

Therefore, the thickness t of the entire mixture can be obtained by the following equation (5).
t = t1 + t2 (5)
Similarly, the average density (effective density) ρ of the mixture can be obtained by the following equation (6).
ρ = ρ1 {t1 / (t1 + t2)} + ρ2 {t2 / (t1 + t2)} (6)

  As described above, the object thickness / density determination unit 8 can obtain the thickness and density of the measurement object 1 made of the mixture of the two substances based on the transmittance of the two energies.

  In addition, although the above showed the example of the mixture which consists of two types of pure substances, also in the case of the mixture which consists of more than N types, by combining the live zero ray source which emits more than N types of energy, Similarly, the overall thickness and effective density of the mixture can be determined.

  If the object 1 to be measured is an object placed in a fixed container such as a tray, the direction other than the thickness can be regarded as a fixed shape, so the shape of the object 1 to be measured is fixed. On the other hand, when the container is not in the fixed container, the approximate shape (area) can be obtained by measuring the weight of the object 1 to be measured by the weight measuring unit 13 shown in FIG.

  This is because, as described above, since the effective density of the measurement object 1 is known, the area of the object can be obtained from the thickness, density and weight. Thereby, the shape in the area direction can be obtained with higher accuracy.

  Here, in FIG. 1, the approximate center portion of the object 1 to be measured is arranged directly below the detector, but this is because the representative value of the thickness of the object 1 to be measured is obtained. Not too much. Therefore, in order to measure the shape of the object 1 to be measured in detail, the thickness at various positions can be obtained by performing measurement while scanning the object 1 to be measured. The shape of the object 1 can be determined with higher accuracy.

  More specifically, between the detector 3 and the live zero source A (12A) and the live zero source B (12B) so that the radiation passes through a plurality of different positions of the object 1 to be measured. It is conceivable to provide a transport mechanism in order to move the position of the object 1 to be measured.

  Next, a method for calculating the distance to the detector, which is another element for selecting the detector response function, will be described. In FIG. 1, the object 1 to be measured is placed on the measurement table 2, and thus the distance between the object 1 to be measured and the radiation detector 3 is obtained when the position of the center of gravity of the object 1 to be measured is obtained. be able to. As described in the previous paragraph, since the thickness (shape) of the object 1 to be measured is known, if the object 1 to be measured is homogeneous, the center-of-gravity position determination unit 9 of the object naturally obtains the position of the center of gravity. be able to.

  As described above, the representative position of the object 1 to be measured may be a physical center of gravity position in many cases. However, in order to further improve accuracy, the representative position may be as follows. Since the number of radiation incident on the detector is inversely proportional to the square of the distance between the detector and the radioactive substance, the square root of the mean square value of the distance may be employed. Specifically, the object 1 to be measured is virtually divided into small pieces, the distance between the center of each piece and the center of the detector is obtained, and the accurate center of gravity position can be obtained from the square root of the root mean square value. .

  From the above, it was possible to obtain, as parameter information, the dimensions, composition, density, center of gravity, and distance to the detector, which are factors that determine the optimum response function. Therefore, the response function selection unit 10 in FIG. 1 selects an optimum response function corresponding to the obtained parameter information from the response functions stored in the response function database 11 corresponding to the parameter information. Then, the inverse problem calculation unit 6 performs calculation using the optimum response function selected by the response function selection unit 10.

  FIG. 7 is an example of a source spectrum obtained by unfolding the measured pulse wave height distribution according to the first embodiment of the present invention. In FIG. 7, the count value c is the energy E1, the count value d is the energy E2, and the count value e is the energy E3. From these count values, the radioactivity of each nuclide can be converted. it can. Here, since the energy of the γ-ray emitted from the measurement target nuclide is E3, the amount of radioactive substance, that is, the radioactivity is obtained from the count value corresponding to E3 using the conversion coefficient. Moreover, the radioactivity per unit weight, ie, the radioactivity density | concentration, can also be calculated | required using the result of the weight measurement part 13 of FIG.

  As described above, the radioactivity analysis apparatus and radioactivity analysis method according to the first exemplary embodiment are optimal detector responses considering parameter information including at least one of the density, shape, center of gravity, and position of the measurement object. A function can be selected. In other words, it is possible to select an accurate response function considering the self-absorption of radiation by the measurement object.

  Therefore, even when the parameter information such as the shape and density of the object to be measured varies from sample to sample, the inverse problem can be solved using an accurate response function corresponding to the obtained parameter information. As a result, the measurement accuracy of radioactivity is improved. Furthermore, the equipment necessary for obtaining parameter information such as the position, thickness, density, etc. of the measurement object uses a radiation detector itself that measures the radioactivity of the measurement object. For this reason, it is not necessary to use another means, and cost and installation space can be saved.

  By the way, the factors that determine the optimum response function are the dimension shape, composition, and density of the measurement object 1 and the distance to the detector, as described above. The response function database 11 of FIG. 1 is provided with a plurality of parameters such as shape, composition, density, and distance, that is, values for multiple dimensions. Therefore, it is necessary to mount a memory having a capacity necessary for storing them. I must.

  Of the factors that determine the optimum response function, the most dominant factor that affects accuracy is the distance to the detector. Therefore, by setting the parameter of the response function mounted in the response function database 11 only to the distance, it is possible to significantly reduce the capacity of the mounted memory and reduce the cost.

  In addition, since the radiation of fixed energy and intensity | strength discharge | releases from the live zero source A (12A) or the live zero source B (12B) of FIG. 1, the role which calibrates the radiation detector 3 can also be played. . For example, in addition to daily calibration for confirming the sensitivity and energy characteristics of the radiation detector 3, it is possible to correct environmental fluctuations such as temperature and aging degradation.

Embodiment 2. FIG.
FIG. 8 is a block diagram showing a radioactivity analyzer according to Embodiment 2 of the present invention. The difference from FIG. 1 in the first embodiment is that the number of live zero radiation sources embedded in the measurement table 2 is one, and the other components are as shown in FIGS. Is the same.

  The second embodiment is applied when the object to be measured 1 is a single substance (pure substance). For example, water, plastic, metal, etc., whose density and composition are known. In order to perform the inverse problem calculation with high accuracy, it is necessary to select an optimal response function as in the first embodiment, but in the second embodiment, the density of the object 1 to be measured is known. Therefore, it is only necessary to know the dimension and shape as the parameter information.

The dimension shape of the measurement object 1 can be obtained as follows. Similar to the first embodiment, the count values of the energy peaks when the object 1 to be measured is present and when it is not present are compared, and the attenuation rate is obtained. When the linear attenuation coefficient determined by the material of the object 1 to be measured and the energy of γ rays is μ and the thickness of the object 1 to be measured is t, the attenuation rate corresponds to exp (−μt). Since the object 1 to be measured is a single substance, the value of μ is known, so the thickness t can be obtained. In addition, since the shape such as the area can be obtained in the same manner as in the first embodiment, description thereof is omitted.

  As described above, the radioactivity analysis apparatus and radioactivity analysis method according to the second exemplary embodiment have the optimum detector response in consideration of parameter information including at least one of the density, shape, center of gravity, and position of the measurement object. A function can be selected. In other words, it is possible to select an accurate response function considering the self-absorption of radiation by the measurement object.

  Therefore, even when the parameter information such as the shape and density of the object to be measured varies from sample to sample, the inverse problem can be solved using an accurate response function corresponding to the obtained parameter information. As a result, the measurement accuracy of radioactivity is improved. Furthermore, the equipment necessary for obtaining parameter information such as the position, thickness, density, etc. of the measurement object uses a radiation detector itself that measures the radioactivity of the measurement object. For this reason, it is not necessary to use another means, and cost and installation space can be saved.

  1 object to be measured, 2 measuring table, 3 radiation detector, 4 amplifier, 5 multi-wave height analyzer, 6 inverse problem calculator, 7 display unit, 8 object thickness / density determination unit (parameter determination unit), 9 center of gravity Position determination unit (parameter determination unit), 10 Response function selection unit, 11 Response function database (database), 12, 12A, 12B Live zero radiation source, 13 Weight measurement unit.

Claims (6)

A database that stores in advance an input / output relationship between an energy spectrum of radiation radiated from an object to be measured and a pulse wave height distribution measured by a detector according to the energy spectrum as a detector response function;
A response function selector for extracting the detector response function from the database;
By performing inverse problem calculation using the detector response function extracted by the response function selection unit and the measured pulse wave height distribution, an energy spectrum of the radiation is obtained, and the radioactivity contained in the object to be measured A radioactivity analyzer equipped with an inverse problem calculation unit for analyzing and quantifying nuclides,
In the database, as the detector response function, a plurality of detector response functions corresponding to parameter information including the shape of the object to be measured are stored in advance,
Based on the pulse wave height distribution measured by the detector, a parameter determination unit that calculates the parameter information related to the shape of the object to be measured ;
One or more live beams that are embedded in a measurement table on which the object to be measured is placed and emit radiation of different energies that are different from the measurement target nuclide of the object to be measured toward the detector. A zero source ,
The parameter determination unit is radiated from the one or more live zero ray sources and incident on the detector in the absence of the measurement target, and the detection through the measurement target. Based on the respective pulse wave height distribution measured by the detector according to the energy of the radiation incident on the device, the thickness of the object to be measured is calculated as the shape included in the parameter information,
The response function selection unit extracts from the database a detector response function corresponding to the parameter information calculated by the parameter determination unit corresponding to the pulse wave height distribution measured by the detector. . The radioactivity analyzer according to claim 1 ,
When the object to be measured is a mixture composed of N substances (N is an integer of 2 or more), N or more live zero radiation sources are used as the live zero radiation source,
In the database, as the detector response function, a plurality of detector response functions corresponding to parameter information including the shape of the object to be measured and the densities of the N substances are stored in advance.
The parameter determination unit radiates energy of the N or more radiations emitted from the N or more live zero ray sources and incident on the detector without the measurement target, and the measurement target. Based on the respective pulse height distributions measured by the detector according to the energy of the N or more radiations that have passed through and entered the detector, the thickness of the object to be measured and the N A radioactivity analyzer that calculates the density of each substance as the parameter information. The radioactivity analyzer according to claim 1 or 2 ,
A weight measuring unit for measuring the weight of the object to be measured placed on the measuring table;
The parameter determination unit, the detector by measured the said pulse-height distribution, and on the basis of the weight measured by the weight measuring unit includes a thickness and area of the object to be measured on the parameter information Radioactivity analyzer that calculates as the shape . The radioactivity analyzer according to any one of claims 1 to 3 ,
A transport mechanism for moving the position of the measurement object existing between the detector and the live zero source so that the radiation passes through a plurality of different positions of the measurement object;
The parameter determining unit is radiated from the live zero source, and is measured by the detector according to energy of radiation that has passed through a plurality of different positions of the measurement target and is incident on the detector. A radioactivity analyzer that calculates a thickness distribution in the moving direction of the object to be measured as the shape included in the parameter information based on a pulse height distribution. The radioactivity analyzer according to any one of claims 1 to 4 ,
The parameter determination unit is based on a pulse height distribution measured by the detector according to energy of radiation emitted from at least one live zero source and incident on the detector in the absence of the measurement object. A radioactivity analyzer for calibrating the detector. A database for storing in advance, as a detector response function, an input / output relationship between an energy spectrum of radiation radiated from an object to be measured and a pulse wave height distribution measured by a detector according to the energy spectrum; An instrument response function is extracted from the database, and an inverse problem calculation is performed using the extracted detector response function and the measured pulse wave height distribution, thereby obtaining an energy spectrum of the radiation, A radioactivity analysis method applied to a radioactivity analyzer for analyzing and quantifying contained radionuclides,
A storage step of previously storing a plurality of detector response functions according to parameter information including the shape of the measurement target object as the detector response function with respect to the database;
Based on the pulse wave height distribution measured by the detector, a parameter determination step for calculating the parameter information related to the shape of the object to be measured ;
A response function selection step of extracting from the database a detector response function corresponding to the parameter information calculated in the parameter determination step corresponding to the pulse height distribution measured by the detector;
By performing inverse problem calculation using the detector response function extracted in the response function selection step and the pulse wave height distribution measured by the detector, an energy spectrum of the incident radiation is obtained, and the measured object An inverse problem calculation step for analyzing and quantifying the radionuclide contained in the object ,
The parameter determination step is embedded in a measurement table on which the object to be measured is placed, and emits radiation of different energy from the measurement object nuclide of the object to be measured toward the detector. Energy of radiation emitted from one or more live zero sources that are incident on the detector in the absence of the object to be measured, and radiation incident on the detector through the object to be measured A radioactivity analysis method for calculating a thickness of the object to be measured as the shape included in the parameter information based on each pulse wave height distribution measured by the detector according to energy .

Images