JP2013213807A - Radiation measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily measure radiation of a sample with desired accuracy.SOLUTION: A radiation measuring device 10 comprises: a radiation detector 15 for detecting radiation emitted from a sample; and a processor 13 that corrects self-absorption of the sample on the basis of a correction coefficient and calibrates detection efficiency of the radiation detector 15. The processor 13 comprises: a storage section 41 for storing data that describe the correction coefficient corresponding to any attenuation coefficient of the sample by a parameter corresponding to a shape of the sample and a shape of crystal of the radiation detector 15; and a parameter calculating section 42 for calculating the parameter on the basis of the detection efficiency of the radiation detector 15 obtained by performing an operation of radiation transportation by simulation in a case where the sample having any attenuation coefficient is accommodated in a predetermined container 16 and the radiation emitted from the sample is detected by the radiation detector 15 having a germanium crystal with a predetermined shape.

Description

  The present invention relates to a radioactivity measurement apparatus.

  Conventionally, for example, when the amount of radioactivity of a sample filled in a container is quantified, radiation behavior in the container and the sample and the radiation detector is traced by Monte Carlo simulation, and the radiation emitted from the sample in the container is detected. There is known a method of calculating the total absorption peak efficiency of and correcting self-absorption (see, for example, Patent Documents 1 and 2).

JP 2002-98768 A WO1998 / 39628

  By the way, according to the efficiency calculation and self-absorption correction according to the above prior art, the calculation load required for the simulation is increased and the calculation time is increased. In addition, the calculation process is performed every time the shape of the container and the material of the sample are different. Therefore, there is a problem that complicated labor is required to quantify the amount of radioactivity of the sample filled in the container.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a radioactivity measuring apparatus capable of easily measuring the radioactivity of a sample with a desired accuracy.

  In order to solve the above problems and achieve the object, a radioactivity measurement apparatus according to claim 1 of the present invention is a radiation detector that detects radiation emitted from a sample (for example, radiation detection in an embodiment). And a calculation means (for example, the processing apparatus 13 in the embodiment) for correcting the self-absorption of the sample based on a correction coefficient and calibrating the detection efficiency of the radiation detector, The calculation means stores storage means (for example, an embodiment) that stores data describing the correction coefficient according to an arbitrary attenuation coefficient of the sample by parameters according to the shape of the sample and the shape of the crystal of the radiation detector. The storage unit 41) and the parameter, the radiation having the arbitrary attenuation coefficient stored in a predetermined container (for example, the container 16 in the embodiment), and the radiation emitted from the sample. Compared to the case where detection is performed by the radiation detector having a crystal having a predetermined shape (for example, the germanium crystal 20 in the embodiment), the detection efficiency of the radiation detector obtained by calculating the transport of the radiation by simulation is increased. Parameter calculation means (for example, parameter calculation unit 42 in the embodiment) that calculates based on the above.

  Furthermore, in the radioactivity measurement apparatus according to claim 2 of the present invention, the parameter calculation means sets the crystal having the predetermined shape to an average shape crystal based on a plurality of different crystal shapes of the radiation detector.

  Furthermore, in the radioactivity measurement apparatus according to claim 3 of the present invention, the parameter calculation means uses the crystals of the predetermined shape as crystals of a plurality of different radiation detectors, and the plurality of the radiation detectors with respect to the plurality of different radiation detectors. Based on a plurality of parameter calculation results, parameter data indicating the correspondence between the parameter and the crystal shape is created.

  Furthermore, in the radioactivity measurement apparatus according to claim 4 of the present invention, the storage unit is configured to obtain a plurality of groups obtained by classifying the plurality of different radiation detectors according to relative efficiency based on the parameter data. On the other hand, a single parameter that is commonly associated with all the radiation detectors in each group is stored.

Furthermore, in the radioactivity measurement apparatus according to claim 5 of the present invention, the correction coefficient f is described by a predetermined mathematical formula using the attenuation coefficient μ, the first parameter a, and the second parameter b. The mathematical formula is f = 1 / (1 + a × μ + b × μ ² ).

Furthermore, in the radioactivity measuring apparatus according to claim 6 of the present invention, the correction coefficient f is a predetermined value based on the attenuation coefficient μ, the first parameter a, the second parameter b, and the third parameter c. The predetermined mathematical formula is f = 1 / (1 + a × μ + b × μ ² + c × μ ³ ).

  Furthermore, in the radioactivity measurement apparatus according to claim 7 of the present invention, the predetermined container is coaxial with the bottomed cylindrical container body (for example, the container body 31 in the embodiment) and the central axis of the container body. A cylindrical recess (for example, a cylindrical recess 32 in the embodiment) provided on the bottom surface (for example, the bottom surface 31A in the embodiment) of the container body, A sample can be accommodated, and the inner peripheral wall surface (for example, inner peripheral wall surface 31C in the embodiment) of the container body has a diameter of 130.6 mm to 139 mm, and the inside of the container body according to the cylindrical recess. The diameter of the columnar portion (for example, the columnar portion 34 in the embodiment) provided in the container is 81 mm to 95 mm, and the inner peripheral wall surface from the inner bottom surface (for example, the inner bottom surface 31B in the embodiment) of the container body Accommodation of the sample provided above The distance to (for example, the accommodation end 33 in the embodiment) is 90 mm to 129 mm, and the distance from the inner bottom surface of the container body to the distal end surface of the cylindrical portion (for example, the distal end surface 34A in the embodiment). 79 mm to 100 mm, the inner volume from the inner bottom surface of the container body to the receiving end is 1 liter, the first parameter a is 1.33 to 1.43, and the second parameter b is 0. .633 to 0.750.

  Furthermore, in the radioactivity measurement apparatus according to claim 8 of the present invention, the predetermined container is coaxial with the bottomed cylindrical container body (for example, the container body 31 in the embodiment) and the central axis of the container body. A cylindrical recess (for example, a cylindrical recess 32 in the embodiment) provided on the bottom surface (for example, the bottom surface 31A in the embodiment) of the container body, A circle that is capable of accommodating a sample, has an inner peripheral wall surface of the container main body (for example, an inner peripheral wall surface 31C in the embodiment) of 122 mm, and is provided inside the container main body according to the cylindrical recess. The diameter of the columnar portion (for example, the columnar portion 34 in the embodiment) is 89 mm, and the inner diameter is provided on the inner peripheral wall surface from the inner bottom surface (for example, the inner bottom surface 31B in the embodiment) of the container body. Sample storage end (for example, in the embodiment The distance from the inner end 33) is 102 mm, the distance from the inner bottom surface of the container body to the tip surface of the cylindrical portion (for example, the tip surface 34A in the embodiment) is 79 mm, and the inner bottom surface of the container body The internal volume from the storage end to the storage end is 0.7 liter, the first parameter a is 1.06 to 1.18, and the second parameter b is 0.373 to 0.460.

  Furthermore, in the radioactivity measuring apparatus according to claim 9 of the present invention, the predetermined container is coaxial with the bottomed cylindrical container body (for example, the container body 31 in the embodiment) and the central axis of the container body. A cylindrical recess (for example, a cylindrical recess 32 in the embodiment) provided on the bottom surface (for example, the bottom surface 31A in the embodiment) of the container body, A circle that is capable of accommodating a sample, has an inner peripheral wall surface of the container main body (for example, an inner peripheral wall surface 31C in the embodiment) of 160 mm, and is provided inside the container main body according to the cylindrical recess. The diameter of the columnar portion (for example, the columnar portion 34 in the embodiment) is 89 mm, and the inner diameter is provided on the inner peripheral wall surface from the inner bottom surface (for example, the inner bottom surface 31B in the embodiment) of the container body. Sample storage end (for example, in the embodiment The distance to the container end 33) is 124 mm, the distance from the inner bottom surface of the container body to the tip surface of the cylindrical portion (for example, the tip surface 34A in the embodiment) is 79 mm, and the inner bottom surface of the container body The internal volume from the storage end to the storage end is 2 liters, the first parameter a is 2.18 to 2.41, and the second parameter b is 1.21 to 1.37.

  Furthermore, a radioactivity measuring apparatus according to claim 10 of the present invention includes a radiation detector that detects radiation emitted from a sample, and corrects self-absorption of the sample based on a correction coefficient, so that the radiation detector Arithmetic means for calibrating the detection efficiency (for example, the processing device 13 in the embodiment), and the arithmetic means calculates the correction coefficient according to the attenuation coefficient of the sample, the shape of the sample, and the radiation detector. Storage means for storing data described by parameters according to the shape of the crystal (for example, the storage unit 41 in the embodiment), and parameter acquisition means for acquiring the parameters from the outside.

  According to the radioactivity measuring apparatus according to claim 1 of the present invention, the correction coefficient for correcting the self-absorption of the sample is determined by the attenuation coefficient of the sample and the parameters corresponding to the shape of the sample and the crystal shape of the radiation detector. By describing, it is possible to prevent the calculation load from increasing and the calculation time from becoming long, and to easily correct the self-absorption.

Further, since the parameter is calculated based on the detection efficiency of the radiation detector obtained by calculating the transport of radiation by simulation for a sample having an arbitrary attenuation coefficient, for example, a standard volume source is used. Compared with the case where the parameter is calculated by actual measurement, self-absorption can be corrected with high accuracy in a wider range of attenuation coefficients.
Moreover, the generation of radioactive waste can be suppressed without the need for a standard volume source.

  In addition, the self-absorption is corrected for a sample having an arbitrary attenuation coefficient by executing parameter calculation only once for a combination of a predetermined container for storing a sample and a radiation detector having a crystal having a predetermined shape. Therefore, it is possible to prevent troublesome work when quantifying the amount of radioactivity of the sample filled in the container.

  Furthermore, according to the radioactivity measuring apparatus according to claim 2 of the present invention, the parameter calculation is executed only once for the combination of the predetermined container for storing the sample and the radiation detector having the average shape crystal. This makes it possible to correct the self-absorption of a sample having an arbitrary attenuation coefficient for a radiation detector having a plurality of crystals having different shapes, and is complicated when quantifying the amount of radioactivity of the sample filled in the container. It is possible to prevent troublesome work.

Furthermore, according to the radioactivity measuring apparatus according to claim 3 of the present invention, an appropriate parameter can be easily obtained by searching parameter data based on the crystal shape of an appropriate radiation detector.
Thereby, self-absorption can be easily and accurately corrected with respect to a sample having an arbitrary attenuation coefficient accommodated in a predetermined container.

  Furthermore, according to the radioactivity measuring apparatus according to claim 4 of the present invention, the parameters can be easily obtained without requiring the details of the crystal shape of the radiation detector, and the sample filled in the container can be obtained. It is possible to prevent troublesome work when quantifying the amount of radioactivity.

  Furthermore, according to the radioactivity measuring apparatus according to claim 5 or claim 6 of the present invention, self-absorption can be accurately corrected within a wide range of attenuation coefficients.

  Furthermore, according to the radioactivity measuring apparatus according to claim 7 of the present invention, the self-accuracy of a sample having an arbitrary attenuation coefficient stored in a predetermined container (for example, a marinelli container) having an internal volume of 1 liter can be accurately measured. Absorption can be corrected.

  Furthermore, according to the radioactivity measuring apparatus according to claim 8 or claim 9 of the present invention, an arbitrary attenuation coefficient stored in a predetermined container (for example, a marinelli container) having an internal volume of 0.7 liter or 2 liter. Self-absorption can be accurately corrected for a sample having

According to the radioactivity measuring apparatus of claim 10 of the present invention, the correction coefficient for correcting the self-absorption of the sample is a parameter corresponding to the attenuation coefficient of the sample, the shape of the sample, and the shape of the crystal of the radiation detector. Therefore, it is possible to prevent the calculation load from increasing and the calculation time from becoming long, and to easily correct the self-absorption.
Furthermore, by acquiring the parameters from the outside, versatility can be improved as compared with the case where the parameters are calculated by a predetermined arithmetic processing set in advance, for example.

It is a block diagram of the radioactivity measuring apparatus which concerns on embodiment of this invention. It is sectional drawing of the radiation detector which concerns on embodiment of this invention. It is sectional drawing of the container of the sample for radioactivity measurement which concerns on embodiment of this invention. It is sectional drawing of the container of the sample for radioactivity measurement which concerns on embodiment of this invention. It is a graph which shows the change of the total absorption peak efficiency according to the diameter D1 of the sample container for the radioactivity measurement which concerns on embodiment of this invention with respect to three radiation detectors from which a crystal size differs. It is a figure which shows an example of the correction coefficient f (micro) according to the arbitrary attenuation coefficients micro which concern on embodiment of this invention. It is a figure which shows an example of the correspondence of the 1st parameter a and 2nd parameter b which concern on embodiment of this invention, and the shape of the crystal | crystallization of a radiation detector. It is a figure which shows an example of the correction coefficient f (micro) according to the arbitrary attenuation coefficients micro which concern on embodiment of this invention.

Hereinafter, a radioactivity measurement apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, for example, the radioactivity measuring apparatus 10 according to the present embodiment accommodates an input device 11, an output device 12, a processing device 13, a pulse height analyzer 14, a radiation detector 15, and a sample. And the container 16 to be configured.

The input device 11 includes, for example, various switches and a keyboard that output signals according to an input operation by the operator, and outputs various command signals according to the input operation by the operator to the processing device 13.
The output device 12 includes, for example, a speaker and a display device, and outputs various types of information output from the processing device 13.

  The wave height analyzer 14 is, for example, a multi-channel analyzer, and calculates the wave height distribution of the output signal pulse output from the radiation detector 15, that is, the count value for each of a plurality of channels set according to the wave height value. For example, when an output signal pulse having a peak value corresponding to the energy of the radiation is output from the radiation detector 15, the pulse height analyzer 14 creates an energy spectrum as a pulse height distribution of the output signal pulse of the radiation detector 15.

  The radiation detector 15 is, for example, a closed-end coaxial type germanium semiconductor detector, and as shown in FIG. 2, a germanium crystal 20, an end cap housing 21, a vacuum region 22 inside the end cap housing 21, and a vacuum A crystal holder 23 that holds the germanium crystal 20 in the region 22 and a resin film 24 provided on the crystal holder 23 are provided.

The radiation detector 15 has a relative efficiency value of 20% to 40%, for example.
The germanium crystal 20 formed in a bottomed cylindrical shape includes a sensitive region 25 for radiation and a surface insensitive layer 26.
The germanium crystal 20 held by the crystal holder 23 is accommodated in an end cap housing 21 having a radiation incident window (not shown), for example, and the inside of the end cap housing 21 is in a vacuum state.

  For example, the diameter A of the germanium crystal 20 is 48 mm to 60 mm, and the length B of the germanium crystal 20 is 30 mm to 70 mm.

The crystal holder 23 is formed in a box shape having an opening. The germanium crystal 20 is accommodated inside the crystal holder 23, and the opening is closed by a resin film 24.
And the opening part obstruct | occluded by the resin film 24 is arrange | positioned so that it may face the entrance window of the end cap housing 21, and opposes it.

  For example, as shown in FIG. 3, the container 16 is a so-called marinade container, and is provided on the bottom surface 31 </ b> A of the container body 31 coaxially with the bottomed cylindrical container body 31 and the central axis O of the container body 31. A cylindrical recess 32, and a sample can be accommodated inside the container body 31.

For example, as shown in FIG. 4, the container 16 has an internal volume of 1 liter from the inner bottom surface 31B of the container body 31 to the sample storage end 33 provided on the inner peripheral wall surface 31C.
And the diameter D1 of the inner peripheral wall surface 31C of the container main body 31 is 130.6 mm to 139 mm, and the diameter D2 of the cylindrical portion 34 provided inside the container main body 31 according to the cylindrical concave portion 32 is 81 mm to 95 mm, For example, the diameter D1 = 135 mm and the diameter D2 = 89 mm.
Furthermore, the distance L1 from the inner bottom surface 31B of the container body 31 to the receiving end 33 is 90 mm to 129 mm, and the distance L2 from the inner bottom surface 31B of the container body 31 to the tip surface 34A of the cylindrical portion 34 is 79 mm to 100 mm. For example, the distance L1 = 104.18 mm and the distance L2 = 79 mm.
And the cylindrical recessed part 32 of the container 16 is formed so that the end cap of the radiation detector which has a relative efficiency value of 20%-40%, for example, the end cap housing 21 of the radiation detector 15 mentioned above, can be accommodated.

The size ranges of the diameters D1 and D2 and the distances L1 and L2 of the container 16 are set such that the diameters D1 and D2 of the container 16 are, for example, for a plurality of radiation detectors having a relative efficiency value of 20% to 40%. The distances L1 and L2 are set by predetermined calculations that are appropriately changed.
This predetermined calculation is systematically executed for a plurality of radiation detectors frequently used for measuring the environmental radioactivity. For example, the transport of γ rays is calculated by a simulation such as a Monte Carlo method, and the calculation result is calculated. Based on this, the total absorption peak efficiency with respect to γ rays of the radiation detector is calculated.
The size ranges of the diameters D1 and D2 and the distances L1 and L2 of the container 16 are a plurality of radiation detectors, particularly a plurality of relative efficiency values of 20% to 40% that are frequently used for measuring environmental radioactivity. It is set so as to ensure a desired detection efficiency for the radiation detector.

For example, in FIG. 5, three radiation detectors having different combinations of the diameter D and the length L of the crystal dimensions of the germanium crystal 20 (for example, three radiations with D / L = 0.8, 1.0, and 1.4). The correlation between the total absorption peak efficiency (y) of the detector) for 661 keV γ rays and the diameter D1 (x) of the container 16 is shown.
For each radiation detector, when the change in the total absorption peak efficiency (y) according to the diameter D1 (x) of the container 16 is approximated by a quadratic expression, the diameters D1 = 139.0 mm, 136.0 mm, It can be seen that the total absorption peak efficiency is maximized at 130.6 mm.
Thus, for a radiation detector having a relative efficiency value of 20% to 40%, which is frequently used for measurement of environmental radioactivity, the range of the combination of the crystal dimension diameter D and length L is D / L = 0. If it is set to 8-1.4, the diameter D1 of the container 16 will be 130.6 mm-139 mm, More preferably, it is a substantially median diameter D1 = 135 mm.

  For example, as illustrated in FIG. 1, the processing device 13 includes a storage unit 41, a parameter calculation unit 42, and a calculation unit 43.

  The storage unit 41 stores, for example, various preset data, data of various calculation results of the processing device 13, data output from the wave height analyzer 14, and the like.

  Further, the storage unit 41, for example, sets a correction coefficient f (μ) corresponding to an arbitrary attenuation coefficient μ of the sample with respect to the correction coefficient for correcting the self-absorption of the sample, the shape of the sample, and the radiation detector 15. Data described by parameters according to the shape of the germanium crystal 20 (for example, a predetermined mathematical formula using parameters to be described later) is stored.

  The parameter calculation unit 42 is a parameter stored in the storage unit 41, that is, a parameter corresponding to the shape of the sample and the shape of the germanium crystal 20 of the radiation detector 15, and a correction coefficient corresponding to an arbitrary attenuation coefficient μ of the sample. A parameter describing f (μ) is calculated.

  For example, the parameter calculation unit 42 stores a sample made of a medium having an arbitrary attenuation coefficient μ in a predetermined container 16, and emits γ rays emitted from the sample in the container 16 with a germanium crystal 20 having a predetermined shape. In contrast to the case of detection by the detector 15, the transport of γ rays is calculated by a simulation such as the Monte Carlo method. Then, based on the calculation result, the total absorption peak efficiency e for the γ-ray of the radiation detector 15 is calculated.

Parameter calculator 42, the calculation by the simulation, a plurality of media i (i = 1, ...) having any attenuation coefficient mu _i running against, calculates a plurality of the whole peak efficiency e _i.
For example, among the plurality of total absorption peak efficiencies e _i , in particular, with reference to the total absorption peak efficiency e ₀ when the attenuation coefficient μ is zero, as shown in the following formula (1), for example, A correction coefficient f _i corresponding to the peak efficiency e _i is calculated.

Then, for example, as shown in FIG. 6, the parameter calculation unit 42 determines the correspondence between the attenuation coefficient μ _i and the correction coefficient f _i (calculated value) of the plurality of media i, the shape of the sample, and the germanium of the radiation detector 15. It is described by a predetermined mathematical formula with parameters corresponding to the shape of the crystal 20, and the parameters are calculated from this mathematical formula. Then, the calculated parameter is stored in the storage unit 41.

For example, the predetermined formula is a quadratic approximate formula using the first parameter a and the second parameter b as shown in the following formula 2, and the parameter calculation unit 42 calculates the attenuation coefficient μ _i of the plurality of media _i and The parameters a and b are calculated by executing function fitting using the quadratic approximate expression on the correspondence relationship with the correction coefficient f _i (calculated value).

  For example, for the container 16 shown in FIG. 4, the first parameter a is 1.33 to 1.43 and the second parameter b is 0.634 to 0.750.

  For example, the calculation unit 43 performs, based on the data of the correction coefficient f (μ) corresponding to the arbitrary attenuation coefficient μ of the sample stored in the storage unit 41 with respect to the data output from the wave height analyzer 14, the sample Is corrected, the energy dependence data of the total absorption peak efficiency with respect to the γ rays of the radiation detector 15 is calibrated, and the amount of radioactivity contained in the sample is calculated.

  As described above, according to the radioactivity measuring apparatus 10 according to the present embodiment, the correction coefficient f (μ) for correcting the self-absorption of the sample, the attenuation coefficient μ of the sample, the shape of the sample, and the radiation detector 15 By describing the parameters according to the shape of the germanium crystal 20 (for example, the first parameter a and the second parameter b), it is easy to prevent an increase in calculation load and an increase in calculation time. Self-absorption can be corrected.

Furthermore, since the parameter is calculated based on the detection efficiency (total absorption peak efficiency e) of the radiation detector 15 obtained by calculating the transport of radiation by simulation for a sample having an arbitrary attenuation coefficient μ, For example, self-absorption can be corrected with high accuracy in a wider range of attenuation coefficients than in the case of calculating parameters by actual measurement using a standard volume source or the like.
Moreover, the generation of radioactive waste can be suppressed without the need for a standard volume source.

  In addition, by executing the parameter calculation only once for the combination of the container 16 containing the sample and the radiation detector 15 having the germanium crystal 20 having a predetermined shape, the sample having an arbitrary attenuation coefficient μ can be obtained. Self-absorption can be corrected, and troublesome work can be prevented when the amount of radioactivity of the sample filled in the container 16 is quantified.

  In the above-described embodiment, the parameter calculation unit 42 sets the predetermined shape of the germanium crystal 20 used when calculating the parameters as, for example, an average shape based on the shapes of the germanium crystals 20 of a plurality of different radiation detectors 15. Also good.

For example, the average diameter of the germanium crystal 20 having a relative efficiency value of about 20% to 40% used for the purpose of measuring environmental samples is 53 mm, and the average length is about 45 mm.
For the combination of the radiation detector 15 having the germanium crystal 20 and the container 16 shown in FIG. 4, for example, the first parameter a of the second-order approximation shown in the above equation (2) is 1.356162, and The parameter b of 2 is 0.708220.

In this case, the calculation of the parameter is executed only once for the combination of the container 16 for containing the sample and the radiation detector 15 having the average shape germanium crystal 20, whereby a plurality of germanium crystals 20 having different shapes are obtained. The self-absorption of a sample having an arbitrary attenuation coefficient μ can be corrected with respect to the radiation detector 15 having.
Thereby, it is possible to prevent troublesome work when the amount of radioactivity of the sample filled in the container 16 is quantified.

  In the above-described embodiment, the parameter calculation unit 42 calculates parameters for the radiation detector 15 having a plurality of germanium crystals 20 having different shapes, for example, and based on a plurality of parameter calculation results, Parameter data indicating a correspondence relationship with the shape of the germanium crystal 20 may be created.

For example, the diameter of the germanium crystal 20 having a relative efficiency value of about 20% to 40% used for the purpose of measuring environmental samples is about 48 mm to 60 mm and the length is about 30 mm to 70 mm.
The parameter calculation unit 42 calculates a parameter for the radiation detector 15 having a plurality of differently shaped germanium crystals 20 within the dimensional range of these diameters and distances, and based on the plurality of parameter calculation results, for example, FIG. As shown in FIG. 4, the shape of the germanium crystal 20 (for example, the diameter A and the length B) and the parameters (for example, the first parameter a and the second parameter b of the quadratic approximation expressed by the above formula (2)) Create parameter data indicating the correspondence between

In this case, an appropriate parameter corresponding to the shape of the germanium crystal 20 can be easily obtained by searching parameter data based on the shape of the germanium crystal 20 of the appropriate radiation detector 15 or performing interpolation of data points. Can be acquired.
Thereby, self-absorption can be easily and accurately corrected for a sample having an arbitrary attenuation coefficient μ accommodated in the container 16.

  Further, the storage unit 41 includes, for each of a plurality of groups obtained by dividing a plurality of different radiation detectors 15 according to relative efficiency, based on the parameter data created by the parameter calculation unit 42. A single parameter commonly associated with all the radiation detectors 15 may be stored.

For example, the storage unit 41 includes a plurality of different radiation detectors 15 having a relative efficiency value of about 20% to 40% used for the purpose of measuring environmental samples, and the relative efficiency values are sequentially 20% and 25%. And 35% and 40%.
For each group, a single parameter representing each group (for example, an average value of a plurality of parameters) is stored based on the parameter data.

  In this case, it is possible to easily obtain the parameters without requiring the details of the shape of the germanium crystal 20 of the radiation detector 15, and it is complicated when quantifying the radioactivity amount of the sample filled in the container 16. It is possible to prevent troublesome work.

  In the above-described embodiment, the parameter calculation unit 42 describes the correction coefficient f (μ) corresponding to the arbitrary attenuation coefficient μ of the sample by the quadratic approximate expression shown in the mathematical expression (2). However, the present invention is not limited to this. For example, it may be described by a third-order approximation represented by the following formula (3) or a fourth-order or higher order polynomial.

For example, when the possible range of the linear attenuation coefficient μ of the sample exceeds 4 g / cm ^{3 in} terms of the density of soil (SiO ₂ ), for example, when it is necessary to consider up to about 15 g / cm ³ , for example, FIG. As shown in FIG. 8, the correction coefficient f (μ) corresponding to an arbitrary attenuation coefficient μ of the sample can be described with high accuracy by a cubic approximation formula.

In the above-described embodiment, the processing device 13 may include a parameter acquisition unit that can acquire parameters from the outside instead of the parameter calculation unit 42 or in addition to the parameter calculation unit 42.
The parameter acquisition unit acquires parameters in accordance with, for example, an operator's input operation on the input device 11 and stores the acquired parameters in the storage unit 41.

  In the above-described embodiment, the container 16 is a marinelli container having an internal volume of 1 liter, but the present invention is not limited to this. For example, any other internal volume (for example, 0.7 liter, 2 liter) Etc.) and other arbitrary shapes and containers with an arbitrary internal volume.

For example, in the container 16 shown in FIG. 3, if the diameter D1 = 122 mm, the diameter D2 = 89 mm, the distance L1 = 102 mm, the distance L2 = 79 mm, and the internal volume is 0.7 liter, the first parameter a is 1 .06 to 1.18, and the second parameter b is 0.373 to 0.460.
For example, in the container 16 shown in FIG. 3, if the diameter D1 = 160 mm, the diameter D2 = 89 mm, the distance L1 = 124 mm, the distance L2 = 79 mm, and the internal volume is 2 liters, the first parameter a is 2 .18 to 2.41 and the second parameter b is 1.21 to 1.37.

  Further, the present invention may be applied to, for example, a sample having an appropriate shape that is exposed without the container 16.

  In the above-described embodiment, the radiation detector 15 is a germanium semiconductor detector, but is not limited to this, and may be another detector.

DESCRIPTION OF SYMBOLS 10 ... Radioactivity measurement apparatus 13 ... Processing apparatus (calculation means) 15 ... Radioactivity measurement apparatus 16 ... Container (predetermined container) 20 ... Germanium crystal (crystal) 41 ... Memory | storage part (memory | storage means) 42 ... Parameter calculation part (parameter calculation) Part)

Claims (10)

A radiation detector for detecting radiation emitted from the sample, and a calculation means for correcting self-absorption of the sample based on a correction coefficient to calibrate the detection efficiency of the radiation detector,
The computing means is
Storage means for storing data describing the correction coefficient according to an arbitrary attenuation coefficient of the sample by parameters according to the shape of the sample and the shape of the crystal of the radiation detector;
In the case where the sample having the arbitrary attenuation coefficient is stored in a predetermined container and the radiation emitted from the sample is detected by the radiation detector having a crystal having a predetermined shape, the radiation And a parameter calculating means for calculating based on the detection efficiency of the radiation detector obtained by calculating the transport of the radiation by a simulation.   The radioactivity measurement apparatus according to claim 1, wherein the parameter calculation unit uses the crystal having the predetermined shape as a crystal having an average shape based on a plurality of different crystal shapes of the radiation detector.   The parameter calculation means uses the crystal of the predetermined shape as a plurality of different crystals of the radiation detector, and based on a plurality of calculation results of the parameter for the plurality of different radiation detectors, the parameter and the shape of the crystal The radioactivity measuring apparatus according to claim 1, wherein parameter data indicating a correspondence relationship between the radioactivity and the radioactivity is created.   The storage means, for each of a plurality of groups obtained by dividing the plurality of different radiation detectors according to relative efficiency based on the parameter data, to all the radiation detectors in each group. The radioactivity measuring apparatus according to claim 3, wherein a single parameter that is associated in common is stored. The correction coefficient f is described by a predetermined mathematical formula using the attenuation coefficient μ, the first parameter a, and the second parameter b.
The radioactivity measurement apparatus according to claim 1, wherein the predetermined formula is f = 1 / (1 + a × μ + b × μ ² ). The correction coefficient f is described by a predetermined mathematical formula using the attenuation coefficient μ, the first parameter a, the second parameter b, and the third parameter c.
The radioactivity measurement apparatus according to claim 1, wherein the predetermined formula is f = 1 / (1 + a × μ + b × μ ² + c × μ ³ ). The predetermined container is:
A bottomed cylindrical container body, and a columnar recess provided on the bottom surface of the container body coaxially with the central axis of the container body, the sample being able to be accommodated inside the container body, ,
The diameter of the inner peripheral wall surface of the container body is 130.6 mm to 139 mm, and the diameter of the columnar portion provided inside the container body according to the columnar recess is 81 mm to 95 mm, and from the inner bottom surface of the container body The distance to the sample storage end provided on the inner peripheral wall surface is 90 mm to 129 mm, the distance from the inner bottom surface of the container body to the tip surface of the cylindrical portion is 79 mm to 100 mm, and the container body The internal volume from the inner bottom surface to the accommodation end is 1 liter,
6. The radioactivity measuring apparatus according to claim 5, wherein the first parameter a is 1.33-1.43, and the second parameter b is 0.633-0.750. The predetermined container is:
A bottomed cylindrical container body, and a columnar recess provided on the bottom surface of the container body coaxially with the central axis of the container body, the sample being able to be accommodated inside the container body, ,
The diameter of the inner peripheral wall surface of the container main body is 122 mm, and the diameter of the columnar portion provided inside the container main body according to the cylindrical concave portion is 89 mm, and the inner bottom surface of the container main body extends from the inner bottom surface to the inner peripheral wall surface. The distance from the provided sample storage end to 102 mm, the distance from the inner bottom surface of the container body to the tip surface of the cylindrical portion is 79 mm, and the inner volume from the inner bottom surface of the container body to the storage end Is 0.7 liters,
The radioactivity measuring apparatus according to claim 5, wherein the first parameter a is 1.06 to 1.18, and the second parameter b is 0.373 to 0.460. The predetermined container is:
A bottomed cylindrical container body, and a columnar recess provided on the bottom surface of the container body coaxially with the central axis of the container body, the sample being able to be accommodated inside the container body, ,
The diameter of the inner peripheral wall surface of the container main body is 160 mm, and the diameter of the columnar portion provided inside the container main body according to the cylindrical recess is 89 mm, and from the inner bottom surface of the container main body to the inner peripheral wall surface The distance from the provided sample storage end to 124 mm, the distance from the inner bottom surface of the container body to the tip surface of the cylindrical portion is 79 mm, and the inner volume from the inner bottom surface of the container body to the storage end Is 2 liters,
6. The radioactivity measurement apparatus according to claim 5, wherein the first parameter a is 2.18 to 2.41, and the second parameter b is 1.21 to 1.37. A radiation detector for detecting radiation emitted from the sample, and a calculation means for correcting self-absorption of the sample based on a correction coefficient to calibrate the detection efficiency of the radiation detector,
The computing means is
Storage means for storing data describing the correction coefficient according to the attenuation coefficient of the sample by parameters according to the shape of the sample and the shape of the crystal of the radiation detector;
And a parameter acquisition means for acquiring the parameter from the outside.

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