JP7606086B2 - Radioactive strontium measuring device, radioactive strontium measuring method, and program - Google Patents

Description

The present invention relates to a radioactive strontium measuring device, a radioactive strontium measuring method, and a program that can accurately measure the radioactivity of strontium-89, a type of radioactive strontium.

At nuclear power plants and other nuclear facilities, various radioactive materials (waste, treated water, etc.) are discharged. These radioactive materials are managed according to prescribed standards according to the radioactivity of the nuclide. Radioactive materials include, for example, radioactive strontium (Sr) such as strontium-90 (hereinafter referred to as Sr-90) derived from spent fuel and its radioisotope strontium-89 (hereinafter referred to as Sr-89), as well as yttrium-90 (hereinafter referred to as Y-90) which is generated by the decay of Sr-90, and it may be necessary to measure the radioactivity of each radioactive nuclide individually. Sr-90 has a half-life of approximately 29 years, while Sr-89 has a half-life of approximately 51 days.

The radioactivity of radioactive strontium is obtained by measuring the beta rays emitted from the sample. However, this beta ray measurement includes the radioactivity of Sr-89, Sr-90, and Y-90. To date, the following methods have been proposed to individually measure the radioactivity of radioactive Sr, including Sr-90 and Sr-89.

For example, Non-Patent Document 1 proposes a method of using a GM counter or the like to measure the radioactivity of the strontium fraction and the radioactivity of Y-90 separated from the fraction by milking, determining the radioactivity of Sr-90 from this amount, and then determining the radioactivity of Sr-89 by subtracting it from the radioactivity of the strontium fraction. With this method, it is necessary to wait for Y-90 to be produced from Sr-90 in the strontium fraction and for it to reach a state of radioactive equilibrium, and it takes about three weeks from the occurrence of nuclear fission to the end of measurement in order to obtain a measured value.

Non-Patent Document 2 also proposes a method of using a GM counter or similar to measure the radioactivity of the separated strontium fraction at two different times, and then calculating the radioactivity amounts of Sr-89 and Sr-90 from the decay or increase. With this method, it is necessary to wait for a change in the decay curve due to the production of Y-90 from Sr-90 in the strontium fraction, and it takes about one week from the occurrence of nuclear fission to obtain a measurement value.

Non-Patent Document 3 also proposes a method of using a device capable of measuring the spectrum of beta rays to directly separate and measure the radioactivity of Sr-89 and Sr-90 using beta ray spectrometry, a method of analyzing beta rays, and then using the least squares method based on the measured values to determine the radioactivity of each. With this method, it is possible to obtain measured values in about two days after the occurrence of nuclear fission.

Guidelines for the measurement of radioactive materials released from light water nuclear power reactor facilities (Nuclear Safety Commission, partially revised on March 29, 2001) Radioactive Strontium Analysis Method (Ministry of Education, Culture, Sports, Science and Technology, revised in 2003) Rapid determination of 89Sr and 90Sr in radioactive waste using Sr extraction disk and beta-ray spectrometer, JAEA Y. Kameo et al.

When Sr radioactivity measurement results must be obtained within a few days, the most effective method among the above methods is measurement using beta-ray spectrometry as described in Non-Patent Document 3. However, with this method, when the amount of Sr-89 is, for example, about 1/5 (Sr-89/Sr-90≦0.2) or less compared to the amount of Sr-90, the concentration error (2σ) of Sr-89 may become nearly as large as the concentration of Sr-89, and the lower detection limit may become larger than that of Sr-90.

While it is possible to determine the amount of radioactivity of Sr-90 in a short period of time using beta ray spectrometry, there is an issue with the measurement of the radioactivity of Sr-89, which can lead to large errors. For this reason, there is a need for a method of measuring radioactive strontium that is less affected by the amount of coexisting Sr-90 when it comes to the radioactivity of Sr-89.

The present invention aims to provide a radioactive strontium measuring device, a radioactive strontium measuring method, and a program that can reduce the error in the amount of Sr-89 and lower the detection limit when measuring the amount of radioactive Sr contained in a sample, even when the amount of Sr-89 is lower than that of Sr-90.

One aspect of the present invention is a radioactive strontium measuring device comprising: a measuring unit that measures the count of beta rays emitted from a sample containing radioactive materials Sr-90, Y-90, and Sr-89 , from which a scavenging operation has been performed in advance to remove the Y-90 , and the spectrum of the beta rays; and a calculation unit that calculates the count of the sample based on an output value of the measuring unit, performs a spectrum analysis of the beta rays, calculates the amount of radioactivity of Sr-90 in the sample individually based on the analysis result, calculates the amount of radioactivity of the Y-90 based on the calculation result and the elapsed time from the scavenging operation, calculates a first count of beta rays emitted from Sr-90 and the Y-90 in the sample, calculates a second count of Sr-89 by subtracting the first count from the count of the sample, and calculates the amount of radioactivity of the Sr-89 contained in the sample based on the second count.

According to the present invention, the radioactivity of Sr-89 is calculated based on the calculated radioactivity of Sr-90, so even if the amount of Sr-89 is lower than that of Sr-90, the error in the amount of Sr-89 can be reduced and the lower detection limit can be made smaller.

In one aspect of the present invention, the measurement unit has a GM counter tube capable of counting β rays emitted from the sample, the measurement unit includes a scintillator that emits light in response to the β rays, and a photomultiplier tube that outputs an output value based on the light emitted by the scintillator, and the calculation unit calculates the count of the sample based on the output value of the GM counter tube and the output value from the photomultiplier tube, and may perform the spectral analysis based on the output value from the photomultiplier tube.

The present invention can be applied to existing coincidence-type measurement devices, reducing the cost of introducing the device.

In one aspect of the present invention, the measurement unit includes a first scintillator that emits light in response to the β rays, a second scintillator that emits light in response to the β rays, and a photomultiplier tube that outputs an output value based on the light emitted by the first scintillator and the second scintillator, and the calculation unit may calculate the count of the sample based on the output value of the photomultiplier tube and perform the spectral analysis.

The present invention can be applied to existing anti-coincidence counting type measurement devices, which reduces the cost of introducing the device.

In one aspect of the present invention, the sample may be subjected to a scavenging operation in advance to remove the Y-90.

According to the present invention, the time required to accurately calculate the amount of radioactivity of Sr-89 can be performed almost simultaneously with the time required to calculate Sr-90 using beta ray spectrometry.

The amount of radioactivity of the Y-90 may be calculated based on the amount of radioactivity of the Y-90 and the time elapsed since the scavenging operation.

According to the present invention, the radioactivity of Y-90 can be calculated as a function of Sr-90.

a spectrum of the beta rays emitted from a sample containing radioactive substances Sr-90, Y-90, and Sr-89 , the sample having been previously subjected to a scavenging operation to remove the Y-90 ; a count of the beta rays emitted from the sample and a spectrum of the beta rays; a count of the sample based on the measurement of the beta rays; an analysis of the spectrum of the beta rays based on the measurement of the beta rays; an amount of radioactivity of Sr-90 in the sample based on a result of the analysis; an amount of radioactivity of the Y-90 in the sample based on the result of the analysis and the time elapsed since the scavenging operation ; a first count of beta rays emitted from Sr-90 and the Y-90 in the sample; a second count of Sr-89 by subtracting the first count from the count of the sample; and a calculation of the amount of radioactivity of the Sr-89 contained in the sample based on the second count, the method comprising the steps of:

According to the present invention, the radioactivity of Sr-89 is calculated based on the calculated radioactivity of Sr-90, so even if the amount of Sr-89 is lower than that of Sr-90, the error in the amount of Sr-89 can be reduced and the lower detection limit can be made smaller.

One aspect of the present invention is a program that causes a computer to execute the following processes: measure the count of beta rays emitted from a sample containing radioactive materials Sr-90, Y-90, and Sr-89, which has been previously subjected to a scavenging operation to remove the Y-90, and the spectrum of the beta rays; calculate the count of the sample based on the measurement of the beta rays; analyze the spectrum of the beta rays based on the measurement of the beta rays; calculate the amount of radioactivity of Sr-90 in the sample individually based on the analysis result; calculate the amount of radioactivity of the Y-90 based on the calculation result and the elapsed time from the scavenging operation ; calculate a first count of beta rays emitted from Sr-90 and the Y-90 in the sample; calculate a second count of Sr-89 by subtracting the first count from the count of the sample; and calculate the amount of radioactivity of the Sr-89 contained in the sample based on the second count.

According to the present invention, the radioactivity of Sr-89 is calculated based on the calculated radioactivity of Sr-90, so even if the amount of Sr-89 is lower than that of Sr-90, it is possible to realize a program that reduces the error in the amount of Sr-89 and lowers the detection limit.

According to the present invention, when measuring the amount of radioactive Sr contained in a sample, even if the amount of Sr-89 is lower than that of Sr-90 (for example, Sr-89/Sr-90≦0.2), it is possible to reduce the error in the amount of Sr-89 and lower the detection limit.

1 is a block diagram showing a configuration of a radioactive strontium measuring device according to an embodiment of the present invention. FIG. 1 is a diagram showing the configuration of a coincidence type radioactive strontium measuring device. FIG. 1 is a diagram showing the configuration of an anti-coincidence type radioactive strontium measuring device. FIG. 2 is a diagram showing the energy spectrum of β rays emitted from a sample. FIG. 1 is a diagram showing a conventional spectrum analysis process. 1 is a flowchart showing the process of a conventional method for measuring radioactive strontium. 1 is a flowchart showing the process of a radioactive strontium measuring method.

The following describes a radioactive strontium measurement device, a radioactive strontium measurement method, and a program according to an embodiment of the present invention, with reference to the drawings.

A radioactive strontium measuring device according to an embodiment of the present invention measures radiation emitted from a sample from which strontium has been isolated, and calculates the amount of radioactivity for each nuclide contained in the sample based on the measurement results. In particular, it accurately calculates the amount of radioactivity of Sr-89. A general radiation measuring device can be used to measure beta rays emitted from the sample. The following is a description of the schematic configuration of the radioactive strontium measuring device.

As shown in FIG. 1, the radioactive strontium measuring device 1 includes, for example, a measuring unit 2 that measures β rays from a sample S, and a computing device 10 connected to the measuring unit 2. The sample S is strontium (Sr), a radioactive nuclide that undergoes β decay. The sample S is, for example, taken from spent nuclear fuel, and then Sr is isolated. The sample S is further subjected to a scavenging operation from the isolated Sr, and yttrium-90 (Y-90) is removed.

In sample S, after the scavenging operation, Sr-90 undergoes beta decay over time to produce Y-90. Therefore, sample S contains radioactive Sr-90 and the radioisotopes Sr-89 and Y-90. Sr-90, Y-90, and Sr-89 in sample S each emit beta rays.

The measurement unit 2, for example, individually calculates the amount of radioactivity of the nuclides contained in the sample S. The measurement unit 2 is composed of general measuring equipment as described below. The measurement unit 2 outputs a first output value related to the count of β rays emitted from the sample S, and a second output value related to the energy spectrum of the β rays. The first output value and the second output value output by the measurement unit 2 are set in a data format according to the type of the measurement unit 2.

The calculation device 10 includes, for example, a calculation unit 12 that performs a predetermined calculation based on the output value output from the measurement unit 2, a memory unit 14 that stores data necessary for the calculation, and a display unit 16 that outputs the calculation result.

The calculation unit 12 calculates the number of beta rays emitted from the sample S based on the output value output from the measurement unit 2, and also performs spectral analysis. As described below, the calculation unit 12 calculates the amount of radioactivity of Sr-89 contained in the sample S based on the number of beta rays emitted from the sample S and the results of the spectral analysis.

The calculation unit 12 is realized, for example, by a processor such as a CPU executing a program (software) stored in the storage unit 14. In addition, some or all of the functions of these components may be realized by hardware (including circuitry) such as an LSI, ASIC, FPGA, or GPU, or may be realized by a combination of software and hardware. The program may be stored in a storage device such as a HDD or flash memory in advance, or may be stored in a removable storage medium such as a DVD or CD-ROM and installed by inserting the storage medium into a drive device. The details of the calculation process of the calculation unit 12 will be described later.

The memory unit 14 stores programs and various data necessary for the calculations of the calculation unit 12. The memory unit 14 is realized by a storage medium such as a RAM, a ROM, a HDD, or a flash memory.

The display unit 16 is a display device to which the calculation results of the calculation unit 12 are output. The display unit 16 is a display device such as a liquid crystal display or an organic EL display. The display unit 16 may be configured separately from a personal computer, a tablet terminal, a smartphone, etc.

Next, we will explain the specific configuration of the radioactive strontium measurement device 1. The radioactive strontium measurement device 1 is composed of a measurement unit 2 that uses a general radiation measurement device.

Figure 2 shows the schematic configuration of a coincidence-type radioactive strontium measurement device 1. The radioactive strontium measurement device 1 includes a measurement unit 2 that measures β-rays emitted from the sample S, and a calculation device 10 that calculates the amount of radioactivity of each nuclide contained in the sample S individually based on the measurement value.

The measurement unit 2 is covered by a radiation-shielding housing 2A made of lead or the like. Inside the measurement unit 2, a measurement chamber 3 in which a sample S is placed is provided. A GM counter tube 4 is disposed above the measurement chamber 3. A scintillator 5 is disposed above the GM counter tube 4. A photomultiplier tube 6 is disposed above the scintillator 5.

When β rays emitted from the sample S are input, the GM counter tube 4 counts the number of such rays. When the GM counter tube 4 counts the number of such rays, it outputs an output value. The scintillator 5 is, for example, a plastic scintillator made of an organic material such as plastic. The scintillator 5 is excited by the β rays emitted from the sample S and transmitted through the GM counter tube 4, and emits light. The photomultiplier tube 6 detects the level of the pulse height of the light emitted from the scintillator 5. The photomultiplier tube 6 outputs a detection value based on the light emitted from the scintillator 5.

The calculation unit 12 calculates the number of coincidences by counting the number of times when the output value of the count counted in the GM counter tube 4 and the count output of the detection value of the light emission detected in the photomultiplier tube 6 are simultaneous. This makes it possible to eliminate the number of counts due to cosmic radiation and natural radiation. This number of coincidences is the count of the sample S. The count of the sample S includes the count of multiple beta rays emitted from multiple nuclides emitted from the sample S.

The calculation unit 12 also calculates the energy spectrum of the beta rays emitted from the sample S by beta ray spectrometry based on the detection value based on the pulse height level of the light emission detected by the photomultiplier tube 6.

Figure 3 shows the schematic configuration of an anti-coincidence type radioactive strontium measurement device 1. The radioactive strontium measurement device 1 includes a measurement unit 2 that measures β rays emitted from the sample S, and a calculation device 10 that calculates the amount of radioactivity of each nuclide contained in the sample S based on the measurement value.

The measurement unit 2 has an internal measurement chamber 3 covered with an active shield 2B that blocks radiation such as lead. The active shield 2B reduces background radiation such as cosmic radiation and natural radiation. A first scintillator 5A is disposed above the measurement chamber 3. A second scintillator 5B is disposed above the first scintillator. A photomultiplier tube 6 is disposed above the second scintillator 5B. The first scintillator 5A and the second scintillator 5B are plastic scintillators. The second scintillator 5B is formed to have a thicker thickness in the vertical direction than the first scintillator 5A.

When the active shield 2B detects cosmic radiation or natural radiation, it outputs a detection value. The first scintillator 5A is excited by β rays emitted from the sample S and transmitted through the GM counter 4, and emits light. The second scintillator 5B is excited by β rays emitted from the sample S and transmitted through the first scintillator 5A, and emits light. The photomultiplier tube 6 detects the wave height level of the light emitted from the first scintillator 5A and the second scintillator 5B. The photomultiplier tube 6 outputs a detection value based on the light emitted from the first scintillator 5A and the second scintillator 5B.

The calculation unit 12 counts the number of detection values of light emission caused by the difference in wavelength of the spectrum from the first scintillator 5A and the second scintillator 5B detected in the photomultiplier tube 6, and calculates the number of β rays emitted from the sample S. If the detection by the active shield 2B and the detection by the photomultiplier tube 6 are simultaneous, the calculation unit 12 does not count the number of detections, assuming that it is an anti-coincidence count.

This makes it possible to eliminate counts due to cosmic radiation and natural radiation. The calculation unit 12 also calculates the energy spectrum of beta rays emitted from the sample S by beta ray spectrometry, based on the detection value based on the wave height level of the light emission detected by the photomultiplier tube 6.

Next, we will explain the radioactive strontium measurement method using the radioactive strontium measurement device 1.

As shown in Figure 4, the energy spectrum of beta rays emitted from sample S is the sum of the beta rays emitted from multiple nuclides Sr-90, Sr-89, and Y-90.

但し

である。 As shown in FIG. 5, in the radioactive strontium measurement method implemented in the conventional radioactive strontium measurement device, the β-ray spectrum is divided into five fractions, and the contributions of the three nuclides in each fraction are calculated by the least squares method based on the following formula (1).

however

It is.

Figure 6 shows the process flow of a conventional method for measuring radioactive strontium. The beta ray count of sample S is measured (step S100). Beta ray spectrometry is performed to analyze the energy spectrum of beta rays (step S102). The least squares method is used to individually calculate the amounts of radioactivity of Sr-89, Sr-90, and Y-90 contained in sample S (step S104). With this method, when the amount of Sr-89 is, for example, about 1/5 or less of the amount of Sr-90 as described above, the lower detection limit may be higher than that of Sr-90.

Figure 7 shows the process flow of the radioactive strontium measurement method of the embodiment. In the radioactive strontium measurement device 1, a sample S from which Y-90 has been removed after a scavenging operation is set in the measurement chamber 3 of the measurement unit 2. The measurement unit 2 measures beta rays emitted from the sample S, which contains the radioactive substances Sr-90, Y-90, and Sr-89 (step S200). The calculation unit 12 calculates the count of the sample S based on the output value of the measurement unit 2 (step S202).

At this time, in the case of a coincidence type radioactive strontium measuring device 1 (see FIG. 2), the output value of the counting of the sample S measured in the GM counter tube 4 is acquired by the calculation device 10 and is taken in as counting data. In the coincidence type radioactive strontium measuring device 1, coincidence counting that reduces the influence of background when the outputs of the GM counter tube 4 and the photomultiplier tube 6 are simultaneous is used for counting the sample S.

In the case of the anti-coincidence type radioactive strontium measuring device 1 (see FIG. 3), the count of the sample S is calculated in the calculation device 10 based on the output value of the photomultiplier tube 6, utilizing the difference in wavelength of the β-ray spectrum between the first scintillator 5A and the second scintillator 5B. In the anti-coincidence type radioactive strontium measuring device 1, the anti-coincidence count is not counted when the detection of the active shield 2B and the detection of the photomultiplier tube 6 are simultaneous, and the number of outputs of the photomultiplier tube 6 with reduced background effects is used as the count.

The calculation unit 12 performs a spectrum analysis of the energy of β rays based on the output value of the measurement unit 2 (step S204). At this time, in a coincidence type radioactive strontium measurement device 1, the calculation unit 12 calculates the energy spectrum of β rays based on the output value of the photomultiplier tube 6 that detects the emission of the scintillator 5. In an anti-coincidence type radioactive strontium measurement device 1, the calculation unit 12 calculates the energy spectrum of β rays based on the output value of the photomultiplier tube 6 that detects the emission of the first scintillator 5A and the second scintillator 5B.

The calculation unit 12 individually calculates the amount of radioactivity (concentration) of Sr-90 in the sample S based on the analysis results (step S206). At this time, the calculation unit 12 analyzes the spectrum of β-ray energy using least squares approximation based on the output value of the pulse height level output from the photomultiplier tube 6, resolves it into a single spectrum of Sr-90, and then calculates the amount of radioactivity of Sr-90 alone.

The calculation unit 12 calculates the radioactivity of Y-90 as a function of Sr-90 based on the calculation result and the time elapsed since the purification of the sample S (step S208). The calculation unit 12 converts the total value of the calculated radioactivity of Sr-90 alone and the radioactivity of Y-90 alone calculated as a function of Sr-90 into a first count, which is the total value of the counts of β rays emitted from Sr-90 and Y-90 in the sample S (step S210).

The calculation unit 12 calculates a second count of Sr-89 by subtracting the first count from the count of the sample S calculated in step S202 (step S212). The calculation unit 12 converts the second count into the amount of radioactivity of Sr-89 contained in the sample S and calculates it (step S214).

Conventionally, in coincidence-type radioactive strontium measuring devices 1, the measurement value of the GM counter tube 4 was used to calculate coincidence counts with reduced background effects. In anti-coincidence-type radioactive strontium measuring devices 1, the counts calculated based on the output of the photomultiplier tube 6, excluding anti-coincidence counts, were used to reduce background effects.

In contrast, with the radioactive strontium measuring device 1, the second count is calculated by subtracting the first count, which is the sum of the Sr-90 and Y-90 counts calculated by spectrum analysis of the energy of β rays, from the calculated count excluding the coincidence and anti-coincidence counts, and the amount of radioactivity of Sr-89 can be accurately calculated based on the second count.

The radioactive strontium measuring device 1 described above can be realized by changing the calculation method, without changing the configuration of a conventional coincidence type radioactive strontium measuring device or an anti-coincidence type radioactive strontium measuring device. With the radioactive strontium measuring device 1, the radioactivity of Sr-89 can be calculated based on the calculated value of the radioactivity of Sr-90, regardless of the detection limit of Sr-89. With the radioactive strontium measuring device 1, the radioactivity of Sr-89 can be calculated in a short period of time after the scavenging operation.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as well as the scope and gist of the invention. For example, the above embodiments have been exemplified by those using a plastic scintillator, but this is not limiting and a liquid scintillator may also be used.

When measuring the amount of Sr radioactivity using a liquid scintillator, the same process can be performed by first determining the beta ray count due to Sr radioactivity, performing beta ray spectrometry using the output value of the photomultiplier tube based on Cherenkov light, and then subtracting the Sr-90 count determined based on the calculated amount of Sr-90 radioactivity from the beta ray count.

Reference Signs List 1 Radioactive strontium measuring device 2 Measuring section 2A Housing 2B Active shield 3 Measuring chamber 4 GM counter tube 5 Scintillator 5A First scintillator 5B Second scintillator 6 Photomultiplier tube 10 Calculating device 12 Calculating section 14 Memory section 16 Display section S Sample

Claims (5)

A measuring unit that measures the number of beta rays emitted from a sample that contains radioactive materials Sr-90, Y-90, and Sr-89 and that has been previously subjected to a scavenging operation to remove the Y-90 , and measures the spectrum of the beta rays;
a calculation unit which calculates the count of the sample based on the output value of the measurement unit, performs spectrum analysis of the beta rays, calculates the amount of radioactivity of Sr-90 in the sample individually based on the analysis result, calculates the amount of radioactivity of the Y-90 based on the calculation result and the elapsed time from the scavenging operation , calculates a first count of Sr-90 in the sample and beta rays emitted from the Y-90, calculates a second count of Sr-89 by subtracting the first count from the count of the sample, and calculates the amount of radioactivity of the Sr-89 contained in the sample based on the second count.
Radioactive strontium measuring device. the measurement unit has a GM counter capable of counting β rays emitted from the sample,
The measurement unit includes a scintillator that emits light by the β rays,
a photomultiplier tube that outputs an output value based on the light emitted by the scintillator;
The calculation unit calculates a count of the sample based on an output value of the GM counter and an output value from the photomultiplier tube,
performing the spectral analysis based on an output value from the photomultiplier tube;
2. The radioactive strontium measuring device according to claim 1. the measurement unit includes a first scintillator that emits light in response to the β rays, a second scintillator that emits light in response to the β rays, and a photomultiplier tube that outputs an output value based on the light emitted by the first scintillator and the second scintillator,
The calculation unit calculates the count of the sample based on the output value of the photomultiplier tube and performs the spectrum analysis.
2. The radioactive strontium measuring device according to claim 1. Counting the number of beta rays emitted from a sample containing radioactive materials Sr-90, Y-90, and Sr-89 , from which a scavenging operation has been performed in advance to remove the Y-90 , and measuring the spectrum of the beta rays;
Calculating the count of the sample based on the measurement of the beta rays;
Analyzing a spectrum of the beta rays based on the measurement of the beta rays;
The amount of radioactivity of Sr-90 in each sample is calculated based on the analysis results.
Calculate the amount of radioactivity of the Y-90 based on the calculation result and the elapsed time from the scavenging operation ;
Calculate the first count of beta rays emitted from Sr-90 and the Y-90 in the sample;
calculating a second count of Sr-89 by subtracting the first count from the count of the sample;
A radioactive strontium measuring method, comprising: a computer executing a process of calculating the amount of radioactivity of the Sr-89 contained in the sample based on the second count. Counting the number of beta rays emitted from a sample containing radioactive materials Sr-90, Y-90, and Sr-89 , from which a scavenging operation has been performed in advance to remove the Y-90 , and measuring the spectrum of the beta rays;
Calculating the count of the sample based on the measurement of the beta rays;
analyzing a spectrum of the beta rays based on the measurement of the beta rays;
The amount of radioactivity of Sr-90 in each sample is calculated based on the analysis results.
Calculating the amount of radioactivity of the Y-90 based on the calculation result and the elapsed time from the scavenging operation ;
Calculating the first count of beta rays emitted from Sr-90 and the Y-90 in the sample;
calculating a second Sr-89 count by subtracting the first count from the sample count;
A program that causes a computer to execute a process of calculating the amount of radioactivity of the Sr-89 contained in the sample based on the second count.

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