JP7422032B2 - Radionuclide production system and method - Google Patents

Description

The present invention relates to a radionuclide production system using an accelerated electron beam, and more particularly to a system and method for monitoring the production status during the production of radionuclides.

Although various radionuclides used in radiation therapy are being researched and developed, there are only a few facilities around the world that can supply radionuclides that can be used clinically. For example, actinium-225 (Ac-225), a type of radionuclide that emits alpha particles, is produced by decay from its parent nuclide, thorium-229 (Th-229), and is currently located in Karlsruhe, Germany. It is supplied by only three locations: the Institute for Transuranic Elements, the Oak Ridge National Laboratory in the United States, and the Institute of Physical Energy of the Russian National Science Center in Obninsk, Russia.

Th-229, the raw material for Ac-225, does not exist in nature and is produced through the decay of uranium-233 (U-233). However, due to nuclear protection concerns, U-233 will no longer be manufactured, so it is widely used worldwide. Currently, the only amount that can be produced is the amount produced by the decay of Th-229, which is produced by the decay of U-233 held in the world. Although it is sufficient for use in preclinical tests, it is predicted that there will be a large shortage in the future, and production using an accelerator is desired.

Regarding the production of Ac-225 using an accelerator, production tests using a cyclotron using the Ra-226(p,2n)Ac-225 reaction using naturally occurring radium-226 (Ra-226) have been conducted by ORNL and Quantum Science and Technology. The research and development organization is working on this, but it has not been commercialized. Production using a cyclotron does not allow for mass production even if the target Ra-226 is made thicker due to the short range of the accelerated protons in the Ra-226 target. Since most of the heat is lost in the target, it becomes difficult to remove heat from the target, resulting in problems such as the inability to improve current value and energy for mass production.

Another method of producing Ac-225 using an accelerator is a method of producing Ac-225 by beta decay of Ra-225 produced using the Ra-226(n,2n)Ra-225 reaction. A method of producing fast neutrons by irradiating deuterons accelerated by a cyclotron onto a target such as a carbon target or a metal that occludes tritium, and then irradiating Ra-226 with the generated fast neutrons. It is. Fast neutrons have a long range in Ra-226, so mass production is possible by making the raw material Ra-226 thicker, but it is necessary to shield the large amount of fast neutrons that are generated, so the equipment There are problems such as the device becoming large and the entire device structure being strongly activated by a large amount of fast neutrons.

Therefore, there is a need for a production system using an electron beam accelerator that can efficiently produce radionuclides with a small and lightweight device.

Japanese Patent Application Publication No. 2015-099117

In order to solve the problems of the conventional method for producing medical nuclides mentioned above, the present inventors developed a production system using an accelerated electron beam (Patent Document 1), and further applied this production system to actinium-225. We are currently conducting research to apply this method to nuclides such as

In order to put into practical use the production of radionuclides using the production system described in Patent Document 1, it is necessary to understand the status of the radionuclides, such as the health of the radionuclides and the amount of production. The soundness and production amount can be determined by, for example, extracting raw material nuclides and manufactured nuclides from the production system and analyzing them, but this requires stopping the production of radionuclides, which reduces production efficiency. significantly reduced. Therefore, a system is desired that can monitor the health of radionuclides and the amount of production while continuing production.

The present invention has been made to meet such demands, and the status of the system can be grasped by monitoring changes in gamma rays emitted from manufactured nuclides and radionuclides.

That is, the radionuclide production system of the present invention includes an electron beam accelerator, a target that receives an electron beam irradiated from the electron beam accelerator and emits bremsstrahlung radiation, and a radionuclide production unit disposed in the direction of movement of the bremsstrahlung radiation. , further comprising: a gamma ray detector that detects gamma rays emitted from nuclides contained in the radionuclide production section; and a state evaluation section that determines the state of the radionuclide production section using the output of the gamma ray detector. Equipped with.

According to the present invention, while operating a radionuclide production system, it is possible to grasp the health of nuclides contained therein, the production status of manufactured nuclides, and the like. Thereby, it is possible to estimate the time required to produce the desired production amount of the produced nuclide.

A diagram showing a configuration example of a radionuclide production system according to Embodiment 1 of the present invention 1 is a flowchart illustrating an example of the steps of the radionuclide manufacturing method of the present invention. Diagram showing an example of the wave height peak of the detected gamma ray spectrum This is a diagram showing temporal changes in peak count rate, where (A) shows normal times and (B) shows abnormal times. This is a diagram showing changes in production volume over time, with (A) showing normal times and (B) showing abnormal times. A diagram showing an example of controlling electron beam output in the radionuclide production system according to Embodiment 2 of the present invention FIG. 6 is a diagram illustrating the wave height peak of the detected gamma ray spectrum detected in Embodiment 2, in which (A) shows the time of electron beam irradiation, and (B) shows the time of stopping the electron beam irradiation. A diagram showing a configuration example of a radionuclide production system according to Embodiment 3 of the present invention A diagram showing a modification of the configuration of the radionuclide production system of Embodiment 3 FIG. 6 is a diagram illustrating the wave height peak of the detected gamma ray spectrum detected in Embodiment 3, in which (A) shows the case when no shield or collimator is installed, and (B) shows when the shield or collimator is installed. Diagram showing an example of arrangement of gamma ray detectors FIG. 4 is a diagram showing a configuration example of a radionuclide production system according to Embodiment 4 of the present invention, in which (A) is an example of the arrangement of gamma detectors along the electron beam irradiation direction, and (B) is a diagram showing an example of the arrangement of gamma detectors along the electron beam irradiation direction; An example of gamma detector arrangement is shown below. A diagram showing a configuration example of a radionuclide production system according to Embodiment 5 of the present invention It is a figure explaining the abnormality detection in the radionuclide manufacturing system of Embodiment 5, (A) is a figure which shows the electric current value of an electron beam accelerator, and (B) is a figure which shows an example of the change of a dose rate meter. A diagram illustrating an example of a determination flow by the state evaluation unit of Embodiment 5

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a radionuclide production system and production method of the present invention will be described with reference to the drawings. In the radionuclide production system and method of the present invention, the target raw material nuclide and production nuclide are not limited, but in the following explanation, Ra-226 is used as the raw material nuclide, and Ac-225 or its descendant nuclide is used as the raw material nuclide. The case of manufacturing Fr-221 and Bi-213 will be explained as an example.

<Embodiment 1>
The radionuclide production system of this embodiment basically includes an electron beam accelerator 10, a target 20, and a radionuclide production section (hereinafter simply referred to as the nuclide production section) 30.

Although not shown, the electron beam accelerator 10 includes an electron gun and an accelerator that accelerates electrons emitted from the electron gun in a predetermined direction, and emits an electron beam with a predetermined irradiation energy. The electron beam accelerator 10 is connected to an electron beam accelerator control unit (hereinafter simply referred to as a control unit) 50 that adjusts the power (current value) supplied to the electron beam accelerator and controls ON/OFF of the electron beam accelerator. ing.

The electronic target 20 is installed in front of the electron beam accelerator 10 in the direction in which the electron beam travels, and emits bremsstrahlung radiation when irradiated with the high-energy electron beam. The material of the target 20 is not particularly limited, but is made of a known material such as tungsten. The emitted bremsstrahlung radiation travels in the same direction as the electron beam.

The nuclide production unit 30 is a container containing a raw material nuclide, and the raw material nuclide is usually fixed to the inner wall surface of the container by sputtering or the like. The nuclide production unit 30 is arranged so that the surface to which the raw material nuclide is fixed is irradiated with bremsstrahlung radiation from the target. The raw material nuclide is a material that generates different nuclides through a nuclear reaction with controlled radiation. In this embodiment, Ra-226 is used.

The radionuclide production system of this embodiment further includes, near the nuclide production unit 30, a gamma ray detector 40 that detects gamma rays generated by raw material nuclides, production nuclides produced by nuclear reactions, and descendant nuclides produced by their decay; A data processing unit 60 processes and analyzes the detection results of gamma rays detected by the gamma ray detector 40, and the analysis results of the analysis unit 60 are used to evaluate the state of the nuclide production unit 30, such as determining the soundness and controlling the production amount. A state evaluation unit 70 that performs evaluation is provided.

As the gamma ray detector 40, a known gamma ray detector with energy resolution, such as a germanium semiconductor detector or a detector using a scintillator, can be used, and the gamma ray detector 40 is placed at a position shifted from the direction of movement of the bremsstrahlung radiation. Bremsstrahlung radiation travels in approximately the same direction as the electron beam, whereas gamma rays emitted from radionuclides in the nuclide production unit 30 travel in all directions. Therefore, by moving the gamma ray detector 40 away from the direction of movement of the bremsstrahlung radiation, the amount of bremsstrahlung radiation detected as background can be reduced. In this embodiment, the gamma ray detector 40 is arranged so that a line connecting the nuclide production unit 30 (its center) and the gamma ray detector 40 (its center) is perpendicular to the traveling direction of the bremsstrahlung radiation. However, when the amount of bremsstrahlung radiation is high, means for limiting the amount of bremsstrahlung radiation incident on the gamma ray detector 40 and the arrangement of the gamma ray detector 40 need to be devised. Specific examples thereof will be explained in other embodiments. The gamma ray detector 40 detects gamma rays with higher energy than the discret value (detection threshold) and higher dose than the background.

The data processing unit 60 processes the gamma ray spectrum output from the gamma ray detector 40, and calculates, for example, the count rate of the wave height peak of the gamma ray spectrum for each peak. The measurement rate is the value obtained by dividing the peak area by the measurement time. When the raw material nuclide is Ra-226, Ac-225 (half-life) is generated by a nuclear reaction with bremsstrahlung radiation, and Fr-221 and Bi-213 are generated as descendant nuclides by the decay of Ac-225. Since gamma ray emission from Ac-225 is extremely small, in this example, the count rate of gamma rays from Ra-226, Fr-221, and Bi-213 is calculated.

The data processing unit 60 calculates the peak count rate for each gamma ray energy at predetermined intervals using the gamma ray spectrum acquired by the gamma ray detector 40.

The condition evaluation unit 70 uses the peak count rate for each energy calculated by the data processing unit 60 to determine the health of the radionuclide production unit 30 and calculate the time required to reach the target production amount of the manufactured nuclide. . The function of the state evaluation unit 70 may be performed by, for example, a general-purpose computer equipped with a CPU and memory, or part or all of it may be implemented by hardware such as ASIC or FPGA. When carried out by a computer, it can be realized by the CPU uploading a program stored in advance in a memory or a storage device (not shown). Note that the functions of the data processing section 60 can also be realized by the same or different computers.

Next, the flow of operation of the radionuclide production system 100 having the above-described configuration will be explained with reference to FIG. 2.

Prior to electron beam irradiation, detection of gamma rays is started by the gamma ray detector 40 placed close to the radiation nuclide production unit 30 where the raw material nuclide is installed (S201). The gamma ray detector 40 detects gamma rays that have a higher energy than its discret value (detection threshold) and a higher dose than the background. Detection is performed at predetermined time intervals, and gamma ray spectra measured at predetermined time intervals are output to the data processing section 60. The data processing unit 60 calculates the peak count rate of the gamma ray peak at each measurement time and outputs it to the state evaluation unit 70 (S202).

Manufacturing is started while the gamma ray detection described above is continued, and the target 20 is irradiated with the electron beam 11 from the electron beam accelerator 10. As a result, bremsstrahlung radiation 21 is emitted from the target 20 and is irradiated to Ra-226, which is the raw material nuclide installed in the nuclide production section 30. A nuclear reaction between Ra-226 and bremsstrahlung radiation causes a reaction that generates neutrons (Ra-226(γ,n)Ra-225) to generate Ra-225. The target nuclide, Ac-225, is produced from Ra-225 by β-decay (S203).

With the start of production, the nuclide production unit 30 emits gamma rays from the manufactured nuclide in addition to gamma rays from the raw material nuclide, and the gamma ray spectrum detected by the gamma ray detector 40 changes. FIG. 3 schematically shows a graph of the count rate obtained from the gamma ray spectrum detected by the gamma ray detector 40. In FIG. 3, the horizontal axis represents the peak value (energy) of the gamma ray spectrum, and the vertical axis represents the peak count rate. As shown in the figure, peaks appear corresponding to the energy of gamma rays generated from each nuclide, and the peak count rate is highest for Ra-226, which is the raw material nuclide. In addition, Fr-221 and Bi-213, which are descendant nuclides of Ac-225, appear as gamma ray peaks with higher energy than Ra-226.

The data processing unit 60 calculates the peak count rate for each measurement time of the gamma ray detector 40 and for each gamma ray spectrum measurement time, and sends it to the state evaluation unit 70. The condition evaluation unit 70 determines the health of the raw material nuclide based on the gamma ray peak count rate for each measurement time sent from the data processing unit 60 (S204, S205), and estimates the production amount of the manufactured nuclide (S206). ).

Determination of the integrity of the raw material nuclide and estimation of the production amount of the manufactured nuclide are performed based on the reaction proceeding as follows. In the process of manufacturing a manufactured nuclide by the reaction between Ra-226 and bremsstrahlung radiation, most of the raw material nuclide Ra-226 does not react with the bremsstrahlung radiation, and only a very small amount of Ra-226 reacts. Therefore, the amount of Ra-226 at the time of manufacture remains approximately constant, and the peak count rate of gamma rays emitted from Ra-226 is also maintained approximately constant. On the other hand, the manufactured nuclide, Ac-225, decays into its progeny nuclides, Fr-221 and Bi-213, but the half-life of these progeny nuclides is very short compared to that of Ac-225. Ac-225, Fr-221 and Bi-213 are in permanent equilibrium. Therefore, the peak count rate of gamma rays emitted from Fr-221 or Bi-213 also changes in proportion to the amount of Ac-225 produced.

Based on the above, by measuring the time change in the peak count rate of gamma rays emitted from Ra-226 and confirming that the peak count rate is almost constant, we can evaluate the health of Ra-226, which is the raw material nuclide. Can be confirmed. Furthermore, by measuring the temporal change in the peak count rate of gamma rays emitted from Fr-221 or Bi-213, it is possible to quantify the production amount of Ac-225. The production amount is determined by the time change of the acceleration energy of the electron beam and the acceleration current value, and if these are constant, it becomes a linear function proportional only to the irradiation time of the electron beam, so it can be estimated from the irradiation time. Furthermore, based on data on changes in the production volume of Ac-225 over time, it is possible to evaluate the production time until the target production volume of Ac-225 is reached.

An example in which the condition evaluation unit 70 uses the peak count rate to determine the health of raw material nuclides, estimate the production amount of manufactured nuclides, and evaluate the production time until the target production amount is reached is shown in FIGS. 4 and 5. show. Figure 4 is a diagram showing an example of determining the integrity of the raw material nuclide using the gamma ray detection results from Ra-226, which is the raw material nuclide, and Figure 5 is a diagram showing an example of determining the integrity of the raw material nuclide using the gamma ray detection results from the descendant nuclide of Ac-225. FIG. 3 is a diagram showing an example of estimating the amount of produced nuclide and the required irradiation time.

Figure 4 (A) is a graph showing the peak count rate of raw material nuclides under normal conditions. As shown, the peak count rate of gamma rays from Ra-226 remains almost constant at each time the gamma rays were measured. If so, the condition evaluation unit 70 determines that the soundness of the raw material nuclide is maintained. On the other hand, as shown in FIG. 4(B), if the peak count rate suddenly decreases or increases, it is determined that some abnormality has occurred in the raw material nuclide. The causes of the change in the peak count rate of the raw material nuclide include leakage of the raw material nuclide from the nuclide production section 30, a change in the position of the nuclide production section 30, and a change in the positional relationship with the gamma ray detector 40. etc. are possible. Since all of these abnormalities appear as changes in the peak count rate of the raw material nuclide, it is possible to confirm the soundness and confirm the abnormality.

Figure 5 (A) is a diagram showing the peak count rate of progeny nuclides under normal conditions. Before the start of electron beam irradiation, the peak count rate from these nuclides is zero, but as the electron beam irradiation starts, the irradiation amount (irradiation amount) The peak count rate increases linearly with time). The amount of produced nuclide is determined by the acceleration energy E of the electron beam, the acceleration current value I, and the irradiation time T of the electron beam, so if these are constant, it is determined by the irradiation time T. Further, as described above, the amount of produced nuclides is proportional to the peak count rate of descendant nuclides in this example. From this relationship, the production amount can be calculated, and in FIG. 5, the vertical axis is shown as the production amount. That is, using the peak count rate, it is possible to calculate the amount of produced nuclide during gamma ray measurement.

In addition, by understanding the temporal changes in the production amount, the slope of the line (predicted line) showing the temporal changes in the production amount can be determined from the slope of the line (prediction line) indicating the temporal change in the production amount, as shown in Figure 5 (A). The required time can be estimated.

On the other hand, as shown in FIG. 5(B), when the calculated production amount (peak count rate) deviates from the predicted production amount line, it is determined that some abnormality has occurred (S207). The reason why the production amount (peak count rate) at a certain time shows an abnormal value is not only due to an abnormality during the soundness evaluation of the manufactured nuclide (S205), but also due to bremsstrahlung radiation due to a change in the position of the raw material nuclide in the nuclide production section 30. There may be cases where the raw material nuclide is not irradiated or the amount of irradiation is significantly reduced, or where the nuclear reaction is reduced or increased due to changes in the acceleration energy of the electron beam or the current value. Therefore, by monitoring the peak count rate of the manufactured nuclide in addition to monitoring the peak count rate of the raw material nuclide, it becomes easier to identify the cause of the abnormality. Note that to determine whether the value deviates from the predicted line, a threshold value (upper limit, lower limit) may be set for the value on the predicted line, and when the value deviates from the threshold value, it may be determined that there is an abnormality.

When the condition evaluation section 70 calculates the required irradiation time from the graph shown in FIG. Turn off the power supply to the accelerator 10 and terminate the production. Also, when the condition evaluation unit 70 detects an abnormality (S207), the power supply to the electron beam accelerator 10 is turned off and manufacturing is stopped. In this case, although not shown in the configuration example of FIG. 1, this fact is displayed on a monitor (display device) or indicator light attached to the control unit 40 or the like. In addition to or in place of the display, the abnormality may be notified by audio, warning sound, or the like.

As described above, according to this embodiment, in the production of nuclides using an electron beam accelerator, it is possible to confirm the integrity of the nuclides and estimate the amount of production and required irradiation time while continuing production. can. Also, if there is an abnormality during manufacturing, it can be detected.

<Embodiment 2>
In this embodiment, the influence of the background is reduced by intermittently switching the electron beam accelerator to the off state and performing gamma ray detection during the off state. The configuration of this embodiment is similar to the configuration of Embodiment 1 shown in FIG. 1, but includes a switching control section (not shown) that switches the current value of the electron beam on and off. The switching control unit is provided in the electron beam accelerator 10 or its control unit 50, and may be a switch that can be manually operated by the user, or may be a switch that can be operated manually by the user, or can automatically change the amount of power supplied to the electron beam accelerator 10 by a control signal from the control unit 50. It is also possible to adopt a configuration in which control is performed.

An example of control of the electron beam accelerator 10 is shown in FIG. FIG. 6 is a timing chart when the acceleration energy of the electron beam accelerator 10 is kept constant and the current value of the electron beam is changed. During this period, the current value is set to zero or a very small value (collectively referred to as the Low state). The current value can be controlled, for example, by controlling on/off the power supplied to the electron gun. The time period for which the current value of the electron beam is maintained after the start of production is long after the start of production, and is gradually shortened after a predetermined period of time has elapsed. This makes it possible to detect gamma rays exceeding the discret value of the gamma ray detector 40 even when the amount of gamma rays emitted from the produced nuclide is small after the start of production.

When the electron beam accelerator 40 is controlled in this way, the spectrum (or the peak count rate calculated by the data processing unit 60) that is the output of the gamma ray detector 40 is as follows when the current value of the electron beam is High. As shown in 7(A), there is a high possibility that the gamma ray peak of the nuclide to be detected is buried within the spectrum of the bremsstrahlung radiation generated upon irradiation with the electron beam and captured by the gamma ray detector 40. When the electron beam current value is low, bremsstrahlung radiation, which is the main cause of the background, is not emitted, so as shown in Figure 7 (B), the descendant nuclide Fr- of the raw material nuclide Ra-226 and the manufactured nuclide Ac-225. Gamma ray peaks from 221 and Bi-213 can be detected with high accuracy.

The data processing unit 60 calculates the peak count rate of the peak detected by the gamma ray detector 40 when the electron beam current is in the Low state, and the state determination unit 70 uses the peak count rate to determine the health of the raw material nuclide. The amount of produced nuclide and the required radiation time are estimated. This method is similar to the first embodiment.

Note that the measurement by the gamma ray detector 40 may be switched according to the current value of the electron beam, and gamma rays may be measured only when the current value is in a low state. Note that if the electron beam current value is zero or very small for a long time, the manufacturing time will become longer. It is better to minimize the time during which the electron beam current value is zero or very small.

According to this embodiment, when the amount of bremsstrahlung radiation is large, it is possible to prevent gamma ray detection accuracy from decreasing due to an increase in background dose.

<Embodiment 3>
This embodiment also attempts to suppress background, as in Embodiment 2, but in this embodiment, a means for physically blocking radiation other than the gamma rays to be measured that enters the gamma ray detector 40 is provided. It is characterized by

That is, the radionuclide production system of this embodiment includes a shield 41 that covers the gamma ray detector 40, as shown in FIG. In FIG. 8, the same elements as those shown in FIG. 1 are indicated by the same reference numerals, and redundant explanation will be omitted.

The shielding body 41 is made of a material such as lead or tungsten that has high gamma ray shielding performance, and is arranged to cover the gamma ray detector 40. The shielding body 41 may have a cylindrical shape or a cylindrical shape with a polygonal cross section as long as it has a shape that accommodates many gamma ray detectors 40. The thickness may be uniform, but it may be thicker on the side closer to the target 20. This makes it possible to more effectively obtain a bremsstrahlung radiation shielding effect with less material.

The shield 41 may further be provided with a collimator 42, as shown in FIG. The collimator 42 reduces the background by limiting the angle of incidence of the background radiation onto the gamma ray detector 40. As for the material of the collimator 42, a material with high gamma ray shielding performance can be used similarly to the shielding body 41. , the nuclide production section 30 are preferably located. The shape of the collimator 42 may be cylindrical like the shield 41, or may be plate-shaped and installed at least on the side to which bremsstrahlung radiation is irradiated.
By arranging the collimator 42 in this manner, an even higher background suppression effect can be obtained.

Also in the configuration of this embodiment, as shown in FIG. 10(A), if the shield 41 or the shield 41 and the collimator 42 are not provided, the gamma rays from the nuclide manufacturing unit 30 to be detected will be buried in the background. Even when it cannot be detected, by arranging the shield 41 or the shield 41 and collimator 42, as shown in FIG. 10(B), not only gamma rays from the raw material nuclide Ra-226 but also Fr Gamma rays from -221 and Bi-213 can be detected with high accuracy.
Although FIG. 9 shows a case where the shield 41 and the collimator 42 are installed, the present embodiment also includes a case where only the collimator 42 is installed.

<Embodiment 4>
The embodiment is an embodiment of the arrangement of the gamma ray detector 40 with respect to the nuclide production unit 30, and includes a case where a plurality of gamma ray detectors are provided.

First, the arrangement of the gamma ray detector 40 with respect to the nuclide production section 30 will be explained with reference to FIG. 11. In FIG. 11, the traveling direction of the electron beam and bremsstrahlung radiation is represented by z, and the line connecting the nuclide production unit 30 (center) and the gamma ray detector 40 (center) is represented by L.

The bremsstrahlung radiation 21 generated by the bremsstrahlung radiation generating target 20 is generated strongly in the same direction as the direction of electron beam irradiation, and is generated weakly in the direction opposite to the direction of electron beam irradiation. On the other hand, gamma rays emitted from the raw material nuclide, the descendant nuclide of the raw material nuclide, and the manufactured nuclide and the descendant nuclide of the manufactured nuclide are emitted isotropically. Therefore, the larger the angle φ between the electron beam irradiation direction z and the straight line L from the center of the nuclide production unit 30 to the center of the gamma ray detector 40, the greater the difference between the raw material nuclide and the raw material nuclide with respect to the background intensity of the bremsstrahlung radiation. The intensity of gamma rays emitted from the descendant nuclides, the produced nuclides, and the descendants of the produced nuclides increases, allowing highly accurate measurement. Specifically, it is desirable that the angle φ formed between the irradiation direction Z of the electron beam and the straight line L from the center of the nuclide production unit to the center of the gamma ray detector is 30 degrees or more. In the configuration shown in FIG. 1, φ is 90 degrees, but φ (φ') may be larger than 90 degrees, as shown by the dotted line in FIG.

The arrangement of the gamma ray detectors 40 described above can be applied to the case where there is only one gamma ray detector 40, but it can also be applied when a plurality of gamma ray detectors 40 are installed. FIG. 12 shows an arrangement example when a plurality of gamma ray detectors 40 are installed. As an example, FIG. 12A shows a case where two gamma ray detectors 40A and 40B are installed equidistantly from the nuclide production unit 30, but the number of gamma ray detectors is not limited to two, It may be 3 or more. Furthermore, instead of arranging the two gamma ray detectors 40A and 40B horizontally, any arrangement is possible, such as arranging them vertically as shown in FIG. 12(B). Further, the distance from the nuclide production unit 30 and the angle φ may be varied.

By installing multiple gamma ray detectors in this way, the detection accuracy of gamma rays emitted from the nuclide production unit 30 is improved due to the effect of adding the detection results, and it is also possible to detect abnormalities in one of the gamma ray detectors. It is possible to prevent erroneous determination by the state evaluation unit 70 in the case of For example, if an abnormality is detected in the peak count rate of gamma rays emitted from Ra-226 or the time change in the production amount of Ac-225 shown in FIGS. Another possible cause is an abnormality in the gamma ray detector 40 or an abnormality in the bremsstrahlung radiation generating target 20. If an abnormality occurs in only one of the gamma ray detectors installed, it can be determined that the abnormality is in that gamma ray detector and not in the radionuclide manufacturing unit 30 or the bremsstrahlung radiation generating target 20.

Furthermore, if multiple gamma ray detectors 40 are arranged at different distances and angles φ from the nuclide production unit 30, the characteristics of bremsstrahlung radiation (angle and distance dependence) can be understood by analyzing them. , it is also possible to correct the detection results of the gamma ray detector 40.

Note that this embodiment can be implemented in appropriate combination with the configurations of Embodiments 1 to 3 described above.

<Embodiment 5>
The present embodiment is characterized in that a dosimeter for detecting the dose or dose rate of bremsstrahlung radiation from the target is added to the above-described first to fourth embodiments.

An example of the radionuclide production system of this embodiment will be described with reference to FIG. 13. As shown in the figure, the radionuclide production system of this embodiment installs a dose rate meter 80 near the bremsstrahlung radiation generation target 20, inputs the signal from the dose rate meter 80 to the data processing unit 60, and then Measure changes in rate over time. Further, information on the acceleration energy and current value of the electron beam from the electron beam accelerator control device 50 is input to the data processing unit 60.

As the dose rate meter 80, a known measuring device for measuring radiation dose or dose rate can be used, and a plurality of measuring devices may be installed. When a plurality of them are installed, they may be installed at symmetrical positions with respect to the acceleration direction of the electron beam, or at non-symmetrical positions. When installed in symmetrical positions, an abnormality in the dose rate meters can be detected from the difference in the measured values of the plurality of dose rate meters. Furthermore, when installed at a non-symmetrical position, it is possible to detect the dose rate according to the position from the target.

The data processing unit 60 inputs information on the acceleration energy and current value of the electron beam, monitors that they are constant, and, under the condition that they are constant, changes in the measured value of the dose rate meter. Monitor.

FIG. 14 shows an example of a time change in the current value when the electron beam acceleration energy is constant and a time change in the dose rate measured by a dose rate meter. If the value of the dose rate meter 80 increases or decreases under conditions where the acceleration energy and current value of the electron beam are approximately constant, it can be assumed that an abnormality in the target 20 is the cause. If an abnormality occurs in only one of multiple dose rate meters installed under conditions where the electron beam energy and current value are almost constant, it is an abnormality in that dose rate meter and not due to an abnormality in target 20. It can be determined that

Note that in determining whether the value of the dose rate meter 80 is abnormal, a threshold value (upper and lower limits) is set in consideration of the measurement accuracy of the dose rate meter 80, and a case outside the range of the threshold value is determined to be abnormal.

FIG. 15 shows an example of the evaluation flow of the state evaluation unit 70 of the fifth embodiment. The condition evaluation unit 70 inputs the gamma ray peak count rate from the data processing unit 60 and the dose rate measured by the dose rate meter 80 (S301, S302). If the dose rate is abnormal (S303), for example, it is determined that there is an abnormality (abnormality 1) in the target 20 (S306), a warning is issued, and the system is stopped as necessary (S307). In addition, if there is no abnormality in the dose rate, but the peak count rate of gamma rays of the raw material nuclide changes (S304), it is determined that there is a problem (abnormality 2) in the health of the nuclide production section 30 (S306), and the system (S307). Furthermore, although the gamma ray peak count rate of the raw material nuclide is kept constant, if the linear increase in the gamma ray peak count rate of the manufactured nuclide or its descendant nuclides breaks down (S305), for example, an abnormality in the nuclear reaction ( It is determined that there is an abnormality 3) and the system is stopped (S307).

If no abnormality is detected, production continues until the required production amount is reached (S308). When continuing production, although not shown in FIG. 15, as shown in steps S206 and S208 in FIG. The production is continued until the target production amount is reached, and when the target production amount or the required time for production is reached, the electron beam irradiation is stopped and the production is completed.

Note that FIG. 15 is an example of the judgment flow by the condition evaluation unit 70, and the order of the judgment steps is not limited to this example. It is possible to make changes such as adding a determination step to determine whether only one device or multiple devices are detecting an abnormality, and then determining the abnormality.

As described above, according to the present embodiment, by determining abnormalities in multiple stages, abnormalities in the manufacturing process due to various causes can be determined, and appropriate measures can be taken.

10: Electron beam accelerator, 20: Target, 30: Nuclide production department, 40: Gamma ray detector, 50: Electron beam accelerator control section, 60: Data processing section, 70: Condition evaluation section, 80: Dose rate meter (dose measurement vessel)

Claims (9)

A radionuclide production system comprising an electron beam accelerator, a target that receives an electron beam irradiated from the electron beam accelerator and emits bremsstrahlung radiation, and a radionuclide production unit disposed in the direction of movement of the bremsstrahlung radiation. hand,
a gamma ray detector that detects gamma rays emitted from nuclides contained in the radionuclide production section; a state evaluation section that determines the state of the radionuclide production section using the output of the gamma ray detector ; and the gamma ray detector. further comprising a data processing unit that calculates the peak count rate of the peak of the peak value spectrum corresponding to the energy of the gamma ray using the output of the
The radionuclide production unit includes radium-226 as a raw material nuclide,
The data processing unit calculates a temporal change in a peak count rate of a peak corresponding to the energy of gamma rays emitted from the raw material nuclide,
The condition evaluation section determines the condition of the radionuclide production section based on the temporal change in the peak count rate calculated by the data processing section.
A radionuclide production system characterized by: The radionuclide production system according to claim 1,
further comprising a switching control unit that intermittently switches the electron beam accelerator off or into a low current state,
The condition evaluation section is characterized in that the state of the radionuclide production section is determined using the detection result of gamma rays detected by the gamma ray detector when the electron beam accelerator is off or in a low current state. Radionuclide production system. The radionuclide production system according to claim 1,
A radionuclide production system, further comprising a shielding body around the gamma ray detector that blocks radiation other than gamma rays from the radionuclide production unit. The radionuclide production system according to claim 1,
A radionuclide production system further comprising a collimator between the radionuclide production unit and the gamma ray detector that limits radiation other than gamma rays from the radionuclide production unit. The radionuclide production system according to claim 1,
The gamma ray detector is installed at a position where a line connecting the center of the radionuclide manufacturing unit and the center of the gamma ray detector makes an angle of 30 degrees or more with respect to the traveling direction of the bremsstrahlung radiation. radionuclide production system. The radionuclide production system according to claim 1,
A radionuclide production system comprising a plurality of the gamma ray detectors. The radionuclide production system according to claim 1,
A radionuclide production system further comprising a dosimeter that detects the dose or dose rate of bremsstrahlung radiation from the target. A method for producing a radionuclide, the method comprising: irradiating a target with an electron beam accelerated by an electron beam accelerator, and thereby irradiating a raw material nuclide with bremsstrahlung radiation generated from the target to produce at least one production nuclide,
Detecting gamma rays emitted from at least one type of radionuclide including the raw material nuclide and the production nuclide,
Calculating the peak count rate of the peak of the peak value spectrum corresponding to the energy of gamma rays from the raw material nuclide,
A method for producing a radionuclide, characterized in that the soundness of the production state of the radionuclide is evaluated using the temporal change in the peak count rate. A method for producing a radionuclide according to claim 8, comprising:
A radioactive substance characterized by detecting gamma rays emitted from a radionuclide at multiple locations different from the radionuclide, and determining and evaluating the production status of the radionuclide based on the detection results at the multiple locations. Method for producing nuclides.

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