JP7170301B2 - Portable radiation measuring instrument for thyroid monitor and radiation measuring method - Google Patents

Description

The present invention relates to a portable radiation meter for thyroid monitors that quantifies radioactive iodine accumulated in the thyroid gland of a human body, and a radiation measurement method using the same.

Radioactive iodine taken into the human body by inhalation or oral ingestion tends to accumulate in the thyroid gland located in the front of the neck. Conventionally, as a radiation measuring device for quantifying the radioactive iodine accumulated in the thyroid gland of a subject by in-vitro measurement and estimating the internal exposure dose of the subject, an open port is formed only on one side of the periphery, and the open port a first shielding wall having an inner space through which a subject can enter; a radiation detector disposed in the inner space and generating a signal in response to incidence of radiation; A whole-body counter is known that includes a second shielding wall that is installed at a distance between two entrances on both sides, and a thyroid monitor that is attached to the inside of the second shielding wall via a coupling mechanism. (See Patent Document 1).

JP 2017-44516 A

By the way, among radioactive iodine, ¹³¹ I (iodine 131), which has a relatively long half-life, decays with a half-life of 8.02 days. It is necessary to measure within the target.

However, although the whole body counter is excellent in quantitative performance of radioactive iodine, it takes a long time to move and set up due to its large size and weight. It is difficult to bring it to a place and start using it. Therefore, in order to use the whole body counter, the subject himself/herself must go to the facility where the whole body counter is installed, and the measurement of a large number of subjects can be completed in a short period of time. It has been difficult to perform measurements on subjects who have difficulty moving, such as the elderly and sick. Furthermore, whole-body counters require one person to enter a narrow space surrounded by shielding walls and remain still for a certain period of time while holding the thyroid monitor against the throat. was extremely difficult or impossible.

In the past, there was an example of a simple thyroid measurement using a NaI survey meter for air dose measurement instead of a whole body counter. It is not suitable for highly reliable quantification because it is not easy to distinguish from the signal corresponding to the intensity of radiation entering the measuring instrument from the tissue or environment.

For the above reasons, in the event of a nuclear accident, etc., it is difficult to perform highly reliable quantitative measurement of thyroid iodine in a large number of subjects in a short period of time. It was a big problem in evaluating exposure dose.

The present invention has been made in order to solve such problems of the prior art. An object of the present invention is to provide a portable radiation measuring device for monitor and a radiation measuring method using the same.

In order to solve such problems of the conventional technology, one aspect of the present invention provides a radiation shield that shields background radiation, a recess formed in the top surface of the radiation shield, and a bottom surface of the recess. a radiation detector, wherein the radiation shield has a periphery of the radiation detector made of tungsten or a tungsten alloy and other parts made of lead ; and a cable insertion groove is formed in the radiation shield. , wherein the cable insertion groove is inclined with respect to the longitudinal edge of the radiation shield and extends linearly .

According to the present invention, highly reliable quantitative measurement of thyroid iodine can be performed in a short period of time for a large number of diverse subjects. Problems, configurations, and effects other than those described above will be clarified by the description of the embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially broken perspective view of a portable radiation measuring instrument for thyroid monitor according to an embodiment; 1 is a front view of a portable radiation measuring instrument for a thyroid monitor according to an embodiment in which a cover member is attached to the upper surface; FIG. 4 is a configuration diagram of an adjustment unit according to the embodiment; FIG. 1 is a block diagram showing the configuration of a signal processing circuit according to an embodiment; FIG. FIG. 4 is a diagram showing a radiation measurement method using the portable radiation meter for thyroid monitor according to the embodiment; FIG. 4 is an image diagram showing the positional relationship between the thyroid gland of a subject and the radiation detector provided in the portable radiation measuring instrument for thyroid monitor according to the embodiment during radiation measurement. FIG. 4 is a graph showing an example of pulse height data detected by a radiation detector; FIG. 3 is a graphical representation evaluating the achievable lower limit of detection for thyroid equivalent dose in measurements under high background radiation environments using a CdZnTe semiconductor detector or a LaBr ₃ scintillation detector as a radiation detector. FIG. 10 is a diagram showing another embodiment of the portable radiation meter for thyroid monitor according to the present invention; FIG. 10 is a diagram showing still another embodiment of the portable radiation meter for thyroid monitor according to the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a portable radiation measuring device for thyroid monitor and a radiation measuring method according to the present invention will be described below with reference to the drawings. It should be noted that the scope of the present invention is not limited to the scope of the embodiments described below, and includes various modifications and implementations within the scope of the present invention.

FIG. 1 is a partially broken perspective view of a portable radiation meter for thyroid monitor according to an embodiment. As shown in FIG. 1, a portable radiation measuring instrument 1 for a thyroid monitor of this example includes a radiation shield 2 having a rectangular parallelepiped external shape, and a bottom surface of a concave portion 3 formed on the upper surface of the radiation shield 2. Two radiation detectors 4a and 4b and two signal processing circuits 5a and 5b installed in the apparatus, and an adjustment unit 6 (see FIG. 3) for adjusting the set interval between the two radiation detectors 4a and 4b there is In order to block the radiation incident on the radiation detectors 4a and 4b from obliquely upward direction, the radiation shielding body 2 is provided with radiation shielding bodies outside the arrangement positions of the radiation detectors 4a and 4b as necessary. 2c can also be provided.

The radiation shielding body 2 is made of a radiation shielding material and is formed into a portable type that can be held and moved by a person. The width dimension W of the radiation shield 2 is set to a size that allows the subject's neck to be pressed against the upper surface. Further, the width dimension S of the concave portion 3 is set so that the subject's thyroid gland can face the radiation detectors 4a and 4b. Furthermore, the length dimension L of the radiation shield 2 is such that the radiation detectors 4a, 4b and the signal processing circuits 5a, 5b can be accommodated, and a radiation shielding material having a practically sufficient thickness is arranged outside. do. Subjects include adults, infants, infants, and newborns.

FIG. 2 is a perspective view of a portable radiation meter for thyroid monitor according to an embodiment having a cover member attached to the upper surface. As shown in FIG. 2, the upper surface of the radiation shield 2 is provided with a cover member 7 made of a heat insulating material such as urethane in order to alleviate discomfort when the neck is pressed against the metal radiation shield 2. can also The cover member 7 can be formed with a positioning recess 7a for receiving the neck of the subject so that the thyroid gland of the subject is correctly opposed to the radiation detectors 4a and 4b. The cover member 7 can be formed integrally with the radiation shield 2 or can be formed detachably from the radiation shield 2 .

The radiation shield 2 according to the embodiment is integrally formed using a γ-ray shielding material such as tungsten, an alloy with a high tungsten content (tungsten alloy), or lead. The radiation shield 2 according to the embodiment, as shown in FIG. are made of relatively inexpensive lead 2b. With such a configuration, the radiation shield 2 having a high γ-ray shielding effect can be obtained at a low cost. When lead is used for all or part of the radiation shield 2, in order to prevent characteristic X-rays (80 keV) from lead from entering the radiation detectors 4a and 4b, It is desirable to line the interior with a plate material 8 made of a substance with a small atomic number, such as a tungsten plate, a copper plate, or a stainless steel plate.

Cable insertion grooves 10 are formed at the ends of the radiation shield 2 in the longitudinal direction for drawing out cables 9 connected to the signal processing circuits 5a and 5b. The cable insertion groove 10 is inclined with respect to the lengthwise edge of the radiation shield 2 in order to reduce the amount of radiation reaching the radiation detectors 4a and 4b from the surrounding environment through the cable insertion groove 10. It is formed. In addition, the planar shape of the cable insertion groove 10 is not limited to a linear shape, and may be a curved structure such as a corrugated shape. As the cable 9, a USB cable is preferably used because it can be easily connected to an analysis device using a personal computer, a tablet terminal, or the like.

Radiation detectors 4a and 4b measure gamma rays (365 keV, 80.2 keV, etc. emitted from ¹³¹ I) emitted from radioactive iodine accumulated in the thyroid gland of the subject, and are semiconductor detectors with good energy resolution. A detector or scintillation detector is used. As a semiconductor detector, one using a CdZnTe-based semiconductor, a CdTe-based semiconductor, or a TlBr-based semiconductor can be used. The scintillation detector is a combination of a scintillator and a photosensor, and as the scintillator, an inorganic scintillator such as LaBr ₃ , SrI ₂ or CeBr ₃ or an organic scintillator such as a plastic scintillator can be used. A photomultiplier tube, a photodiode, an MPPC (Multi-Pixel Photon Counter), or the like can be used as the optical sensor.

The radiation detectors 4a and 4b of this example are superior in ability to distinguish background radiation from scintillation detectors using NaI (sodium iodine crystals), and thus are superior in quantitative performance of radioactive iodine. In addition, unlike a semiconductor detector using a Ge-based semiconductor, there is no need to cool the semiconductor detector using liquid nitrogen or the like during use. also becomes easier.

The two radiation detectors 4a and 4b and the adjustment unit 6 for adjusting the set interval between the two radiation detectors 4a and 4b are suitable for an unspecified number of patients with different physiques (thickness of the neck). This is to accommodate examiners. That is, for a subject with a large neck, the adjuster 6 is operated to increase the distance between the two radiation detectors 4a and 4b, and the radiation is measured. Also, for a subject with a small neck, the adjuster 6 is operated to reduce the distance between the two radiation detectors 4a and 4b, and radiation measurement is performed. As a result, gamma rays emitted from radioactive iodine accumulated in the thyroid gland can be measured with substantially maximum efficiency for all subjects. In addition, compared to the case where only one radiation detector is used, it is possible to reduce the influence of misalignment between the thyroid gland and the radiation detector on the uncertainty of measurement results.

FIG. 3 is a configuration diagram of an adjustment unit according to the embodiment. As shown in FIG. 3, the adjustment unit 6 of this example includes a bolt 11 rotatably attached to one end of the radiation shield 2 in the length direction, radiation detectors 4a and 4b, and signal processing circuits 5a and 5b. , connecting portions 13a and 13b formed on the holders 12a and 12b, and threaded portions 14a and 14b of the bolt 11 formed on the connecting portions 13a and 13b. The threaded portion of the bolt 11 has a right-handed thread 11a with a large diameter and a left-handed thread 11b with a small diameter. The threaded portion 14a is threaded onto the right-hand thread 11a, and the threaded portion 14b is threaded onto the left-hand thread 11b. Therefore, by rotating the bolt 11 clockwise or counterclockwise, the two radiation detectors 4a, 4b and the signal processing circuits 5a, 5b can be moved toward or away from each other. Note that the configuration of the adjustment unit 6 is not limited to this, and the two radiation detectors 4a and 4b may be individually operated.

FIG. 4 is a block diagram showing the configuration of the signal processing circuit according to the embodiment. As shown in FIG. 4, the signal processing circuits 5a and 5b of this example process electrical signals output from the radiation detectors 4a and 4b, and include a preamplifier 21, a shaping amplifier 22, and an A/D converter. 23 and a multi-channel pulse height analyzer 24 .

Next, a radiation measurement method using the portable radiation measuring device 1 for thyroid monitor according to the embodiment will be described.

FIG. 5 is a diagram showing a radiation measurement method using the portable radiation measuring device 1 for thyroid monitor according to the embodiment. As shown in FIG. 5, when measuring radiation, the thyroid monitor portable radiation meter 1 is placed on a table A, and a subject B sits on a chair C. As shown in FIG. The thyroid monitor portable radiation measuring instrument 1 is covered with a contamination prevention sheet (not shown). The thyroid monitor portable radiation meter 1 is connected to the analysis device D via a cable 9 extending from the signal processing circuits 5a and 5b. As the analysis device D, for example, a personal computer or a tablet terminal is used. The analysis device D takes in the wave height data output from the signal processing circuits 5a and 5b, analyzes them with dedicated software, and displays the analysis results on the display unit. In addition, the analysis device D performs setting of measurement conditions and control of the measuring device on dedicated software. Power is supplied to the signal processing circuits 5a and 5b from the analysis device D using a USB cable or from an external battery. According to this configuration, it is possible to measure radiation during a power failure.

A subject B sits on a chair C, takes a posture of laying the upper half of the body down on the table A, and brings the portable radiation measuring instrument 1 for a thyroid monitor into close contact with the throat. At this time, in order to allow the subject B to take a comfortable posture, the chin or forehead of the subject B can be supported by a support, or the height of the body can be adjusted with cushions. When the subject B is an infant, an infant, or a newborn, the parent or guardian sits next to the subject B, puts the subject on the guardian's lap, or lays the subject B on the table A in a prone position for measurement. There are no particular restrictions on the desks and chairs that can be used.

After the posture of the subject B is stabilized, the measurer operates the adjuster 6 to adjust the distance between the two radiation detectors 4a and 4b so that the γ-ray detection efficiency is maximized. As a result, the two radiation detectors 4a and 4b are arranged at positions facing the thyroid gland E of the subject B, as shown in FIG. After that, the measurer presses a measurement start button (for example, an ENTER key) of the analysis device D to start taking in the wave height data into the analysis device D. FIG.

FIG. 7 is a graph showing an example of pulse height data detected by a radiation detector. The horizontal axis of FIG. 7 is the wave height expressed in units of γ-ray energy (keV), and the vertical axis is the count rate (cnts/sec) of the detector signal for each wave height. Note that ¹³³ Ba (356 keV) was used instead of ¹³¹ I (365 keV) when acquiring this data. The background signal was also simulated with ¹³⁷ Cs (662 keV). Analysis device D quantifies ¹³¹ I (365 keV) accumulated in the thyroid gland of the human body from this wave height data, and estimates the internal exposure dose of subject B.

Effects of the portable radiation measuring device 1 for thyroid monitor and the radiation measuring method according to the embodiment will be described below.

As described above, the thyroid monitor portable radiation measuring instrument 1 according to the embodiment has the radiation detectors 4a and 4b and the signal processing circuits 5a and 5b installed on the bottom surface of the concave portion 3 formed on the top surface of the radiation shield 2. Therefore, the background radiation incident on the radiation detectors 4a, 4b can be effectively shielded. Therefore, the portable radiation measuring device 1 for thyroid monitor according to the embodiment is excellent in quantitative performance of radioactive iodine accumulated in the thyroid gland of the subject, and can estimate the internal exposure dose with high reliability.

FIG. 8 is a graphical representation evaluating the lower limit of detection of thyroid equivalent dose that can be achieved in measurement under a high background radiation environment using CdZnTe semiconductor detectors or LaBr ₃ scintillation detectors as radiation detectors 4a and 4b. . The data in the figure are the measurement time (seconds) on the horizontal axis and the thyroid equivalent dose (mSv) on the vertical axis. The worker was obtained by simulation. The simulation conditions were as follows. , 4b, an adult (nuclear power plant worker) used a CdZnTe semiconductor detector (1.5 cm ³ ), and others used a LaBr ₃ scintillation detector (16.4 cm ³ ). Moreover, it is assumed that the periphery of the radiation detectors 4a and 4b is not covered with a radiation shield.

Calculation of the data shown in FIG. 8 was performed according to the following procedure. First, from the detection data (pulse height data) of the radiation detectors 4a and 4b shown in FIG. Ask. Also, the count rate (cnts/second) of the radiation detectors 4a and 4b due to background radiation (20 μSv/h) is obtained from experimental values. Next, from these two data, the detection limit (Bq) of thyroid iodine for each measurement time (second) under high background radiation environment is calculated. Next, divide the obtained thyroid iodine detection limit (Bq) by the thyroid residual rate after 5 days, multiply it by the dose conversion factor (Sv/Bq), and convert it to the thyroid equivalent dose detection limit (Sv). do. Finally, the relationship between the measurement time (seconds) and the lower limit of detection (Sv) is plotted on a graph for infants, 7-year-old children, adults, and workers.

As is clear from the data shown in FIG. 8, when a CdZnTe semiconductor detector or _LaBr3 scintillation detector is used as the radiation detectors 4a and 4b, practically sufficient detection lower limits are obtained even in a high background radiation environment. , adults, 7-year-olds, infants, and nuclear power plant workers. Therefore, by covering the circumference of the radiation detectors 4a, 4b with an appropriate radiation shield, even lower lower limits of measurable thyroid equivalent dose can be achieved.

As described above, the portable radiation measuring device for thyroid monitor 1 according to the embodiment effectively detects background radiation by setting the radiation detectors 4a and 4b at the bottom of the concave portion 3 formed in the radiation shield 2. can be shielded, there is no need for the subject to enter the space surrounded by the shield as in the conventional art, and the feeling of oppression and fear that the subject feels during measurement can be reduced. In addition, since there is no need for the subject to enter the space surrounded by the shield as in the conventional art, radiation measurement can be performed easily and efficiently. In addition, since it is possible for an attendant to take care of the patient, it is possible to easily and efficiently measure the radiation of infants, young children, the elderly, the sick, and the like.

In addition, since the portable radiation measuring instrument 1 for thyroid monitor according to the embodiment is formed in a portable type that can be moved by hand, it can be brought to an evacuation center or a command post immediately after a radiological accident occurs. It can be put into use and can rapidly perform radiological measurements on a large number of diverse subjects. In addition, since a large number of portable radiation measuring instruments 1 for thyroid monitors can be brought into an evacuation center or a command post, radioactivity measurements can be efficiently performed on a large number of diverse subjects in a short period of time.

Other embodiments of the portable radiation measuring device for thyroid monitor and radiation measuring method according to the present invention will be described below.

In the above embodiment, the signal processing circuits 5a and 5b are incorporated inside the radiation shield 2, but part or all of the signal processing circuits 5a and 5b may be separated from the radiation detectors 4a and 4b as necessary. , may be installed outside the radiation shield 2 .

When measuring radiation, as shown in FIG. 5, a viewing window F is attached to the top plate of the table A, and a video device G such as a television, personal computer, tablet, or smartphone may be placed below it to play moving images such as animation. . Also, instead of the image device G or together with the image device F, an appreciation object such as an ornamental animal or plant may be placed. In this way, the healing effect of moving images and animals and plants reduces the stress of the subject and facilitates radiation measurement. In particular, when the subject is a child or infant who moves a lot, it is difficult to force the subject to maintain the same posture. It is possible to

In the above embodiment, the portable radiation measuring instrument for thyroid monitor 1 is placed directly on the table A. However, as shown in FIG. The portable radiation measuring device 1 for thyroid monitor can also be attached to a pivoting arm 34 of a support member 31 which consists of a pivoting arm 34 pivotably connected via a . By doing so, the rotation angle of the portable radiation measuring instrument 1 for thyroid monitor can be adjusted according to the posture of the subject, so that more accurate radiation measurement becomes possible.

Furthermore, in the above-described embodiment, the radiation measurement was performed while the neck of the subject was pressed against the portable radiation measuring device 1 for thyroid monitor. The neck of the subject B crouching over the radiation measuring instrument 1 can also be covered with an arch-shaped or portal-shaped radiation shield 40 . By doing so, the amount of background radiation incident on the radiation detectors 4a and 4b from the upper portion of the portable radiation measuring device 1 for thyroid monitor can be reduced, so that more accurate radiation measurement becomes possible.

In addition, the portable radiation meter 1 for thyroid monitor according to the above embodiment can be used not only at the site of a radioactive accident, but also for quantitative measurement of radioactive iodine taken into the thyroid gland by internal radioactive iodine therapy. . Moreover, the portable radiation measuring instrument 1 for thyroid monitor according to the above embodiment can be applied not only to measure the radiation accumulated in the thyroid gland of the subject B, but also to quantitatively measure body surface contamination or wound contamination.

DESCRIPTION OF SYMBOLS 1... Portable radiation measuring instrument for thyroid monitor, 2... Radiation shield, 3... Recessed part, 4a, 4b... Radiation detector, 5a, 5b... Signal processing circuit, 6... Adjustment unit, 7... Cover member, 7a... Positioning Recess 8 Plate 9 Cable 10 Cable insertion groove 11 Bolt 12a, 12b Holder 13a, 13b Connecting portion 14a, 14b Threaded portion 21 Preamplifier 22 Shaping Amplifier 23 A/D converter 24 Multi-channel pulse height analyzer 31 Supporting member 32 Pedestal 33 Connecting pin 34 Swivel arm 40 Arch or portal radiation shield A Table, B... Examinee, C... Chair, D... Analyzer, E... Thyroid gland, F... Peephole, G... Image device.

Claims (4)

A radiation shield that shields background radiation, a recess formed on the top surface of the radiation shield, and a radiation detector installed on the bottom surface of the recess,
The radiation shield is formed of tungsten or a tungsten alloy around the radiation detector, and the other portion is formed of lead ,
A thyroid monitor, characterized in that a cable insertion groove is formed in the radiation shield, and the cable insertion groove is inclined with respect to a longitudinal end side of the radiation shield and extends linearly. Portable radiation meter. two of the radiation detectors are arranged opposite to each other on the bottom surface of the recess formed on the top surface of the radiation shield;
2. The portable radiation measuring instrument for a thyroid monitor according to claim 1, wherein said radiation shield is provided with an adjusting section for adjusting a set interval between said two radiation detectors. A portion where the portable radiation measuring device for thyroid monitoring according to claim 1 or 2 is placed on a table, the portable radiation measuring device for thyroid monitoring is connected to an analysis device, and the subject faces the radiation detector A radiation measurement method, wherein the neck is pressed against the upper surface of the radiation shield and fixed so that the thyroid gland is positioned at the center of the radiation shield. A portable radiation measuring device for a thyroid monitor, comprising: a radiation shield that shields radiation from the outside; a recess formed on the top surface of the radiation shield; and a radiation detector installed on the bottom surface of the recess Place it on a table with a viewing window formed on the top plate, place a video device and/or an object to be viewed under the top plate, connect the portable radiation measuring device for thyroid monitor to an analysis device, and The neck is pressed against the upper surface of the radiation shield so that the thyroid gland is located in the portion facing the radiation detector, and fixed;
A radiation measurement method, comprising measuring radiation with the radiation detector in a state in which a subject can view the display screen of the imaging device and/or the viewing object through the observation window.

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