JPS6236583A - Radiation-measuring apparatus - Google Patents

Abstract

PURPOSE:To enable constant displaying and monitoring of total radiation dose, by adding up differences in the transmission loss which are calculated for each operation cycle of starting and stopping the release of radiation to determine the total amount of transmission loss, from which total radiation irradiation is calculated. CONSTITUTION:A computer 15 receives a radiation release start timing signal 18 to measure and memorize the light intensity D1 at this timing. Likewise, it receives a radiation release stop timing signal 19 to measure and memorize the light intensity D2. Between the signals 18 and 19, the transmission loss increases with the sensor optical fiber 12 receiving the irradiation with radiation and the increased loss d1 gives d1=D2-D1. The resulting loss d1 is added to the total transmission loss determined by the previous processing to obtain a history of increase in the transmission loss due to radiation and the total radiation dose gamma is determined and displayed by using polygon approximation from the value thus obtained. When the radiation dose gamma is larger than a specified value, an alarm output signal is outputted to make an LED display 16 and an alarm display 17.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to radiation measurement using optical fibers, and in particular, the operation is pulse-like, such as in nuclear fusion and accelerators, and radiation is output in accordance with this operation. It concerns the measurement of intermittent radiation sources such as those used in

[Technical background of the invention and its problems] Research on the radiation resistance characteristics of optical fibers is currently being actively conducted, and as a result, various radiation characteristics of optical fibers are being clarified.

Therefore, the characteristics of this optical fiber will be explained below. FIG. 2 is a schematic structural diagram showing an optical fiber transmission mechanism. In the figure, the central core 1 that transmits light is made of pure silica glass (Si 02 ) and germanium (Ge).
) and phosphorus (P) are chemically bonded to use silica glass, which has a higher refractive index than pure silica glass. Pure silica glass is used for the cladding 2 around the core 1.

By the way, since the core 1 and the cladding 2 have different refractive indexes, the light 3 is totally reflected at the interface thereof to confine the light 3 inside the core 1, thereby transmitting the light.

When an optical fiber with such a transmission mechanism is irradiated with high-energy radiation, defects occur in the chemical bonds.
This becomes the nucleus and a light absorbing part called a color center is generated. It is known that the color center increases in proportion to the radiation dose if the production process or the material and structure of the optical fiber are the same. In addition, this color center has a wavelength characteristic in which its absorption rate changes depending on the wavelength of the light transmitted within the optical fiber, but in the short wavelength band (around 0.85 μm) used in general optical communication, it is relatively Shows high absorption rate. This absorption by the color center is observed as an increase in the transmission loss of the optical fiber itself.

FIG. 3 shows the relationship between the gamma ray irradiation amount and the transmission loss of the optical fiber at a constant irradiation dose rate using cobalt 60 ([10CO)] in a common quartz glass fiber for optical communications, with the light wavelength being 0.85 μm. As shown in the graph, the transmission loss of the optical fiber increases as the radiation dose increases, and gradually recovers when the radiation dose ends. This characteristic will be explained below.

The color center generated in the optical fiber by γ-ray irradiation gradually disappears during and after γ-ray irradiation, and the transmission loss is recovered. However, during irradiation with γ-rays, the production speed of the color center exceeds the extinction speed of the color center, so the transmission loss actually increases.

The color center disappearing process occurs when the trap units of electrons, etc. that formed the color center in the optical fiber by radiation irradiation absorb energy given from the outside and are once raised to a conduction level, and then recombine. As a result, the color center disappears, there is no light absorption part in the optical fiber, and the transmission loss is recovered. There are two types of external energy that can extinguish the color center: heat and light transmitted through the optical fiber itself; the former is called thermal breathing, and the latter is called photobreathing.

As mentioned above, the rate of generation and extinction of color centers is the same even if the optical fiber is made of the same material and structure, the external temperature is approximately constant, and the wavelength and incident intensity of the light transmitted through the optical fiber are constant. For example, the transmission loss characteristics of an optical fiber for a specific radiation dose can be observed as a reproducible phenomenon. Furthermore, proposals have been made for the material and structure of the optical fiber and the wavelength of the light source, which have almost no dependence on the dose rate (irradiation amount per unit time) of the specific radiation, and these transmission loss characteristics have been skillfully improved. When used selectively, a radiation measuring device that is proportional to the total radiation dose becomes possible. Measuring this total radiation dose is an important element in determining the lifespan of surrounding materials.

Therefore, a method has been proposed in which the irradiation radiation dose is measured using the characteristic that the transmission loss increases almost in proportion to the irradiation radiation dose of the optical fiber.

Next, a conventional method of measuring the total radiation dose using such characteristics will be explained with reference to FIG.

In the figure, a light source 4 is a general stabilized light source composed of a light emitting diode (LED), a laser diode (LD), etc., and is a device that stably outputs light of a constant wavelength and constant output. The radiation 1II5 corresponds to cobalt-60 ([+0CO), for example, as a gamma ray output source. The power meter 7 is a device that measures the light intensity of incident light, and is a general optical measurement device that uses a photodiode (PD) using silicon or germanium as a sensor.

The recorder 8 is a device that records temporal changes in the intensity of the incident light measured by the power meter 7. The sensor optical fiber 6 is an optical fiber in which the relationship between the amount of optical loss and the amount of irradiated radiation is known in advance. As shown, this sensor optical fiber 6 is placed near the radiation source 5, and a part thereof forms a measurement system that is irradiated with radiation. After all, the constant wavelength, constant output light emitted from the light source 4 is connected to the sensor optical fiber 6.
The configuration is such that the signal is transmitted through the power source and input into the power meter 7. At this time, a part of the sensor optical fiber 6 is connected to the radiation source 5
irradiation, the optical loss increases for the reasons mentioned above.

Then, this optical loss is measured as a decrease in the amount of light incident on the power meter 7, and this is recorded by the recorder 8.

Next, in this measurement system, data recorded by the recorder 8 when the radiation output from the radiation source 5 is intermittent will be explained.

FIG. 5 is a graph showing an example of this data. Here, the loss dO is unique to the optical fiber 6 and has nothing to do with radiation. Radiation irradiation starts from time T1 and reaches time T2.
Stop at. During this time, the light intensity of the sensor optical fiber 6 that has been irradiated with radiation decreases from Dl to Dl for the reason described above, and the amount of loss is dl. During the radiation irradiation stop time T2 to T3, the loss of the sensor optical fiber 6 decreases due to the reasons described above, and the light intensity recovers to D3.

Next, at time T3, the sensor optical fiber 6 is irradiated with radiation again, and the loss increases, and at time T4, the light intensity is D4.
The amount of loss increased during this period t2 is d2.

The total amount of radiation received by the sensor optical fiber 6 was determined from the increase in loss di + d2 compared to the initial characteristics of the optical fiber 6 measured in advance.

By the way, the problem here is that when calculating the total irradiation radiation dose, it is necessary to calculate and add the loss increases dl and d2 for each radiation dose that is intermittently irradiated, respectively.
The point is that the radiation interval cannot be directly determined from the current increase Wid3. This is due to the radiation characteristics of the optical fiber mentioned above, and since the optical fiber itself has recovery characteristics such as thermal breathing and photobreathing, the increase in transmission loss due to radiation irradiation cannot be saved while it is not irradiated. Depends on the characteristics. Since the amount of loss increase is proportional to the radiation irradiance rsm, a method is required to obtain all the amounts of increase individually, and it is necessary to keep a history of all the losses using a recorder or the like.

If this method is applied to nuclear fusion, etc., which uses pulsed operation and emits radiation, it would require a huge amount of records, which would be inconvenient both economically and in terms of data management.

[Purpose of the Invention] The present invention has been made based on the above circumstances, and its purpose is to measure the total irradiation radiation dose over a wide range using an optical fiber in estimating the lifetime of materials surrounding an intermittent radiation source. Another object of the present invention is to provide a safe and economical radiation measuring device that is capable of constantly displaying and monitoring the total irradiated radiation dose and outputting an alarm when a predetermined value is exceeded.

[Summary of the Invention] In order to achieve the above object, the present invention provides a radiation measuring device that measures a radiation source that emits radiation intermittently using an optical fiber, which is synchronized with a radiation emission start signal and a radiation emission stop signal. a measuring means for measuring the light intensity from the optical fiber, a storage means for storing the measured light intensity, and a difference calculated from 21i11 of the light intensity stored every 5 ills within the operation of the emission start and emission stop. a subtracting means, an adding means for adding all the difference values of the transmission loss calculated for each operation cycle, a calculation means for calculating the total radiation dose corresponding to the amount of transmission loss added by the adding means; and display means for displaying the total radiation dose calculated by the calculation means.

Further, an alarm means is provided which outputs an alarm when the total radiation dose corresponding to the total amount of transmission loss exceeds a predetermined value.

[Embodiments of the invention] An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration diagram of an embodiment of the present invention.

In the figure, a light source 10 is a stabilized light source that stably outputs light of a constant wavelength and a constant output, and is composed of a light emitting diode (LED), a laser diode (LD), etc. Cobalt-60 (60CO) released
) etc. are equivalent. The power meter 13 is a device that measures the light intensity of incident light, and is a general optical measurement device that uses a photodiode (PD) using silicon or germanium as a sensor. Sensor optical fiber 1
2 is an optical fiber in which the relationship between the amount of optical loss and the amount of irradiated radiation is known in advance. Then, this sensor optical fiber 12 is placed near the radiation source 11 as shown,
A part of it constitutes a measurement system that is irradiated with radiation. That is, the light having a constant wavelength and constant output output from the light source 10 is transmitted through the sensor optical fiber 12 and is configured to enter the power meter 13. At this time, a portion of the sensor optical fiber 12 is irradiated by the radiation source 11, and optical loss increases for the reason described above. This optical loss is measured as a decrease in the amount of light incident on the power meter 13. Then, the sensor optical fiber 1 measured by the power meter 13
The incident light intensity of 2 is input to the computer 15 via the input/output device (PIlo>14).

Next, a flowchart showing the functions within the computer 15 of this embodiment in the computer 15 of FIG. 1 will be described. now,
When the emission tJ4wA measurement start command 20 is issued, the timing at which radiation is emitted from the radiation source 11, for example, in the case of a nuclear fusion device, this corresponds to the plasma ignition timing, and the signal 18 of this radiation emission start timing is input/output. The information is input to the computer 15 via the device 14. Therefore, in the first step 21, the computer 15 measures the light intensity D1 at the timing when this signal 18 is input, and in the next second step 22, this measured value is temporarily stored. Similarly, the radiation emission stop timing signal 19 is input/output device! ! 14
The information is input to the computer 15 via the . Then, in the third step 23, the light intensity D2 at this time is measured, and in the next fourth step 24, this measured value is temporarily stored. While the start signal 18 and stop signal 19 are being input, the sensor optical fiber 12 is irradiated with radiation and its transmission loss increases. In the next fifth step 25, this increased transmission loss is reduced by 02
−D+=process with dl. And the 6th step 2
In step 6, the dl measured and processed this time is added to the total transmission loss amount previously determined by the same process. That is, the value is determined by assuming that the history of increase in transmission loss due to radiation up to this point is Σdn.

On the other hand, this sensor optical fiber 12 has radiation characteristics similar to those shown in the graph shown in FIG. 3, which have already been explained, and these have been measured in advance. The relationship between transmission loss and radiation dose in this optical fiber is generally non-linear. Therefore, in order to approximate and obtain this non-linear curve, the transmission loss value is divided into predetermined sections, and the radiation dose in this section is calculated using a broken line approximation method, assuming that the radiation dose changes in a straight line.

In the next seventh step 21, the total radiation dose γ is determined from the transmission loss increase history Σdn using a polygonal line approximation. Then, in the eighth step 28, the radiation dose γ obtained in the preceding seventh step 27 is processed and displayed. Next, in the ninth step 29, γ obtained in the previous eighth step 28 is calculated.
and the magnitude of a predetermined value α is determined, and if γ is smaller than α, the process returns to the first step 21 and preparations for the next operation are made.
Performs processing to permit reception of a radiation emission start signal. Further, if γ is larger than α, in the next tenth step 30, a warning output process is performed as a dangerous state, and a warning display signal is outputted via the input/output device W14, and the LED display 16 and alarm display 17 are displayed. , take appropriate measures such as stopping operations (stopping radiation emission). Note that this predetermined value α is determined by the upper limit value of the radiation resistance characteristics of surrounding materials that are irradiated with radiation. - For example, 1 as an insulating material
Polyethylene (PE), which is widely used in flils and cables, has an upper limit of 1 x 108 rad for gamma rays. In addition, in this explanation, the polygonal line approximation was used as a method for calculating the total radiation dose from the history of increase in transmission loss, but other approximation methods may be used.
Further, a plurality of upper limit values for alarm output can be set, and these can be implemented with various modifications without departing from the gist of the present invention.

[Effects of the Invention] As explained above, according to the present invention, the total irradiation radiation dose can be measured over a wide range using an optical fiber in estimating the lifespan of materials surrounding an intermittent radiation source, and the total irradiation radiation dose can be constantly measured. It can be displayed and monitored, and by setting an upper limit value, it is safe and economical. An il measuring device can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a structural diagram of an optical fiber, Fig. 3 is a characteristic diagram showing changes in transmission loss in response to γ-ray irradiation of the optical fiber, and Fig. 4 is a diagram of the structure of an optical fiber. FIG. 5, which is a configuration diagram of a conventional radiation measuring device, is a characteristic diagram showing changes in transmission loss of an optical fiber with respect to radiation emitted from an intermittent radiation source. 10...Light source 11...Radiation source 12...Sensor optical fiber 13...Power meter 14...Input/output device 15...Keijinki agent Patent attorney Noriyuki Chika Yudo Hiroshi Mimata Sentence No. t Diagram 2 ■ Time Diagram 4-

Claims (2)

[Claims] (1) In a radiation measuring device that measures a radiation source that emits radiation intermittently using an optical fiber, a measuring means that measures the light intensity from the optical fiber in synchronization with a radiation emission start signal and a radiation emission stop signal. , a storage means for storing the measured light intensity, a subtraction means for calculating a difference from two values of the light intensity stored for each operation cycle of the emission start and emission stop, and a transmission calculated for each operation cycle. Addition means for adding up all loss difference values, calculation means for calculating the total radiation dose corresponding to the amount of transmission loss added by this addition means, and a display for displaying the total radiation dose calculated by this calculation means. A radiation measuring device characterized by comprising: means. (2) The radiation measuring device according to claim 1, further comprising an alarm means for outputting an alarm when the total radiation dose exceeds a predetermined value.