JP4552009B2 - Radiation distribution line sensor - Google Patents

Description

  The present invention relates to a radiation distribution line sensor for detecting a radioactive substance with high energy particle beam, gamma ray or gamma ray emission.

  A plurality of detectors have been proposed so far in which light generated when radiation is incident on an optical fiber is captured by photodetectors installed at both ends of the fiber and the radiation incident position is identified from the time difference. A method of detecting scintillation light emission using a scintillation fiber mainly due to a difference in light emission mechanism (for example, Japanese Patent Laid-Open No. 8-94758 “distributed detector using scintillation fiber”) and Cherenkov light using an optical fiber (For example, Japanese Patent Application Laid-Open No. 6-294871 "Radiation intensity distribution measuring apparatus"). Also, detectors specialized in function have been created by making the fiber into various shapes.

  However, in any of the methods, an optical fiber having a core and a clad made of solid is used, and the radiation damage problem that the light transmittance deteriorates is unavoidable, and there are few examples of actual industrial application.

  In view of the above, an object of the present invention is to provide a radiation distribution line sensor that overcomes the radiation damage problem.

The invention described in claim 1
Liquid core fiber,
First and second photodetectors respectively connected to both ends of the liquid core fiber ;
Means for connecting to the liquid core fiber and exchanging the liquid core in the liquid core fiber,
The means for exchanging the liquid core in the liquid core fiber is a radiation distribution line sensor characterized in that the liquid core in the liquid core fiber is supplied continuously from the outside of the liquid core fiber .

  According to a second aspect of the present invention, in the radiation distribution line sensor according to the first aspect, the first and second photodetectors include a photomultiplier tube, and the time-of-flight analysis is connected to the photomultiplier tube. The radiation distribution line sensor further comprises means.

  The invention according to claim 3 is the radiation distribution line sensor according to claim 2, wherein the time-of-flight difference analyzing means is connected to each of the first preamplifier connected to each of the photomultiplier tubes and each of the first preamplifiers. A constant fraction discriminator, a delay line connected to one of the constant fraction discriminator, a time wave height converter connected to the other of the constant fraction discriminator and the delay line, and the time A radiation distribution line sensor comprising a wave height analyzer connected to a wave height converter.

  According to the present invention, the occurrence of radiation damage is suppressed by using a liquid in a fiber core part that transmits light generated by interaction with radiation to a photodetector, and the liquid core material is made into an external supply flow type. The effect of loss can be eliminated by replacing the material before radiation damage occurs.

  FIG. 1 is a block diagram showing an example of the configuration of a radiation distribution line sensor according to the present invention. The radiation distribution line sensor 1 includes a liquid core fiber 2, first and second photomultiplier tubes (PMT) 3 and 4 connected to both ends of the liquid core fiber 2, and photomultiplier tubes 3 and 4, respectively. First and second first preamplifiers (FPAs) 5 and 6 connected to the first preamplifiers 5 and 6, first and second constant fraction discriminators (CFD) 7 and 8 connected to the first preamplifiers 5 and 6, respectively. A delay line (DL) 9 connected to the constant fraction discriminator 8, a time wave height converter (TAC) 10 connected to the first constant fraction discriminator 7 and the delay line 9, and a time wave height converter 10 And a wave height analyzer (MCA) 11 connected to the. The liquid core fiber 2 may be commercially available as a liquid light guide.

  A gamma ray measurement will be described as an example. The gamma rays incident on the radiation distribution line sensor 1 cause a photoelectric effect or Compton scattering in the liquid core of the liquid core fiber 2 or in the vicinity of the liquid core, and generate fast electrons. When the generated fast electrons move through the liquid core and have a speed faster than the light speed in the liquid core, Cherenkov light is generated. The emission direction of the Cherenkov light depends on the velocity of the fast electrons, and is emitted conically with respect to the electron traveling direction. The angle θ is cos θ = 1 / nβ, and in the case of β to 1, θ = about 48 degrees. Become. A commercially available liquid light guide has a liquid core with a refractive index of about 1.5, and can sufficiently transmit Cherenkov light toward the left and right sides of the liquid core fiber 2. The light transmitted left and right in the liquid core fiber 2 is incident on each of the first and second photomultiplier tubes 3 and 4 to generate an electric pulse. The first and second photomultiplier tubes 3 and 4 supply this electric pulse to the first and second first preamplifiers 5 and 6, respectively. The first and second first preamplifiers 5 and 6 amplify the supplied electric pulses and supply them to the first and second constant fraction discriminators 7 and 8, respectively. The first and second constant fraction discriminators 7 and 8 respectively convert the supplied amplified electrical pulses into logic pulses. The first constant fraction discriminator 7 directly supplies the logic pulse to the time wave height converter 10, and the second constant fraction discriminator 8 supplies the logic pulse to the time wave height converter 10 via the delay line 9. The time wave height converter 10 converts the two logic pulses into a signal proportional to the arrival time difference between the left and right signals and supplies the signal to the wave height analyzer 11. The wave height analyzer 11 records this time difference information.

FIG. 2 is a graph showing the results of measurement with the radiation distribution line sensor 1 configured as shown in FIG. 1 in which a ⁶⁰ Co gamma ray source is brought into close contact with the center of the 2 m long liquid core fiber 2. A peak capturing gamma rays from the radiation source is clearly observed near the center 1280 ch. The peaks near the left and right 870 ch and 1680 ch are considered to be caused by reflection at the end face of the liquid core fiber 2.

  FIG. 3 is a diagram illustrating another example of the configuration of the liquid core fiber. The liquid core in the liquid core fiber is continuously supplied from the outside in a flow type. In this way, damage to the core due to radiation can be avoided.

  Although the above example has been described for the case of gamma rays, any radiation that emits Cherenkov light in a liquid core can be measured by the radiation distribution line sensor according to the present invention.

  It exhibits excellent performance under conditions where dosimetry is performed over a long period of time in a space of several hundred meters under a high dose rate, such as a temporary storage facility for high-level waste.

It is a block diagram which shows an example of a structure of the radiation distribution line sensor by this invention. It is a graph which shows the measurement result by the radiation distribution line sensor by this invention. It is a figure which shows the other example of a structure of a liquid core fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radiation distribution line sensor 2 Liquid core fiber 3 1st photomultiplier tube 4 2nd photomultiplier tube 5 1st first preamplifier 6 2nd first preamplifier 7 1st constant fraction discriminator 8 2nd constant fraction discriminator 9 Delay line 10 Time wave height converter 11 Wave height analyzer

Claims (3)

Liquid core fiber,
First and second photodetectors respectively connected to both ends of the liquid core fiber ;
Means for connecting to the liquid core fiber and exchanging the liquid core in the liquid core fiber,
The radiation distribution line sensor according to claim 1, wherein the means for exchanging the liquid core in the liquid core fiber continuously supplies the liquid core in the liquid core fiber by flowing from the outside of the liquid core fiber .   2. The radiation distribution line sensor according to claim 1, wherein the first and second photodetectors include a photomultiplier tube, and further include a time-of-flight analysis unit connected to the photomultiplier tube. Radiation distribution line sensor.   The radiation distribution line sensor according to claim 2, wherein the time-of-flight analysis means includes a first preamplifier connected to each of the photomultiplier tubes, a constant fraction discriminator connected to each of the first preamplifiers, A delay line connected to one of the constant fraction discriminators, a time wave height converter connected to the other of the constant fraction discriminators and the delay line, and a wave height analysis connected to the time wave height converter A radiation distribution line sensor characterized by comprising:

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