JPH06235768A - Radioactive liquid monitor - Google Patents

Abstract

PURPOSE:To improve symmetrical efficiency and to miniaturize a detector by constituting the detector with the cylindrical bundles of scintillation optical fibers which are made to adhere to the inner wall of a tank and then laying out a photomultiplier at one edge. CONSTITUTION:A scintillation optical fiber 1 is bundled in parallel to the inside of the side wall of a liquid sampling tank 2, the surrounding of the tank 2 is covered with an optical shielding film 3, and then a photomultiplier 4 is laid out at one edge of the optical fiber 1, thus constituting a detector. The core of the optical fiber 1 consists of a scintillator and scintillation light is led to both terminals of the optical fiber 1 by a clad with a small refractive index. Liquid entrance and exit are provided at one terminal of the tank 2. liquid is flown into the tank vi a pipe which is extended to a center, and then a convection is generated inside the tank 2. Synchrotron radiation discharged from the liquid toward the side wall of the tank 2 generates interaction with the optical fiber 1 and releases scintillation light inside the optical fiber 1. Then, propagation light reaches the photomultiplier 4, is amplified by amplifiers 5 and 6, and then the amount is measured by an indicating instrument 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid monitor that can be used for radiation measurement and radiation control in nuclear reactor facilities, nuclear fuel facilities, accelerator facilities, etc. that handle radioactive materials.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring and managing radiation, a radioactive liquid monitor in which a cylindrical detector or a plate detector is closely attached to a liquid sampling tank has been used.

FIG. 4 is a diagram showing a detector using a NaI (T1) scintillator. A cylindrical NaI scintillator 21 and a photomultiplier (PMT) 22 are provided on the wall of the liquid sampling tank 20 and the periphery thereof. A lead shielding material 23 is provided on the. At the time of detection, the liquid is introduced from the liquid inlet 24 and discharged from the liquid outlet 25, and the PMT 22 detects the scintillation light when the radiation from the liquid in the liquid sampling tank 20 enters the scintillator.

FIG. 5 is a diagram showing a detector using a plastic scintillator, in which the liquid sampling tank 30 and the plastic scintillator 3 are surrounded by a lead shielding material 34.
1, a PMT 32 and a preamplifier (PA) 33 are provided, and these detectors are attached to a base 37. The PMT 32 detects the scintillation light when the radiation from the radioactive substance in the liquid that flows in from the liquid inlet 35 enters the scintillator.

[0005]

In order to improve the sensitivity of the conventional radioactive liquid monitor, the size of the cylindrical detector itself should be increased, or the detector size should be left unchanged and many detectors should be installed around the liquid tank. It is necessary to have a complicated structure provided. In addition, the sampling solution had to be evaporated and the radioactivity in the residue had to be measured with a measuring instrument such as a gas flow detector.
Both were forced to grow in size. However, as it gets larger, it becomes more susceptible to background radiation,
The entire liquid sampling tank including the detector had to be shielded from lead, which inevitably led to an increase in weight and an increase in installation area.

The present invention is intended to solve the above-mentioned problems. The geometrical efficiency can be improved, the detector can be miniaturized, and the radiation reflected in the tank can be captured to enhance the sensitivity. It is an object to provide a radioactive liquid monitor.

[0007]

SUMMARY OF THE INVENTION The present invention is a radioactive liquid monitor in which a detector is arranged inside a liquid sampling tank and which guides the liquid into the tank to detect the radiation emitted from the liquid. It is characterized in that it is composed of scintillation optical fibers which are bundled in a cylindrical shape and closely adhered to the inner wall of the tank, and a photomultiplier is arranged at one end of the optical fibers.

The present invention is also characterized in that the inner surface of the liquid sampling tank is coated with a material that easily emits secondary electrons.

Further, the present invention is characterized in that the liquid sampling tank has a liquid inlet and a liquid outlet on the same side and allows the liquid to convect in the tank.

[0010]

According to the present invention, the scintillation optical fibers which are bundled in parallel inside the liquid sampling tank to form a tube are fixed, a photomultiplier is connected to one end of the scintillation optical fiber, and the liquid is introduced into the inside of the tube-shaped optical fiber bundle. When radiation from a radioactive substance in a liquid enters an optical fiber, scintillation light is emitted, propagates through the optical fiber, and is detected by a photomultiplier.

Since the optical fibers are arranged in parallel, the geometrical efficiency of the detector can be improved with a simple structure, the detection sensitivity is improved, and the radiation reflected from the tank can be captured and detected. Higher sensitivity can be achieved.

[0012]

1 is a diagram showing the structure of a radioactive liquid monitor detector according to the present invention, FIG. 2 is a diagram showing the structure of a detector of a liquid monitor, and FIG. 3 is a diagram explaining a scintillation optical fiber. In the figure, 1 is a scintillation optical fiber, 2
Is a liquid sampling tank, 3 is a light shielding film, 4 is a photomultiplier, 5 is a preamplifier, 6 is a main amplifier, 7 is an indicator, 1
1 is a core and 12 is a clad. The detector of the present invention has a structure in which scintillation optical fibers are bundled in parallel inside the side wall of the liquid sampling tank 2, the periphery of the liquid sampling tank 2 is covered with a light shielding film 3, and a photomultiplier 4 is arranged at one end of the scintillation optical fiber. It has become. As shown in FIG. 3, the scintillation optical fiber 1 includes a core 11 made of a scintillator and a clad 12 having a smaller refractive index than the core 11, and scintillation light is emitted from the scintillator of the core when radiation such as β rays enters. This scintillation light propagates in both directions as shown in the figure, and since the refractive index of the core is higher than that of the cladding, it is effectively guided to both ends of the fiber.

A liquid inlet and a liquid outlet provided on one end side of the tank are used for the liquid sampling tank 2. The liquid is introduced through a pipe extending from the liquid inlet to the central portion, and is convected to flow out the liquid from the liquid outlet. To do so. In this way, when the liquid is introduced into the liquid sampling tank 2 and the liquid contains a radioactive substance that emits radiation, the radiation emitted toward the side wall of the tank causes an interaction such as collision with the optical fiber and the optical fiber. Emits scintillation light inside. Also, if the tank is made of a high-density material such as iron or coated with a material that easily emits secondary electrons, the radiation that did not interact with the optical fiber will also collide with the tank wall and be partially scattered, Alternatively, secondary electrons are emitted and again enter the optical fiber to interact with each other to emit scintillation light. The scintillation light thus generated in the optical fiber is propagated to both ends of the fiber. Half of the light reaches the optoelectronic amplifier directly arranged at one end of the tank, and the light propagating to the other end also reflects at the end point and reaches the optoelectronic amplifier. It is converted into an electric signal by the photomultiplier 4 and amplified by the preamplifier 5 and the main amplifier 6, and the amount can be measured by the indicator 7.

[0014]

As described above, according to the present invention, since the optical fiber is plastic and can be elongated,
Moreover, since a plurality of optical fibers can be bundled and used, a detector having an arbitrary detection area and shape can be manufactured, and the sensitivity of the liquid monitor can be easily increased. Also, by sticking a bundle of optical fibers inside the tank, the geometrical efficiency of the detector can be increased,
Higher sensitivity can be achieved. Moreover, if the tank is made of a high-density material such as iron or coated with a material that easily emits secondary electrons, part of the radiation emitted in the tank and colliding with the tank wall is scattered in the tank, Alternatively, secondary electrons may be emitted and re-enter the optical fiber, and the sensitivity can be further increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a liquid monitor detector of the present invention.

FIG. 2 is a diagram showing a structure of a liquid monitor detection unit of the present invention.

FIG. 3 is a diagram for explaining a scintillation optical fiber.

FIG. 4 is a diagram showing a detector using a NaI scintillator.

FIG. 5 is a diagram showing a detector using a plastic scintillator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Scintillation optical fiber, 2 ... Liquid sampling tank, 3 ... Light-shielding film, 4 ... Photoelectronic multiplier, 5 ... Front spreader, 6 ... Main spreader, 7 ... Indicator, 11 ... Core, 12
… Cladding.

Claims (3)

[Claims] 1. A radioactive liquid monitor in which a detector is arranged inside a liquid sampling tank and which guides the liquid into the tank to detect radiation emitted from a radioactive substance in the liquid. A radioactive liquid monitor comprising a scintillation optical fiber closely attached to the inner wall of a tank, and a photomultiplier arranged at one end of the optical fiber. 2. The radioactive liquid monitor according to claim 1, wherein the inner surface of the liquid sampling tank is coated with a material that easily emits secondary electrons. 3. The liquid monitor according to claim 1, wherein the liquid sampling tank has a liquid inlet and a liquid outlet on the same side, and has a structure for causing convection of the liquid in the tank.