JP2851492B2 - Radioactive gas monitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radioactive gas monitor which can be used for radiation measurement and radiation management in a nuclear reactor facility, a nuclear fuel facility, an accelerator facility, etc. which handle radioactive materials.

[0002]

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

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

FIG. 5 is a view showing a detector using a plastic scintillator. A gas sampling tank 30 and a plastic scintillator 3 surrounded by a lead shielding material 34 are shown.
1, a PMT 32 and a premultiplier (PA) 33 are provided, and these detectors are mounted on a base 37. Then, the scintillation light when the radiation from the gas enters the scintillator through the gas inlet 35 is converted into PM.
The detection is performed at T32.

[0005]

In order to increase the sensitivity of a conventional radioactive gas monitor, a cylindrical detector itself is enlarged or a large number of detectors are provided around a gas tank while keeping the detector size unchanged. It is necessary to have a complicated structure. Also, the ventilation type ionization chamber had to be enlarged in order to expand the ionization area. However, as the size increases,
It became susceptible to background radiation, and the entire gas sampling tank, including the detector, had to be shielded from the lead, which inevitably increased the weight. This is also evident in the detectors shown in FIGS.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and can improve the geometric efficiency without increasing the background count rate, can reduce the size of the detector, and capture the radiation reflected in the tank. It is an object of the present invention to provide a radioactive gas monitor capable of improving sensitivity.

[0007]

According to the present invention, there is provided a radioactive gas monitor in which a detector is arranged inside a gas sampling tank and the gas is guided into the tank to detect radiation emitted from the gas. A scintillation optical fiber is bundled and adhered to the inner wall of the high-density material cylindrical tank, and a photomultiplier is arranged at one end of the optical fiber.

Further, the invention is characterized in that the inner surface of the gas sampling tank is coated with a material which easily emits secondary electrons.

Further, the present invention is characterized in that the gas sampling tank has a gas inlet and a gas outlet in the same direction, and convects the gas in the tank.

[0010]

According to the present invention, a cylindrical scintillation optical fiber bundled in parallel and fixed inside a gas sampling tank is fixed, a photomultiplier is connected to one end of the fiber, and gas is ventilated inside the cylindrical optical fiber bundle. When radiation from the gas enters the optical fiber, scintillation light is emitted, propagates through the optical fiber, and is detected by the photomultiplier.

Since the optical fibers are merely arranged in parallel, the geometric efficiency of the detector is enhanced by a simple structure, so that the detection sensitivity is improved, and it is possible to capture and detect the radiation reflected from the tank. Higher sensitivity can be achieved.

[0012]

FIG. 1 is a view showing the structure of a gas monitor detector according to the present invention, FIG. 2 is a view showing the structure of a detection unit of the gas monitor, and FIG.
FIG. 3 is a diagram illustrating a scintillation optical fiber.
In the figure, 1 is a scintillation optical fiber, 2 is a gas 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, 11 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 a gas sampling tank 2, the periphery of the gas 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. Has become. As shown in FIG. 3, the scintillation optical fiber 1 includes a core 11 composed of a scintillator and a clad 12 having a smaller refractive index than the core 11, and when radiation such as β-rays enters, scintillation light is emitted from the scintillator of the core. This scintillation light propagates in both directions as shown, and is effectively guided to both ends of the fiber because the refractive index of the core is larger than that of the cladding.

Therefore, when gas is passed through the gas sampling tank 2 and the gas contains a gas that emits radiation, the radiation emitted toward the side wall of the tank causes interaction such as collision with the optical fiber. And emits scintillation light in the optical fiber. Also, if the tank is made of a high-density substance such as iron, even radiation that did not interact with the optical fiber collides with the tank wall and is partially scattered. Release. The scintillation light generated in the optical fiber is propagated to both ends of the fiber. Half of the light reaches the opto-electronic amplifier located directly at one end of the tank, and the light that has propagated to the other end is also reflected at the end and reaches the opto-electronic amplifier. The signal is converted into an electric signal by the photomultiplier 4, amplified by the preamplifier 5 and the main amplifier 6, and 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,
Further, since a plurality of optical fibers can be bundled and used, a detector having an arbitrary detection area and shape can be made, and the sensitivity of the gas monitor can be easily increased. In addition, by attaching the bundle of optical fibers to the inside of the tank, the geometric efficiency of the detector can be increased, and the sensitivity can be increased. In addition, by making the tank from a high-density substance such as iron, some of the radiation emitted in the tank and hitting the tank wall is scattered in the tank and may re-enter the optical fiber, further increasing the sensitivity. It is possible to increase.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a structure of a gas 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 ... Gas sampling tank, 3 ... Light shielding film, 4 ... Opto-electronic gift maker, 5 ... Present gift maker, 6 ... Main gift maker, 7 ... Indicator, 11 ... Core, 12
... clad.

Continuation of front page (56) References JP-A-3-194485 (JP, A) JP-A-4-24582 (JP, A) JP-A-6-59043 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) G01T 1/00-7/12

Claims (3)

(57) [Claims] 1. A place detector inside the gas sampling tank, the radioactive gas monitor for detecting the radiation emitted from the gas leading the gas into the tank, a high-density material made of tubular bundled in parallel said detector It is composed of scintillation optical fiber attached to the tank inner wall,
A radioactive gas monitor comprising a photomultiplier disposed at one end of an optical fiber. 2. The radioactive gas monitor according to claim 1, wherein a material that easily emits secondary electrons is applied to the inner surface of the gas sampling tank. 3. The radioactive gas monitor according to claim 1, wherein the gas sampling tank has a structure in which an inlet and an outlet of the gas are in the same direction, and the gas is convected in the tank.