JP2851487B2 - 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, radiation management, and the like of a nuclear reactor facility, a nuclear fuel facility, and an accelerator facility.

[0002]

2. Description of the Related Art Conventionally, a radioactive gas monitor using a scintillator is measured by bringing a cylindrical detector or a plate-like detector into close contact with a gas sampling tank. FIG. 3 is a view showing a detector using a NaI (Tl) scintillator.
Scintillator 21, Photomultiplier (PMT) 2
2 are provided, and a lead shielding member 23 is provided therearound. 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. 4 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 photomultiplier (PA) 33 are provided, and these detectors are mounted on a base 37. Then, the gas is introduced from the gas inlet 35 and discharged from the gas outlet 36, and the PMT 32 detects scintillation light when radiation from the gas in the gas sampling tank 30 enters the scintillator.

[0004]

By the way, in order to increase the sensitivity of the detector shown in FIG. 3, the gas sampling tank or the cylindrical detector itself must be increased in size, or the size of the detector must be kept unchanged. It is necessary to provide many detectors around the sampling tank, the structure becomes complicated, and it becomes susceptible to the influence of the background radiation. Therefore, as shown in the figure, the entire gas sampling tank must be lead shielded. Weight will increase. This is the same in the detector shown in FIG. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a radioactive gas monitor capable of increasing the geometric efficiency of a detector and achieving high sensitivity.

[0005]

According to the present invention, a detector is arranged inside a gas sampling tank made of a high-density material surrounded by a shielding material, and a gas is introduced into the tank to emit radiation emitted from the gas. In the radioactive gas monitor for detection, the detector is formed of a scintillation optical fiber wound in a coil shape of one or more layers and closely attached to the inner wall of the tank, and photomultipliers are arranged at both ends of the optical fiber. . Further, the present invention is characterized in that both ends of the plurality of optical fibers are opposed to the photomultiplier.

[0006]

According to the present invention, a scintillation optical fiber is wound into a coil inside a gas sampling tank, and photomultipliers are arranged at both ends of the optical fiber. When gas is ventilated inside the coil and radiation from the gas is incident on the optical fiber. , Scintillation light is emitted, propagates through the optical fiber, and is detected by the photomultiplier. Since the optical fiber can be wound in a coil shape without gaps, the geometric efficiency of the detector is increased with a simple structure, the detection sensitivity is improved, and it is also possible to detect radiation reflected from the tank. Sensitivity can be improved.

[0007]

FIG. 1 is a diagram showing a configuration of a gas monitor detector according to the present invention, and FIG. 2 is a diagram for explaining a scintillation optical fiber. In the figure, 1 is a scintillation optical fiber, 2 is a gas sampling tank, 3 is a shielding material, 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. is there.

In the detector according to the present invention, one or two or more layers of a scintillation optical fiber are wound in a coil shape on the inner surface of the gas sampling tank 2.
Is surrounded by a shielding material 3, and a photomultiplier 4 is arranged at both ends of the scintillation optical fiber. As shown in FIG. 2, 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 is incident, scintillation light is emitted from the scintillator of the core. The 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 the refractive index of the clad.

Therefore, when a 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 collected at both ends of the fiber, converted into an electric signal by the photomultiplier 4, amplified by the preamplifier 5 and the main amplifier 6, and measured by an indicator 7. Can be.

In the above embodiment, one optical fiber is used. However, as the length of the fiber increases, the attenuation of light increases. Therefore, a plurality of short optical fibers are used. If the photomultiplier 4 detects the light passing through the material, the attenuation can be reduced.

[0011]

As described above, according to the present invention, since an optical fiber which is flexible and can be elongated is used as a detecting material, it is formed corresponding to a gas sampling tank having an arbitrary volume. However, by winding the optical fiber without any gap, the geometric efficiency of the detector can be increased with a simple structure, and the sensitivity of the gas monitor can be increased. Also,
By making the tank from a high-density material such as iron, some of the radiation that hits the tank wall that is emitted inside the tank is scattered into the tank and can re-enter the optical fiber, further increasing sensitivity It becomes possible.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining a scintillation optical fiber.

FIG. 3 is a diagram showing a detector using a NaI scintillator.

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

[Description of Signs] 1 ... Scintillation optical fiber, 2 ... Gas sampling tank, 3 ... Shielding material, 4 ... Photomultiplier, 5 ... Preamplifier, 6 ... Main amplifier, 7 ... Indicator, 11 ... Core, 12
... clad.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01T 1/00-7/12

Claims (2)

(57) [Claims] A detector is disposed inside a gas sampling tank made of a high-density material surrounded by a shielding material, and a radioactive substance is introduced into the tank to detect the radiation emitted from the gas. In a gas monitor, a radioactive gas monitor is characterized in that the detector is formed of a scintillation optical fiber wound in a coil shape in one or more layers and is closely attached to an inner wall of a tank, and photomultipliers are arranged at both ends of the optical fiber. 2. The radioactive gas monitor according to claim 1, wherein a plurality of optical fibers are provided, and both ends of each optical fiber are opposed to the photomultiplier.