JPH11118933A - Fiber type radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the sensitivity of a fiber type radiation detector which is constituted by combing a scintillator with a fluorescent optical fiber. SOLUTION: A fiber type radiation detector is constituted in such a way that one end of a fluorescent optical fiber 1 which has a light wavelength converting function, a light condensing function, and such a function that changes the transmitting direction of light to the axial direction is inserted into the center axis section of an acrylic resin member 6 having high light transmissivity and a radiation-sensitive layer 15 containing scintillator particles or powder 11 is formed on the outer peripheral surface of the member 6. In addition, the outer periphery of the optical fiber 1 including the outer periphery of the radiation-sensitive layer 15 is coated with a light shielding material 17 and an optical fiber 8 for transmission is connected to the end section of the optical fiber 1 trough an optical connector 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scintillator for detecting gamma rays, neutron rays and alpha rays, and a fiber type radiation detector having a structure in which a transmission optical fiber is connected to a fluorescent optical fiber via an optical connector.

[0002]

2. Description of the Related Art In a "radiation detection light transmission device" (JP-A-6-201835) developed earlier by the present applicant, a cylindrical scintillator which emits light upon incidence of radiation and one end is attached to the center axis of the scintillator. Is inserted, a fluorescent optical fiber that receives light emitted from the scintillator, converts the light into a wavelength of light with low transmission loss, and transmits the converted light, and light connected to the other end of the fluorescent optical fiber via an optical connector. A transmission fiber is provided.

Further, in the previously proposed "fiber-type radiation detector" (Japanese Patent Application No. 8-44903), a fluorescent light having a light wavelength conversion function, a light condensing function, and a function of changing a light transmission direction in an axial direction. Form a radiation-sensitive layer including a particulate or powdery scintillator on the outer peripheral surface of the conductive optical fiber,
The outer periphery of the fluorescent optical fiber including the outer periphery of the sensitive layer is covered with a light shielding material, and an end of the fluorescent optical fiber is provided with a transmission optical fiber via an optical connector.

The above-described radiation detecting light transmission device is a new type of radiation detector capable of transmitting information on radiation such as gamma rays over a long distance without using a power supply for the detecting unit. This is because the radiation detection unit has no power supply compared to the previous radiation detector, so that a relatively small cylindrical Nal (Tl) scintillator or the like can be used, and the detection unit can be downsized. It has become. The above-mentioned fiber type radiation detector is a new type of radiation that makes it possible to detect multiple types of radiation such as gamma rays and neutron rays with a single detector while taking advantage of the characteristics of the radiation detection optical transmission device. It is a detector. This is a method in which a radiation-sensitive layer containing a particulate or powdery scintillator is provided on the outer peripheral surface of the end of a fluorescent optical fiber having a light wavelength conversion function, a light focusing function, and a function of transmitting light after focusing in a certain direction. This is realized by forming and covering only the end and the outer periphery or the outer periphery of the fluorescent optical fiber including the outer periphery of the sensitive layer with a light shielding material.

[0005]

In the above-mentioned fiber type radiation detector, although the light-collecting sensitivity is proportional to the amount of scintillator in the radiation-sensitive layer of a particulate or powdery scintillator,
Since the surface area of the outer peripheral portion and the end portion of the fluorescent optical fiber is limited, it is technically difficult to improve the light collection sensitivity. Therefore, a fiber-type radiation detector that can simultaneously detect radiations of multiple gamma rays and neutrons with a single detection unit, and cannot be realized by the fiber-type radiation detector, and that is sufficient for practical use. The purpose is to provide.

[0006]

In order to solve the above-mentioned problems, a fiber type radiation detector according to the present invention is provided with a light wavelength conversion function and a light wavelength conversion function in a central axis portion of a resin member having high light transmittance such as acrylic resin. Insert one end of a fluorescent optical fiber having a light collecting function and a function of transmitting light after light collection in a certain direction,
Forming a radiation-sensitive layer of a particulate or powdery scintillator on the outer peripheral surface of the resin member, and covering only the end and the outer peripheral portion or the outer peripheral portion of the fluorescent optical fiber including the sensitive layer with a light shielding material. Features. The fiber radiation detector of the present invention, when the radiation to be detected is a gamma ray,
It is preferable to use Nal (Tl), Csl (Tl) or the like as the radiation sensitive substance. When the radiation to be detected is alpha rays, it is preferable to use ZnS (Ag) or the like as the alpha ray sensitive substance. Further, when the radiation to be detected is a neutron beam, the alpha ray-sensitive substance;
A neutron beam is emitted to emit alpha rays, ie, (n,
α) It is preferred to use a mixture with a neutron-sensitive substance which causes a reaction. As the neutron beam-sensitive substance, a substance having a large neutron reaction cross section such as a lithium compound and a boron compound is preferable. Also, when the radiation to be detected is a gamma ray and a neutron ray, it is preferable to use a mixture of the alpha ray sensitive substance and the neutron sensitive substance.

As the fluorescent optical fiber having a light wavelength conversion function, a light collecting function, and a function of transmitting light after light collection in the axial direction, there is, for example, a product manufactured by Optectron of France. Used to implement type radiation detectors. The wavelength conversion function is, for example, that radiation enters a scintillator to generate fluorescence having a wavelength of around 410 nm, and this fluorescence enters a fluorescent optical fiber and is included in a core portion of the fluorescent optical fiber. It means that it is absorbed by the body and emits another fluorescence. This fluorescent light has a larger wavelength than the fluorescent light generated by the scintillator and is converted into light having a wavelength near 520 nm. 520 from fluorescence of wavelength 410nm
By converting the wavelength to about nm, the transmission loss of the optical fiber for transmitting the fluorescence signal is greatly improved, and the effect is reduced from 180 dB / km to 70 dB / km when using, for example, a plastic fiber manufactured by Asahi Kasei. The light condensing function is that the scintillator fluorescence incident on the core from the cladding on the outer surface side of the fluorescent optical fiber excites a fluorescent dye in the core of the fiber to emit fluorescence of a different wavelength. This fluorescence is generated at the core of the fluorescent optical fiber, is totally reflected by the cladding surface of the fiber, and is transmitted in the axial direction of the fluorescent optical fiber.

[0008] Generally, gamma ray and alpha ray radiation
According to the present invention, the light is directly detected by using a scintillator made of the above-mentioned substance since the fluorescent light is emitted upon being incident on the scintillator. Regarding neutron rays, since fluorescence from the direct scintillator is hardly detected, according to the present invention, neutrons such as the lithium compounds and boron compounds, which are irradiated with neutron rays to cause an (n, α) reaction to emit alpha rays A mixture of a neutron-sensitive substance with a large reaction cross-section and an alpha-ray sensitive substance is used to convert the alpha rays emitted by neutron irradiation into fluorescence with the alpha-ray sensitive substance, which is detected indirectly. Neutron beam is detected.

The principle that gamma rays and neutron rays can be detected simultaneously is based on the principle that a neutron sensitive substance having a large neutron reaction cross section, such as a lithium compound or a boron compound, emits fluorescence when irradiated with neutron rays and gamma rays. Utilizing that the decay time of the fluorescence pulse due to gamma rays is sufficiently shorter than the decay time of the fluorescence pulse caused by the alpha rays emitted as a result of the (n, α) reaction by the neutron beam, Due to the ability to distinguish species.

A fiber-type radiation detector for detecting alpha rays used when both alpha rays and neutron rays are mixed has a short range (the range indicates the distance over which the alpha rays travel, and one sheet of paper). The light-shielding material attached to the radiation-sensitive layer for detecting alpha rays has a very small thickness, or has no light-shielding material. The fiber type radiation detector for detecting the alpha ray is different from the detection process for detecting the alpha ray generated inside the radiation sensitive layer by the (n, α) reaction of the neutron beam. The radiation is applied and the alpha radiation is incident on the radiation sensitive layer. By comparing the measured value of the fiber radiation detector by external irradiation of such alpha rays with the measured value of the fiber radiation detector that detects neutron rays, individual radiation in the mixed field of alpha rays and neutron rays Is determined.

In the primary process of neutron beam detection, a neutron beam is absorbed by a substance having a large neutron reaction cross section contained in the radiation-sensitive layer, and alpha rays are generated by the (n, α) reaction. In the secondary process, this alpha ray is further absorbed by ZnS (Ag) or the like, and fluorescence is generated from the ZnS (Ag) or the like. The primary and secondary processes are performed in a chain. For neutron detection, only the fluorescence from ZnS (Ag) or the like obtained in the secondary process is used. Alpha ray detecting material Zn contained in radiation sensitive layer
Constituent materials other than S (Ag) react to gamma rays and absorb the energy of incident gamma rays to generate fluorescence. The decay time of this fluorescence is shorter than that of the alpha-ray detecting material. When radiation enters the fiber radiation detector, the reaction process performed in the radiation-sensitive layer varies depending on the incident radiation, and the decay time of the generated fluorescence varies. Therefore, a fluorescent pulse corresponding to the type of radiation to be applied is obtained at the light output end of the fiber radiation detector.

The obtained fluorescent pulse contains information for each type of different radiation. The decay time of the fluorescent pulse is converted into an electric signal, and pulse waveform discrimination is performed. It is described in "Radiometry Handbook" by Nor, published by Maruzen Co., Ltd.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 schematically shows an enlarged detection unit of an alpha-ray detector. A fluorescent optical fiber 1 is formed of a clad 5 arranged coaxially with a core 3 at the center. An optical connector 7 is connected to the output end. The optical connector 7 is connected to a photoelectric converter such as a photomultiplier (not shown) via a transmission optical fiber 8. White particulate Zn, alpha-sensitive substance
The S (Ag) scintillator 11 and an optically transparent resin 13 having a low refractive index such as Araldite CY221 or HY2967 manufactured by Ciba Geigy Japan are appropriately mixed, applied to the outer peripheral surface of the acrylic resin member 6, and subjected to alpha rays. The sensitive layer 15 is formed. Alternatively, the alpha ray sensitive layer 15
May be formed by sandwiching a radiation-sensitive material such as a scintillator with an optically transparent adhesive tape such as HJ-9150W, a transparent, weather-resistant and heat-resistant double-sided tape manufactured by Nitto Denko Corporation. The sensitive layer 15 and the acrylic resin member 6 are optically bonded to each other, and the outer surface excluding the connector 7 is covered with a light-shielding material 17 such as a very thin Teflon sheet, aluminum foil, or a deposited silver sheet. Have been done. The light shielding member 17 has both a function of blocking external light and a function of reflecting the fluorescence of the scintillator 11. The acrylic resin constituting the acrylic resin member 6 is a typical example of a resin having high light transmittance, and can be replaced with another resin having similar properties.

The detection operation of the alpha ray detector having the above configuration will be described with reference to the conceptual diagram of FIG. The alpha ray A enters the sensitive layer 15 through the light shielding material 17, is absorbed by the scintillator 11, and emits fluorescence B. This fluorescent light B passes through the acrylic resin member 6 and the fluorescent material C of the fluorescent optical fiber 1
Is absorbed by The fluorescent substance C emits fluorescent light D converted to an emission wavelength different from that of the fluorescent light B. This fluorescent light D travels through the core 3 as shown by the arrow, passes through the optical connector 7, and further in the transmission optical fiber 8. Through the photoelectric converter, where it is converted into an electric signal and measured.

Next, an embodiment in which the present invention is embodied as a neutron detector is shown in FIG. In the figure, the same parts as those of the above-mentioned alpha ray detector are denoted by the same reference numerals and described.
In FIG. 3, the neutron beam-sensitive layer 21 formed by being applied to the outer peripheral surface of the acrylic resin member 6 is formed of white particulate ZnS.
(Ag) Scintillator 11 and scintillator 2 made of a compound containing a particulate lithium compound or boron compound
3 and the low-refractive-index optically transparent resin 13 are appropriately mixed. Of course, it may be formed by the double-sided tape or the like of the previous operation. A light-shielding member 17 is disposed on the outside thereof in the same manner as described above, and the optical connector 7 is also connected to the output end of the fluorescent optical fiber 1. Light shielding material 17
Has a function of a reflector so that the fluorescence generated in the neutron sensitive layer 21 is efficiently incident on the fluorescent optical fiber 1. Then, the operation of the detection unit of the neutron detector will be described with reference to FIG. 4 in the same manner as described above. The neutron beam N enters the neutron beam sensitive layer 21, is absorbed by the scintillator 23, and (n, α) The reaction emits alpha rays A. This alpha ray A is emitted from the adjacent ZnS (Ag) scintillator 11.
And emits fluorescence B. After that, the fluorescence B is converted to the fluorescence D and finally measured by the photoelectric converter as in the above-described example.

FIG. 5 shows a measurement result obtained by irradiating a neutron beam on the neutron detector shown in FIG. This measurement is shown in FIG.
After connecting the transmission fiber to the fiber neutron detector shown in (1) through an optical connector and performing photoelectric conversion of the transmitted fluorescent pulse with a photomultiplier tube, pulse discrimination based on the difference in the decay time of the fluorescent pulse was described above. The waveform discrimination method was used. In FIG. 5, the horizontal axis represents the area ratio of the neutron-sensitive layer when the conventional fiber radiation detector is set to 1, and the vertical axis represents the neutron sensitivity ratio when the conventional fiber radiation detector is set to 1. Represents. As can be understood from the graph of FIG. 5, the neutron sensitivity is proportional to the total area of the neutron sensitive layer 21. Therefore, by increasing the outer diameter of the acrylic resin member, the neutron sensitive layer 2
1, the total area increases, and as a result, the neutron sensitivity is improved. Also, when the outer diameter of the acrylic resin member 6 increases,
The volume of the acrylic resin member 6 increases, the incident angle of the fluorescent light B on the fluorescent optical fiber 1 increases, and the neutron beam sensitive layer 2
It can be understood that the neutron sensitivity increases to a total area ratio of 1 or more.

[0017]

As described above, according to the present invention,
Since a resin material with high light transmittance such as acrylic resin was interposed between the fluorescent optical fiber having the light wavelength conversion function and the light condensing function and the function of changing the light transmission direction in the axial direction, and the radiation sensitive layer, The total area of the radiation-sensitive layer is increased, and the incident angle of the fluorescent light incident on the fluorescent optical fiber is increased, so that the radiation sensitivity can be greatly increased.

[Brief description of the drawings]

FIG. 1 is a conceptual sectional view showing a main part of an embodiment of the present invention.

FIG. 2 is an operation explanatory view of the embodiment.

FIG. 3 is a conceptual sectional view showing a main part of another embodiment of the present invention.

FIG. 4 is an operation explanatory view of the another embodiment.

FIG. 5 is a graph showing measurement results obtained by the neutron detector of the embodiment shown in FIG. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fluorescent optical fiber 3 core 5 clad 6 acrylic resin member 7 optical connector 8 optical fiber 11 ZnS (Ag) scintillator 13 resin 15 sensitive layer 17 light shielding material 21 sensitive layer 23 scintillator A alpha ray B fluorescence C phosphor D fluorescence N neutron line

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Masanori Takebe, 2-23-26 Aoyama, Taishiro-ku, Sendai, Miyagi Prefecture, Japan (72) Katsumi Urayama 2-5-1, Marunouchi, Chiyoda-ku, Tokyo (72) Inventor Nobuyuki Imai 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Heavy Industries, Ltd.

Claims (5)

[Claims] 1. One end of a fluorescent optical fiber having a light wavelength conversion function, a light condensing function, and a function of changing a light transmission direction in an axial direction is inserted into a central axis portion of a resin member having high light transmittance, Forming a radiation-sensitive layer containing a particulate or powdery scintillator on the outer peripheral surface of the resin member, covering the outer periphery of the fluorescent optical fiber including the outer periphery of the sensitive layer with a light shielding material,
A fiber type radiation detector comprising a transmission optical fiber connected to an end of the fluorescent optical fiber via an optical connector. 2. The fiber type radiation detector according to claim 1, wherein said resin member is formed of an acrylic resin. 3. One end of the fluorescent optical fiber is covered with a light-shielding material and the radiation-sensitive layer is formed including the end face, and a transmission optical fiber is connected to the other end via an optical connector. The fiber type radiation detector according to claim 1 or 2, wherein: 4. The scintillator included in the sensitive layer,
The fiber radiation detector according to any one of claims 1 to 3, wherein the fiber radiation detector is any one, two, or all of the substances sensitive to gamma rays, neutron rays, or alpha rays. 5. The scintillator, wherein a substance sensitive to gamma rays is Nal (Tl) or Cs (Tl), a substance sensitive to alpha rays is ZnS (Ag), and a substance sensitive to neutron rays is lithium. The fiber radiation detector according to any one of claims 1 to 4, wherein the radiation detector is a substance having a large neutron reaction cross-sectional area, such as a compound or a boron compound.