JP6041484B2 - Neutron detector - Google Patents

Description

  The present invention relates to a neutron detector including a boron trifluoride gas proportional counter for counting neutrons.

  The proportional counter is a kind of gas-filled detector, and can be taken out as an electric signal when the radiation and the gas react. The structure of the proportional counter is that when a high electric field is applied to the gas and the radiation reacts with the gas, an avalanche phenomenon occurs due to the high electric field and the charge is amplified.

  As a proportional counter for detecting neutrons, a boron trifluoride gas proportional counter is used (see Patent Document 1). Further, a boron trifluoride gas proportional counter that can be used in an atmosphere at a high temperature of about 80 ° C. or higher has been proposed. The boron trifluoride gas proportional counter of Patent Document 2 uses an MI cable (Mineral Insulated Cable), a silica insulated coaxial cable, or a Teflon (registered trademark) insulated coaxial cable as a high voltage application and signal extraction cable.

  In the boron trifluoride gas proportional counter, the fluorine gas generated by the reaction between incident neutrons and boron trifluoride gas shortens the lifetime of the boron trifluoride gas proportional counter element. Patent Document 3 discloses a technique for reducing the generated fluorine gas by lowering the gas pressure filled with boron trifluoride gas. The neutron detector of Patent Document 3 also connects boron trifluoride gas proportional counter elements in parallel to compensate for the neutron detection sensitivity deteriorated by lowering the gas pressure. Configure the tube.

Japanese Patent Laid-Open No. 3-133047 Japanese Patent Laid-Open No. 4-121687 JP 2000-149864 A

  The neutron detector of Patent Document 3 has a structure in which two boron trifluoride gas proportional counters disclosed in Patent Document 1 are connected in parallel. In such a structure, the connection part of the two boron trifluoride gas proportional counters forms an ionization chamber, and there is a problem that radiation other than the measurement target is detected as an electric signal and detection accuracy is lowered. The boron trifluoride gas proportional counter detects neutrons, but radiation that is not measured is radiation such as gamma rays emitted from the reactor, and gamma rays emitted by the activation of detector parts. .

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to reduce errors in neutron detection that occur in a neutron detector due to a reaction of radiation that is not a measurement target.

Each of the neutron detectors according to the present invention has an anode wire stretched in a boron trifluoride gas sealed at a predetermined pressure, and generates a pulse signal corresponding to the number of neutrons. A plurality of boron trifluoride gas proportional counters. The neutron detector electrically connects one cable to which the anode wires of a plurality of boron trifluoride gas proportional counters are connected, and the anode wire and one cable of each boron trifluoride gas proportional counter. A signal line to be connected, a solid electric insulator covering the periphery of the signal line, a plurality of boron trifluoride gas proportional counters, a cable, an outer cylinder containing the signal line and the electric insulator, an outer cylinder and a plurality of And nitrogen filled between boron trifluoride gas proportional counters.

  According to the present invention, the signal lines connecting the anode lines of a plurality of boron trifluoride gas proportional counters and one cable are each covered with an electrical insulator, so that electrons generated around the signal lines are detected. There is no. As a result, neutron detection errors can be reduced.

It is a perspective view which shows the structure of the neutron detector which concerns on embodiment of this invention. It is sectional drawing of the neutron detector which concerns on embodiment. It is sectional drawing of the insulator for the signal wire | line protection which concerns on embodiment. It is sectional drawing and the side view of other insulators for signal line protection concerning an embodiment. It is a figure explaining the effect | action of the insulator which concerns on embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure, the same or equivalent members and parts are described with the same reference numerals.

  FIG. 1 is a perspective view showing the structure of a neutron detector according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the neutron detector according to the embodiment. In FIG. 1, the outer cylinder of the neutron detector 20 is omitted. The neutron detector 20 includes two boron trifluoride gas proportional counters 1. The boron trifluoride gas proportional counter 1 is disposed at a position symmetrical to the central axis of the neutron detector 20. The sectional view of FIG. 2 is vertically symmetric.

  The boron trifluoride gas proportional counter 1 is a part that has an anode wire stretched in a boron trifluoride gas sealed at a predetermined pressure and detects a neutron beam. The counter-holding metal 2 is made of a metal such as titanium, and is a mechanism for holding two boron trifluoride gas proportional counters 1 in combination.

  In the boron trifluoride gas proportional counter 1, a neutron sensitive gas that also serves as an ionizing gas such as boron trifluoride gas is sealed inside a tube that also serves as a negative electrode. An anode wire is provided inside the tube so as to extend in the axial direction of the tube. A high voltage is applied between the negative electrode tube and the anode wire. Neutrons incident on the tube cause a nuclear reaction with a neutron-sensitive gas that also serves as an ionization gas, generating positive ions and electrons. Further, the generated electrons ionize the neutron-sensitive gas that also serves as the ionization gas in the vicinity of the anode line to generate positive ions. When these positive ions reach the tube also serving as the negative electrode, an induced charge is generated in the anode wire. Detecting neutrons by introducing a pulse signal due to the induced charge generated in the anode wire to the outside of the boron trifluoride gas proportional counter 1 with the signal wire 12 (see FIG. 2), and amplifying and counting the pulses. Can do.

  A signal line 12 (see FIG. 2) exiting from the boron trifluoride gas proportional counter 1 is formed of a metal such as nickel having an outer cylinder 13 and connected to the MI cable 8. The cross-sectional view of FIG. 2 shows a connection state between the signal line 12 and the MI cable. The signal lines 12 on both sides are twisted together and connected to the MI cable 8.

  The insulator 4, the insulator 5, and the insulator 6 are electrical insulators made of an electrical insulator such as ceramic. The shape is cylindrical and the signal line 12 passes through the inside. The insulator 4 covers at least a portion from where the signal line 12 exits from the boron trifluoride gas proportional counter 1 to at least the first bent portion of the signal line 12. The insulator 5 penetrates the side surface of the insulator 4 and covers a portion from the first bent portion to the next bent portion of the signal line 12. The other end of the insulator 5 penetrates the side surface of the insulator 6. The insulator 6 covers a portion from the second bent portion of the new synthetic fiber 12 until it is connected to the MI cable.

  The insulator 4 is held by an insulator holding member 3 and an insulator stop component 7 made of a metal such as titanium. The insulator holding member 3 is formed with a hole through which the insulator 4 is fitted so that the insulator 4 stands upright. The insulator stop component 7 is a component that prevents the insulator 4 from falling off the insulator holding member 3.

  The outer cylinder 11 shown in FIG. 2 is a cylindrical member made of a metal such as titanium. The upper lid 9 is made of a metal such as titanium and seals the MI cable 8 side of the outer cylinder 11. The lower lid 10 is made of a metal such as titanium and seals the bottom of the outer cylinder 11. The upper lid 9, the lower lid 10, and the outer cylinder 11 constitute a sealed container, which is filled with a gas such as nitrogen. The MI cable 8 passes through the upper lid 9 and transmits an electrical signal generated by the boron trifluoride gas proportional counter 1 to the outside of the neutron detector 20.

  FIG. 3 is a cross-sectional view of an insulator for signal line protection according to the embodiment. FIG. 3 shows the insulator 4. The insulator 4 is formed in a cylindrical shape using an electrical insulator such as ceramic as a material. A lateral hole 41 is formed on the side surface of the insulator 4. One end of the insulator 5 penetrates into the horizontal hole 41. The insulator 5 is formed in a cylindrical shape using an electrical insulator such as ceramic (see FIG. 2).

  FIG. 4 is a cross-sectional view and a side view of another insulator for signal line protection according to the embodiment. FIG. 4 shows the insulator 6. 4A is a sectional view, and FIG. 4B is a side view. The insulator 6 is formed in a cylindrical shape using an electrical insulator such as ceramic as a material. U-shaped notches 61 are formed on both side surfaces of the end portion of the insulator 6. The other end of the insulator 5 is fitted into the notch 61.

  Since the neutron detector 20 is used in a vertical orientation with the upper lid 9 as an upper portion, the insulator 6 is supported by the insulator 5, and the insulator 5 is supported by a lateral hole 41 of the insulator 4. For this reason, the signal line 12 is not burdened. Hereinafter, the operation of the insulators 4, 5 and 6 will be described.

  FIG. 5 is a diagram for explaining the operation of the insulator according to the embodiment. In FIG. 5, the boron trifluoride gas proportional counter 1 of the neutron detector 20 is representatively shown as one. Further, the insulators 4, 5 and 6 are collectively shown as one insulator 21. Since the signal line 12 is completely covered with the insulators 4, 5 and 6, it can be considered that the signal line 12 is electrically covered with one insulator 21.

  A signal is sent from the boron trifluoride gas proportional counter 1 to the MI cable 8 via the signal line 12. The high voltage power supply 23 applies a voltage of about 1 kV to the anode of the boron trifluoride gas proportional counter 1 via the signal line 12. The amplifier 22 amplifies the signal from the neutron detector 20. The potential of the outer cylinder 13 is grounded.

  Now consider the situation that is actually used. Nitrogen filled around the connection between the boron trifluoride gas proportional counter 1 and the MI cable 8 emits electrons by reaction with γ rays. Electrons are collected by the electric field generated by the signal line 12. If there is no obstacle, the collected electrons are absorbed as they are into the signal line 12 and are detected as noise signals. Since the noise signal cannot be distinguished from the neutron detection signal, the noise signal causes an error in neutron detection.

  However, since the insulator 21 is an electrical insulator having a sufficiently high resistance, the electron capture cross-sectional area is large. Therefore, the generated electrons are absorbed by the insulator 21 and generation of noise signals is suppressed. As a result, neutron detection errors can be reduced.

  The configuration of the present embodiment is an example, and the present invention is not limited to this. For example, not only the configuration including two boron trifluoride gas proportional counters 1 but also a configuration in which three or more are connected in parallel has the same effect by covering the signal line 12 with an insulator. When three or more boron trifluoride gas proportional counters 1 are provided, the boron trifluoride gas proportional counters 1 may be rotationally symmetric with respect to the axis of the neutron detector 20 or arranged side by side on a plane. May be. When the boron trifluoride gas proportional counter 1 is rotationally symmetrical, for example, the insulator 5 can be rotationally symmetrical around the insulator 6 to cover the signal line 12. When the boron trifluoride gas proportional counter 1 is arranged on a flat surface, for example, the position where the insulator 5 penetrates the insulator 4 and the insulator 6 is shifted in the longitudinal direction, and the signal line 12 can be covered.

  The electrical insulator covering the signal line 12 is not limited to the structure of the insulators 4, 5 and 6 of the embodiment. For example, the electrical insulator corresponding to the insulators 4 and 5 may be inclined with respect to the axis of the boron trifluoride gas proportional counter 1. Further, the electrical insulator is not limited to a cylindrical shape, and may be tubular with various cross sections. The same effect can be obtained if the signal line 12 is completely covered so that it can be electrically insulated from the portion where surrounding electrons are generated. The material constituting the electrical insulator is not limited to ceramic, and an electrical insulator such as fluororesin or silicone can be used.

1 Boron trifluoride gas proportional counter
2 Counter tube holding member
3 Insulator holding member 4, 5, 6 Insulator
7 Insulator stop parts
8 MI cable
9 Top cover
10 Lower lid
11 outer cylinder
12 signal lines
13 outer cylinder
20 Neutron detector
21 Insulator
22 Amplifier
23 High voltage power supply

Claims (4)

A plurality of boron trifluoride gas proportional counts, each of which has an anode wire stretched in boron trifluoride gas sealed at a predetermined pressure and generates a pulse signal corresponding to the number of neutrons Tube,
One cable to which anode wires of the plurality of boron trifluoride gas proportional counters are connected;
A signal line for electrically connecting the anode line of each boron trifluoride gas proportional counter and the one cable;
A solid electrical insulator covering the periphery of the signal line;
An outer cylinder containing the plurality of boron trifluoride gas proportional counters, the cable, the signal line, and the electrical insulator;
Nitrogen filled between the outer cylinder and the plurality of boron trifluoride gas proportional counters;
A neutron detector comprising:   The neutron detector according to claim 1, wherein the electrical insulator has a structure in which a plurality of cylindrical members are combined.   3. The neutron detection according to claim 2, wherein each of the cylindrical members covers a section sandwiched between adjacent bent portions of the signal line, and an end portion of one member penetrates a side surface of another one member. vessel.   The neutron detector according to any one of claims 1 to 3, wherein the electrical insulator is made of ceramics.

Images