JPH0247581A - Neutron detector - Google Patents

Abstract

PURPOSE:To obtain a compact detector which can measure an effective dose equivalent and a tissue dose equivalent at the same time by coating a hydrogen compound film on the inner surface of a container for a BF3 proportional counter tube, and discriminating the output with a discriminating circuit for wave crests or waveforms. CONSTITUTION:A hydrogen compound film 14 comprising polyethylene and the like is coated on the inner surface of a container of a proportional counter tube 10. A conductor is applied on the surface of the film 14, and an outer electrode 15 is formed. A high voltage is applied across the outer electrode 15 and a core wire 12 for a central electrode. BF3 gas is sealed into the container 11. The output signal from an output terminal 13 is amplified in an amplifier 22. A signal caused by alpha particles and a signal caused by recoil protons are discriminated in a signal discriminating circuit 23 based on an energy level or a waveform. The signals are counted in counter circuits 25 and 24. The dose equivalent and the average energy are computed in an operating circuit 26 based on the ratio between the counted values and displayed on a display part 27.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a neutron detector that can be used for radiation measurement and radiation management in particle accelerator handling facilities, nuclear fuel facilities, nuclear reactor facilities, and the like.

[Prior Art] Generally, when evaluating the effects of radiation on a living body, the concept of dose equivalent is used, and is given as the product of absorbed dose and radiation quality coefficient. The radiation quality factor is the local energy addition rate to biomolecules along the trajectory of the particle, that is, it increases with the addition of linear energy.
It is 1 for gamma rays, etc., and becomes a large value for α particles, neutrons, etc. Further, dose equivalent is classified into effective dose equivalent and tissue dose equivalent, and dose equivalent rate is defined as the value of dose equivalent per unit time.

Conventionally, the measurement of neutron dose equivalent rate involves moderating neutrons with a neutron moderator such as polyethylene,
The (n, α) reaction is caused by injecting the gas into a container made of aluminum or stainless steel, etc., and the α particles (α) released at this time ionize the gas, which is then sent as an electrical signal pulse from the output terminal. I was about to take it out.

[Problem to be solved by the invention]

However, conventional neutron detectors use a large amount of neutron moderating material such as polyethylene so that the dose response characteristics remain constant over a wide energy range, which tends to make the equipment large and heavy. This was an obstacle in efforts to reduce weight. In addition, with this type of dose equivalent rate meter, it is impossible to measure different dose equivalents such as effective dose equivalent and tissue dose equivalent with one detector, and it is also difficult to obtain energy information such as the average energy of neutrons. I couldn't do it.

The present invention is intended to solve the above-mentioned problems.It is possible to simultaneously measure dose equivalents whose response characteristics differ depending on energy, such as neutron effective dose equivalent and tissue dose equivalent, and also to determine the average energy of neutrons. An object of the present invention is to provide a neutron detector that can reduce the size and weight of a survey meter or monitor.

[Means to solve the problem]

To this end, the neutron detector of the present invention is filled with boron trifluoride and utilizes the (n, α) reaction of boron, and is a neutron detector using a proportional counter. The inner surface is coated with a film of hydrogen compound such as polyethylene, the output of the proportional counter is discriminated by a wave height or waveform discrimination circuit, and two or more types of electrical signals are extracted. It is characterized in that two types of electrical signals are counted, and the dose equivalent and average energy are determined from the ratio of each counted value.

[Effect]

The neutron detector of the present invention coats the inner surface of the container of the BF and proportional counter tube with a film of a hydrogen compound such as polyethylene,
Electrical signals are extracted by the (n, α) reaction for slow neutrons and by the (n, p) reaction for fast neutrons, and take advantage of the fact that the wave height or waveform differs depending on the (nα) reaction and (n, ρ) reaction. , are counted separately, and by using the fact that there is a predetermined functional relationship between the counting ratio and the dose equivalent and average energy, it is possible to calculate the dose equivalent and average energy, etc., using a single detector. Effective dose equivalent and tissue dose equivalent can be measured simultaneously, and since hydrogen compounds such as polyethylene react with fast neutrons, a large amount of moderator is not required, making the device smaller and lighter.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing the structure of the neutron detector of the present invention, in which lO is a proportional counter, 11 is a counter container, 12 is a core wire for the center electrode, 13 is an output terminal, and 14 is a hydrogen compound membrane. ,1
5 is an outer electrode.

In the figure, a proportional counter 10 has a container 11 whose inner surface is coated with a film 14 of a hydrogen compound such as polyethylene, and a conductor is applied to the surface of the film to form an outer electrode 15.
A high voltage is applied between the center electrode core wire 12,
BF and gas are sealed inside.

When a slow neutron with low energy enters (n,
α) A reaction occurs and α particles are released into the proportional counter. The gas is ionized by these α particles, and the ionized particles are accelerated by the high voltage between the cylindrical or spherical outer electrode 15 and the core wire 12, which is the center electrode, and a current flows between the two electrodes and is amplified. 13, it is output as an electrical signal pulse. In addition, when fast neutrons are incident, a (n, p) reaction occurs with the hydrogen in the film 14 of a hydrogen compound such as polyethylene coated on the inside of the container 11 of the proportional counter 10, and the recoil protons (p) is released into the proportional counter. These recoil protons ionize the gas in the same way as α particles, and are extracted from the output terminal as electrical signal pulses.

Since the output signals when slow neutrons and fast neutrons are incident have different voltage levels and waveforms, they can be discriminated by a signal discrimination circuit and each can be counted separately.

FIG. 2 is a diagram showing the configuration of a detection circuit according to the present invention having such a discrimination circuit.
6 is an arithmetic processing circuit, and 27 is a representation section.

A high voltage is applied to the proportional counter tube 10 between the outer electrode and the center electrode by the high voltage circuit 21, and as described above, when a neutron is incident, an electric signal pulse is extracted from the output terminal, and this output pulse is sent to the amplifier 22. The signal is amplified by a signal discrimination circuit 23 and discriminated into an α signal (a signal generated by α particles) or a p signal (a signal generated by recoil protons) depending on the energy level or waveform, and a counting circuit 24 respectively.
Count by ゜25.

By the way, the (nρ) reaction to neutron energy, (
n, α) The sensitivity of the reaction shows the characteristics as shown in Figure 3,
Each reaction differs depending on the energy of the neutron, and occurs with a predetermined probability. Therefore, the counting circuit 24 in FIG.
By setting the count value in 02 and the count value in the counting circuit 25 as CI, the count ratio C
2/CI and i1D per dose, or mean energy, V.

For example, a functional curve as shown in FIG. 4 is obtained between . Note that the function curve in the figure is normalized by dividing by the count value CI. By programming this function, storing it in the arithmetic processing circuit 26, and measuring it at a location with an arbitrary neutron energy distribution, it is possible to perform arithmetic processing using the functional relationship shown in Figure 4 from l\CI and C2. circuit 26
The dose equivalent and average energy can be calculated by

In this way, the arithmetic processing circuit 22 calculates the dose equivalent and the average energy, and the values are displayed on the display section 27.

[Effects of the Invention] As described above, according to the present invention, it is possible to simultaneously measure the effective dose equivalent and the &[I-weave dose equivalent] with one detector, and it is also possible to measure energy information such as the average energy of the measurement location. It becomes possible to obtain.

Since a hydrogen compound such as polyethylene reacts with fast neutrons, a large amount of moderator is not required as in the conventional method, so the neutron detector can be made smaller and lighter.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of the neutron detector of the present invention, FIG. 2 is a diagram showing the configuration of the neutron detection circuit of the present invention, FIG. 3 is a diagram showing the sensitivity characteristics of the reaction to neutron energy, and FIG.
The figure is a diagram showing the relationship between the count ratio C2/C1 and the ID per dose, t, or the average energy E @ V 1+. 10... Proportional counter tube, II... Counter tube container, 12.
... Core wire for center fi17ji, 13 ... Output terminal, 1
4... Hydrogen compound membrane, 15... Outer electrode, 21.
...High voltage circuit, 22...Amplifier, 23...Signal discrimination circuit, 24.25...Counting circuit, 26...Arithmetic processing circuit, 27...Display unit. Applicant Patent attorney representing the Power Reactor and Nuclear Fuel Development Corporation Masanobu Hirukawa (4 others) Figure 4 Hokuto & Buhi (C2/C1)

Claims (3)

[Claims] (1) In a neutron detector using a BF_3 proportional counter filled with boron trifluoride and utilizing the (n, α) reaction of boron, hydrogen compounds such as polyethylene are added to the inner surface of the proportional counter container. A neutron detector characterized by a membrane coating. (2) The neutron detector according to claim 1, wherein the output of the proportional counter tube is discriminated by a wave height or waveform discrimination circuit to extract two or more types of electrical signals. (3) The neutron detector according to claim 2, wherein the two or more types of electrical signals discriminated by the wave height or waveform discrimination circuit are each counted, and the dose equivalent and average energy are determined from the ratio of each counted value.