JPH09318759A - Apparatus for measuring neutron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain total equivalent dose by measuring equivalent dose at each neutron energy range and adding them. SOLUTION: A detector 10 has a fast neutron detector 18, an intermediate speed neutron detector 16 and thermal neutron detectors 14A, 14B. Fast neutron is detected by utilizing recoiling, the intermediate speed neutron is transformed to thermal neutron by a moderator layer 44 and detected. The neutrons are individually detected at respective energy ranges. The layer 44 is utilized only for detecting the intermediate speed neutron.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutron measuring device, and more particularly to a neutron measuring device for detecting neutrons in each energy range over a wide energy range from thermal neutrons to fast neutrons.

[0002]

2. Description of the Related Art Thermal neutrons (0.0025 eV) to fast neutrons (eg 14 Me) are used for radiation protection.
It is necessary to measure neutrons in a wide energy range over 9 digits up to V). Conventionally, a REM counter (trade name) is known as a device capable of detecting neutrons over a relatively wide energy range.

[0003]

By the way, ICRP
According to the (International Commission on Radiation Protection) Recommendation in 1990, it is required to calculate the equivalent dose by multiplying the absorbed dose by the radiation weighting factor for each energy range as shown in Table 1 below.

[0004]

[Table 1] Range of neutron energy Radiation weighting factor Neutron energy less than 10 keV 5 Neutron energy 10 keV to 100 keV 10 Neutron energy more than 100 keV to 2 MeV 20 Neutron energy to more than 20 MeV 10 Neutron energy more than 20 MeV 5 However, the above REM In conventional neutron measuring devices such as counters, neutrons for each energy are not separated and measured, and a device for measuring in accordance with the above ICRP recommendation has not been put into practical use.

Further, the conventional neutron measuring apparatus has a problem that it is relatively heavy because it uses a large amount of moderator and the like in order to adjust the energy sensitivity. Further, for the same reason, most of the incident thermal neutrons are shielded and only a part of the thermal neutrons is detected, and there is a problem that the detection sensitivity of thermal neutrons in particular has to be lowered.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide a neutron measuring apparatus capable of measuring a predetermined dose for each neutron energy range.

Another object of the present invention is to provide a neutron measuring apparatus which has a high detection sensitivity for neutrons in each energy range and is lightweight.

[0008]

In order to achieve the above object, the present invention provides a neutron detector comprising a plurality of neutron detectors having different detection energy ranges, and a detection result of each neutron detector. On the other hand, a multiplication unit for multiplying a predetermined weighting coefficient for each neutron detector to obtain a predetermined dose for each energy range is included.

According to the above configuration, neutron detection is independently performed for each neutron detector, and the detection result is multiplied by the weighting coefficient to obtain, for example, the equivalent dose for each energy range. it can. Here, the adjustment of the detection sensitivity and the calculation of the dose can be performed by the numerical calculation for each detector in the form of the multiplication of the weighting coefficient. Does not require a large amount of. That is, according to the present invention, the weight can be reduced, and the sensitivity of each neutron detector can be effectively exhibited.

In a preferred aspect of the present invention, the predetermined dose is an equivalent dose, and an adding unit for adding up the equivalent doses in the respective energy ranges to obtain a total equivalent dose is included.

In a preferred aspect of the present invention, the neutron detector is a fast neutron detector for detecting fast neutrons,
It is composed of a detector for medium-speed neutrons that detects medium-speed neutrons and a detector for thermal neutrons that detects thermal neutrons.

Here, the fast neutron detector is an ionization chamber in which a recoil material layer that produces recoil particles by fast neutrons is formed inside and a gas that causes ionization by the recoil particles is placed inside. It is desirable to be composed of. Further, the detector for medium-speed neutrons, desirably, a moderator layer to decelerate medium-speed neutrons to thermal neutrons, and is wrapped in the moderator layer,
A detector for detecting thermal neutrons generated by deceleration. In this case, it is preferable to form a thermal neutron shielding layer that shields thermal neutrons around the medium-speed neutron detector and at least one of the medium-speed neutron detector and the thermal neutron detector.

In the above structure, the moderator is used only in the detector for medium-speed neutrons, that is, the moderator is not used in the detectors for thermal neutrons and fast neutrons. Can reduce the weight of. According to the experiment, the weight of the conventional apparatus was about 8 kg, but according to the present invention, it has been confirmed that the apparatus weight can be halved to 4 kg or less. Further, a plurality of thermal neutron detectors may be provided, and in that case, the directivities of the detectors may be different from each other. Further, in the above configuration, Table 1 above
According to the above, detectors are provided for each of the three energy ranges, but more detectors may be provided.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred embodiment of the neutron measuring apparatus according to the present invention, and FIG. 1 is an overall configuration diagram thereof.

In FIG. 1, the neutron measuring apparatus is roughly divided into a detecting section 10 and a calculating section 12. In the present embodiment, the detection unit 10 includes a thermal neutron detector 14, a medium neutron detector 16, and a fast neutron detector 18. That is, the detection unit 10 is composed of a plurality of neutron detectors having different detection energy ranges. The specific configuration of each detector will be described later with reference to FIG.

The detection signal output from the thermal neutron detector 14 is amplified by the preamplifier 20A and further amplified by the amplifier 22A, and the amplified detection signal is input to the weight multiplier 24A. Weight multiplier 24A
Then, the detection signal is multiplied by a weight considering both the response of the thermal neutron detector 14 and the radiation weighting coefficient, and the ICRP is multiplied by the weight multiplier 24A.
The equivalent dose based on the 1990 recommendations is calculated. Then, the calculated equivalent dose is displayed on the display 26A.

Similarly to the above, the detection signal output from the detector 16 for medium speed neutrons is amplified in the preamplifier 20B and the amplifier 22B, and the amplified detection signal which is the detection result of the medium speed neutrons in the weight multiplier 24B. Is multiplied by a predetermined weight, and the equivalent dose is obtained as a result of the multiplication. Then, the equivalent dose is displayed on the display 26B. This is the same in the fast neutron detector 18, and the detection signal amplified in the preamplifier 20C and the amplifier 22C is multiplied by a predetermined weight in the weight multiplier 24C, and the equivalent dose as the calculation result is It is displayed on the display 26C.

The adder 28 includes weight multipliers 24A, B, and
The total equivalent dose is calculated by adding the equivalent doses output from C, and the total equivalent dose is displayed on the display 26D.

The weight coefficient in the above-mentioned weight multiplier is
The radiation weighting factor and the sensitivity of each detector based on Table 1 above are taken into consideration. As described above, according to the neutron measuring apparatus of the present invention, the equivalent dose can be calculated for each neutron in each energy range, and the total equivalent dose can be calculated by adding them. In addition,
In the conventional device, for example, the sensitivity to thermal neutrons was sacrificed for energy sensitivity adjustment, but according to the device of the present embodiment, as will be described later in detail, it is effective without causing such sensitivity sacrifice. Can detect neutrons. By the way, the sensitivity is adjusted by adjusting the weighting coefficient, and since the sensitivity can be adjusted by electronic calculation, the weight of the entire device is higher than that of the device in which the sensitivity is adjusted using a moderator or a shielding material. There is an advantage that can be reduced.

Next, the specific configuration of the detecting section 10 will be described in detail with reference to FIG.

As shown in FIG. 2, the detector 10 comprises a fast neutron detector 18, a medium fast neutron detector 16 and a plurality of thermal neutron detectors 14A and 14B. In the fast neutron detector 18, a recoil material layer 32 made of, for example, polyethylene is provided inside the ionization chamber container 30 made of a cylindrical metal by coating. An extremely thin conductive film 34 is formed inside the recoil material layer 32. The ionization chamber container 30 holds the collector electrode 38 via the insulating member 36. An ionization gas 39 made of, for example, argon is enclosed in the ionization chamber container 30.

Therefore, fast neutrons are generated in this ionization chamber container 3
When it is incident inside 0, a so-called recoil phenomenon occurs in the recoil material layer 32, and the recoil particles generated by this phenomenon are ionized gas 3
Ionize 9. Between the collecting electrode 38 and the conductive film 34,
Since a high DC voltage is applied, the electrons or ions generated by the ionization of the ionized gas 39 are collected by the collecting electrode 38, and an electric pulse is generated through the collecting electrode 38, and the calculation unit 12 shown in FIG. Is output to. That is, the fast neutron detector 18 is an ionization chamber that detects fast neutrons by utilizing the recoil phenomenon. By using such an ionization chamber, the influence of, for example, X-rays can be eliminated as much as possible. As is clear from the above description, the fast neutron detector 18 has almost no sensitivity to thermal neutrons and medium-speed neutrons, and can detect only fast neutrons.

Incidentally, the diameter of the fast neutron detector 18 is, for example, 15 cm, and the length thereof is, for example, 20 c.
m. The thickness of the recoil material layer 32 is, for example, 2 mm of polyethylene.

Although the ionization chamber container 30 is cylindrical in this embodiment, it may be spherical or box-shaped, for example.

In the medium speed neutron detector 16, the deceleration layer 4
4 is composed of a moderator such as polyethylene having a certain thickness, and a detector 40 for detecting thermal neutrons is embedded in the moderator 4. A thermal neutron shielding layer 42 is formed outside the moderation layer 44, and the thermal neutron shielding layer 42 is made of, for example, Cd having a predetermined thickness. As understood from this configuration, the medium speed neutrons are decelerated in the moderation layer 44 to become thermal neutrons, and the thermal neutrons are detected by the detector 40. Thermal neutrons coming from the outside are shielded by the thermal neutron shielding layer 42, and only medium-speed neutrons can be selectively and indirectly detected. The thickness of the deceleration layer 44 is adjusted so that it has no sensitivity to fast neutrons. The detector 44 is, for example, ¹⁰
It is an ionization chamber in which BF ₃ gas containing B or ³ He gas is enclosed, or a proportional counter in which such gas is enclosed. When such a detector 40 has a cylindrical shape, its diameter is, for example, 3 cm, and its length is, for example, 4 cm.
cm. In the present embodiment, the deceleration layer 44 is formed, for example, in a columnar shape, and has a diameter of 7 cm and a length of 8 cm, for example. The thermal neutron shielding layer 42 has a thickness of, for example, Cd of 1 mm.

As shown in FIG. 2, a plurality of thermal neutron detectors 14A and 14B are provided in the vicinity of the fast neutron detector 18 and the medium neutron detector 16 in the present embodiment. Each of the thermal neutron detectors 14A and 14B is composed of, for example, an ionization chamber or a proportional counter tube in which a gas that causes the above-described nuclear reaction is sealed, and the same detector 40 is used. In the present embodiment, a thermal neutron shielding layer 46 is provided on the back side of the thermal neutron detectors 14A and 14B to block thermal neutrons flying from the back. Such a thermal neutron shielding layer 4
According to 6, it is possible to give directivity to the detectors 14A and B for thermal neutrons, and it is possible to remove noise coming from behind.

In this embodiment, two detectors for thermal neutrons are provided, but of course, three or four detectors for thermal neutrons may be provided. Alternatively, one detector for thermal neutrons may be used.

The moderator layer 44 is provided in the detector 16 for medium-speed neutrons as described above, and the thermal neutron shielding layer 42 detects the thermal neutrons generated by the moderator layer 44 in the detector 14 for thermal neutrons.
It also has the function of not being detected by A or 14B.
The thermal neutron shielding layer 46 also has such a function.
Therefore, in order to prevent thermal neutrons other than the original thermal neutrons generated in the moderator layer 44 from being detected by the thermal neutron detectors 14A and 14B, at least the thermal neutron shielding layer 4
2 or the thermal neutron shielding layer 46 must be provided. In the present embodiment, the thermal neutron shielding layers 42 and 46 of both are provided to completely shield the thermal neutrons converted into thermal neutrons.

Incidentally, the thermal neutron shielding layer 46 is made of, for example, Cd, like the thermal neutron shielding layer 42, and its thickness is, for example, about 1 mm. The thermal neutron detectors 14A and 14B are configured to be sensitive only to thermal neutrons, that is, they are almost insensitive to fast neutrons and medium speed neutrons.

In this embodiment, the fast neutron detector 18,
Detector 16 for medium-speed neutrons and detector 14A for thermal neutrons,
Each of the B detectors is housed in a case made of metal, for example.

According to the detection unit 10 shown in FIG. 2, since the moderator layer 44, which is heavy in weight, is used only in the detector 16 for medium-speed neutrons, its weight should be halved as compared with the conventional device. You can Further, the detection result can be multiplied by the weighting coefficient for each energy range, and the equivalent dose can be accurately obtained as described above. In addition, the above configuration is not only for measuring the equivalent dose,
It can also be applied to the measurement of dose equivalents currently stipulated by law. Further, in the above-described embodiment, the dedicated detectors are provided in each of the three energy ranges, but more neutron detectors may be provided.

Furthermore, it is expected that the ICRP and legal values will be updated in the future. In that case, the present invention has an advantage that it can be dealt with each time only by changing the weight.

[0034]

As described above, according to the present invention,
It is possible to measure the equivalent dose for each neutron energy range, and to add them to obtain the total equivalent dose. Further, according to the present invention, it is possible to provide a lightweight neutron measuring apparatus capable of measuring neutrons of various energies with high sensitivity and in real time.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a neutron detection device according to the present invention.

FIG. 2 is a cross-sectional view showing a specific configuration of a detection unit.

[Explanation of Codes] 10 detector, 12 arithmetic unit, 14 thermal neutron detector, 16 medium speed neutron detector, 18 speed neutron detector, 24A, 24B, 24C weight multiplier, 26A, 2
6B, 26C, 26D Display, 28 Adder.

Claims (6)

[Claims] 1. A neutron detector comprising a plurality of neutron detectors having detection energy ranges different from each other, and a detection result of each neutron detector is multiplied by a predetermined weighting coefficient for each neutron detector. A neutron measurement apparatus comprising: a multiplication unit that obtains a predetermined dose for each energy range. 2. The neutron measurement according to claim 1, wherein the predetermined dose is an equivalent dose, and an addition unit for adding up the equivalent doses of the respective energy ranges to obtain a total equivalent dose. apparatus. 3. The apparatus according to claim 1, wherein the neutron detector detects a fast neutron, a detector for fast neutrons, a detector for medium speed neutrons, and a detector for thermal neutrons. A neutron measuring device comprising: a detector for thermal neutrons. 4. The apparatus according to claim 3, wherein the fast neutron detector has a recoil material layer inside which recoil particles are generated by fast neutrons, and ionizes inside the recoil particles. Neutron measuring device characterized by comprising an ionization chamber filled with gas 5. The apparatus according to claim 3, wherein the detector for medium-speed neutrons is a moderator layer that decelerates medium-speed neutrons into thermal neutrons, and thermal neutrons that are wrapped by the moderator layer and generated by deceleration. A neutron measuring device comprising: a detector for detecting. 6. The apparatus according to claim 5, wherein at least one of the periphery of the detector for medium-speed neutrons and between the detector for medium-speed neutrons and the detector for thermal neutrons,
A neutron measuring device having a thermal neutron shielding layer for shielding thermal neutrons.