Neutron moisture meter and moisture measurement method

Abstract

The present invention provides a neutron moisture meter and a moisture measurement method that can measure the amount of moisture in a target object with high accuracy or in a short time by increasing the count of neutrons detected by a neutron detector. [Solution] The neutron moisture meter 1 measures the amount of moisture in a target by counting neutrons slowed down by the moisture contained in the target, and comprises a neutron source 10 that generates fast neutrons, a neutron detector 20 that detects neutrons, a calculation device 50 that calculates the amount of moisture in the target 30 based on the neutron detection results, and a neutron moderator 40 installed so as to surround the target 30. The moisture measurement method involves installing the neutron moderator 40 so as to surround the target 30, generating fast neutrons and irradiating the target 30 or the neutron moderator 40 with them, detecting the neutrons slowed down by the target 30 and the neutron moderator 40, and determining the amount of moisture in the target 30 based on the neutron detection results.

Description

Technical Field

[0001] The present invention relates to a neutron moisture meter and a moisture measurement method for measuring the moisture content of a measurement target by counting neutrons decelerated by collision with hydrogen atoms.

Background Art

[0002] In nuclear power plants, chemical plants, bridges, etc., concrete and reinforcing bars are used as materials for structures. Also, metal pipes may be covered with heat insulation materials or concrete. Since these materials corrode and deteriorate according to the moisture content, monitoring of the moisture content is performed. As a means for nondestructively measuring the moisture content of a measurement target, a neutron moisture meter is known.

[0003] A neutron moisture meter irradiates a measurement target with neutrons and measures the moisture content by counting the neutrons decelerated by moisture. When fast neutrons are irradiated onto the measurement target, they collide with hydrogen atoms constituting moisture and are decelerated by elastic scattering. The thermal neutrons generated by the deceleration of the fast neutrons can be discriminated from the fast neutrons and detected. The detected intensity of the thermal neutrons is proportional to the moisture content. Therefore, the moisture content of the measurement target can be measured by detecting the thermal neutrons emitted from the measurement target.

[0004] Patent Document 1 describes a moisture measurement method using a neutron moisture meter. In this method, a test object and a sample of the same material as the test object are irradiated with fast neutrons. After the irradiation of the fast neutrons, thermal neutrons are captured and the neutron count rate is measured. Two types of operations are performed on the test object and the sample, in which the distance between the measurement target and the neutron moisture meter is changed. Based on these results, an accurate water content is measured even when moisture is unevenly distributed.

[0005] In the method described in Patent Document 1, when detecting thermal neutrons emitted from the object under test, neutrons slowed down by substances surrounding the object under test are also detected. For example, when measuring the moisture content of insulation material covering a pipe, neutrons slowed down by liquid present inside the pipe are also detected. Such neutrons cannot be distinguished from neutrons slowed down by moisture in the insulation material. When liquid or other substances are present around the object under test, background noise increases, which presents a problem in that the moisture content cannot be measured with high accuracy.

[0006] Patent Document 2 describes a moisture detection method that can measure the moisture content of insulation material covering pipes, even during the operation of a plant where liquid is present inside the pipes. In this method, pulsed fast neutrons are irradiated onto the insulation material, and thermal neutrons traveling in the opposite direction to the irradiation direction of the fast neutrons are detected. Based on the detection signal of the thermal neutrons, the time change in the intensity of the thermal neutrons is calculated, starting from the time of generation of the fast neutrons. Based on the time change in the intensity of the thermal neutrons and the distance between the neutron injection device and the object being inspected, moisture present inside the insulation material is detected. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 3-94148 [Patent Document 2] Japanese Patent Publication No. 2010-175362 [Overview of the project] [Problems that the invention aims to solve]

[0008] There is a need for a non-destructive and highly accurate technology to measure the moisture content of structures such as plants and bridges, and objects whose internal structure is difficult to confirm. The method described in Patent Document 2 has the problem that the placement of the neutron source and neutron detector is limited because it detects thermal neutrons that travel in the opposite direction to the irradiation direction of fast neutrons. When the placement of these is limited, the number of counts detected by the neutron detector decreases, which reduces the accuracy of the measurement and increases the time required for measurement. In addition, it is more susceptible to the influence of the shape of the object being measured, making it easier for measurement errors to occur. Furthermore, since thermal neutrons emitted from sources other than the object being measured are inevitably detected, there is also the problem of increased background noise. Because the signal-to-noise ratio of the measurement results becomes small, it is difficult to determine the moisture content of the object with high accuracy.

[0009] Therefore, the present invention aims to provide a neutron moisture meter and a moisture measurement method that can increase the number of neutrons detected by a neutron detector and measure the amount of moisture in a target object with high accuracy or in a short time. [Means for solving the problem]

[0010] To solve the aforementioned problems, the neutron moisture meter according to the present invention is a neutron moisture meter that measures the amount of moisture in a measurement target by counting neutrons slowed down by the moisture contained in the measurement target, comprising: a neutron source that generates fast neutrons; a neutron detector that detects neutrons; a calculation device that calculates the amount of moisture in the measurement target based on the detection results of the neutrons; and a neutron moderator installed so as to surround the measurement target, wherein the fast neutrons generated by the neutron source are irradiated onto the measurement target or the neutron moderator, the neutrons slowed down by the measurement target and the neutron moderator are detected by the neutron detector, and the amount of moisture in the measurement target is determined based on the detection results of the neutrons.

[0011] Furthermore, the moisture content measurement method according to the present invention is a moisture content measurement method that measures the amount of moisture in a measurement target by counting neutrons slowed down by the moisture contained in the measurement target, wherein a neutron moderator is installed so as to surround the measurement target, high-speed neutrons are generated and irradiated onto the measurement target or the neutron moderator, neutrons slowed down by the measurement target and the neutron moderator are detected, and the amount of moisture in the measurement target is determined based on the detection results of the neutrons. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a neutron moisture meter and a moisture measurement method that can increase the number of neutrons detected by a neutron detector and measure the amount of moisture in a target object with high accuracy or in a short time. [Brief explanation of the drawing]

[0013] [Figure 1] This diagram shows the configuration of a neutron moisture meter according to the first embodiment of the present invention. [Figure 2] This figure shows the results of a numerical analysis of the relationship between the thermal neutron flux emitted from a measurement target irradiated with fast neutrons and time. [Figure 3] This figure shows the results of a numerical analysis of the relationship between the thermal neutron flux emitted from a measurement target irradiated with fast neutrons and time. [Figure 4] This figure shows the relationship between the cumulative thermal neutron flux emitted from a measurement target irradiated with fast neutrons and the cumulative time. [Figure 5] This figure shows the configuration of a neutron moisture meter according to a second embodiment of the present invention. [Figure 6] This figure shows the results of a numerical analysis of the relationship between the thermal neutron flux emitted from a measurement target irradiated with fast neutrons and time. [Figure 7] This figure shows the relationship between the cumulative thermal neutron flux emitted from a measurement target irradiated with fast neutrons and the cumulative time. [Figure 8] This diagram shows the configuration of a neutron moisture meter according to the third embodiment of the present invention. [Figure 9]This is a diagram showing the configuration of a neutron moisture meter according to a fourth embodiment of the present invention.

Embodiment for Carrying Out the Invention

[0014] Hereinafter, a neutron moisture meter and a moisture measurement method according to an embodiment of the present invention will be described with reference to the drawings. In the following respective drawings, the same reference numerals are assigned to common configurations and redundant descriptions are omitted.

[0015] <First Embodiment> FIG. 1 is a diagram showing the configuration of a neutron moisture meter according to a first embodiment of the present invention. As shown in FIG. 1, the neutron moisture meter 1 according to the first embodiment includes a neutron source 10, a neutron detector 20, and an arithmetic unit 60. The neutron moisture meter 1 is installed in the vicinity of the measurement target 30 when measuring the moisture content. Around the measurement target 30, a neutron moderator 40 is installed so as to surround the measurement target 30.

[0016] In FIG. 1, the neutron moderator 40 is installed so as to surround the measurement target 30 from the side and below. The neutron moderator 40 surrounds the entire circumference of the side surface of the measurement target 30 and is arranged so as to cover the lower surface of the measurement target 30.

[0017] The neutron moisture meter 1 is a scattering type measuring instrument that irradiates the measurement target with neutrons and counts the neutrons decelerated by the moisture contained in the measurement target to measure the moisture content of the measurement target. The neutron moisture meter 1 irradiates the measurement target 30 with fast neutrons. When the fast neutrons collide with hydrogen atoms constituting the moisture contained in the measurement target 30, they are decelerated by elastic scattering. The neutron moisture meter 1 counts neutrons such as thermal neutrons generated when the fast neutrons are decelerated, and obtains the moisture content of the measurement target 30 based on the correlation between the thermal neutron flux and the moisture content.

[0018] In this specification, fast neutrons mean neutrons having a kinetic energy of 0.1 MeV or more and 20 MeV or less. Thermal neutrons mean neutrons having a kinetic energy of 0.001 eV or more and 0.4 eV or less.

[0019] The neutron source 10 is a device that generates fast neutrons and irradiates the measurement target 30 and the neutron moderator 40 with fast neutrons having a single energy. The neutron source 10 is installed in the vicinity of the measurement target 30, which is less than or equal to the diffusion distance of fast neutrons. The neutron source 10 includes a neutron generator that generates fast neutrons, a drive power supply that applies a drive voltage to the neutron generator, and a control device that controls the drive power supply.

[0020] As the neutron source 10, for example, a fast neutron source utilizing the nuclear fusion reaction (DT reaction) between deuterium and tritium can be used. The DT reaction can generate fast neutrons of 14.1 MeV. Since fast neutrons are generated at low voltages of several tens of kV to 100 kV, the neutron moisture meter can be miniaturized. However, as the neutron source 10, other devices may be used as long as they generate fast neutrons. For example, nuclear fusion reactions between deuterium and deuterium (DD reaction), nuclear reactions between protons and lithium-7, nuclear reactions between protons and beryllium-9, spontaneous nuclear fission reactions of californium, nuclear reactions of a mixture of americium and beryllium, nuclear reactions of a mixture of radium and beryllium, etc. can be used.

[0021] The neutron detector 20 is a device that detects neutrons, such as thermal neutrons, emitted from the object to be measured 30. The neutron detector 20 is installed near the object to be measured 30, at a distance less than the diffusion distance of thermal neutrons, so that thermal neutrons emitted from the object to be measured 30 can be detected with high sensitivity. The neutron detector 20 includes a detection unit for detecting neutrons and a power supply that applies a high voltage to the detection unit in order to detect the charge generated by the neutron capture reaction.

[0022] As the neutron detector 20, for example, a proportional counter that utilizes the neutron capture reaction with boron-10 can be used. Since boron-10 is less susceptible to gamma rays, it is suitable for use in environments with high background noise due to gamma rays. However, as the neutron detector 20, other devices may be used as long as they can detect thermal neutrons. For example, a proportional counter that utilizes the neutron capture reaction with helium-3, a scintillator coated with boron-10 or lithium-6 on its surface, or a scintillator doped with boron-10 or lithium-6 in its crystal can be used.

[0023] In Figure 1, the neutron detector 20 is positioned above the object to be measured 30, in parallel with the neutron source 10. No neutron moderator 40 is placed between the neutron source 10, the neutron detector 20, and the object to be measured 30. This structure allows for a reduction in the distance between the neutron source 10 and the object to be measured 30, thereby increasing the high-speed neutron flux to the object to be measured 30. Furthermore, the object to be measured 30 can be easily moved in and out of the neutron moderator 40.

[0024] However, the neutron detector 20 can be installed at any position relative to the measurement target 30, regardless of the positional relationship between the neutron source 10 and the measurement target 30. The neutron detector 20 may be installed on the same side as the neutron source 10 in the direction of irradiation of fast neutrons from the neutron source 10 to the measurement target 30, or it may be installed on the opposite side from the neutron source 10 in the direction of irradiation of fast neutrons. Alternatively, it may be installed in a direction perpendicular to the direction of irradiation of fast neutrons.

[0025] The object to be measured 30 is the object whose moisture content is measured by the neutron moisture meter 1. The object to be measured 30 may be a solid or a semi-solid with fluidity. Preferably, the object to be measured 30 is a structure that has voids to hold moisture inside, or a mixture of solids of various materials. Furthermore, it is preferable that the object to be measured 30 is a structure or mixture that is difficult to measure electrically, such as when there is no place to install electrodes or when multiple materials with different electrical resistances are mixed together. It is also preferable that the object to be measured is a structure or mixture that is difficult to measure optically, such as when the infrared transmittance is low.

[0026] Specific examples of the 30 items to be measured include fuel debris formed from solidified molten nuclear fuel, low-level radioactive waste, high-level radioactive waste, concrete, reinforced concrete, ready-mix concrete, mortar, gravel, soil, ore, sintered bodies, insulation materials used to keep plant equipment warm, and plant equipment covered with insulation materials or exterior materials. Examples of plant equipment include pipes, fittings, valves, tanks such as chemical tanks and oil tanks, vessels such as reaction vessels and mixing vessels, and towers such as reaction towers, distillation towers, and adsorption towers.

[0027] The object to be measured 30 may consist of an object whose moisture content is to be measured and a container containing the object. The container may be formed in any shape, such as cylindrical or rectangular, and in any material, such as metal or resin. Examples of containers include drums. The container may be open or sealed. The neutron source 10, neutron detector 20, and neutron moderator 40 can be installed outside the container containing the object.

[0028] The neutron moderator 40 is a component that slows down neutrons, scattering and slowing down neutrons irradiated onto the object to be measured 30. The neutron moderator 40 is made of a material that has a large scattering cross-section for fast neutrons and a small absorption cross-section for neutrons. The neutron moderator 40 is installed in the vicinity of the object to be measured 30, which is less than or equal to the diffusion distance of fast neutrons, so as to slow down fast neutrons irradiated onto the object to be measured 30 and fast neutrons emitted from the object to be measured 30, and surrounds the object to be measured 30 from at least one direction.

[0029] For example, polyethylene can be used as the neutron moderator 40. Polyethylene with a density of 0.94 kg / m³ can be used. 3 High-density polyethylene, as described above, and deuterated polyethylene, in which hydrogen is replaced with deuterium, are more preferable. Polyethylene can efficiently slow down neutrons while suppressing the generation of secondary radiation. It can also be easily processed and molded. However, other materials may be used as the neutron moderator 40, as long as they slow down fast neutrons. For example, water contained in a container, resin materials such as polypropylene, polystyrene, and phenolic resin, carbon materials such as graphite and carbon fiber, beryllium, and paraffin can be used.

[0030] As shown in Figure 1, the neutron moderator 40 does not have to be installed between the object to be measured 30 and the neutron source 10 or neutron detector 20, or it may be installed between the object to be measured 30 and the neutron source 10 or neutron detector 20. The neutron moderator 40 can be installed, for example, in a configuration that surrounds the object to be measured 30 from all directions, or in a configuration that surrounds the object to be measured 30 from directions other than the direction in which the neutron source 10 or neutron detector 20 is installed. The neutron moderator 40 can be installed considering the irradiation angle of neutrons from the neutron source 10 and the diffusion distribution of fast neutrons scattered from the object to be measured 30.

[0031] As the neutron source 10, a pulsed neutron source that generates pulsed fast neutrons may be used. By applying a pulsed drive voltage to the neutron source, fast neutrons can be generated in an intermittent pulsed manner. By generating pulsed fast neutrons and irradiating the object to be measured 30 or the neutron moderator 40, and detecting thermal neutrons originating from each pulse of fast neutrons, the flight time of the thermal neutrons from the time of thermal neutron generation to the time of thermal neutron detection, and the flight distance of the thermal neutrons from the thermal neutron generation location to the thermal neutron detection location can be estimated based on the time from the time of fast neutron generation to the time of thermal neutron generation. Since the location of thermal neutron generation can be identified based on the flight time and flight distance of the thermal neutrons, the distribution of moisture in the object to be measured 30 can be determined.

[0032] The calculation unit 60 is a device that calculates the amount of moisture in the object to be measured 30. Based on the detection results detected by the neutron detector 20, the calculation unit 60 calculates the amount of moisture in the object to be measured 30 and the distribution of moisture in the object to be measured 30. The calculation unit 60 includes a preamplifier that amplifies the detection signal, a converter that converts the current signal into a voltage signal, a pulse height analyzer that performs pulse height analysis on the output signal, and a processing unit that controls the equipment and performs calculations.

[0033] The calculation unit 60 can determine the amount of moisture present inside and on the surface of the object to be measured 30 based on the detection results detected by the neutron detector 20. The count rate detected by the neutron detector 20 can be calibrated using a calibration curve that shows the relationship between the count rate and the amount of moisture. By fitting the count rate corresponding to the neutron flux to the calibration curve, the average amount of moisture and the amount of moisture per unit volume of the object to be measured 30 can be determined. The calibration curve can be determined in advance using the object to be measured 30 with a known amount of moisture or a material equivalent to the object to be measured 30.

[0034] Furthermore, when pulsed fast neutrons are used for measurement, the computing unit 60 can determine the profile of thermal neutrons emitted from the object to be measured 30 based on the detection results detected by the neutron detector 20, and based on the thermal neutron profile, it can determine the amount of moisture present inside and on the surface of the object to be measured 30, as well as the distribution of moisture in the object to be measured 30. The amount of moisture in the object to be measured 30 can be determined according to the distance between the thermal neutron generation location and the detection location. The distribution of moisture in the object to be measured 30 can be determined as a two-dimensional or three-dimensional distribution.

[0035] The thermal neutron profile is spectral data that shows the relationship between the thermal neutron flux detected by the neutron detector 20 and the time elapsed since the thermal neutron was generated. The thermal neutron profile can be determined by irradiating with pulsed fast neutrons and detecting the thermal neutrons originating from each pulse of fast neutrons, based on the thermal neutron flux detected by the neutron detector 20 and the time elapsed from the generation of fast neutrons to the detection of the thermal neutrons.

[0036] As the processing unit constituting the arithmetic unit 60, for example, a PC capable of executing a program to calculate the amount of moisture can be used. The processing unit constituting the arithmetic unit 60 may include a CPU (Central Processing Unit), memory as a main memory for storing programs and data, secondary memory for storing programs and data, input devices such as a keyboard and mouse, and output devices such as a display.

[0037] The processing unit constituting the calculation device 60 can output as an image the calculation results of the amount of moisture present inside and on the surface of the object to be measured 30, as well as the calculation results of the moisture distribution in the object to be measured 30. When pulsed fast neutrons are used for measurement, the processing unit constituting the calculation device 60 can output the counting rate of neutrons detected by the neutron detector 20 for each pulse of fast neutrons, the average value of the amount of moisture in the object to be measured 30, and the two-dimensional and three-dimensional distribution of moisture in the object to be measured 30.

[0038] Furthermore, a neutron reflector may be installed outside the neutron moderator 40 so as to surround the object to be measured 30. The neutron reflector is made of a material that has a large neutron scattering cross-section, a small neutron absorption cross-section, and an atomic number greater than that of the neutron moderator 40. Examples of neutron reflectors include lead and iron.

[0039] The neutron moisture meter 1 may be portable or stationary, depending on the type and size of the object to be measured 30. Depending on the type and size of the object to be measured 30, the neutron moisture meter 1 may be a surface type in which the neutron detector 20 is placed on the surface of the object to be measured 30, or an insertion type in which a probe-shaped neutron detector 20 is inserted into the inside of the object to be measured 30.

[0040] The moisture content measurement method according to the first embodiment is a method for measuring the moisture content of a target by counting neutrons slowed down by the moisture contained in the target. In this embodiment, the moisture content measurement method involves setting up a neutron moderator so as to surround the target, generating fast neutrons and irradiating the target or the neutron moderator with them, detecting the neutrons slowed down by the target and the neutron moderator, and determining the moisture content of the target based on the neutron detection results.

[0041] In the moisture content measurement method according to this embodiment, the moisture content of the object to be measured is determined based on the correlation between the neutron flux at the detection position and the moisture content of the object to be measured. The correlation between the neutron flux and the moisture content of the object to be measured may be corrected according to the neutron attenuation rate due to the neutron moderator. The neutron attenuation rate due to the neutron moderator can be determined in advance using the neutron moderator used for measuring the moisture content or an equivalent system.

[0042] In the moisture measurement method according to this embodiment, fast neutrons may be irradiated toward the object to be measured, toward the neutron moderator, or toward both. The neutrons detected are thermal neutrons or other neutrons that have been slowed by both the object to be measured and the neutron moderator. The amount of moisture in the object to be measured may be the amount of moisture present inside or on the surface of the object, or the two-dimensional or three-dimensional distribution of moisture in the object may be determined.

[0043] In the moisture measurement method according to this embodiment, pulsed fast neutrons may be used for measurement. Pulsed fast neutrons are generated and irradiated onto the object to be measured or a neutron moderator, and neutrons originating from each pulse of fast neutrons are detected in synchronization with the generation of fast neutrons. Based on the detection results of the neutrons for each pulse, the amount of moisture present inside or on the surface of the object to be measured, and the distribution of moisture in the object to be measured can be determined.

[0044] The moisture measurement method according to the first embodiment can be performed using a neutron moisture meter 1. The neutron moisture meter 1 is installed near the measurement target 30 surrounded by a neutron moderator 40. The neutron moisture meter 1 is pre-prepared with a calibration curve showing the relationship between the neutron counting rate detected by the neutron detector 20 and the moisture content of the measurement target 30, as well as information indicating the distance between the measurement target 30 and the neutron detector 20. Furthermore, a correction curve showing the neutron attenuation rate due to the neutron moderator 40 and a correction curve for correcting the moisture content of the measurement target 30 according to its assumed specific gravity can also be pre-prepared.

[0045] During moisture content measurement, the calculation unit 60 controls the neutron source 10 to irradiate the measurement target 30 or the neutron moderator 40 with fast neutrons generated by the neutron source 10. When pulsed fast neutrons are used for measurement, the power supply for the neutron source 10 operates based on a clock signal generated by a clock generator and applies a drive voltage to the neutron source at predetermined time intervals. The neutron source to which the drive voltage is applied emits fast neutrons in pulses at predetermined time intervals.

[0046] When fast neutrons emitted from the neutron source 10 collide with hydrogen atoms and other elements that make up the water contained in the object being measured 30, they are slowed down by elastic scattering and become thermal neutrons. As a result, the neutron flux detected by the neutron detector 20 changes depending on the amount of water in the object being measured 30 and the distribution of water in the object being measured 30. The neutron flux is proportional to the amount of water contained in the object being measured 30. Therefore, based on the neutron flux and thermal neutron profiles, the amount of water present inside and on the surface of the object being measured 30, and the distribution of water in the object being measured 30 can be determined.

[0047] In the thermal neutron profile, a peak is observed where the thermal neutron flux has reached its maximum value. This is because the thermal neutron flux detected by the neutron detector 20 increases as the number of fast neutrons colliding with hydrogen atoms constituting water increases, and decreases as the thermal neutrons diffuse. The position of this peak indirectly indicates the flight time of the thermal neutrons from the time of their generation to the time of their detection. Therefore, by identifying the position of this peak, the location of the thermal neutron generation, i.e., the location of water in the measurement target 30, can be estimated.

[0048] The flight speed of fast neutrons is significantly faster than that of thermal neutrons. Therefore, the time from the generation of a fast neutron to the detection of a thermal neutron can be ignored in calculations. Thus, by counting the time from the generation of a fast neutron to the detection of a thermal neutron for each pulse, the flight time of the thermal neutron from generation to detection can be estimated. Since the location of thermal neutron generation can be identified based on the flight time and distance of the thermal neutron, the distribution of moisture in the measurement target 30 can be determined.

[0049] The neutron source 10 may or may not have directionality in the direction of neutron emission. The fast neutrons emitted from the neutron source 10 may be directed toward the object to be measured 30, toward the neutron moderator 40, or toward both. The neutron detector 20 detects thermal neutrons that have been slowed down by both the object to be measured 30 and the neutron moderator 40.

[0050] For example, fast neutrons may be directly incident on the object to be measured 30 from the neutron source 10, scattered by the object to be measured 30, incident on the neutron moderator 40, slowed down by the neutron moderator 40, incident on the object to be measured 30, slowed down by the moisture in the object to be measured 30, and then detected by the neutron detector 20. Alternatively, fast neutrons may be incident on the neutron moderator 40 from the neutron source 10, slowed down by the neutron moderator 40, incident on the object to be measured 30, slowed down by the moisture in the object to be measured 30, and then detected by the neutron detector 20.

[0051] When fast neutrons are emitted from the neutron source 10, the computing unit 60 controls the neutron detector 20 to detect neutrons that have been decelerated by the measurement target 30 and the neutron moderator 40. When pulsed fast neutrons are used for measurement, the neutron detector 20 performs differential detection in synchronization with the timing of the emission of fast neutrons from the neutron source 10, and detects neutrons originating from each pulse of fast neutron generated by the neutron source 10. Based on a clock signal, the detection unit of the neutron detector 20 performs sampling at multiple time intervals shorter than the time interval between fast neutron emission.

[0052] When a neutron is detected by the neutron detector 20, the calculation unit 60 integrates the counts recorded by the neutron detector 20 to determine the count rate detected by the neutron detector 20. The calculation unit 60 reads data from a pre-determined calibration curve and applies the count rate detected by the neutron detector 20 to the calibration curve that shows the relationship between the count rate and the amount of moisture to determine the amount of moisture in the object being measured 30 corresponding to the count rate of neutrons detected by the neutron detector 20.

[0053] Alternatively, when pulsed fast neutrons are used for measurement, the computing unit 60 may determine a thermal neutron profile showing the relationship between the thermal neutron flux detected by the neutron detector 20 and the time calculated from the time of thermal neutron generation. The thermal neutron flux detected by the neutron detector 20 is determined as the thermal neutron counting rate by the neutron detector 20. The time calculated from the time of thermal neutron generation indicates the time of flight of the thermal neutron from the time of thermal neutron generation to the time of thermal neutron detection, and is determined based on the clock signal and input data.

[0054] For example, when thermal neutrons are detected by the neutron detector 20, the electrical pulse signal sampled by the detection of thermal neutrons is amplified, converted into a voltage signal, and then subjected to pulse height analysis. In pulse height analysis, the counting rate of thermal neutrons by the neutron detector 20 is determined for each pulse height by counting the pulse height values. By setting an appropriate threshold, noise such as gamma rays is removed. The counting rate data is stored in the processing unit of the arithmetic unit 60.

[0055] Thermal neutron profiles can be collected for each irradiation axis relative to the measurement target 30 by performing multiple measurements while changing the positional relationship between the neutron source 10 and the neutron detector 20 and the measurement target 30. By performing multiple measurements with changed positional relationships, the two-dimensional and three-dimensional distribution of water in the measurement target 30 can be determined. The water distribution may also be determined using X-ray CT (Computed Tomography) analysis, a gamma-ray densimeter, a transmission-type neutron moisture meter, etc.

[0056] The relationship between the counting rate and the moisture content may be corrected according to the neutron attenuation rate due to the neutron moderator 40 and the assumed specific gravity of the object being measured 30. Similarly, the thermal neutron profile may be corrected according to the thermal neutron attenuation rate due to the neutron moderator 40 and the assumed specific gravity of the object being measured 30. The calculation device 60 can calculate the corrected moisture content by, for example, reading the calibration curve or calibration result and performing corrections such as inverse calculations by dividing by the attenuation rate or assumed specific gravity.

[0057] Figure 2 shows the results of a numerical analysis of the relationship between the thermal neutron flux emitted from a measurement target irradiated with fast neutrons and time. Figure 2 shows the results of a numerical analysis of the thermal neutron flux emitted from a measurement target when it is irradiated with fast neutrons, using Monte Carlo simulation, and the results are shown for the case where the measurement target is not surrounded by a neutron moderator.

[0058] The simulation was performed using a calculation system that simulated a measurement target of a predetermined shape as shown in Figure 1. Boundary conditions were set to infinity around the measurement target without the use of a neutron moderator. The neutron source was set on the upper surface of the measurement target. The tally for counting thermal neutron flux was also set on the upper surface of the measurement target.

[0059] In the simulation, the thermal neutron flux emitted from the upper surface of the object being measured was calculated every 1 μs, and the calculation results were plotted against the measurement time. Thermal neutrons with an energy of 0.4 eV or less were counted. In Figure 2, the horizontal axis represents the time [μs] calculated from the start of fast neutron irradiation, and the vertical axis represents the thermal neutron flux [cm²] per 1 μs. -2 ·s -1 This indicates ].

[0060] The simulations were performed on three different measurement targets: one with a water content of 0.1 wt%, one with a water content of 1.0 wt%, and one with a water content of 20 wt%. The measurement targets were radioactive materials that spontaneously emit fast neutrons. In the simulations, the thermal neutron flux generated by the deceleration of fast neutrons irradiated onto the measurement target, as well as the thermal neutron flux generated by the deceleration of fast neutrons spontaneously emitted from the measurement target, were determined as background noise.

[0061] Typical neutron detectors are primarily sensitive to thermal neutrons. The measurement results obtained by typical neutron detectors are thought to be proportional to the number of thermal neutrons and the count rate, which is the rate of change of the number of thermal neutrons per unit time. Therefore, when using a typical neutron detector, if thermal neutrons emitted from the object being measured are detected, a count rate similar to the trend of the thermal neutron flux shown in Figure 2 can be obtained.

[0062] As shown in Figure 2, when the water content was 0.1 wt% or 1.0 wt%, the thermal neutron flux was lower than the background noise, and the thermal neutron count rate was also lower than the background noise. Because there were few fast neutrons colliding with the hydrogen atoms that make up the water, and the thermal neutron count was small, only some of the detection results were plotted. If the object being measured is not surrounded by a neutron moderator, the count and count rate will be small, making it difficult to measure the water content of the object with high precision or in a short time.

[0063] Figure 3 shows the results of a numerical analysis of the relationship between the thermal neutron flux emitted from a measurement target irradiated with fast neutrons and time. Figure 3 shows the results of a numerical analysis of the thermal neutron flux emitted from a measurement target when it is irradiated with fast neutrons, using Monte Carlo simulation, and the results are shown when the measurement target is surrounded by a neutron moderator.

[0064] The simulation was performed using a calculation system that simulated a predetermined shape of the measurement target and neutron moderator, as shown in Figure 1. Neutron moderators were set up around the measurement target so as to surround it from the sides and below. The neutron source was set up on the top surface of the measurement target. The tally for counting thermal neutron flux was also set up on the top surface of the measurement target.

[0065] In the simulation, the thermal neutron flux emitted from the upper surface of the object being measured was calculated every 1 μs, and the calculation results were plotted against the measurement time. Thermal neutrons with an energy of 0.4 eV or less were counted. In Figure 3, the horizontal axis represents the time [μs] calculated from the start of fast neutron irradiation, and the vertical axis represents the thermal neutron flux [cm²] per 1 μs. -2 ·s -1 This indicates ].

[0066] The simulation was performed for three different measurement targets, similar to the case in Figure 1, with water content of 0.1 wt%, 1.0 wt%, and 20 wt%. The measurement targets were radioactive materials that spontaneously emit fast neutrons. In the simulation, the thermal neutron flux generated by the deceleration of fast neutrons irradiated onto the measurement target, as well as the thermal neutron flux generated by the deceleration of fast neutrons spontaneously emitted from the measurement target, were determined as background noise.

[0067] As shown in Figure 3, in all cases where the water content was 0.1 wt%, 1.0 wt%, or 20 wt%, the thermal neutron flux became larger than the background noise over time, and the thermal neutron count rate also became larger than the background noise. This suggests that arranging neutron absorbers around the object being measured improves the sensitivity of measuring the water content of the object, even when the water content of the object is low.

[0068] A typical neutron source has a three-dimensional spread in the direction from which neutrons are emitted. Some of the neutrons emitted from a typical neutron source diffuse into the surroundings without directly impacting the object being measured. In the simulation shown in Figure 2, since the object being measured is not surrounded by a neutron-absorbing material, the fast neutrons that did not directly impact the object are not used to measure the moisture content and are instead diffused into the surroundings and lost.

[0069] On the other hand, in the simulation shown in Figure 3, since the object being measured is surrounded by a neutron moderator, fast neutrons that did not directly incident on the object can still be incident on it through scattering by the neutron moderator. Furthermore, neutrons that were incident on the object but not sufficiently slowed down can be incident on the neutron moderator to slow them down, and then incident on the object again through scattering by the neutron moderator. As a result, the number of thermal neutrons used to measure the moisture content can be increased.

[0070] Furthermore, in the simulation shown in Figure 3, since the object being measured is surrounded by a neutron moderator, the fast neutrons generated by the neutron source can be slowed down by scattering by the neutron moderator. For example, when using a DT reaction, fast neutrons with an energy of 14.1 MeV are generated. Even if such high-energy fast neutrons are irradiated onto the water in the object being measured, they may not be slowed down to thermal neutrons. From the perspective of detecting thermal neutrons slowed down by water, it may be more efficient to inject fast neutrons with lower kinetic energy into the water. By injecting fast neutrons with reduced kinetic energy into the object being measured, the number of thermal neutrons used to measure the amount of water can be increased.

[0071] As shown in Figure 3, the thermal neutron flux counted by the neutron detector varies depending on the water content of the sample being measured. This difference in thermal neutron flux occurs only for a short period of time, up to a few microseconds after the start of fast neutron irradiation. As the measurement time progresses, the number of neutron scattering experiences increases, and the neutron energy and neutron flight paths become more homogenized. Therefore, it is preferable to limit the detection of thermal neutrons by the neutron detector to a short period of time from the start of fast neutron irradiation.

[0072] Figure 3 shows that when comparing the cases with a water content of 0.1 wt% and 20 wt%, a difference in thermal neutron flux occurs during the period from the start of fast neutron irradiation until approximately 30 μs has elapsed. Therefore, when the object being measured is surrounded by a neutron moderator, it is preferable to detect thermal neutrons with a neutron detector within 30 μs from the start of fast neutron irradiation.

[0073] Figure 4 shows the relationship between the cumulative thermal neutron flux emitted from a measurement target irradiated with fast neutrons and the cumulative time. Figure 4 shows the results of a numerical analysis of the thermal neutron flux emitted from a measurement target when it is irradiated with fast neutrons, using Monte Carlo simulation, and the results are shown when the measurement target is surrounded by a neutron moderator. The cumulative thermal neutron flux is the cumulative value of the thermal neutron flux accumulated over time from the start of fast neutron irradiation.

[0074] The integrated thermal neutron flux was calculated based on the analysis results shown in Figure 3. The integrated thermal neutron flux was normalized using the integrated result including background noise. The normalized calculation result was plotted against the integration time. As thermal neutrons, neutrons with an energy of 0.4 eV or less were counted. In Figure 4, the horizontal axis represents the integration time [μs] calculated from the start of fast neutron irradiation, and the vertical axis represents the normalized integrated thermal neutron flux.

[0075] As shown in Figure 4, there is a difference in the integrated thermal neutron flux between the cases with a water content of 0.1 wt% and 1.0 wt% during the period from the start of fast neutron irradiation to approximately 8 μs. Therefore, it can be said that the amount of water in the sample can be quantitatively evaluated within the range of water content of 1.0 wt% or less during the period from the start of fast neutron irradiation to several 8 μs.

[0076] As shown in Figure 4, comparing the cases with a water content of 1.0 wt% and 20 wt%, there is a difference in the integrated thermal neutron flux during the period from the start of fast neutron irradiation to approximately 30 μs. When the water content is low, such as 1.0 wt%, it is necessary to complete the counting of thermal neutrons within a short time, such as less than approximately 10 μs from the start of fast neutron irradiation. This is because as the number of neutron scattering experiences increases, the neutron energy and neutron flight paths become more homogenized. On the other hand, when the water content is high, such as 20 wt%, the counting of thermal neutrons can be continued until at least 30 μs has elapsed.

[0077] In Figure 4, integration begins from the start of fast neutron irradiation. However, in actual measurements, a pulsed drive voltage is applied when fast neutrons are emitted, generating electromagnetic waves that cause noise. In addition, fast neutrons emitted from the neutron source undergo nuclear reactions with surrounding material, generating a large amount of previously emitted gamma rays that also cause noise. Therefore, it is preferable to start neutron detection after a predetermined time has elapsed from the start of fast neutron irradiation, for example, after 1 to 3 μs has elapsed.

[0078] In the neutron moisture meter 1 and moisture measurement method according to the first embodiment, it is preferable that the neutron detector 20 starts detecting neutrons with a delay from the generation of fast neutrons by the neutron source 10, and stops detecting neutrons when a preset measurement time has elapsed. It is preferable that the neutron detector 20 starts detecting neutrons when 1 μs or more has elapsed from the generation of fast neutrons, and it is preferable that it stops detecting neutrons within 30 μs from the generation of fast neutrons.

[0079] According to the neutron moisture meter 1 and moisture measurement method described above, a neutron moderator is installed surrounding the object to be measured, so that fast neutrons emitted from the neutron source can be slowed down before being incident on the object to be measured. In addition, fast neutrons that are incident on the object to be measured and scattered can be scattered and slowed down by the neutron moderator outside the object to be measured, and then incident on the object again. The neutron moderator can reduce the kinetic energy of fast neutrons and randomize the direction of their flight.

[0080] This effect makes it easier for fast neutrons emitted from the neutron source to enter the object being measured and collide with hydrogen atoms that make up the water inside or on the surface of the object. As a result, a large amount of neutrons, such as thermal neutrons, that need to be detected to measure the amount of water are emitted from the water inside the object being measured. This results in an increase in the neutron count and count rate measured by the neutron detector.

[0081] Therefore, even when the neutron flux emitted by the neutron source is small, or when the amount of moisture present inside or on the surface of the object being measured is minute, increasing the neutron count and count rate makes it possible to measure the amount of moisture in the object with high precision. Furthermore, increasing the neutron count and count rate makes it possible to measure the amount of moisture in the object in a short amount of time.

[0082] Furthermore, with the neutron moisture meter 1 and moisture measurement method described above, a neutron moderator is installed to surround the object to be measured, thereby increasing the high-speed neutron flux in the space where the object to be measured is installed. In the space where the object to be measured is installed, high-speed neutrons are present at high density, and the flight direction of the high-speed neutrons is randomized. Conventional neutron moisture meters are configured to detect neutrons scattered in the opposite direction to the neutron irradiation direction, so it was necessary to install the neutron detector in an appropriate location. In contrast, when the flight direction of high-speed neutrons is randomized, the bias in the flight direction of neutrons emitted from moisture is reduced, and the restrictions on the installation location of the neutron detector are relaxed.

[0083] <Second Embodiment> Figure 5 shows the configuration of a neutron moisture meter according to a second embodiment of the present invention. As shown in Figure 5, the neutron moisture meter 2 according to the second embodiment comprises a neutron source 10, a neutron detector 20, and a computing device 60. The neutron moisture meter 2 is installed near the object to be measured 30 when measuring the amount of moisture. A neutron moderator 40 and a neutron absorber 50 are installed around the object to be measured 30 so as to surround the object to be measured 30.

[0084] In Figure 5, the neutron moderator 40 is installed so as to surround the object to be measured 30 from the side and below. The neutron moderator 40 surrounds the entire side of the object to be measured 30 and is positioned to cover the bottom surface of the object to be measured 30.

[0085] Furthermore, the neutron absorber 50 is installed inside the neutron moderator 40, surrounding the object to be measured 30 from the sides and below. Inside the neutron moderator 40, the neutron absorber 50 is positioned to surround the entire side of the object to be measured 30 and to cover the bottom surface of the object to be measured 30.

[0086] The neutron moisture meter 2 is a scattering-type measuring instrument that measures the amount of moisture by irradiating the object to be measured with neutrons and counting the neutrons that are slowed down by the moisture contained in the object. The difference between the neutron moisture meter 2 according to the second embodiment and the neutron moisture meter 1 described above is that a neutron absorber 50 is installed between the object to be measured 30 and the neutron moderator 40. The other main components of the neutron moisture meter 2 are the same as those of the neutron moisture meter 1 described above.

[0087] The neutron absorber 50 is a component that absorbs neutrons, primarily absorbing thermal neutrons incident on the object to be measured 30. The neutron absorber 50 is made of a material with a large thermal neutron absorption cross-section. The neutron absorber 50 is installed between the object to be measured 30 and the neutron moderator 40 so as to surround the object to be measured 30 from at least one direction. With the neutron absorber 50, thermal neutrons generated by the deceleration of fast neutrons by the neutron moderator 40 are absorbed before they can enter the object to be measured 30 or the neutron detector 20.

[0088] For example, cadmium can be used as the neutron absorber 50. Cadmium provides a large absorption cross-section for thermal neutrons and allows for macroscopically efficient absorption in the form of metal foil or metal plate. However, other materials may be used as the neutron absorber 50, as long as they absorb unwanted thermal neutrons. For example, water contained in a container, boron compounds such as boron carbide containing boron, boron-containing alloys, gadolinium, hafnium, and their alloys can be used.

[0089] As shown in Figure 5, it is preferable that the neutron absorber 50 is not placed between the object to be measured 30 and the neutron source 10 or the neutron detector 20. The neutron absorber 50 can be placed, for example, between the object to be measured 30 and the neutron moderator 40, or between the neutron moderator 40 and the neutron detector 20, but not between the object to be measured 30 and the neutron detector 20. The neutron absorber 50 can be placed considering the irradiation angle of neutrons from the neutron source 10 and the diffusion distribution of thermal neutrons scattered from the neutron moderator 40.

[0090] Furthermore, a neutron reflector may be installed outside the neutron moderator 40 so as to surround the object to be measured 30. The neutron reflector is made of a material that has a large neutron scattering cross-section, a small neutron absorption cross-section, and an atomic number greater than that of the neutron moderator 40. Examples of neutron reflectors include lead and iron.

[0091] The neutron moisture meter 2 may be portable or stationary, depending on the type and size of the object to be measured 30. Depending on the type and size of the object to be measured 30, the neutron moisture meter 2 may be a surface type in which the neutron detector 20 is placed on the surface of the object to be measured 30, or an insertion type in which a probe-shaped neutron detector 20 is inserted into the inside of the object to be measured 30.

[0092] The moisture content measurement method according to the second embodiment is a method for measuring the moisture content of a measurement target by counting neutrons slowed down by the moisture contained in the measurement target. In this embodiment, the moisture content measurement method involves setting up a neutron moderator so as to surround the measurement target, setting up a neutron absorber between the measurement target and the neutron moderator, generating fast neutrons and irradiating the measurement target or the neutron moderator, absorbing the neutrons emitted from the neutron moderator with the neutron absorber, detecting the neutrons slowed down by the measurement target and the neutron moderator, and determining the moisture content of the measurement target based on the neutron detection results.

[0093] In the moisture content measurement method according to this embodiment, the moisture content of the object to be measured is determined based on the correlation between the neutron flux at the detection position and the moisture content of the object to be measured. The correlation between the neutron flux and the moisture content of the object to be measured may be corrected according to the neutron attenuation rate due to the neutron moderator or neutron absorber. The neutron attenuation rate due to the neutron moderator or neutron absorber can be determined in advance using the neutron moderator or neutron absorber used for measuring the moisture content or an equivalent system.

[0094] In the moisture measurement method according to this embodiment, fast neutrons may be irradiated toward the object to be measured, toward the neutron moderator, or toward both. Fast neutrons may be irradiated so as to pass through the neutron absorber, or they may be irradiated so as not to pass through the neutron absorber. As for the neutrons, neutrons such as thermal neutrons slowed by both the object to be measured and the neutron moderator are detected. The amount of moisture in the object to be measured may be the amount of moisture present inside or on the surface of the object, or the two-dimensional or three-dimensional distribution of moisture in the object may be determined.

[0095] In the moisture measurement method according to this embodiment, pulsed fast neutrons may be used for measurement. Pulsed fast neutrons are generated and irradiated onto the object to be measured or a neutron moderator, and neutrons originating from each pulse of fast neutrons are detected in synchronization with the generation of fast neutrons. Based on the detection results of the neutrons for each pulse, the amount of moisture present inside or on the surface of the object to be measured, and the distribution of moisture in the object to be measured can be determined.

[0096] The moisture measurement method according to the second embodiment can be performed using a neutron moisture meter 2. The neutron moisture meter 2 is installed near the measurement target 30, which is surrounded by a neutron moderator 40 and a neutron absorber 50. The neutron moisture meter 2 is pre-prepared with a calibration curve showing the relationship between the neutron counting rate detected by the neutron detector 20 and the moisture content of the measurement target 30, as well as information indicating the distance between the measurement target 30 and the neutron detector 20. Furthermore, correction curves showing the neutron attenuation rate due to the neutron moderator 40 and the neutron absorber 50, and correction curves for correcting the moisture content of the measurement target 30 according to its assumed specific gravity can be pre-prepared.

[0097] The moisture measurement method using the neutron moisture meter 2 can be carried out in the same manner as the moisture measurement method using the neutron moisture meter 1 described above. The calibration curve can be determined in advance using a system in which the object to be measured 30 is surrounded by a neutron moderator 40 and a neutron absorber 50. When measuring the amount of moisture, the calculation unit 60 controls the neutron source 10 to irradiate the object to be measured 30 or the neutron moderator 40 with fast neutrons generated by the neutron source 10. The neutrons emitted from the neutron moderator 40 are absorbed by the neutron absorber 50, and the neutron detector 20 is controlled to detect neutrons that have been slowed down by the object to be measured 30 and the neutron moderator 40.

[0098] When a neutron is detected by the neutron detector 20, the calculation unit 60 integrates the counts recorded by the neutron detector 20 to determine the count rate detected by the neutron detector 20. Alternatively, when pulsed fast neutrons are used for measurement, the calculation unit 60 may determine a thermal neutron profile that shows the relationship between the thermal neutron flux detected by the neutron detector 20 and the time elapsed since the generation of the thermal neutrons. The relationship between the count rate and the moisture content, as well as the thermal neutron profile, may be corrected according to the neutron decay rate due to the neutron moderator 40 and the neutron absorber 50, and the assumed specific gravity of the object being measured 30.

[0099] Figure 6 shows the results of a numerical analysis of the relationship between the thermal neutron flux emitted from a measurement target irradiated with fast neutrons and time. Figure 6 shows the results of a numerical analysis of the thermal neutron flux emitted from a measurement target when it is irradiated with fast neutrons, using Monte Carlo simulation, where the measurement target is surrounded by a neutron moderator and a neutron absorber is placed between the measurement target and the neutron moderator.

[0100] The simulation was performed using a calculation system that simulated a predetermined shape of the measurement target, as well as neutron moderators and neutron absorbers, as shown in Figure 5. Neutron moderators were set up around the measurement target, surrounding it from the sides and below. Neutron absorbers were set up between the measurement target and the neutron moderators. The neutron source was set up on the top surface of the measurement target. The tally for counting thermal neutron flux was also set up on the top surface of the measurement target.

[0101] In the simulation, the thermal neutron flux emitted from the upper surface of the object being measured was calculated every 1 μs, and the calculation results were plotted against the measurement time. Thermal neutrons with an energy of 0.4 eV or less were counted. In Figure 6, the horizontal axis represents the time [μs] calculated from the start of fast neutron irradiation, and the vertical axis represents the thermal neutron flux [cm²] per 1 μs. -2 ·s -1 This indicates ].

[0102] The simulation was performed for three different measurement targets, similar to the case in Figure 1, with water content of 0.1 wt%, 1.0 wt%, and 20 wt%. The measurement targets were radioactive materials that spontaneously emit fast neutrons. In the simulation, the thermal neutron flux generated by the deceleration of fast neutrons irradiated onto the measurement target, as well as the thermal neutron flux generated by the deceleration of fast neutrons spontaneously emitted from the measurement target, were determined as background noise.

[0103] As shown in Figure 6, the thermal neutron flux and thermal neutron count rate increased with increasing water content. This increasing trend continued for at least 50 μs from the start of fast neutron irradiation. By placing neutron absorbers around the object being measured, and also between the object and the neutron moderator, the sensitivity of measuring the water content of the object can be improved, even when the water content of the object is low.

[0104] As shown in Figure 3, when the object being measured is surrounded only by a neutron moderator, thermal neutrons slowed down by the moderator may reach the neutron detector and be detected. Since these thermal neutrons are not slowed down by moisture present inside or on the surface of the object being measured, they can be a source of error when measuring the moisture content of the object.

[0105] On the other hand, as shown in Figure 6, when a neutron absorber is placed between the object being measured and the neutron moderator, thermal neutrons slowed by the neutron moderator are absorbed by the neutron absorber, preventing them from reaching the neutron detector. Only thermal neutrons slowed by moisture present inside or on the surface of the object being measured can reach the neutron detector. Therefore, the amount of moisture in the object can be measured with greater accuracy.

[0106] Figure 7 shows the relationship between the cumulative thermal neutron flux emitted from a measurement target irradiated with fast neutrons and the cumulative time. Figure 7 shows the results of a numerical analysis of the thermal neutron flux emitted from a measurement target when it is irradiated with fast neutrons, using Monte Carlo simulation, where the measurement target is surrounded by a neutron moderator and a neutron absorber is placed between the measurement target and the neutron moderator. The cumulative thermal neutron flux is the cumulative value of the thermal neutron flux accumulated over time from the start of fast neutron irradiation.

[0107] The integrated thermal neutron flux was calculated based on the analysis results shown in Figure 6. The integrated thermal neutron flux was normalized using the integrated result including background noise. The normalized calculation result was plotted against the integration time. As thermal neutrons, neutrons with an energy of 0.4 eV or less were counted. In Figure 7, the horizontal axis represents the integration time [μs] calculated from the start of fast neutron irradiation, and the vertical axis represents the normalized integrated thermal neutron flux.

[0108] As shown in Figure 7, the curve showing the relationship between the integrated thermal neutron flux and integration time reaches its maximum value between 20 μs and 30 μs after the start of fast neutron irradiation, and gradually decreases as the measurement time progresses. This is because, as shown in Figure 6, each curve reaches its maximum value between 20 and 30 μs after the start of fast neutron irradiation, and the integrated value of background noise shows a monotonically increasing value.

[0109] As shown in Figure 7, regardless of whether the water content is 0.1 wt%, 1.0 wt%, or 20 wt%, there is a difference in the cumulative thermal neutron flux during the period from the start of fast neutron irradiation until approximately 100 μs has elapsed. Therefore, if a neutron absorber is installed, thermal neutron counting can be continued until at least 100 μs has elapsed. However, from the viewpoint of measuring the amount of water with high accuracy, it is preferable to end the detection of thermal neutrons before 50 μs has elapsed.

[0110] In Figure 7, integration begins from the start of fast neutron irradiation. However, in actual measurements, a pulsed drive voltage is applied when fast neutrons are emitted, generating electromagnetic waves that cause noise. In addition, fast neutrons emitted from the neutron source undergo nuclear reactions with surrounding material, generating a large amount of previously emitted gamma rays that also cause noise. Therefore, it is preferable to start neutron detection after a predetermined time has elapsed from the start of fast neutron irradiation, for example, after 1 to 3 μs has elapsed.

[0111] In the neutron moisture meter 2 and moisture measurement method according to the second embodiment, it is preferable that the neutron detector 20 starts detecting neutrons with a delay from the generation of fast neutrons by the neutron source 10, and stops detecting neutrons when a preset measurement time has elapsed. It is preferable that the neutron detector 20 starts detecting neutrons when 1 μs or more has elapsed from the generation of fast neutrons, it is preferable that it stops detecting neutrons within 100 μs from the generation of fast neutrons, and it is more preferable that it stops detecting neutrons within 50 μs from the generation of fast neutrons.

[0112] According to the neutron moisture meter 2 and moisture measurement method described above, since the neutron moderator is installed to surround the object to be measured, the effect of increasing the number of neutrons counted by the neutron detector and the count rate is obtained, similar to the neutron moisture meter 1 and moisture measurement method described above. In addition, since a neutron absorber is installed between the object to be measured and the neutron moderator, neutrons such as thermal neutrons that are generated when fast neutrons are slowed down by the neutron moderator can be absorbed before they enter the object to be measured. Neutrons emitted by the neutron moderator become less likely to reach the object to be measured or the neutron detector, and only neutrons slowed down by the moisture contained in the object to be measured become easier to detect. Therefore, noise caused by neutrons that have not passed through moisture can be reduced, and the signal-to-noise ratio of the neutron detection results can be increased.

[0113] Therefore, even when the neutron flux emitted by the neutron source is small, or when the amount of water present inside or on the surface of the object being measured is minute, it becomes possible to measure the amount of water in the object with high accuracy by reducing noise caused by neutrons emitted from sources other than water and increasing the count number and count rate of neutrons that pass through water. Furthermore, by reducing noise caused by neutrons emitted from sources other than water and increasing the count number and count rate of neutrons that pass through water, it becomes possible to measure the amount of water in the object being measured in a short amount of time.

[0114] Neutrons, such as thermal neutrons, which are noise-causing particles emitted by substances other than water, have a long flight time to reach the neutron detector. Therefore, their impact becomes greater as time elapses from the start of high-speed neutron irradiation. By placing a neutron absorber between the object being measured and the neutron moderator, the influence of such neutrons can be reduced, allowing for higher-precision measurements with reduced noise over a longer period. Consequently, the water content of the object being measured can be determined with greater accuracy.

[0115] Furthermore, with the neutron moisture meter 2 and moisture measurement method described above, a neutron moderator and a neutron absorber are installed surrounding the object to be measured, thereby increasing the fast neutron flux in the space where the object to be measured is installed. In the space where the object to be measured is installed, fast neutrons are present at high density, and the flight direction of the fast neutrons is randomized. When the flight direction of fast neutrons is randomized, the bias in the flight direction of neutrons emitted from moisture is reduced, and the restrictions on the installation location of the neutron detector are relaxed.

[0116] <Third Embodiment> Figure 8 shows the configuration of a neutron moisture meter according to the third embodiment of the present invention. As shown in Figure 8, the neutron moisture meter 3 according to the third embodiment comprises a neutron source 10, a neutron detector 20, and a computing device 60. The neutron moisture meter 3 is installed near the object to be measured 30 when measuring the amount of moisture. A neutron moderator 40a and a neutron absorber 50a are installed around the object to be measured 30 so as to surround the object to be measured 30.

[0117] In Figure 8, the neutron moderator 40a is installed so as to surround the measurement target 30 from above, the sides, and below. The neutron moderator 40a surrounds the entire side of the measurement target 30 and is positioned to cover the top and bottom surfaces of the measurement target 30.

[0118] Furthermore, the neutron absorber 50a is installed inside the neutron moderator 40a, surrounding the object to be measured 30 from above, the sides, and below. Inside the neutron moderator 40a, the neutron absorber 50a is positioned to surround the entire side of the object to be measured 30, as well as to cover the top and bottom surfaces of the object to be measured 30.

[0119] The neutron moisture meter 3 is a scattering-type measuring instrument that irradiates the object to be measured with neutrons and counts the neutrons slowed down by the moisture contained in the object to measure, thereby measuring the amount of moisture. The difference between the neutron moisture meter 3 according to the third embodiment and the neutron moisture meter 1 described above is that the neutron moderator 40a and the neutron absorber 50a are installed so as to surround the object to be measured 30 from all directions. The other main components of the neutron moisture meter 3 are the same as those of the neutron moisture meter 2 described above.

[0120] The neutron moderator 40a is a component that slows down neutrons, scattering and slowing down neutrons irradiated onto the object to be measured 30. The neutron moderator 40a is made of a material that has a large scattering cross-section for fast neutrons and a small absorption cross-section for neutrons. The neutron moderator 40a is installed in the vicinity of the object to be measured 30, which is less than the diffusion distance of fast neutrons, so as to slow down fast neutrons irradiated onto the object to be measured 30 and fast neutrons emitted from the object to be measured 30, and surrounds the object to be measured 30 from all directions.

[0121] For example, polyethylene can be used as the neutron moderator 40a. Polyethylene with a density of 0.94 kg / m³ can be used. 3 High-density polyethylene, as described above, and deuterated polyethylene, in which hydrogen is replaced with deuterium, are more preferable. Polyethylene can efficiently slow down neutrons while suppressing the generation of secondary radiation. It can also be easily processed and molded. However, other materials may be used as the neutron moderator 40a, as long as they slow down fast neutrons. For example, water contained in a container, resin materials such as polypropylene, polystyrene, and phenolic resin, carbon materials such as graphite and carbon fiber, beryllium, and paraffin can be used.

[0122] The neutron absorber 50a is a component that absorbs neutrons, primarily thermal neutrons incident on the measurement target 30. The neutron absorber 50a is made of a material with a large thermal neutron absorption cross-section. The neutron absorber 50a is installed between the measurement target 30 and the neutron moderator 40 so as to surround the measurement target 30 from all directions. With the neutron absorber 50a, thermal neutrons generated by the deceleration of fast neutrons by the neutron moderator 40a are absorbed before they can enter the measurement target 30 or the neutron detector 20.

[0123] For example, cadmium can be used as the neutron absorber 50a. Cadmium provides a large absorption cross-section for thermal neutrons and allows for macroscopically efficient absorption in the form of metal foil or metal plate. However, other materials may be used as the neutron absorber 50a, as long as they absorb unwanted thermal neutrons. For example, water contained in a container, boron compounds such as boron carbide containing boron, boron-containing alloys, gadolinium, hafnium, and their alloys can be used.

[0124] As shown in Figure 8, the neutron source 10 may be installed inside the neutron moderator 40a and inside the neutron absorber 50a, or inside the neutron moderator 40a and outside the neutron absorber 50a, or outside the neutron moderator 40a and outside the neutron absorber 50a. When the neutron source 10 is installed outside the neutron moderator 40a, fast neutrons slowed by the neutron moderator 40a can be irradiated onto the object to be measured 30.

[0125] As shown in Figure 8, it is preferable to install the neutron detector 20 inside the neutron moderator 40a and inside the neutron absorber 50a. Installing the neutron detector 20 inside suppresses the incidence of background neutrons and allows for the direct detection of neutrons such as thermal neutrons emitted from the object to be measured 30 before they are decelerated. When the neutron moderator 40a is installed to surround the object to be measured 30 from all directions, the neutron detector 20 may be installed inside the neutron moderator 40a and outside the neutron absorber 50a, but it is preferable that no neutron absorber 50a is installed between the neutron detector 20 and the object to be measured 30.

[0126] Furthermore, a neutron reflector may be installed outside the neutron moderator 40a so as to surround the object to be measured 30. The neutron reflector is made of a material that has a large neutron scattering cross-section, a small neutron absorption cross-section, and an atomic number greater than that of the neutron moderator 40a. Examples of neutron reflectors include lead and iron.

[0127] The neutron moisture meter 3 may be portable or stationary, depending on the type and size of the object to be measured 30. Depending on the type and size of the object to be measured 30, the neutron moisture meter 3 may be a surface type in which the neutron detector 20 is placed on the surface of the object to be measured 30, or an insertion type in which a probe-shaped neutron detector 20 is inserted into the inside of the object to be measured 30.

[0128] The moisture content measurement method according to the third embodiment is a method for measuring the moisture content of a target by counting neutrons slowed down by the moisture contained in the target. In this embodiment, a neutron moderator is installed so as to surround the target from all directions, a neutron absorber is installed between the target and the neutron moderator, fast neutrons are generated and irradiated onto the target or the neutron moderator, the neutrons emitted from the neutron moderator are absorbed by the neutron absorber, and the neutrons slowed down by the target and the neutron moderator are detected, and the moisture content of the target is determined based on the neutron detection results.

[0129] In the moisture content measurement method according to this embodiment, the moisture content of the object to be measured is determined based on the correlation between the neutron flux at the detection position and the moisture content of the object to be measured. The correlation between the neutron flux and the moisture content of the object to be measured may be corrected according to the neutron attenuation rate due to the neutron moderator or neutron absorber. The neutron attenuation rate due to the neutron moderator or neutron absorber can be determined in advance using the neutron moderator or neutron absorber used for measuring the moisture content or an equivalent system.

[0130] In the moisture measurement method according to this embodiment, fast neutrons may be irradiated toward the object to be measured, toward the neutron moderator, or toward both. Fast neutrons may be irradiated so as to pass through the neutron absorber, or they may be irradiated so as not to pass through the neutron absorber. As for the neutrons, neutrons such as thermal neutrons slowed by both the object to be measured and the neutron moderator are detected. The amount of moisture in the object to be measured may be the amount of moisture present inside or on the surface of the object, or the two-dimensional or three-dimensional distribution of moisture in the object may be determined.

[0131] In the moisture measurement method according to this embodiment, pulsed fast neutrons may be used for measurement. Pulsed fast neutrons are generated and irradiated onto the object to be measured or a neutron moderator, and neutrons originating from each pulse of fast neutrons are detected in synchronization with the generation of fast neutrons. Based on the detection results of the neutrons for each pulse, the amount of moisture present inside or on the surface of the object to be measured, and the distribution of moisture in the object to be measured can be determined.

[0132] The moisture measurement method according to the third embodiment can be performed using a neutron moisture meter 3. The neutron moisture meter 3 is installed near the object to be measured 30, which is surrounded by a neutron moderator 40a and a neutron absorber 50a. The neutron moisture meter 3 is pre-prepared with a calibration curve showing the relationship between the neutron count rate detected by the neutron detector 20 and the moisture content of the object to be measured 30, as well as information indicating the distance between the object to be measured 30 and the neutron detector 20. Furthermore, correction curves showing the neutron attenuation rate due to the neutron moderator 40a and the neutron absorber 50a, and correction curves for correcting the moisture content of the object to be measured 30 according to its assumed specific gravity can also be pre-prepared.

[0133] The moisture measurement method using the neutron moisture meter 3 can be performed in the same manner as the moisture measurement method using the neutron moisture meter 1 described above. The calibration curve can be determined in advance using a system in which the object to be measured 30 is surrounded from all directions by the neutron moderator 40a and the neutron absorber 50a. When measuring the amount of moisture, the calculation unit 60 controls the neutron source 10 to irradiate the object to be measured 30 or the neutron moderator 40a with fast neutrons generated by the neutron source 10. The neutrons emitted from the neutron moderator 40a are absorbed by the neutron absorber 50a, and the neutron detector 20 is controlled to detect the neutrons that have been slowed down by the object to be measured 30 and the neutron moderator 40a.

[0134] When a neutron is detected by the neutron detector 20, the calculation unit 60 integrates the counts recorded by the neutron detector 20 to determine the count rate detected by the neutron detector 20. Alternatively, when pulsed fast neutrons are used for measurement, the calculation unit 60 may determine a thermal neutron profile that shows the relationship between the thermal neutron flux detected by the neutron detector 20 and the time calculated from the time of thermal neutron generation. The relationship between the count rate and the moisture content, as well as the thermal neutron profile, may be corrected according to the neutron decay rate due to the neutron moderator 40a and the neutron absorber 50a, and the assumed specific gravity of the object to be measured 30.

[0135] According to the neutron moisture meter 3 and moisture measurement method described above, since the neutron moderator is installed so as to surround the object to be measured from all directions, the effect of increasing the number of neutrons counted by the neutron detector and the count rate is obtained, similar to the neutron moisture meter 1 and moisture measurement method described above. In addition, since a neutron absorber is installed between the object to be measured and the neutron moderator, neutrons such as thermal neutrons that are generated by the deceleration of fast neutrons by the neutron moderator can be absorbed before they enter the object to be measured, similar to the neutron moisture meter 2 and moisture measurement method described above. Because the object to be measured is surrounded from all directions by the neutron moderator and neutron absorber, the effects of reducing the kinetic energy of fast neutrons, changing the flight direction of fast neutrons to randomize them, and absorbing unwanted neutrons such as thermal neutrons can be obtained more reliably.

[0136] Therefore, even when the neutron flux emitted by the neutron source is small, or when the amount of water present inside or on the surface of the object being measured is minute, it becomes possible to measure the amount of water in the object with higher accuracy by reducing noise caused by neutrons emitted from sources other than water and increasing the count number and count rate of neutrons that pass through water. Furthermore, by reducing noise caused by neutrons emitted from sources other than water and increasing the count number and count rate of neutrons that pass through water, it becomes possible to measure the amount of water in the object being measured in a shorter amount of time.

[0137] Neutrons, such as thermal neutrons, which are noise-causing particles emitted by substances other than water, have a long flight time to reach the neutron detector. Therefore, their impact becomes greater as time elapses from the start of high-speed neutron irradiation. By placing a neutron absorber between the object being measured and the neutron moderator, the influence of such neutrons can be reduced, allowing for higher-precision measurements with reduced noise over a longer period. Consequently, the water content of the object being measured can be determined with greater accuracy.

[0138] Furthermore, with the neutron moisture meter 3 and moisture measurement method described above, the neutron moderator and neutron absorber are installed so as to surround the object to be measured from all directions, thereby increasing the fast neutron flux in the space where the object to be measured is installed. In the space where the object to be measured is installed, fast neutrons are present at high density, and the flight direction of the fast neutrons is randomized. When the flight direction of fast neutrons is randomized, the bias in the flight direction of neutrons emitted from moisture is reduced, and the restrictions on the installation location of the neutron detector are relaxed.

[0139] <Fourth Embodiment> Figure 9 shows the configuration of a neutron moisture meter according to the fourth embodiment of the present invention. As shown in Figure 9, the neutron moisture meter 4 according to the fourth embodiment comprises a neutron source 10, a neutron detector 20, a computing device 60, and a rotating mechanism 70. The neutron moisture meter 4 is installed near the object to be measured 30 when measuring the amount of moisture. A neutron moderator 40a and a neutron absorber 50a are installed around the object to be measured 30 so as to surround the object to be measured 30.

[0140] In Figure 9, the neutron moderator 40a is installed so as to surround the measurement target 30 from above, the sides, and below. The neutron moderator 40a surrounds the entire side of the measurement target 30 and is positioned to cover the top and bottom surfaces of the measurement target 30.

[0141] Furthermore, the neutron absorber 50a is installed inside the neutron moderator 40a, surrounding the object to be measured 30 from above, the sides, and below. Inside the neutron moderator 40a, the neutron absorber 50a is positioned to surround the entire side of the object to be measured 30, as well as to cover the top and bottom surfaces of the object to be measured 30.

[0142] The neutron moisture meter 4 is a scattering-type measuring instrument that measures the amount of moisture by irradiating the object to be measured with neutrons and counting the neutrons that are slowed down by the moisture contained in the object. The difference between the neutron moisture meter 4 according to the fourth embodiment and the neutron moisture meter 3 described above is that the object to be measured 30 is rotatably mounted by a rotation mechanism 70. The other main components of the neutron moisture meter 4 are the same as those of the neutron moisture meter 3 described above.

[0143] The rotation mechanism 70 is a mechanism for rotating the object to be measured 30. The object to be measured 30 can be rotated by the rotation mechanism 70 so that the relative position of each region constituting the object to be measured 30 with respect to the neutron source 10 and neutron detector 20 changes during the measurement of the amount of water content. The object to be measured 30 can be rotated to a predetermined rotation angle and then stopped before irradiation with fast neutrons. Alternatively, the object to be measured 30 can be continuously rotated while irradiation with fast neutrons is performed. The rotation mechanism 70 includes a shaft connected to the object to be measured 30 and a support member that supports the object to be measured 30, and a drive device such as a motor that drives the rotational motion of the shaft.

[0144] As shown in Figure 9, the neutron source 10 is preferably positioned outside the measurement target 30 in an axial direction parallel to the rotation axis of the measurement target 30, and in the vicinity of the measurement target 30, where it is less than or equal to the diffusion distance of fast neutrons. With such an arrangement, fast neutrons can be irradiated with high uniformity to each region constituting the measurement target 30 as the measurement target 30 rotates. Therefore, it is possible to equalize the timing of neutron generation, such as thermal neutrons due to collisions with water, and to perform continuous detection at each rotation angle to measure the distribution of water.

[0145] As shown in Figure 9, it is preferable to install the neutron detector 20 on the outside of the measurement target 30 in the radial direction perpendicular to the rotation axis of the measurement target 30. With this arrangement, by rotating the measurement target 30, the distance between each region constituting the measurement target 30 and the neutron detector 20, as well as the path from each region to the neutron detector 20, can be changed. Therefore, neutrons such as thermal neutrons emitted from each region constituting the measurement target 30 can be distinguished according to their generation location.

[0146] The moisture content measurement method according to the fourth embodiment is a method for measuring the moisture content of a measurement target by counting neutrons slowed down by the moisture contained in the measurement target. In this embodiment, a neutron moderator is installed so as to surround the measurement target from all directions, a neutron absorber is installed between the measurement target and the neutron moderator, the measurement target is supported by a rotating mechanism, and the moisture content of the measurement target is determined by irradiating the measurement target with fast neutrons and detecting thermal neutrons each time the measurement target is rotated and stopped, or while the measurement target is continuously rotated. The moisture content of the measurement target is measured for each irradiation axis on the measurement target based on the neutron detection results by repeating the operation of rotating the measurement target and then stopping to detect neutrons, or by continuously rotating the measurement target and detecting neutrons.

[0147] In the moisture content measurement method according to this embodiment, the moisture content of the object to be measured is determined based on the correlation between the neutron flux at the detection position and the moisture content of the object to be measured. The correlation between the neutron flux and the moisture content of the object to be measured may be corrected according to the neutron attenuation rate due to the neutron moderator or neutron absorber. The neutron attenuation rate due to the neutron moderator or neutron absorber can be determined in advance using the neutron moderator or neutron absorber used for measuring the moisture content or an equivalent system.

[0148] In the moisture measurement method according to this embodiment, fast neutrons may be irradiated toward the object to be measured, toward the neutron moderator, or toward both. Fast neutrons may be irradiated so as to pass through the neutron absorber, or so as not to pass through the neutron absorber. As neutrons, neutrons such as thermal neutrons slowed by both the object to be measured and the neutron moderator are detected. The moisture content of the object to be measured may be determined by finding the amount of moisture present inside or on the surface of the object, finding the average moisture content of the object, finding the distribution in the circumferential direction perpendicular to the rotation axis of the rotating mechanism of the object, or finding the two-dimensional or three-dimensional distribution of moisture in the object.

[0149] In the moisture measurement method according to this embodiment, pulsed fast neutrons may be used for measurement. Pulsed fast neutrons are generated and irradiated onto the object to be measured or a neutron moderator, and neutrons originating from each pulse of fast neutrons are detected in synchronization with the generation of fast neutrons. Based on the detection results of the neutrons for each pulse, the amount of moisture present inside or on the surface of the object to be measured, and the distribution of moisture in the object to be measured can be determined.

[0150] The moisture measurement method according to the fourth embodiment can be performed using a neutron moisture meter 4. The neutron moisture meter 3 is installed near the object to be measured 30, which is surrounded by a neutron moderator 40a and a neutron absorber 50a. The neutron moisture meter 3 is pre-prepared with a calibration curve showing the relationship between the neutron count rate detected by the neutron detector 20 and the moisture content of the object to be measured 30, as well as information indicating the distance between the object to be measured 30 and the neutron detector 20. Furthermore, correction curves showing the neutron attenuation rate due to the neutron moderator 40a and the neutron absorber 50a, and correction curves for correcting the moisture content of the object to be measured 30 according to its assumed specific gravity can be pre-prepared.

[0151] The moisture measurement method using the neutron moisture meter 4 can be performed in the same manner as the moisture measurement method using the neutron moisture meter 1 described above. The calibration curve can be determined in advance using a system in which the object to be measured 30 is surrounded from all directions by the neutron moderator 40a and the neutron absorber 50a. When measuring the amount of moisture, the calculation unit 60 controls the rotation mechanism 70 to rotate the object to be measured 30 by the rotation mechanism 70 to a predetermined rotation angle and then stop it. Alternatively, the object to be measured 30 is rotated continuously at a predetermined angular velocity. Then, the neutron source 10 is controlled to irradiate the object to be measured 30 or the neutron moderator 40a with high-speed neutrons generated by the neutron source 10. Then, the neutron absorber 50a absorbs the neutrons emitted from the neutron moderator 40a, and the neutron detector 20 is controlled to detect the neutrons that have been slowed down by the object to be measured 30 and the neutron moderator 40a. After detecting neutrons, the measurement target 30 can be rotated by the rotation mechanism 70 to a predetermined rotation angle, and the operation of detecting thermal neutrons can be repeated.

[0152] When a neutron is detected by the neutron detector 20, the calculation unit 60 integrates the counts recorded by the neutron detector 20 to determine the count rate detected by the neutron detector 20. Alternatively, when pulsed fast neutrons are used for measurement, the calculation unit 60 may determine a thermal neutron profile that shows the relationship between the thermal neutron flux detected by the neutron detector 20 and the time calculated from the time of thermal neutron generation. The relationship between the count rate and the moisture content, as well as the thermal neutron profile, may be corrected according to the neutron decay rate due to the neutron moderator 40a and the neutron absorber 50a, and the assumed specific gravity of the object to be measured 30.

[0153] According to the neutron moisture meter 4 and moisture measurement method described above, since the neutron moderator is installed so as to surround the object to be measured from all directions, the effect of increasing the number of neutrons counted by the neutron detector and the count rate is obtained, similar to the neutron moisture meter 3 and moisture measurement method described above. In addition, since a neutron absorber is installed between the object to be measured and the neutron moderator, neutrons such as thermal neutrons that are generated by the deceleration of fast neutrons by the neutron moderator can be absorbed before they enter the object to be measured, similar to the neutron moisture meter 3 and moisture measurement method described above. Because the object to be measured is surrounded from all directions by the neutron moderator and neutron absorber, the effects of reducing the kinetic energy of fast neutrons, changing the flight direction of fast neutrons to randomize them, and absorbing unwanted neutrons can be obtained more reliably.

[0154] Therefore, even when the neutron flux emitted by the neutron source is small, or when the amount of moisture present inside or on the surface of the object being measured is minute, it becomes possible to measure the amount of moisture in the object with higher accuracy by reducing noise caused by neutrons that do not pass through moisture and increasing the count number and count rate of neutrons that do pass through moisture. Furthermore, by reducing noise caused by neutrons that do not pass through moisture and increasing the count number and count rate of neutrons that do pass through moisture, it becomes possible to measure the amount of moisture in the object in a shorter amount of time. In addition, because the object being measured is rotatable, the distribution of moisture in the object can be easily determined by detecting the response due to moisture while changing the neutron flight path.

[0155] Furthermore, with the neutron moisture meter 4 and moisture measurement method described above, the neutron moderator and neutron absorber are installed so as to surround the measurement target from all directions, thereby increasing the fast neutron flux in the space where the measurement target is installed. In the space where the measurement target is installed, fast neutrons are present at high density, and the flight direction of the fast neutrons is randomized. The measurement target is driven to rotate in such a space. When the flight direction of fast neutrons is randomized, the bias in the flight direction of neutrons emitted from moisture is reduced, so regardless of the rotation angle of the measurement target, detection results can be collected that depend only on the distance between each region constituting the measurement target 30 and the neutron detector 20, and the path from each region to the neutron detector 20.

[0156] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, the present invention is not necessarily limited to having all the configurations of the embodiments described above. Some configurations of one embodiment may be replaced with other configurations, some configurations of one embodiment may be added to other forms, or some configurations of one embodiment may be omitted. [Explanation of Symbols]

[0157] 1. Neutron moisture meter 10 Neutron source 20 Neutron detector 30 items to measure 40 Neutron moderator 50 Neutron absorbers 60 Arithmetic unit 70 Rotation Mechanism

Claims

1. A neutron moisture meter that measures the amount of moisture in a sample by counting neutrons slowed down by the moisture contained in the sample, A neutron source that generates fast neutrons, A neutron detector that detects neutrons, A calculation device that calculates the amount of water in the object to be measured based on the neutron detection result, The system comprises a neutron moderator installed so as to surround the object to be measured, A neutron moisture meter that irradiates the object to be measured or the neutron moderator with high-speed neutrons generated by the neutron source, detects the neutrons slowed down by the object to be measured and the neutron moderator with the neutron detector, and determines the amount of moisture in the object to be measured based on the detection results of the neutrons.

2. A neutron moisture meter according to claim 1, A neutron absorber is provided between the object to be measured and the neutron moderator. A neutron moisture meter that absorbs neutrons emitted by the neutron moderator using the neutron absorber.

3. A neutron moisture meter according to claim 2, The neutron moderator and the neutron absorber are installed in a neutron moisture meter that surrounds the object to be measured from all directions.

4. A neutron moisture meter according to claim 3, The system includes a rotation mechanism for rotating the object to be measured, The neutron source is positioned outside the object to be measured in an axial direction parallel to the rotation axis of the object to be measured. The neutron detector is a neutron moisture meter positioned outside the object to be measured in the radial direction perpendicular to the rotation axis of the object to be measured.

5. A neutron moisture meter according to any one of claims 1 to 4, The neutron source generates pulsed high-speed neutrons and irradiates the object to be measured or the neutron moderator. The neutron detector, in synchronization with the neutron source, detects neutrons originating from fast neutrons generated by the neutron source. The aforementioned computing device is a neutron moisture meter that determines the amount of moisture in the object to be measured based on the detection result of the neutron for each pulse.

6. A neutron moisture meter according to claim 5, The neutron detector is a neutron moisture meter that starts detecting neutrons with a delay from the generation of fast neutrons by the neutron source and stops detecting neutrons when a preset measurement time has elapsed.

7. A neutron moisture meter according to claim 6, The neutron detector is a neutron moisture meter that starts detecting the neutron with a delay from the time the fast neutron is generated and ends detecting the neutron within 30 μs from the time the fast neutron is generated.

8. A method for measuring the amount of water in a sample by counting neutrons slowed down by the water contained in the sample, A method for measuring moisture content, comprising: setting up a neutron moderator around a target to be measured; generating high-speed neutrons and irradiating the target to be measured or the neutron moderator with them; detecting the neutrons slowed down by the target to be measured and the neutron moderator; and determining the moisture content of the target to be measured based on the neutron detection results.

9. A method for measuring moisture content according to claim 8, A method for measuring moisture content, comprising placing a neutron absorber between the object to be measured and the neutron moderator, and absorbing neutrons emitted by the neutron moderator with the neutron absorber.

10. A method for measuring moisture content according to claim 9, A method for measuring moisture content, wherein the neutron moderator and the neutron absorber are installed so as to surround the object to be measured from all directions.

11. A method for measuring moisture content according to claim 10, A method for measuring moisture content, wherein each time the object to be measured is rotated and brought to a stop, irradiation with fast neutrons and detection of neutrons are performed to determine the average value or distribution of moisture content of the object to be measured.

12. A method for measuring moisture content according to claim 10, A method for measuring moisture content, comprising irradiating the object to be measured with fast neutrons and detecting the neutrons while continuously rotating the object, to determine the average value or distribution of moisture content of the object to be measured.

13. A method for measuring moisture content according to any one of claims 8 to 12, A pulsed high-speed neutron is generated and irradiated onto the object to be measured or the neutron moderator. A method for measuring moisture content, which involves detecting neutrons originating from fast neutrons in synchronization with the generation of fast neutrons, and determining the moisture content of the object to be measured based on the detection result of the neutrons for each pulse.

14. A method for measuring moisture content according to claim 13, A method for measuring moisture content, in which detection of fast neutrons is started with a delay from the generation of the fast neutrons, and detection of neutrons is terminated when a predetermined measurement time has elapsed.

15. A method for measuring moisture content according to claim 14, A method for measuring moisture, in which the detection of thermal neutrons is started with a delay from the generation of the fast neutrons, and the detection of neutrons is completed within 30 μs from the generation of the fast neutrons.

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