Flight time measurement method and flight time correction device

Abstract

In the present invention, a target object is irradiated with a pulsed charged particle beam to generate neutrons with which a subject is irradiated, and as a result, the neutrons scattered at the subject are detected to determine the time of flight of each of the neutrons (step S5). The determined time of flight is corrected on the basis of delay time data for estimating a delay time related to the flight of each of the neutrons (step S6). The delay time data is obtained in advance on the basis of one or both of the pulse width of the pulsed charged particle beam and the deceleration characteristic of a moderator that decelerates the neutrons toward the subject (steps S1-S4).

Description

Time-of-flight measurement method and time-of-flight correction device

[0001] The present invention relates to a technology for generating a pulsed neutron beam by irradiating a target with a pulsed charged particle beam, irradiating the generated neutron beam on an object such as a sample, detecting neutrons scattered by the object, and determining the time of flight of the neutrons.

[0002] Neutron time-of-flight (TOF) has been used to perform structural analysis of materials. Specifically, the following analysis is performed based on TOF:

[0003] A pulsed neutron beam is generated by irradiating a target with a short pulsed charged particle beam (e.g., a proton beam) from an accelerator. The neutron beam is then decelerated by a moderator and irradiated onto an object (a sample or an infrastructure structure). The neutrons are scattered by the object and then detected by a detector, thereby determining the neutron time of flight. The time of flight is, for example, the time from when the neutrons are generated to when they are detected.

[0004] In this way, neutrons are made to fly a certain distance, their time of flight is measured, and structural analysis of the object (sample or infrastructure structure) is performed based on the measured time of flight. In one example, the speed of the neutrons, i.e., wavelength, is determined based on the measured time of flight and the known flight distance of the neutrons, and structural analysis of the object (material) is performed based on the determined wavelength of the neutrons. In addition, in Patent Document 1 listed below, a pulsed neutron beam is irradiated onto the object, neutrons scattered by the object are detected, and detection number data indicating the number of detected neutrons at the detection time (corresponding to the flight time) is generated, and the presence or absence of defects in the object is inspected based on this detection number data.

[0005] International Publication No. 2017 / 043581

[0006] The inventors of the present application have found that the following problem A occurs in the analysis, inspection, etc. of an object using the neutron time-of-flight method.

[0007] <Problem A> When a generated pulsed neutron beam is decelerated by a moderator and then irradiated onto a target, the deceleration of each neutron causes a delay in the flight of each neutron, which results in a decrease in the accuracy of analysis of the target based on the neutron flight time, as described above.

[0008] Recently, small neutron sources have been developed, and attempts are being made to analyze the structure of samples and perform non-destructive testing of infrastructure structures (e.g., concrete structures), but these small neutron sources have begun to use charged particle beams (e.g., proton beams) with long pulse widths to obtain a predetermined neutron beam intensity. The inventors of the present application have found that when a charged particle beam with a long pulse width as described above is used in the analysis, inspection, etc. of objects using the neutron time-of-flight method, the following problem B occurs.

[0009] <Issue B> When neutrons are generated by irradiating a target with a charged particle beam having a long pulse width, the long pulse width causes a significant delay in the flight of the neutron pulse, which results in a decrease in the accuracy of analysis of the target object based on the neutron time of flight, as described above.

[0010] The present invention has been made based on one or both of the above-mentioned problems A and B.

[0011] An object of one aspect of the present invention is to suppress a decrease in the accuracy of analysis, inspection, etc. of an object due to the deceleration of neutrons when a pulsed neutron beam is generated and then decelerated by a moderator before being irradiated onto the object in a neutron time-of-flight method.

[0012] Another object of the present invention is to suppress a decrease in accuracy of analysis, inspection, etc. of an object due to a long pulse width of a pulsed charged particle beam that generates a pulsed neutron beam in a neutron time-of-flight method.

[0013] According to one aspect of the present invention, there is provided a method for measuring the time of flight of neutrons, comprising: (A) irradiating a target with a pulsed charged particle beam to generate neutrons, which are then irradiated onto an object; (B) detecting the neutrons scattered by the object to determine the time of flight of the neutrons; (C) determining in advance delay time data for estimating the delay time associated with the flight of the neutrons based on one or both of the pulse width of the pulsed charged particle beam and the deceleration characteristics of a moderator that decelerates the neutrons toward the object; and (D) correcting the time of flight based on the delay time data.

[0014] According to another aspect of the present invention, there is provided a time-of-flight correction device that corrects the time-of-flight of neutrons when the time-of-flight of the neutrons is measured by detecting the neutrons generated by irradiating a target with a pulsed charged particle beam, the time-of-flight correction device comprising: a memory unit that stores delay time data for estimating the delay time related to the flight of the neutrons, the delay time data being determined in advance based on one or both of the pulse width of the pulsed charged particle beam and the deceleration characteristics of a moderator that decelerates the neutrons toward the target; and a data processing device that corrects the time-of-flight based on the delay time data.

[0015] According to the present invention, it is possible to suppress a decrease in accuracy of analysis, inspection, etc. of an object in the neutron time-of-flight method.

[0016] 1 shows a neutron measurement device equipped with a time-of-flight correction device according to an embodiment of the present invention. FIG. 1 is an explanatory diagram of delay time associated with the pulse width of a pulsed charged particle beam. FIG. 2 is an explanatory diagram of delay time associated with the neutron slowing down process by a moderator. FIG. 2 shows an example of an impulse response function and its relationship to a reference time τ0. FIG. 3 shows another example of an impulse response function and its relationship to a reference time τ0. FIG. 4 shows a further example of an impulse response function and its relationship to a reference time τ0. FIG. 5 is an explanatory diagram of delay time associated with increased uncertainty. FIG. 6 is a flowchart showing step S6 in FIG. 3. FIG. 7 shows an example of a neutron number time distribution. FIG. 8 is an explanatory diagram showing the flight direction of neutrons generated from a target in terms of solid angle α. FIG. 9 shows the angular distribution of the number of neutrons tallied for each range of the solid angle α. FIG. 10 shows a time distribution function fitted to the neutron number time distribution obtained by particle transport calculation. FIG. 11 shows the reference time t0 (delay time) calculated from the fitted time distribution function f(t). FIG. 11 shows a calculation system for a time-of-flight neutron diffractometer for a pulsed neutron source. FIG. 12 shows simulation results of lattice spacing obtained by an example. The relationship between the lattice spacing and the scattering angle is shown in the simulation results of the lattice spacing obtained by the example.

[0017] An embodiment of the present invention will be described with reference to the drawings. In addition, common parts in the drawings are given the same reference numerals, and duplicated explanations will be omitted.

[0018] 1 shows a neutron measurement device 100 equipped with a time-of-flight correction device 20 according to an embodiment of the present invention. The neutron measurement device 100 is a device that irradiates an object 1 with a neutron beam, detects neutrons scattered by the object 1 such as a sample, calculates the time-of-flight of the neutrons, and generates analytical data (e.g., data representing lattice spacing) related to the object 1 based on the time-of-flight.

[0019] The neutron measurement device 100 includes a neutron source 10, a plurality of detectors 11, a time-of-flight measurement unit 12, a time-of-flight correction device 20, and the like.

[0020] The neutron source 10 includes a charged particle irradiation device 2 , a target 3 , a moderator 4 , a reflector 5 , a shield 6 , a collimator 7 and a slit 8 .

[0021] The charged particle irradiation device 2 generates a charged particle beam and irradiates the target 3 with the beam. The charged particle irradiation device 2 may be configured to include, for example, a charged particle source 2 a and an accelerator 2 b. The charged particle source 2 a generates a pulsed charged particle beam (e.g., a pulsed proton beam or a pulsed electron beam). The accelerator 2 b accelerates the pulsed charged particle beam generated by the charged particle source 2 a. The pulsed charged particle beam accelerated by the accelerator 2 b is irradiated onto the target 3.

[0022] The charged particle irradiation device 2 is not limited to this configuration and may be, for example, a laser-driven device. The laser-driven device generates a pulsed charged particle beam by irradiating a target for generating a charged particle beam with high-power laser light, and irradiates the pulsed charged particle beam onto a target 3 for generating neutrons.

[0023] When the target 3 is irradiated with a pulsed charged particle beam from the charged particle irradiation device 2, a pulsed neutron beam is generated by a nuclear reaction (or nuclear spallation reaction) with the pulsed charged particle beam. The target 3 is made of, for example, beryllium (Be) or lithium (Li). In this case, when a pulsed proton beam is irradiated onto the target 3 as a pulsed charged particle beam, ９ Be(p, n) ９ B and ７ Li(p,n) ７ A pulsed neutron beam can be generated by a nuclear reaction such as Be.

[0024] When this pulsed neutron beam is generated, a reference signal indicating the time of generation of the pulsed neutron beam is input to the time-of-flight measurement unit 12. This reference signal may be input to the time-of-flight measurement unit 12 from a reference signal generation unit 9 in the neutron source 10. The reference signal generation unit 9 may be, for example, a sensor that is placed near the target 3, detects that the pulsed charged particle beam has hit the target 3, and inputs a reference signal indicating this detection to the time-of-flight measurement unit 12.

[0025] The moderator 4 decelerates the pulsed neutron beam generated by the target 3. For example, since each neutron generated by the target 3 has high energy and a short wavelength, it is unlikely to interfere with the object 1 (e.g., the lattice spacing of the metal structure of the object 1), and therefore the moderator 4 (i.e., a moderating member) reduces the energy of the passing neutrons to the thermal neutron range. In this way, the moderator 4 may decelerate the passing high-speed neutrons and convert them into thermal neutrons. The moderator 4 has a neutron emission surface 4a that emits each neutron that has been decelerated as described above by passing through it toward the object 1 (e.g., the collimator 7).

[0026] The material of the moderator 4 may be any material that can slow down the neutrons generated by the target 3. When the ease of installation and availability of the moderator 4 are taken into consideration, the material of the moderator 4 is preferably polyethylene, paraffin, or the like, which contains hydrogen atoms that cause a large loss of neutron energy upon collision with the neutrons.

[0027] The reflector 5 is disposed so as to surround the target 3 and the moderator 4, and reflects fast neutrons generated by the target 3, thereby increasing the number of neutrons (fast neutrons) incident on the moderator 4. From the viewpoint of efficiently reflecting neutrons, the reflector 5 may be made of heavy water, beryllium, graphite, or the like. Note that, to prevent thermal neutrons generated by the reflector 5 from entering the moderator 4, an absorbing member made of cadmium, boron, or the like that absorbs thermal neutrons may be provided between the reflector 5 and the moderator 4.

[0028] The shielding 6 is installed to surround the target 3 and the moderator 4, and reduces radiation leakage to the surrounding area and background radiation (e.g., gamma rays) entering the detector 11. For example, the shielding 6 may be configured by alternately arranging shielding 6a made of boron-containing polyethylene for blocking fast neutrons and shielding 6b made of lead or iron for blocking gamma rays.

[0029] The collimator 7 has an inner peripheral surface that forms a passage hole through which the pulsed neutron beam that has passed through the moderator 4 passes. The collimator 7 shapes the pulsed neutron beam that passes through the passage hole into a pulsed neutron beam (hereinafter also referred to as a neutron beam) with a narrowed cross section. The cross-sectional shape of the neutron beam immediately after passing through the collimator 7 may be, but is not limited to, a vertically elongated rectangle. The size of the opening of the collimator 7 is determined depending on the size of the moderator 4 and the dimensions of the target 1. The collimator 7 may, for example, be formed by alternating portions made of boron-containing polyethylene and portions made of lead or iron, similar to the shielding body 6. The inner peripheral surface of the collimator 7 may be formed from a sintered body of lithium fluoride, boron carbide, boron nitride, or the like, which generates little secondary gamma rays and does not contain hydrogen atoms.

[0030] The slit 8 may be provided to control the irradiation range of the neutron beam on the target 1. The slit 8 may be formed from a sintered body of lithium fluoride, boron carbide, boron nitride, or the like, which generates little secondary gamma rays and does not contain hydrogen atoms. Note that, in one example, the collimator 7 shapes the neutron beam including epithermal neutrons, whereas the slit 8 is made of a material that absorbs thermal neutrons, and therefore cannot control the beam shape of epithermal neutrons.

[0031] The neutron source 10 having the above-described configuration irradiates the object 1 with a pulsed neutron beam (e.g., a pulsed neutron beam of thermal neutrons). That is, the object 1 is placed at a position where the pulsed neutron beam is irradiated by the neutron source 10. When a neutron beam is irradiated at a given angle to an arbitrary position on the object 1 (e.g., a sample), neutrons diffracted in accordance with the internal crystal structure of the irradiated portion of the sample 1 are scattered (Bragg reflected) at a specific scattering angle (e.g., scattering angle 2θ in FIG. 1 ) depending on the neutron wavelength. Although not shown, from the viewpoint of improving work efficiency, the sample 1 may be attached to a stage and a mechanism for moving the stage may be provided.

[0032] The multiple detectors 11 may be arranged in multiple directions as viewed from a reference point on the object 1. Such multiple detectors 11 may be arranged one-dimensionally or two-dimensionally. A large number of neutrons contained in the pulsed neutron beam irradiated from the neutron source 10 to the object 1 are scattered at various scattering angles in the object 1. Each detector 11 detects, of these scattered neutrons (hereinafter simply referred to as scattered neutrons), neutrons scattered at a scattering angle corresponding to the position of the detector 11 (for example, scattering angle 2θ in FIG. 1 ).

[0033] Each time the detector 11 detects a neutron, it may output a detection signal to the time-of-flight measurement unit 12. This detection signal may include information indicating the detection position of the neutron.

[0034] The time-of-flight measurement unit 12 determines the time of flight of each neutron detected by each detector 11 based on the detection signal corresponding to that neutron. This time-of-flight may be the time from when the reference signal is input from the reference signal generation unit 9 to the time-of-flight measurement unit 12 to when the detection signal corresponding to that neutron is input to the time-of-flight measurement unit 12.

[0035] (Delay Time Related to Neutron Flight) The time of flight calculated by the time-of-flight measurement unit 12 includes the following delay times (1) to (4). Therefore, in order to calculate an accurate time of flight, the time of flight is corrected by subtracting all (or part) of the following delay times (1) to (4) from the measured time of flight. (1) Delay Time Related to Electronic Processing An electronic delay time is introduced between the time when the reference signal is input from the reference signal generation unit 9 to the time-of-flight measurement unit 12 and the time when the detection signal is input from the detector 11 to the time-of-flight measurement unit 12. This does not depend on the operating conditions of the pulse or environmental conditions such as the sample 1, and may be treated as a constant specific to the device.

[0036] (2) Delay time associated with the pulse width of a pulsed charged particle beam Conventionally, in time-of-flight neutron diffraction using a large accelerator for a pulsed charged particle beam (pulsed proton beam), the pulse width was set short to improve resolution, so the delay time associated with the pulse width of the pulsed proton beam was not taken into account, and a delta function was used as an input for the initial condition, as seen in the derivation of the well-known Ikeda-Carpenter equation. In contrast, when using a compact neutron source 10, it is necessary to consider the use of a pulsed charged particle beam (e.g., a pulsed proton beam) with a long pulse width in order to increase intensity, and neutrons will continue to be generated from the start of injection of the pulsed charged particle beam into the target 3 until the injection is completed, resulting in a long rise time for the pulsed neutron beam. If the pulse width is negligibly short, there is no problem in regarding the time origin (starting point) of the neutron flight start as being approximately equal to the injection start time of the pulsed charged particle beam, but if the pulse width is long and is equal to or greater than a predetermined value (for example, 20 μsec or 30 μsec), then as shown in FIG. 2A, the median value of the pulse width of the pulsed charged particle beam can be said to be the reference time point (starting point of the flight time) of the neutron group, and therefore, if the injection start time (time of generation) of the pulsed charged particle beam is taken as the time origin, then the time half the pulse width δ of the pulsed charged particle beam becomes the reference time point (starting point of the flight time) of the neutron pulse. Therefore, if the pulse width of the pulsed charged particle beam is equal to or greater than the predetermined value, the delay time is half the pulse width δ (T in FIG. 2A). １ = δ / 2).

[0037] The pulse width of a pulsed charged particle beam is the duration of the pulsed charged particle beam, and may mean, for example, the length of time from when the number of charged particles passing through a specified plane perpendicular to the direction of travel of the pulsed charged particle beam per unit time becomes equal to or greater than a threshold value (e.g., 50% of the maximum value of the number) to when the number becomes smaller than the threshold value again.

[0038] (3) Delay time associated with the neutron deceleration process by the moderator 4 Figure 2B shows a schematic diagram of the delay caused by deceleration of a pulsed neutron beam with an extremely short pulse width in the moderator 4. That is, Figure 2B shows the pulsed neutron beam emitted from the moderator 4 (a response function showing the number of neutrons at the neutron emission surface 4a versus time). The response function for such an extremely short pulse width is called an impulse response function. As shown in Figure 2B, the time T from the start of neutron emission from the moderator 4 to the peak point of the pulsed neutron beam is taken as the reference point. ２ can be the delay time associated with the neutron slowdown process by the moderator 4. However, T ２ should be the time when the neutron number peaks. However, the impulse response functions shown in each of Figures 2C to 2E do not include the time when the neutron number peaks (t ｐ 2C to 2E, the equation on the right side represents the mathematical expression of the impulse response function shown in the graph on the left side. ｐ In the case of an impulse response function that does not include a parameter indicating ｐ In order to calculate the time when the differential function of the impulse response function becomes zero, it is necessary to numerically calculate the time. ｐ The error of T will inevitably be affected by the errors of other parameters. ２ As a reference point, the parameter τ of the impulse response function is used. ０ For example, in the case of the Ikeda-Carpenter function, the origin is the reference time point, so T ２ is zero, and if it is a function obtained by convolving an exponential function with a Gaussian function, T ２ In this case, as will be described later, it is sufficient to obtain a response function for a rectangular pulse charged particle beam (for example, the rectangular shape in FIG. 2A) having a pulse width equal to or greater than the predetermined value, and the delay time T １ , T ２ It is possible to express the neutron number-time distribution that reflects the above.

[0039] (4) Delay Time Due to Increased Uncertainty The time waveform of the pulsed neutron beam emitted from the moderator 4 has an asymmetric shape with a trailing tail, but it does not reach the detector 11 with this waveform as is. The uncertainty increases due to the divergence angle of the pulsed neutron beam (neutron beam), the size of the target object 1 (sample), the resolution of the detector 11, etc., and the pulse width widens. In many cases, the probability density distribution of the uncertainty that contributes to this increase in pulse width is a symmetric distribution (for example, a Gaussian distribution), so the waveform of the pulsed neutron beam emitted from the moderator 4 is observed as a waveform convolved with a Gaussian function. Since the waveform of the pulsed neutron beam emitted from the moderator 4 is an asymmetric waveform (for example, the solid curved waveform in Figure 2F), when this is convolved with a Gaussian function, the sharp part becomes blunted, as in the dashed curved waveform in Figure 2F, and the peak point shifts to the gentler tail side, i.e., in the delay direction, and the delay time T ３ Therefore, the waveform detected by the detector 11 is the waveform shown by the dashed curve in FIG.

[0040] (Time-of-flight correction device) As described above, the time-of-flight correction device 20 is a device that corrects the time-of-flight determined by the time-of-flight measurement unit 12. The time-of-flight correction device 20 includes a storage unit 21 and a data processing device 22.

[0041] The storage unit 21 stores delay time data for estimating the delay time associated with the flight of neutrons emitted from the neutron source 10. The delay time data is the pulse width of the pulsed charged particle beam (the above-mentioned delay time T １ ) and the deceleration characteristics of the moderator 4 that decelerates neutrons to the target 1 (the above-mentioned delay time T ２ However, the delay time data may be determined in advance based on the deceleration characteristic rather than the pulse width, out of the pulse width and the deceleration characteristic.

[0042] In addition, the memory unit 21 stores, for each of the above-mentioned detection signals, the flight time (i.e., flight time including delay time) calculated by the flight time measurement unit 12 and the detection position included in the detection signal as particle bank data (i.e., measurement data).

[0043] The data processing device 22 corrects the time of flight measured by the time of flight measurement unit 12 based on the delay time data and particle bank data stored in the memory unit 21. The correction of the time of flight based on the delay time data and particle bank data will be described in detail later.

[0044] (Time-of-flight measurement method) Figure 3 is a flowchart showing a time-of-flight measurement method according to an embodiment of the present invention. This time-of-flight measurement method includes a delay time acquisition process for acquiring the delay time data described above, a measurement process for actually measuring the time of flight and correcting it based on the delay time data and particle bank data, and an analysis process for performing analysis based on the corrected time of flight. The delay time acquisition process includes steps S1 to S4, the measurement process includes steps S5 and S6, and the analysis process includes step S7.

[0045] <Delay Time Data Acquisition Process> In step S1, a time distribution representing the number of neutrons emitted from the neutron source 10 with respect to time t is obtained by simulation. This simulation relates to the neutron source 10 and may be, for example, a particle transport calculation (neutron transport calculation). More specifically, this simulation is a neutron number time distribution representing, with respect to time, the number of neutrons emitted from a predetermined location in the neutron source 10 (e.g., the neutron emission surface 4a of the moderator 4) to the object 1 by irradiating the target 3 with a pulsed charged particle beam in the neutron source 10. The simulation will be described in more detail later.

[0046] In step S1, the neutron number-time distribution corresponding to each neutron energy value is calculated. The energy value may be, for example, the energy value of the neutrons at the neutron emission surface 4a.

[0047] In step S2, a time distribution function f(t) is created which represents the number of neutrons emitted from the neutron source 10 with respect to time t. More specifically, this time distribution function f(t) is a function which represents, with respect to time t, the number of neutrons f(t) emitted from a predetermined location in the neutron source 10 (e.g., the neutron emission surface 4a of the moderator 4) to the object 1 by irradiating the target 3 with a pulsed charged particle beam in the neutron source 10. That is, the time distribution function f(t) may be a function which represents the number of neutrons at a predetermined location (e.g., the neutron emission surface 4a of the moderator 4) with respect to time. Here, the predetermined location may be a predetermined plane which is perpendicular to the flight direction (central axis) of the pulsed neutron beam.

[0048] The time distribution function f(t) may be a response function obtained by convolving a pulse function representing the pulse shape of the pulsed charged particle beam with an impulse response function representing the moderation characteristics of neutrons by the moderator 4. Alternatively, the time distribution function f(t) may be a function obtained by convolving the response function with a Gaussian function representing uncertainty. The uncertainty is the standard deviation σ contained in the Gaussian function (for example, the uncertainty σ is the σ contained in the Gaussian function g(x) expressed by [Equation 2] described below). The uncertainty causes an increase in the pulse width of the pulsed neutron beam. Examples of uncertainties include, but are not limited to, the following. The uncertainty may include, for example, one or both of the uncertainty after the pulsed neutron beam has passed through the moderator 4 and the uncertainty while the pulsed neutron beam is passing through the moderator 4. The uncertainty after the pulsed neutron beam has passed through the moderator 4 may be caused by, for example, all or any combination of two of the divergence angle of the pulsed neutron beam, the size of the object 1 (sample), and the resolution of the detector 11. The uncertainty when the pulsed neutron beam is passing through the moderator 4 is caused, for example, in the process of the pulsed neutron beam being decelerated by the moderator 4.

[0049] The impulse response function may include a plurality of decay terms. The plurality of decay terms may be two decay terms, or may be three or more decay terms. The decay terms included in the impulse response function may be exponential functions. The time distribution function f(t) may include a constant or a parameter (δ / 2) representing the pulse width δ described above. The time distribution function f(t) includes a plurality of parameters, including a parameter representing the deceleration characteristics of the moderator 4 (the parameter of the decay term described above) and a reference time t indicating the delay time of the neutrons. ０ These parameters may also include a parameter representing the pulse width δ. The time distribution function f(t) will be explained in more detail later.

[0050] In step S3, the time distribution function f(t) is set by determining optimal values ​​of a plurality of parameters of the time distribution function f(t) such that the time distribution function f(t) created in step S2 fits (matches or coincides with) the neutron number time distribution created in the simulation processing of step S1. In other words, the time distribution function f(t) is determined by determining the values ​​of each of the plurality of parameters.

[0051] In step S3, for each neutron energy value, the time distribution function f(t) corresponding to the energy value is set by determining optimal values ​​of a plurality of parameters that fit the time distribution function f(t) to the above-mentioned neutron time distribution corresponding to the energy value. In this way, f(t) corresponding to each neutron energy value is set.

[0052] In step S4, the reference time t ０ In the time distribution function f(t), this reference time t ０ The time difference between the reference time t and the origin of time (i.e., t=0) indicates the delay time for the flight of the neutron. ０ is a time point relative to the origin of time in the time distribution function f(t), and is the distance from the origin to the reference time t ０The time from the start of the neutron flight to the time of flight measurement unit 12 is specified as the delay time. The delay time constitutes delay time data. Note that the origin may coincide with the start of the neutron flight time measured in step S5 (the time point at which the reference signal is input to the time of flight measurement unit 12), which will be described later. However, since an electronic delay generally occurs before the reference signal is input to the time of flight measurement unit 12, the origin may be treated as a delay time specific to the device.

[0053] In step S4, for each neutron energy value, the delay time corresponding to that energy value is identified from the time distribution function f(t) corresponding to that energy value as described above. Therefore, for each energy value, delay time data is created in which the energy value and the identified delay time are associated with each other. This delay time data may be a function representing the delay time as a dependent variable with respect to the energy value as an independent variable, or may be a table in which each energy value is associated with the delay time, but is not limited to these. The delay time data created in step S4 is stored in the memory unit 21. That is, in addition to the delay time data for each neutron energy value, particle bank data from the time-of-flight measurement unit 12 is stored in the memory unit 21 as in step S5 described below. Note that steps S3 and S4 may be performed by a computer.

[0054] <Measurement Process> In step S5, the neutron source 10 generates a pulsed neutron beam by irradiating the target 3 with a pulsed charged particle beam, and the neutron beam is irradiated onto the object 1. As a result, neutrons scattered in the object 1 are detected by the detectors 11.

[0055] The time-of-flight measurement unit 12 determines the time of flight of each neutron detected by each detector 11. That is, each time each detector 11 detects a scattered neutron arriving at that detector 11, it outputs a detection signal including information indicating the detection position of that neutron to the time-of-flight measurement unit 12. For each detector 11, the time-of-flight measurement unit 12 determines the time of flight of the scattered neutron corresponding to that detection signal based on each detection signal from that detector 11 and the above-mentioned reference signal. This time-of-flight may be the time from the start of the time-of-flight (the point at which the reference signal is input to the time-of-flight measurement unit 12) to the time at which the corresponding detection signal is input to the time-of-flight measurement unit 12. For each detected neutron, data on the time of flight and the above-mentioned detection position of the neutron are recorded in the memory unit 21 as particle bank data.

[0056] In step S6, the data processing device 22 corrects the flight times of each neutron calculated in step S5 by subtracting the delay time based on the delay time data created in step S4 and stored in the memory unit 21 (delay time data of the memory unit 21). That is, for each detector 11, the data processing device 22 corrects the flight times of each neutron detected by the detector 11 to the flight times that the neutrons actually traveled, based on the delay time data.

[0057] More specifically, for each neutron detected by each detector 11, the data processing device 22 identifies the delay time corresponding to the energy value and detection position of that neutron in the delay time data, and calculates the corrected delay time by subtracting that delay time from the time of flight calculated in step S5. Here, since the time of flight itself is a function of the neutron energy, iterative calculations (implicit solution) are performed to determine the amount of correction (delay time) for the time of flight.

[0058] Step S6, which is an example of the repetitive calculation, will be described in more detail with reference to Fig. 4. In step S6, for each detector 11, for each neutron detected by the detector 11, the data processing device 22 may repeatedly perform the following steps S61 to S66, as shown in the flowchart of Fig. 4.

[0059] In step S61, the neutron flight time t obtained in step S5 is ｄ The velocity v of the neutron is calculated from the flight distance L of the neutron. For example, the velocity v of the neutron is calculated using the following formula: v = L / (t ｄ -t ０ -t ｃｏｎｓｔ ) where t ｃｏｎｓｔ is the delay time inherent to the neutron measurement device 100 that occurs from the time of neutron generation to the input of the reference signal to the time-of-flight measurement unit 12 (hereinafter the same), and t ０ is zero in the first step S61, but is the delay time provisionally determined in the immediately preceding step S63 in the second and subsequent steps S61. The flight distance L is calculated by the data processing device 22 from the positional relationship between the known position of the neutron source 10, the known position of the target object 1, and the detection position in the particle data bank in the memory unit 21. If the detection position of the neutron is fixed for each detection element of the detector 11, the flight distance L may be calculated in advance for each detection position and stored in the data processing device 22.

[0060] In step S62, the neutron energy value (i.e., kinetic energy 0.5 mv) is calculated based on the neutron velocity v calculated in step S61 and the known neutron mass m. ２ The unit of neutron kinetic energy may be eV.

[0061] In step S63, the neutron delay time t is calculated based on the delay time data obtained in step S4 and the energy value obtained in step S62, as described above. ０ That is, in the delay time data obtained in step S4, the delay time t corresponding to the energy value obtained in step S62 is tentatively specified. ０ Tentatively identify:

[0062] In step S64, the delay time t ０ is the delay time t determined in the previous step S63. ０ In the first step S64, the difference ε is calculated based on the delay time t０ is.

[0063] In step S65, it is determined whether the difference ε calculated in step S64 is smaller than a predetermined convergence value. If the result of this determination is negative, the process returns to step S61 and steps S61 to S65 are performed again. On the other hand, if the result of this determination is positive, the process proceeds to step S66.

[0064] In step S66, the delay time t ０ is finally determined as the delay time and output, and the flight time t measured in step S5 is ｄ The output delay time t ０ The time of flight is corrected by subtracting the value of t. The corrected time of flight, TOF, is calculated as follows: TOF = t ｄ -t ０ -t ｃｏｎｓｔ It may be.

[0065] <Analysis Process> Step S7 is performed by the analysis device 31 of the neutron measurement device 100.

[0066] In step S7, the analysis device 31 generates neutron number distribution data for the object 1 for each detector 11 or for the range of scattering angles to be observed, for each scattering angle (i.e., for each detection position), based on the time of flight TOF corrected in step S6 for each detected neutron.

[0067] The distribution data may be data representing the number of scattered neutrons relative to the time of flight TOF corrected in step S6. That is, the analysis device 31 calculates the t ０ (t output in step S66 ０ ) based on the time of flight TOF = t ｄ -t ０ -t ｃｏｎｓｔ and then generates distribution data of the number of neutrons with respect to the time of flight TOF based on the time of flight TOF of each neutron. The analysis device 31 may store the generated distribution data in the storage device 32 and display it on the display device 33. The storage device 32 and the display device 33 may be components of the neutron measurement device 100.

[0068] Furthermore, in step S7, the analysis device 31 may determine the lattice spacing of the object 1 based on the time of flight TOF corrected in step S6 for each detected neutron, the scattering angle 2θ and flight distance of the neutron corresponding to the detection position of the neutron, and the Bragg condition for scattering of the neutron. In this case, for example, the analysis device 31 may identify the lattice spacing of the object 1 using a lattice spacing distribution function f(d) described later, as will be described later.

[0069] (Detailed explanation of setting the time distribution function f(t)) <Obtaining neutron number time distribution by simulation> For one pulsed neutron beam generated from the target 3, a neutron number time distribution (hereinafter also simply referred to as neutron number time distribution) is obtained in advance, which represents the number of neutrons of each energy present on the neutron emission surface 4a (i.e., passing through the neutron emission surface 4a) versus elapsed time for each neutron energy. The neutron number time distribution may reflect the pulse width of the pulsed charged particle beam. The neutron number time distribution may be obtained by particle transport calculation. For the particle transport calculation, a particle transport calculation code such as PHITS or MVP may be used.

[0070] Figures 5A to 5D show examples of neutron number-time distributions. Figures 5A to 5D show neutron number-time distributions when the neutron energies are 0.001577 eV, 0.026538 eV, 0.123390 eV, and 0.840645 eV, respectively. In Figures 5A to 5D, the horizontal axis represents elapsed time, and the vertical axis represents the number of neutrons present on the neutron emission surface 4a in arbitrary units.

[0071] The neutron number-time distributions in Figures 5A to 5D were obtained as follows. To perform calculations efficiently, the reaction of converting a proton beam (as a charged particle beam) into neutrons at the target 3 was calculated using PHITS, and transport calculations of the generated neutrons were performed using MVP. In PHITS, neutrons generated when a 7 MeV proton beam (beam diameter 150 μm) was irradiated onto a microscopic piece of beryllium (target 3) having a diameter of 300 μm and a thickness of 300 μm was calculated for each range of the solid angle α, and the angular distribution of the neutron number was calculated (see Figures 6A and 6B). Note that JENDL-5 was used for the Be(n, p) cross section used by PHITS. Information about the neutron source 10 calculated by PHITS was incorporated into the input data for MVP, and neutron transport calculations were performed for cases where the pulse width of the proton beam (as a charged particle beam) was 30 μsec and 40 μsec. A tally for compiling the calculation results was placed on the neutron emission surface 4a of the moderator 4, and only the emitted neutrons were tallied. The outline of the calculation system was similar to the structure near the target 3 shown in Figure 1. The distribution of neutron intensity (number of neutrons) on the neutron emission surface 4a of the moderator 4 calculated for a proton beam pulse width of 30 μsec is shown in Figures 5A to 5D described above. As can be seen from Figures 5A to 5D, the time distribution of the number of neutrons on the neutron emission surface 4a of the moderator 4 changes significantly depending on the neutron energy.

[0072] <Time distribution function f(t)> A time distribution function f(t) that fits (matches) the neutron number time distribution obtained as described above is obtained. That is, for each neutron energy, a time distribution function f(t) that matches the above neutron number time distribution for that energy is obtained as follows:

[0073] The time distribution function f(t) may utilize, for example, an exponential function e(x) expressed by the following [Equation 1]: In [Equation 1], x indicates elapsed time, e is the base of the natural logarithm, a is a parameter, and e(x) is the number of neutrons on the neutron emission surface 4 a.

[0074]

[0075] Here, since the results of particle transport calculations may contain statistical errors, a function convolved with a Gaussian function g(x) may be obtained from the beginning. The Gaussian function g(x) is expressed by the following [Equation 2].

[0076]

[0077] When the exponential function e described above is convoluted with a Gaussian function g, the impulse response function specific to the moderator 4 is expressed by the following [Equation 3]: In [Equation 3], erf represents the error function.

[0078]

[0079] Next, a response function is calculated when the pulse width of the charged particle beam is taken into consideration. Assuming that the pulse shape of the charged particle beam is rectangular as shown in FIG. 2A, the Laplace transform is used for the convolution integral of the pulse function representing the rectangular pulse and the Gaussian function g. The Laplace transform of a unit rectangular wave Rect having a pulse width δ is expressed by the following [Equation 4].

[0080]

[0081] Therefore, when the convolution integral of the above-mentioned unit rectangular wave Rect and the exponential function e is expressed by Laplace transform, it is expressed by the following [Equation 5].

[0082]

[0083] By performing an inverse Laplace transform of [Equation 5], the following [Equation 6] is obtained: In [Equation 6], θ is the Heaviesside function.

[0084]

[0085] A response function that reflects the pulse width can be obtained by convolving a Gaussian function with the above [Equation 6]. ａ is expressed by the following [Equation 7].

[0086]

[0087] In the above [Equation 7], the reference of time t (for example, the origin) is the start time of the generation of the pulsed charged particle beam. Therefore, in order to use the time point at half (the center) of the pulse width δ of the pulsed charged particle beam as the reference, t in [Equation 6] is changed to t - t ０ Substituting -δ / 2 gives the following equation (8): ０ is the reference time point indicating the delay time mentioned above.

[0088]

[0089] The actual neutron number-time distribution at the neutron emission surface 4a of the moderator 4 has two decay rate components in its tail, as shown by the known Ikeda-Carpenter peak function, whereas the above [Equation 8] contains only one decay rate component. Therefore, it is preferable to include two decay rate components in the response function representing the neutron number-time distribution. In this case, another response function f having a decay rate b different from the decay rate a in the above [Equation 8] is used. ｂ are prepared, and a composite function obtained by combining them at a coupling ratio R is used as the time distribution function f(t). That is, this composite response function f(t) is expressed by the following [Equation 9].

[0090]

[0091] In this function, the reference point is set to the peak point of the exponential function, similar to the known back-to-back exponential function. ０ varies with the energy of the neutron.

[0092] <Calculation of the reference time point and function> The reference time point t is calculated by the nonlinear least squares method using the time distribution function f(t) of [Equation 9] above, which reflects the pulse width, for the neutron number time distribution for each neutron energy based on the MVP obtained as described above. ０ Ask for.

[0093] The time distribution function f(t) fitted to the neutron number-time distribution obtained by MVP for each neutron energy is shown in Figures 7A to 7D. This fitting was performed using the nonlinear least squares method. That is, by fitting, the parameters a, b, R, σ, t in the above [Equation 9] are ０was defined. δ in f(t) is a known value. In Figs. 7A to 7D, the horizontal axis indicates time, and the vertical axis indicates the number of neutrons at the neutron emission surface 4a. In Figs. 7A to 7D, many points (small white circles) indicate the results calculated using MVP, and the solid curves indicate the above-mentioned time distribution function f(t) fitted to the results of MVP calculation. Figs. 7A to 7D each show the time distribution function f(t) when the neutron energy is 5.623410 x 10 －５ eV, 2.610160×10 －２ eV, 1.211530×10 －１ eV, 8.254040×10 －１ 7A to 7D show the time distribution function f(t) after fitting when the pulse width δ of the charged particle beam is 40 μsec.

[0094] As can be seen from FIGS. 7A to 7D, the time distribution function f(t) is a response function that is simply a combination of two simple exponential functions, but it fits well to the MVP calculation results over a wide energy range.

[0095] FIG. 8 shows the time distribution function f(t) calculated from the reference time t ０ Also, at the reference time t ０ is the time elapsed from the point when neutrons start to be generated at the neutron emission surface 4a (the time elapsed from the origin of the horizontal axis in Figures 7A to 7D). Figure 8 shows the reference time t obtained when the pulse width of the charged particle beam is 30 μsec and 40 μsec. ０ This shows:

[0096] As can be seen from FIG. 8, the reference time t of the time distribution function f(t) ０ is almost constant at high and low energy levels, and transitions in the intermediate region between 0.001 eV and 0.06 eV. In the high energy region, it is approximately half the pulse width. As the energy decreases, the delay time associated with the neutron slowing down process becomes significant. At 0.001 eV or less, the two attenuation coefficients (a and b) become almost constant, and accordingly, the reference time t ０ is also considered to be a constant value.

[0097] (When creating a lattice spacing distribution function) The time distribution function f(t) corresponding to each energy value for each scattering angle can be converted into a lattice spacing distribution function f(d) based on the Bragg condition for neutron scattering. This lattice spacing distribution function f(d) is a function that corresponds to the detection position in each detector 11 (i.e., each scattering angle 2θ), and is a function that represents the number of neutrons f(d) for the lattice spacing d of the object 1. As will be described later, the lattice spacing distribution function f(d) is obtained by fitting the measured lattice spacing distribution to the lattice spacing d. ０ The lattice spacing distribution function f(d) may be stored in the analysis device 31.

[0098] The lattice spacing distribution function f(d) can be determined, for example, as follows.

[0099] The Bragg condition for neutron scattering is λ=2d sin θ, and when the neutron wavelength λ=h / mv is substituted into this, the lattice spacing d is expressed by the following [Equation 10].

[0100]

[0101] Here, h is Planck's constant, 2θ is the scattering angle, m is the mass of a neutron, and v is the velocity of the neutron. In the time-of-flight method, the velocity of a neutron is calculated from the flight distance L and flight time t of the neutron, so by substituting v = L / t into [Equation 10], the following [Equation 11] is obtained. Note that the flight distance L and flight time t may be the flight distance and flight time from the time when the neutron is generated in the target 3, passes through the moderator 4 and collimator 7, is scattered by the sample, and then is detected by the detector 11.

[0102] The time distribution function f(t) fitted as described above can be said to be a probability density distribution df(t) / dt with respect to time, and therefore the probability density distribution df(d) / dd with respect to the lattice spacing d can be transformed into the following [Equation 12].

[0103]

[0104] Here, the coefficient h / (2mL sin θ) included in [Equation 11] has the dimension of velocity, so v ｃ It is defined as:

[0105]

[0106] This V ｃ By substituting each coefficient as in the following [Equation 14] using [Equation 12], the lattice spacing distribution function f(d) of the following [Equation 15] for the lattice spacing d can be obtained from [Equation 12].

[0107]

[0108] It should be noted that the σ of the detected distribution is not the σ of the time distribution function f(t), but is a σ that is larger depending on the size of the object 1 (sample), the beam divergence angle, the position resolution of the detector 11, etc.

[0109] Each coefficient in [Equation 14] is v ｃ Since these coefficients are functions of the scattering angle 2θ and the flight distance L, they are parameters that change depending on the detection position. ０ and R is v ｃ Since it does not depend on , it does not change even if the detection position is different. ０ is the reference time t ０ is the lattice spacing d corresponding to

[0110] The lattice spacing of the object 1 may be determined using such a lattice spacing distribution function f(d). In this case, the above-mentioned step S7 may be performed as follows. In this case, matters not described below are the same as those described above. After steps S1 to S6 are performed as described above, step S7 is performed as follows.

[0111] The analysis device 31 calculates the t ０ (t output in step S66 ０) the lattice spacing d is calculated as follows: If d is the lattice spacing of the object 1, h is the Planck constant, 2θ is the scattering angle, and λ is the neutron wavelength, the Bragg condition for neutron scattering is expressed as λ = 2d sin θ. If the neutron wavelength λ = h / mv is substituted into this (m and v are the mass and velocity of the neutron), the lattice spacing d becomes d = λ / (2 sin θ) = h / (2mv sin θ). Adding to this the t finally obtained in the processing of FIG. ０ The corrected neutron flight speed v = L / (t ｄ -t ０ -t ｃｏｎｓｔ ) is substituted, the lattice spacing d is expressed by the following formula: d = h(t ｄ -t ０ -t ｃｏｎｓｔ ) / (2L sin θ) Therefore, for each neutron, the analysis device 31 uses this formula and the t ０ Here, L is the flight distance calculated or stored by the data processing device 22 as described above.

[0112] Thereafter, the analysis device 31 generates distribution data of the number of neutrons relative to the lattice spacing d (i.e., the above-mentioned lattice spacing distribution) based on the lattice spacing d determined for each neutron. After generating the distribution data through such preprocessing, the analysis device 31 determines a plurality of parameters of the lattice spacing distribution function f(d) that fit the lattice spacing distribution function f(d) to the distribution data. The plurality of parameters include the parameter d ０ The analysis device 31 determines the parameter d ０ is identified as the lattice spacing of the object 1. The analysis device 31 then ０ may be stored in the storage device 32 and displayed on the display device 33.

[0113] (Confirmation of Effects by Example) In order to confirm the effect of the delay time deducting system (data processing device 22) using the above-mentioned distribution functions f(t) and f(d), a simulation of a pulsed neutron source time-of-flight neutron diffractometer was performed using the neutron ray tracing Monte Carlo code McStas. The calculation system of the model pulsed neutron source time-of-flight neutron diffractometer is shown in FIG. 9 . The calculation was performed in two stages. In the first stage, calculations are performed from the neutron emission surface 4 a of the moderator 4 to the exit of the collimator 7 (see FIG. 1 ), and particle information such as the position, time, and vector of the neutrons is dumped at the opening of the slit (corresponding to slit 8 in FIG. 1 ) at the exit of the collimator 7. Next, the dumped particle information is used to perform calculations for the subsequent slit (see FIG. 9 ), through the sample as the target 1, and to the detector. The calculations were performed in two stages because neutrons generated from the moderator 4 are emitted almost isotropically, and it was assumed that calculations up to the exit of the collimator 7 would take a long time. Another advantage of performing the calculation in two stages is that even if the slit size, sample size, detector position, etc. in the latter stage are changed, there is no need to redo the calculation in the former stage.

[0114] The radiation source placed on the surface of the collimator 7 uses a component designed to generate random numbers using the inverse function method based on the neutron spectrum, time distribution, and two-dimensional distribution calculated with MVP. A component refers to a device unit described in McStas. The MCPL_output component placed at the exit of the collimator 7 output particle information to a binary file in mcpl format. Next, in a separate calculation, this mcpl file was read by the MCPL_input component, and downstream calculations up to the detector were performed. For the He-3 neutron position detector, we used the PSD_TOF_d_Detector_offset component, which was based on the PSD_Detector component developed by ILL and modified to allow time and lattice spacing to be used on the horizontal axis. In this study, a delay time deducting system was incorporated into this component, and the lattice spacing was calculated by subtracting the delay time for each detected neutron, and the neutrons were then accumulated in bins (equally spaced accumulation elements). The vertical axis of the distribution obtained by McStas is not the count value, but is the integrated value multiplied by the particle weight.

[0115] The distribution of lattice spacing d simulated by McStas is shown in Figures 10A to 10C. Due to the effect of the delay time deducting system (referred to as DDS in the figures), the correct lattice spacing of the iron (211) plane is 1.1782 × 10 －１０ m (vertical dotted line in the figure). Also, the higher the angle, the sharper the peak becomes, which is a characteristic of time-of-flight neutron diffractometers. As can be seen in the process of repeated calculations described above, the peak point of the curve is the true value of 1.1782 × 10 －１０ m, and the reference time t ０ Lattice spacing d ０ is the value to be found.

[0116] Therefore, the parameter d of f(d) is fitted to the lattice spacing distribution (distribution data of the number of neutrons relative to the lattice spacing) f(d) obtained using the delay time deducting system. ０ Search for and find d ０is plotted against the scattering angle in Figure 11. In Figure 11, the horizontal axis represents the scattering angle 2θ, and the vertical axis represents the lattice spacing d ０ It can be seen that the use of the delay time deducting system allows the lattice spacing to be calculated almost accurately at scattering angles of 60° or more. The disturbance in the values ​​at both ends is due to the calculation being performed with the edge effect of the He-3 detector 11 enabled, and the edge effect needs to be tuned according to the characteristics of the actual He-3 detector 11.

[0117] In this example, we used the simplest exponential function to calculate the distribution functions f(t) and f(d) for the case of pulse width. Simulations were performed under conditions close to reality, confirming the effectiveness of the delay time deducting system. While conventional methods require the use of standard samples to determine calibration constants at each detector position, the method of this example enables nearly accurate lattice spacing measurements over a wide scattering angle range, excluding the low-angle region, by evaluating delay times using particle transport calculations and profile fitting alone, without relying on experimental calibration using standard samples. Furthermore, the fact that the lattice spacing obtained is consistent over a wide scattering angle range is an important characteristic when using time-focusing technology to detect lattice spacings from multiple detectors. In this case, as shown in Figure 11, combining detectors above 60° into one unit improves detector sensitivity and reduces statistical error. However, by combining this with the conventional method and correcting for deviations at low angles, measurements can be performed over a wider range. Therefore, it is anticipated that this method will have a major impact in areas where the pulse width is increased in a small accelerator to increase intensity, and the detector area is enlarged to achieve time focusing.We believe that the importance of this issue will increase as neutron sources become more compact.

[0118] (Program) The time-of-flight correction device 20 according to the above-described embodiment can be realized by a computer, a program, and a storage medium. In this case, the program causes the computer to execute each process (each step) performed by the data processing device. In this case, the storage medium may be a computer-readable medium (for example, a storage medium such as a computer hard disk or memory, or a CD-ROM) that non-temporarily stores the program.

[0119] The present invention is not limited to the above-described embodiments, and various modifications may be made within the scope of the technical concept of the present invention. For example, the method and apparatus according to the embodiments of the present invention may not have all of the above-described features, or may have only some of the above-described features. Furthermore, one or more components described in the claims and this specification may be omitted, or any combination of the components described in the claims and this specification may be used, as long as at least some of the above-described problems can be solved or at least some of the effects described in this specification can be obtained.

[0120] In addition, any one of the following modified examples 1 to 4 may be adopted, or any combination of two or more of modified examples 1 to 4 may be adopted. In this case, the points not described below may be the same as those described above.

[0121] (Modification 1) For example, while the delay time data was generated using the time distribution function f(t) expressed by the above [Equation 9] in the above description, it may be generated by other methods. Furthermore, the above-mentioned time distribution function f(t) and lattice spacing distribution function f(d) are not limited to the above [Equation 9] and [Equation 15], respectively, and may be expressed by other mathematical expressions. However, the reference time point of the impulse response function used when generating f(t) and f(d) must be the same for f(t) and f(d).

[0122] (Modification 2) In the above description, the analysis device 31 calculates, for example, the lattice spacing d of the object 1 based on the corrected time of flight TOF. ０However, other processing related to analysis, inspection, etc. of the object 1 may be performed based on the corrected time of flight TOF (for example, the time of flight TOF of each detected neutron).

[0123] (Modification 3) The delay time data represents a delay time corresponding to a neutron energy value, but may represent a delay time corresponding to a neutron velocity or a neutron wavelength. In this case, in step S6, the flight time of a detected neutron may be corrected based on the velocity or wavelength of the neutron and the delay time data. In this case, the related descriptions "energy value" and "energy" above may be replaced with "neutron velocity or neutron wavelength," and the above content may be applied to this modification 3. Note that when the delay time data represents a delay time corresponding to a neutron velocity, the above-mentioned step S62 may be omitted.

[0124] (Modification 4) The delay time data may be calculated in advance based on one of the deceleration characteristics of the moderator 4 that decelerates neutrons toward the target 1 and the pulse width of the pulsed charged particle beam. For example, if the neutron measurement device 100 does not have a moderator 4 or in other cases, the delay time data may be calculated in advance based on the deceleration characteristics of the moderator 4 or the pulse width of the pulsed charged particle beam, but not on the deceleration characteristics. In this case, the delay time indicated by the delay time data may be, for example, half the pulse width of the pulsed charged particle beam (δ / 2), or may be based on the pulse width of the pulsed charged particle beam and an increase in the pulse width of the pulsed neutron beam due to the above-mentioned uncertainty (e.g., the sum of half the pulse width of the pulsed charged particle beam and half the increase). The delay time may be calculated for each neutron energy value, or may be constant regardless of the neutron energy value. Furthermore, when the pulse width of the pulsed charged particle beam is sufficiently short or in other cases, the delay time data may be obtained in advance based on the deceleration characteristics of the moderator 4 and the pulse width of the pulsed charged particle beam, rather than on the pulse width. In this case, for example, δ may be set to 0 in the above-mentioned time distribution function f(t).

[0125] - Fields related to improving the accuracy of structural analysis using compact neutron sources: In light of the high effectiveness of large neutron facilities for evaluating the crystalline structure characteristics of samples and machine parts, and the needs of a wide range of industries including aerospace, automobiles, railway machinery, and energy, providing general-purpose packaged neutron source technology devices for on-site application by large research and development institutions and industrial users has become a competitive field in the development of cutting-edge scientific equipment. In this context, there are already nearly 100 compact neutron sources around the world, and a wide range of applied experimental research is being actively attempted. The technology of this invention can be equipped as a diffraction technology for these compact neutron sources, and is expected to be a new technology that improves the accuracy of neutron diffraction evaluations aimed at on-site material structure analysis, production quality control, and process optimization, promoting the growth of the international market for compact neutron sources and related technical devices.

[0126] REFERENCE SIGNS LIST 1 Object 1 (sample) 2 Charged particle irradiation device 2a Charged particle source 2b Accelerator 3 Target 4 Moderator 4a Neutron emission surface 5 Reflector 5 6, 6a, 6b Shield 7 Collimator 8 Slit 9 Reference signal generator 10 Neutron source 11 Detector 12 Time-of-flight measurement device 20 Time-of-flight correction device 21 Memory 22 Data processing device 31 Analysis device 32 Storage device 33 Display device 100 Neutron measurement device

Claims

1. A method for measuring the time of flight of neutrons, comprising: (A) irradiating a target with a pulsed charged particle beam to generate neutrons, which are then irradiated onto the object; (B) detecting the neutrons scattered by the object to determine the time of flight of the neutrons; (C) determining in advance delay time data for estimating the delay time associated with the flight of the neutrons based on one or both of the pulse width of the pulsed charged particle beam and the deceleration characteristics of a moderator that decelerates the neutrons toward the object; and (D) correcting the time of flight based on the delay time data.

2. A time-of-flight measurement method according to claim 1, wherein in (C), for each energy value of a neutron, the delay time data representing the delay time corresponding to that energy value, neutron velocity or neutron wavelength is determined in advance, and in (D), for the detected neutron, the flight time is corrected based on the energy value, neutron velocity or neutron wavelength of that neutron and the delay time data.

3. A time-of-flight measurement method according to claim 2, wherein in (D), the energy value, velocity or wavelength of the neutron is determined based on the time-of-flight determined in (B) and the flight distance of the neutron, and the time-of-flight is corrected based on the delay time corresponding to the energy value, velocity or wavelength in the delay time data.

4. A time-of-flight measurement method as described in claim 2, wherein in (B), the time-of-flight of each detected neutron is calculated, and in (D), the energy value, speed or wavelength of the neutron is calculated based on the time-of-flight calculated in (B) and the flight distance corresponding to the detection position of the neutron in (B), and the time-of-flight is corrected based on the delay time corresponding to the energy value, speed or wavelength in the delay time data.

5. A time-of-flight measurement method according to claim 3 or 4, wherein in (D), the energy value, speed or wavelength of the neutron is determined again based on the corrected time-of-flight and the flight distance of the neutron, the time-of-flight is corrected again based on the delay time corresponding to that energy value, speed or wavelength in the delay time data, and the difference between the corrected time-of-flight and the previously corrected time-of-flight is determined repeatedly, and when the difference becomes equal to or less than a predetermined convergence value, the finally corrected time-of-flight is output.

6. In (C) above, with respect to (A) above, (C1) for each neutron energy value, a time distribution function f(t) is created that expresses the number of neutrons with respect to time t, and the time distribution function f(t) is calculated based on the reference time t. ０ (C2) obtaining a time distribution that represents the number of neutrons with respect to time by simulation; (C3) setting the time distribution function f(t) by determining values ​​of the plurality of parameters of the time distribution function f(t) that allow the time distribution function f(t) to fit to the time distribution; (C4) fitting the reference time t, which is the determined parameter, to the set time distribution function f(t). ０ The time-of-flight measurement method according to any one of claims 2 to 5, wherein the delay time data is generated based on:

7. The time-of-flight measurement method according to claim 6, wherein the time distribution function f(t) is a response function obtained by convolving a pulse function representing the pulse shape of the pulsed charged particle beam with an impulse response function representing the deceleration characteristics of neutrons by the moderator, or a function obtained by convolving the response function with a Gaussian function representing uncertainty.

8. The time-of-flight measurement method according to claim 7, wherein the impulse response function includes a plurality of decay terms.

9. A time-of-flight measurement method according to claim 7 or 8, wherein the decay term included in the impulse response function is an exponential function.

10. The time distribution function f(t) is expressed by f in the following equation, ａ is a function of time t including the parameter a of the damping term, and f ｂ is a function of time t including the parameter b of another of the decay terms, δ is the pulse width, R and σ are the parameters, and t ０ The time-of-flight measurement method according to claim 8 or 9, wherein Θ is the reference time point indicating the delay time.

11. A time-of-flight measurement method according to any one of claims 1 to 5, wherein (E) the lattice spacing of the object is determined based on the time-of-flight corrected in (D), the scattering angle and flight distance of the neutron corresponding to the detection position of the neutron, and the Bragg condition for the scattering of the neutron.

12. For each neutron energy value, a lattice spacing distribution function f(d) is created, which expresses the number of neutrons relative to the lattice spacing d. The lattice spacing distribution function f(d) is calculated based on the lattice spacing d of the object. ０ and (E) includes a plurality of parameters including: (E1) generating distribution data representing the number of detected neutrons relative to the lattice spacing based on the time of flight corrected in (D) for each neutron detected in (B) and the Bragg condition for neutron scattering; (E2) determining values ​​of the plurality of parameters of the lattice spacing distribution function f(d) such that the lattice spacing distribution function f(d) fits the distribution data; and (E3) determining the determined parameters, the lattice spacing d ０ The time-of-flight measurement method according to claim 11 , wherein: is specified as the lattice spacing of the object.

13. A time-of-flight correction device that corrects the time-of-flight of neutrons when the time-of-flight of the neutrons is measured by detecting the neutrons generated by irradiating a target with a pulsed charged particle beam, the time-of-flight correction device comprising: a memory unit that stores delay time data for estimating the delay time involved in the flight of the neutrons, the delay time data being calculated in advance based on one or both of the pulse width of the pulsed charged particle beam and the deceleration characteristics of a moderator that decelerates the neutrons toward the target; and a data processing device that corrects the time-of-flight based on the delay time data.

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