Quasi-single-energy neutron generating device

Abstract

The invention discloses a quasi-single-energy neutron generating device, which comprises a vacuum target chamber, a target frame with a driving device, and a target sheet, a plurality of target frames capable of moving up and down are arranged in the target chamber along the beam direction front and back, and a target sheet is mounted at one end, close to the beam, of each target frame, and is characterized in that each target frame is provided with an upper working position and a lower working position, namely a nuclear reaction generating position and a nuclear reaction non-generating position, and the center of the target sheet of the target frame generating the nuclear reaction coincides with the center of an incident proton beam; the center of the target frame and the target sheet which do not generate the nuclear reaction does not coincide with the center of the incident proton beam; when the proton bombards the target piece on the target frame to generate nuclear reaction, the bombarded target piece on the target frame is a combined target piece, the combined target piece is a target piece formed by combining a plurality of target pieces with completely different thicknesses or target pieces with the same thickness, and the center of the combined target piece coincides with the center of an incident proton beam. According to the combined target piece, the thickness of the target piece can be adjusted more flexibly, and the target piece can be inclined to better neutron monochromaticity or higher neutron generation efficiency according to different requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of monoenergetic neutrons, and in particular relates to a quasi-monoenergetic neutron generating device. Background Art

[0002] Monoenergetic neutrons play an indispensable role in the performance evaluation and calibration of neutron detection devices. After decades of development, the technology for generating monoenergetic neutrons below 20 MeV has become relatively mature.

[0003] With the continuous advancement of aerospace technology, the development of quasi-monoenergetic neutron production technology above 20MeV has become urgent and urgent. In the energy range above 20MeV, the conventional method is to set the target thickness according to multiple typical incident proton energies in actual use. The thickness of the target that the proton passes through is composed of one target, that is: one incident proton energy corresponds to one target thickness. One incident proton energy corresponds to one target thickness, which will cause the following problems:

[0004] 1. Only the determined values ​​of several target positions can be replaced, and only discrete adjustments can be made to the target thickness, not continuous adjustments. For example, the application number is: 201911353183.4, and the patent name is: A neutron generating device for a quasi-monoenergetic neutron reference radiation field. Although the drive device can replace the target by moving up and down, an incident proton energy can only target a target of a fixed thickness. When detector calibration and device irradiation do not require too high a neutron flux, but only require more precise requirements for the monochromaticity of neutrons, that is, the quasi-monoenergetic neutron peak is narrower, since the target thickness can only be selected by replacing the determined value of a single target position, it cannot be adjusted continuously and cannot meet the needs. The relationship between neutron peak and monochromaticity is as follows: Figure 7 As shown, in the region of 45MeV to 50MeV, it can be seen that the wider and higher the neutron peak is, the worse the monochromaticity is, and the narrower and shorter the neutron peak is, the stronger the monochromaticity is.

[0005] 2. The utilization rate is low and cannot be replaced online. Each target piece can only be used under the corresponding incident proton energy. When a target piece is damaged, other target pieces cannot be replaced due to different thicknesses, and the corresponding energy neutrons cannot be generated, resulting in a low utilization rate.

[0006] 3. Multiple targets share one cold water channel. Fig. 9 As shown in the figure, the target cooling efficiency is insufficient. In order to reduce the impact on the emitted neutrons, cooling water flows in the channels on the sides of the target and inside the target holder. The cooling performance is limited. When the incident proton flux is increased due to the need for a higher neutron injection, the heat deposited in the target also increases. At this time, the target will face the risk of insufficient cooling efficiency and melting damage. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention proposes a quasi-monoenergetic neutron generating device, aiming to solve the problem in the prior art that one incident proton energy can only correspond to one target thickness, and the target thickness can only be discretely adjusted but not continuously adjusted.

[0008] The present invention proposes the following technical solutions to solve the technical problems:

[0009] A quasi-monoenergetic neutron generating device comprises a vacuum target chamber, a target stand with a driving device, and a target piece. A plurality of target stands movable up and down are arranged front and back in the target chamber along the beam direction, an independent driving device is arranged at one end of each target stand away from the beam channel, and a target piece is installed at one end close to the beam channel. The device is characterized in that each target stand is provided with two upper and lower working positions: a nuclear reaction generating position and a non-nuclear reaction generating position, the center of the target piece of the target stand at the nuclear reaction generating position coincides with the center of the incident proton beam, and the center of the target piece of the target stand at the non-nuclear reaction generating position does not coincide with the center of the incident proton beam; when protons bombard the target piece on the target stand to generate a nuclear reaction, the bombarded target piece on the target stand comprises a combined target piece, which is a target piece composed of a plurality of target pieces with completely different thicknesses or target pieces with partially the same thicknesses, and the center of each target piece of the combined target piece coincides with the center of the incident proton beam.

[0010] Furthermore, the driving device is located at the top of the vacuum target chamber, and the target stand is directly connected to the driving device. The position of the target stand is moved by the driving device to control the working position of each target piece. When the driving device drives the target stand to move downward, the center of the target piece on the target stand coincides with the center of the incident proton beam. At this time, the protons bombard the target piece to generate a nuclear reaction and produce quasi-monoenergetic neutrons. When the driving device drives the target stand to lift up, the target piece and the target stand leave the proton beam line path, and no nuclear reaction occurs at this time.

[0011] Furthermore, the number of target pieces, target racks and driving devices in the vacuum target chamber is the same, and the thickness of each target piece in the vacuum target chamber is the same or different.

[0012] Furthermore, the total length, step length, number of target pieces and thickness of each target piece of the combined target piece are determined according to the selected energy range and control accuracy.

[0013] Furthermore, when the number of target pieces is 6, and 2 of them are 0.5 mm thick, 2 are 1 mm thick, and 2 are 2 mm thick, the position of the target holder is moved by a driving device to combine target pieces of different thicknesses and numbers, so that a total length of 0.5 mm to 6 mm, with a step length of 0.5 mm, and a total of 12 different thicknesses can be achieved, which can cover the production range of almost all quasi-monoenergetic neutrons above 20 MeV.

[0014] Furthermore, when the number of target pieces is 7, and the thicknesses of the target pieces are 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 1 mm, and 2 mm, respectively, by moving the position of the target holder by a driving device to combine target pieces of different thicknesses and numbers, a total length of 0.1 mm to 6 mm, with a step length of 0.1 mm, and a total of 60 different thicknesses can be achieved, which is sufficient to cover the generation range of almost all quasi-monoenergetic neutrons above 20 MeV, and can also achieve more precise and continuous thickness adjustment.

[0015] Furthermore, when conducting neutron irradiation experiments on structural materials and equipment components, more emphasis is placed on neutron flux and less emphasis is placed on the monochromaticity of quasi-monoenergetic neutrons. At this time, the position of the relevant target holder is moved by a driving device to combine target sheets with increased target thickness.

[0016] Furthermore, when performing detector calibration and other tasks, in order to pursue accuracy, the monochromaticity of the quasi-monoenergetic neutrons should be as high as possible. At this time, the position of the relevant target holder is moved by the driving device to combine the target sheets with appropriately reduced target sheet thickness.

[0017] Advantages and effects of the present invention

[0018] 1. Each working state is composed of multiple targets with smaller thickness, which makes the target thickness adjustment more flexible and can be tilted towards better neutron monochromaticity or higher neutron generation efficiency according to different experimental needs;

[0019] 2. A single target can be used in a variety of working conditions, which increases the utilization rate of the target and reduces the overall usage of the target;

[0020] 3. If a single or some target pieces are damaged, the corresponding working state can be composed of other target pieces, which improves the fault resistance of the equipment;

[0021] 4. Each target holder is equipped with a cooling channel, which increases the number of cooling channels and improves the cooling performance of the device, allowing it to withstand higher proton flux intensities and further increase the neutron yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The quasi-monoenergetic neutron generating device of the present invention;

[0023] Figure 2 The working position of the present invention is composed of a target piece;

[0024] Figure 3 The working position of the present invention is composed of two target pieces;

[0025] Figure 4 The working position of the present invention is composed of three target pieces;

[0026] Figure 5 The working position of the present invention is composed of four target pieces;

[0027] Figure 6 The working position of the present invention is composed of five target pieces;

[0028] Figure 7 It is the neutron energy spectrum emitted within 0-5° relative to the proton incident direction when 50MeV protons bombard targets of different thicknesses in the present invention;

[0029] Figure 8 The quasi-monoenergetic neutron peaks generated by 50MeV protons bombarding targets of different thicknesses in the present invention;

[0030] Fig. 9 This is a schematic diagram of the prior art in which the incident proton energy can only correspond to one target thickness, and multiple targets share one water cooling channel. DETAILED DESCRIPTION

[0031] Design principle of the present invention

[0032] 1. Innovation of the present invention: The innovation lies in the invention of a "combination target piece". When the number of target racks is 6 or 7, the "combination target piece" can have 12 and 60 combination methods respectively according to the set step length. The corresponding incident proton energies also have 12 and 60 incident energies. However, in the prior art, if there are 6 target pieces, it can only correspond to 6 incident proton energies, and if there are 7 target pieces, it can only correspond to 7 incident proton energies. After adopting the combination target piece of the present invention, not only the corresponding proton incident energy is multiplied several times, but more importantly, it can be changed from discrete adjustment to continuous adjustment.

[0033] 2. The solution of the present invention: First, each target holder is an independent driving device, while in the prior art, multiple target pieces share one driving device; second, each target piece has two positions, a position for undergoing nuclear reaction with protons, and a position for not undergoing nuclear reaction with protons; third, the target piece for undergoing nuclear reaction with protons is a combined target piece, and the position of each target piece in the combined target piece is a position capable of undergoing nuclear reaction with protons.

[0034] The present invention will be further described below in conjunction with the accompanying drawings:

[0035] A quasi-monoenergetic neutron generating device such as Figure 1-6As shown, it includes a vacuum target chamber, a target stand with a driving device, and a target piece; a plurality of target stands that can move up and down are arranged front and back along the beam direction in the target chamber, and each target stand is installed with a target piece near one end of the beam, and its characteristics are: each target stand is provided with two upper and lower working positions: a nuclear reaction generating position and a non-nuclear reaction generating position, the center of the target piece of the target stand at the nuclear reaction generating position coincides with the center of the incident proton beam, and the center of the target piece of the target stand at the non-nuclear reaction generating position does not coincide with the center of the incident proton beam; when protons bombard the target piece on the target stand to generate a nuclear reaction, the target piece on the bombarded target stand includes a combined target piece, which is a target piece composed of a plurality of target pieces with completely different thicknesses or target pieces with partially the same thicknesses, and the center of each target piece of the combined target piece coincides with the center of the incident proton beam.

[0036] Supplementary Note 1

[0037] A. Target chamber. Figure 1-6 As shown, the target chamber is made of aluminum alloy, titanium alloy or other materials with high structural strength. The front beam inlet is connected to the vacuum pipe of the beam pipeline through a flange, and a thin titanium film is sealed at the inlet to isolate the inside of the target chamber from the vacuum pipe. The rear end is not connected to other equipment at the physical level, and the rear beam outlet is also sealed with an extremely thin titanium film to separate the inside of the target chamber from the outside atmosphere. The bottom of the target chamber is connected to the vacuum device, and an air filling port is provided for the filling of protective gases such as helium and argon. A set of vacuum measuring instruments and equipment is provided at the bottom to measure the vacuum and air pressure inside the target chamber. The absolute air pressure in the target chamber filled with protective gases such as helium or argon is maintained in the positive pressure range, slightly higher than one atmosphere. Five or more drive devices are provided on the top of the target chamber to adjust the working state of each target piece.

[0038] B. Movable target holder. The movable target holder is made of copper and is located inside the target chamber. They are arranged front and back to each other, and their number is the same as the drive device on the top of the target chamber. The top is connected to the drive device, and the bottom is a thin cylindrical shape with a circular hollow in the middle, and a cooling channel is arranged inside. A threaded structure is arranged at the front end of the hollow position, which, together with the copper cover that is also hollowed out, realizes the fixation of the target. The drive device moves the target holder to the set working position. Each target holder has two working positions, namely, lifting and lowering. When lifting, the target piece leaves the incident path of the proton beam. At this time, the target piece is not bombarded by the proton beam, and no nuclear reaction occurs. When lowering, the target piece moves down with the movable target holder, and the center of the target piece coincides with the center of the proton beam. At this time, the proton beam bombards the target piece to produce quasi-monoenergetic neutrons. The target piece thickness is determined according to the monochromaticity of the required quasi-monoenergetic neutrons, the neutron injection, and the energy of the incident protons, so as to select a suitable target piece composition scheme.

[0039] C. Target. The target is a circular thin sheet made of lithium or beryllium, slightly larger than the hollow area on the target stand, and the number of target is the same as the movable target and the drive device. The thickness of each target is different, partially the same, or completely the same, but much smaller than the thickness of a single target used in the traditional scheme. The target is placed in front of the hollow area of ​​the target stand, and is pressed and fixed as the hollow copper cover rotates on the threaded structure of the target stand.

[0040] D. Vacuum device. The vacuum device consists of a mechanical pump and a molecular pump, located below the target chamber and directly connected to its interior. The main function of the vacuum device is to create a high vacuum environment in the target chamber to prevent the target sheet from being easily oxidized and thus failing when it is made of lithium. When working, the mechanical pump is first turned on to reach a low vacuum level, and then the molecular pump is turned on to further achieve a high vacuum environment in the target chamber.

[0041] E. Water cooling channel. Since the target racks of the present invention are arranged side by side rather than stacked up and down, Figure 1-6 As shown, the present invention does not require multiple target holders to share a water cooling channel, but can provide each target holder with a separate water cooling channel. Figure 1-6 The water cooling channel of each target holder is not shown in the figure, but in actual operation, each target holder needs to be equipped with a separate water cooling channel. Compared with the prior art, the problem of insufficient cooling efficiency of the target piece is solved.

[0042] F: The target pieces on the target stand being bombarded include combined target pieces, which means: including but not limited to combined target pieces, and can also be single target pieces.

[0043] Furthermore, the driving device is located at the top of the vacuum target chamber, and the target stand is directly connected to the driving device. The position of the target stand is moved by the driving device to control the working position of each target piece. When the driving device drives the target stand to move downward, the center of the target piece on the target stand coincides with the center of the incident proton beam. At this time, the protons bombard the target piece to generate a nuclear reaction and produce quasi-monoenergetic neutrons. When the driving device drives the target stand to lift up, the target piece and the target stand leave the proton beam line path, and no nuclear reaction occurs at this time.

[0044] Furthermore, the number of target pieces, target racks and driving devices in the vacuum target chamber is the same, and the thickness of each target piece in the vacuum target chamber is the same or different.

[0045] Furthermore, the total length, step length, number of target pieces and thickness of each target piece of the combined target piece are determined according to the selected energy range and control accuracy.

[0046] Furthermore, when the number of target pieces is 6, and 2 of them are 0.5 mm thick, 2 are 1 mm thick, and 2 are 2 mm thick, the position of the target holder is moved by a driving device to combine target pieces of different thicknesses and numbers, so that a total length of 0.5 mm to 6 mm, with a step length of 0.5 mm, and a total of 12 different thicknesses can be achieved, which can cover the production range of almost all quasi-monoenergetic neutrons above 20 MeV.

[0047] Furthermore, when the number of target pieces is 7, and the thicknesses of the target pieces are 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 1 mm, and 2 mm, respectively, by moving the position of the target holder by a driving device to combine target pieces of different thicknesses and numbers, a total length of 0.1 mm to 6 mm, with a step length of 0.1 mm, and a total of 60 different thicknesses can be achieved, which is sufficient to cover the generation range of almost all quasi-monoenergetic neutrons above 20 MeV, and can also achieve more precise and continuous thickness adjustment.

[0048] Furthermore, when conducting neutron irradiation experiments on structural materials and equipment components, more emphasis is placed on neutron flux and less emphasis is placed on the monochromaticity of quasi-monoenergetic neutrons. At this time, the position of the relevant target holder is moved by a driving device to combine target sheets with increased target thickness.

[0049] Furthermore, when performing detector calibration and other tasks, in order to pursue accuracy, the monochromaticity of the quasi-monoenergetic neutrons should be as high as possible. At this time, the position of the relevant target holder is moved by the driving device to combine the target sheets with appropriately reduced target sheet thickness.

[0050] Embodiment 1

[0051] The quasi-monoenergetic neutron generating device in the invention mainly includes components such as a target chamber, a movable target stand, a target plate and a vacuum device. The corresponding materials, positions, mutual connection relationships and functions have been described in the technical solution part. The specific implementation method of the invention is introduced below.

[0052] When the quasi-monoenergetic neutron generating device is used, the mechanical pump and the molecular pump are turned on successively to create a high vacuum environment inside the target chamber. Then, protective gases such as argon or helium are transported into the target chamber through the air inlet to maintain the air pressure in the positive pressure range, slightly higher than one atmosphere.

[0053] The drive device is located at the top of the target chamber. The movable target holder is directly connected to the drive device. The position is adjusted by the drive device, and then the position of the target piece on the target holder is changed to adjust the working state of the whole device. Each movable target holder has two working positions: the drive device drives the target holder to move downward and put it down, so that the center of the target piece on the target holder coincides with the center of the incident proton beam. At this time, the proton bombards the target piece to produce a nuclear reaction and generate quasi-monoenergetic neutrons. When the drive device drives the target holder to lift up, the target piece and the target holder leave the proton beam line path, and no nuclear reaction occurs at this time.

[0054] The number of target pieces, movable target racks and driving devices is the same, the number of target pieces is two or more, and the thicknesses are all the same, partly the same or completely different, which needs to be determined according to the selected energy range and control accuracy. The embodiment listed contains 6 target pieces (see Figure 1 ), of which 2 are 0.5mm thick, 1 is 1mm thick, and 1 is 2mm thick. The target holder is moved by the drive device to control the working position of each target. The combination of target pieces with different thicknesses and different numbers can achieve 12 different thicknesses of 0.5mm to 6mm, with a step length of 0.5mm, to meet different quasi-monoenergetic neutron production needs, covering almost all quasi-monoenergetic neutron production ranges above 20MeV.

[0055] If the number of target sheets is increased to 7 sheets (1 sheet each of 0.1mm, 0.2mm, 0.3mm, and 0.4mm thickness, 1 sheet of 1mm thickness, and 2 sheets of 2mm thickness), a total of 60 different thicknesses from 0.1mm to 6mm, with a step size of 0.1mm, can be achieved. This allows for more precise and continuous thickness adjustment.

[0056] The reason for adjusting the target thickness is that quasi-monoenergetic neutrons are mainly used for detector calibration and neutron dosimetry research. Unlike white light neutrons, which pursue maximum yield, their production focuses more on the monochromaticity of neutrons. Due to the multi-body reaction caused by high energy and the continuous loss of energy of protons in the target due to the ionization process, the neutrons produced have a certain broadened distribution and are not monoenergetic, so they are called quasi-monoenergetic neutrons. It can be predicted that the thinner the target thickness, the lower the quasi-monoenergetic neutron fluence produced. At the same time, the smaller the energy lost by the proton in the target, the narrower the broadening of the quasi-monoenergetic neutron peak, and the better the monochromaticity. In the construction of quasi-monoenergetic neutron reference radiation fields at home and abroad above 20MeV, the range when the proton loses 2~3MeV energy in the target is usually used as the target thickness to take into account the monochromaticity and fluence of quasi-monoenergetic neutrons. Taking lithium target as an example, when the proton energy is 50MeV, the target thickness is 3.8mm, and when it is 40MeV and 30MeV, it is determined to be 3mm and 2mm respectively. Since the stopping power of lithium for protons decreases with increasing energy, the higher the energy of the incident protons, the thicker the target film is that controls the proton loss of 2 to 3 MeV.

[0057] When conducting neutron irradiation experiments on structural materials and equipment, more emphasis is placed on neutron injection and less emphasis is placed on the monochromaticity of quasi-monoenergetic neutrons. In this case, the target thickness needs to be increased. When performing detector calibration and other work, in order to pursue accuracy, the monochromaticity of quasi-monoenergetic neutrons should be as high as possible. In this case, the target thickness needs to be appropriately reduced. In traditional designs, there are only a few target positions with fixed thickness, and the target thickness cannot be accurately adjusted. Therefore, this quasi-monoenergetic neutron generator is designed to meet relevant needs.

[0058] The following figure ( Figure 7 ) shows the energy spectrum of the emitted neutrons in the forward direction (i.e., the application area) when the proton energy is 50 MeV. The angle is limited to 0-5°, which is larger than the area of ​​concern under normal circumstances and is quite representative. It can be clearly seen from the results that the thicker the target, the higher the intensity of the emitted neutrons produced and the wider the width of the quasi-monoenergetic peak. The data are sorted and listed in Table 1, and it can be seen that the quantitative data also supports this view.

[0059] It should be emphasized that the above specific embodiments are merely explanations of the present invention, and they are not limitations of the present invention. After reading this specification, those skilled in the art can make modifications to the above embodiments without any creative contribution as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A quasi-monoenergetic neutron generating device, comprising a vacuum target chamber, a target holder with a driving device, and a target piece; a plurality of target holders movable up and down are arranged front and back in the target chamber along the beam direction, each target holder is provided with an independent driving device at one end away from the beam channel, and a target piece is installed at the other end close to the beam channel, characterized in that: Each target holder is provided with two upper and lower working positions: a nuclear reaction generating position and a non-nuclear reaction generating position. The center of the target piece of the target holder at the nuclear reaction generating position coincides with the center of the incident proton beam, while the center of the target piece of the target holder at the non-nuclear reaction generating position does not coincide with the center of the incident proton beam. When protons bombard the target piece on the target holder to cause a nuclear reaction, the target piece on the bombarded target holder includes a combined target piece, which is a target piece composed of a plurality of target pieces with completely different thicknesses or target pieces with partially the same thicknesses, and the center of each target piece of the combined target piece coincides with the center of the incident proton beam.

2. A quasi-monoenergetic neutron generating device according to claim 1, characterized in that: The driving device is located at the top of the vacuum target chamber, and the target stand is directly connected to the driving device. The position of the target stand is moved by the driving device to control the working position of each target piece. When the driving device drives the target stand to move downward, the center of the target piece on the target stand coincides with the center of the incident proton beam. At this time, the protons bombard the target piece to generate a nuclear reaction and produce quasi-monoenergetic neutrons. When the driving device drives the target stand to be lifted, the target piece and the target stand leave the proton beam line path, and no nuclear reaction occurs at this time.

3. A quasi-monoenergetic neutron generating device according to claim 1, characterized in that: The number of target pieces, target racks and driving devices in the vacuum target chamber is the same, and the thickness of each target piece in the vacuum target chamber is the same or different.

4. A quasi-monoenergetic neutron generating device according to claim 1, characterized in that: The total length, step length, number of target pieces and thickness of each target piece formed by the combination are determined according to the selected energy range and control accuracy.

5. The quasi-monoenergetic neutron generating device according to claim 1, characterized in that: When the number of target pieces is 6, and 2 of them are 0.5 mm thick, 2 are 1 mm thick, and 2 are 2 mm thick, the position of the target holder is moved by a driving device to combine target pieces of different thicknesses and numbers, so that a total length of 0.5 mm to 6 mm, with a step length of 0.5 mm, and a total of 12 different thicknesses can be achieved, which can cover the production range of almost all quasi-monoenergetic neutrons above 20 MeV.

6. The quasi-monoenergetic neutron generating device according to claim 1, characterized in that: When the number of target pieces is 7, and the thicknesses of the target pieces are 0.1mm, 0.2mm, 0.3mm, 0.4mm, 1 piece, 1mm, and 2 pieces, respectively, the position of the target holder is moved by a driving device to combine target pieces of different thicknesses and numbers, so that a total length of 0.1mm to 6mm, with a step length of 0.1mm, and a total of 60 different thicknesses can be achieved, which is sufficient to cover almost all the production range of quasi-monoenergetic neutrons above 20MeV, and can also achieve more precise and continuous thickness adjustment.

7. The quasi-monoenergetic neutron generating device according to claim 1, characterized in that: When conducting neutron irradiation experiments on structural materials and equipment components, more emphasis is placed on neutron flux and less emphasis is placed on the monochromaticity of the quasi-monoenergetic neutrons. At this time, the position of the relevant target holder is moved by a driving device to combine target sheets with increased target thickness.

8. The quasi-monoenergetic neutron generating device according to claim 1, characterized in that: When performing detector calibration and other work, in order to pursue accuracy, the monochromaticity of quasi-monoenergetic neutrons should be as high as possible. At this time, the position of the relevant target holder is moved by the driving device to combine the target pieces with appropriately reduced target thickness.

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