阅读说明：本技术 一种测量d-t中子源源斑尺寸的装置及方法 (Device and method for measuring size of source spot of D-T neutron source ) 是由 张凯 苏明 鲍杰 陈红涛 栾广源 赵芳 阮锡超 龚新宝 刘邢宇 张坤 于 2020-05-26 设计创作，主要内容包括：本发明属于中子源测量技术领域,具体涉及一种测量D-T中子源源斑尺寸的装置及方法,用于对设置在靶头腔室(18)内的氚靶(13)上产生的中子源源斑(12)的尺寸进行测量,该装置包括密封设置在靶头腔室(18)上的关联α探测系统(2)和位于靶头腔室(18)外部、与关联α探测系统(2)相对设置的中子探测装置(1),还包括对中子探测装置(1)测得的第一模拟信号和关联α探测系统(2)测得的第二模拟信号进行关联时间符合、得到中子源的中子源源斑(12)的尺寸的数据获取分析系统(3)。本发明能够实现α粒子图像(11)的实时成像,并实时反映中子源源斑(12)的尺寸和形状变化以及在空间位置随时间的变化。(The invention belongs to the technical field of neutron source measurement, and particularly relates to a device and a method for measuring the size of a D-T neutron source spot, which are used for measuring the size of a neutron source spot (12) generated on a tritium target (13) arranged in a target head chamber (18), wherein the device comprises a correlation alpha detection system (2) which is hermetically arranged on the target head chamber (18), a neutron detection device (1) which is positioned outside the target head chamber (18) and is opposite to the correlation alpha detection system (2), and a data acquisition and analysis system (3) which is used for performing correlation time coincidence on a first analog signal measured by the neutron detection device (1) and a second analog signal measured by the correlation alpha detection system (2) to obtain the size of the neutron source spot (12) of a neutron source. The invention can realize real-time imaging of the alpha particle image (11) and reflect the size and shape change of the neutron source spot (12) and the change of the spatial position along with time in real time.)

1. The utility model provides a device of measurement D-T neutron source spot size for measure the size of the neutron source spot (12) that produce on tritium target (13) that set up in target head cavity (18), the inside vacuum environment that is of target head cavity (18), neutron source spot (12) are bombarded by the ion beam that the neutron source emitted tritium target (13) produce, characterized by: the neutron source detection device comprises an associated alpha detection system (2) which is hermetically arranged on the target head chamber (18), a neutron detection device (1) which is positioned outside the target head chamber (18) and arranged opposite to the associated alpha detection system (2), and a data acquisition and analysis system (3) which is used for performing associated time coincidence on a first analog signal measured by the neutron detection device (1) and a second analog signal measured by the associated alpha detection system (2) to obtain the size of the neutron source spot (12) of the neutron source.

2. The apparatus for measuring source spot size in a D-T neutron source of claim 1, wherein: the neutron detection device (1) is a neutron detector (15) powered by a second power supply (14), the distance from the neutron detector (15) to the center of the tritium target (13) is 2.5m, and the neutron detector (15) is connected with the data acquisition and analysis system (3); the first analog signal is obtained by the neutron detector (15) and comprises a neutron analog signal and a gamma particle analog signal.

3. The apparatus for measuring source spot size in a D-T neutron source of claim 2, wherein: the neutron detector (15) has n/gamma discrimination capability.

4. The apparatus for measuring source spot size in a D-T neutron source of claim 3, wherein: the neutron detector (15) is a combination of a plastic flash detector and a photomultiplier; the second power supply (14) is used for supplying power to the photomultiplier tube.

5. The apparatus for measuring source spot size in a D-T neutron source of claim 4, wherein:

the associated alpha detection system (2) comprises a beam limiting flange (4), a light-proof breathable sponge (5), a light isolation layer, a scintillator (6), a vacuum isolation layer (7), a position-sensitive photomultiplier array (8), a voltage division circuit (9) and a first power supply (10), which are sequentially connected in series, wherein the voltage division circuit (9) is connected with the data acquisition and analysis system (3); the tritium target (13) and the scintillator (6) form an angle of 45 degrees;

the associated alpha detection system (2) is communicated with the target head chamber (18) and is in vacuum, the scintillator (6) can see the whole target surface of the tritium target (13), and the distance from the front surface of the scintillator (6) to the center of the target surface of the tritium target (13) is 5 cm.

6. The apparatus for measuring source spot size in a D-T neutron source of claim 5, wherein:

the beam limiting flange (4) is used for sealing the associated alpha detection system (2) on the target head chamber (18), and the light isolation layer is pressed on the surface of the scintillator (6) through a light-proof and air-permeable sponge (5); the vacuum isolation layer (7) is connected with the beam limiting flange (4) through a vacuum isolation layer bracket;

the position sensitive photomultiplier array (8) and the voltage division circuit (9) are arranged in a shielding box; the top end of the shielding box is connected with the vacuum isolation layer bracket through a bolt, so that the position sensitive photomultiplier array (8) is connected with the vacuum isolation layer (7); the tail end of the shielding box is provided with a data output interface and a power supply input interface, the data output interface is used for connecting the voltage division circuit (9) with the data acquisition and analysis system (3), and the power supply input interface is used for connecting the voltage division circuit (9) with the first power supply (10);

one surface of the vacuum isolation layer (7) is optically coupled with the position-sensitive photomultiplier array (8), and the other surface of the vacuum isolation layer is optically coupled with the scintillator (6);

the space between the shielding box and the vacuum isolation layer (7), the space between the vacuum isolation layer (7) and the beam limiting flange (4) and the space between the beam limiting flange (4) and the target head chamber (18) are all fixed through bolts;

the vacuum isolation layer (7) and the beam limiting flange (4) are sealed through a sealing ring, and the beam limiting flange (4) and the target head cavity (18) are sealed through the sealing ring.

7. The apparatus for measuring source spot size in a D-T neutron source of claim 6, wherein:

the vacuum isolation layer (7) is made of sapphire glass;

the light isolation layer adopts Al foil and is used for preventing deuterium particles scattered by the tritium target (13) and light of the tritium target (13) from generating interference signals on the scintillator (6); the side end of the optical isolation layer is grounded with the beam limiting flange (4) through a metal elastic sheet;

the shielding box is made of aluminum;

the vacuum isolation layer bracket is made of titanium steel;

the scintillator (6) is coupled with the vacuum isolation layer (7) through high-viscosity optical silicone grease;

the vacuum isolation layer (7) is coupled with the position sensitive type photomultiplier array (8) through high-viscosity optical silicone grease, and the periphery of the position where the vacuum isolation layer (7) is coupled with the position sensitive type photomultiplier array (8) is sealed by a black adhesive tape;

the position-sensitive photomultiplier array (8) adopts a Si-PM array, the rear end of the Si-PM array is connected with the voltage division circuit (9) in a voltage division mode, and the voltage division circuit is used for dividing the amplitude of the alpha particle analog signals acquired by the associated alpha detection system (2) into a path A analog signals, a path B analog signals, a path C analog signals and a path D analog signals to form second analog signals.

8. The apparatus for measuring source spot size in a D-T neutron source of claim 7, wherein:

the data acquisition and analysis system (3) comprises a digitizer (16) connected with the neutron detector (15) and the voltage division circuit (9), and further comprises a computer (17) connected with the digitizer (16);

the digitizer (16) is a multi-channel digitizer, and is configured to collect the first analog signal measured by the neutron detection device (1) and the second analog signal measured by the associated alpha detection system (2), perform a/D conversion on the first analog signal and the second analog signal to obtain a corresponding first digital signal and a second digital signal, and input the first digital signal and the second digital signal to the computer (17); the first digital signal comprises a neutron digital signal and a gamma particle digital signal; the second digital signal is an alpha particle digital signal and comprises an A path digital signal, a B path digital signal, a C path digital signal and a D path digital signal;

the data processing program in the computer (17) carries out n/gamma pulse shape discrimination on the first digital signal, selects the neutron digital signal, and then carries out the association time coincidence with the alpha particle digital signal, thereby selecting the alpha particle digital signal associated with the neutron digital signal, and simultaneously carries out the position reconstruction of the alpha particle acquired by the associated alpha detection system (2), thereby acquiring the position information of the alpha particle associated with the neutron digital signal; and after the alpha particle image (11) is obtained, an image of the neutron source spot (12) is obtained according to the position relation between the neutron detector (15) and the associated alpha detection system (2).

9. A method for measuring the size of a source spot of a D-T neutron source for the apparatus for measuring the size of a source spot of a D-T neutron source of claim 8, comprising the steps of:

step S1, vacuumizing the target head chamber (18), and bombarding the tritium target (13) by using the neutron source;

step S2, the neutron detector (15) acquiring the first analog signal, the associated alpha detection system (2) acquiring the second analog signal;

step S3, the digitizer (16) collects the first analog signal and the second analog signal, and performs A/D conversion on the first analog signal and the second analog signal to obtain the corresponding first digital signal and second digital signal, and inputs the first digital signal and the second digital signal into the computer (17);

the first analog signal comprises the neutron analog signal and the gamma particle analog signal;

the second analog signal is an analog signal of the alpha particle and comprises the path A analog signal, the path B analog signal, the path C analog signal and the path D analog signal;

the first digital signal comprises the neutron digital signal and the gamma particle digital signal;

the second digital signal is the alpha-particle digital signal and comprises the A-path digital signal, the B-path digital signal, the C-path digital signal and the D-path digital signal;

step S4, the data processing program in the computer (17) carries out n/gamma pulse shape discrimination on the first digital signal, selects the neutron digital signal, and then carries out the association time coincidence with the second digital signal, thereby selecting the alpha particle digital signal in the second digital signal associated with the neutron digital signal, and simultaneously carries out the position reconstruction of the alpha particle, and obtains the position information of the associated alpha particle; and acquiring the alpha particle image (11) after accumulation for a period of time, and acquiring an image of the neutron source spot (12) according to the position relation between the neutron detector (15) and the associated alpha detection system (2).

10. The method of measuring the source spot size of a D-T neutron source of claim 9, wherein:

in step S4, the neutron digital signal selected after the n/γ pulse shape discrimination is subjected to constant ratio timing to generate a door opening signal; the second digital signal generates a door closing signal through constant ratio timing;

the door opening signal and the door closing signal are subjected to flight time measurement, an n-alpha coincidence time window is selected from a flight time spectrum, and the n-alpha coincidence time window is 5ns, so that the alpha particle digital signal related to the neutron digital signal is selected;

then, the X-axis coordinate and the Y-axis coordinate of the alpha particle signal are obtained for the selected A path digital signal, the B path digital signal, the C path digital signal and the D path digital signal of the alpha particle digital signal according to a second formula and a third formula, so that the position reconstruction of the alpha particle is realized, and the alpha particle image (11) is obtained;

then obtaining a real-time image of the neutron source spot (12) through geometric relation conversion according to a first formula;

x is (A-B)/(A + B) second formula

Third formula of y ═ C-D)/(C + D)

x represents the x-axis coordinate;

y represents a y-axis coordinate;

a represents the A-path digital signal;

b represents the B-path digital signal;

c represents the C-path digital signal;

d represents the D-path digital signal;

φ_trepresents a diameter of the source spot (12);

φ_αrepresenting the size of the alpha particle image (11) measured on the correlation α detection system (2);

φ_nrepresents a diameter of the neutron detector (15);

l represents the distance from the neutron detector (15) to the center point of the tritium target (13);

l represents the distance from the center of the scintillator (6) in the associated alpha detection system (2) to the center point of the tritium target (13).

Technical Field

The invention belongs to the technical field of neutron source measurement, and particularly relates to a device and a method for measuring the size of a source spot of a D-T neutron source.

Background

The D-T neutron source generates 14MeV neutrons through D (T, n) He fusion reactions (14 MeV neutrons are generated by bombardment of a beam flow led out by the D-T neutron source on a target surface), and is widely applied to the research fields of nuclear data measurement, fast neutron photography, explosive detection, nuclear and investigation and the like. In the using process of the neutron source, the size of the source spot of the neutron source influences the practical application process, and particularly in the fields of fast neutron photography and inspection, the size of the source spot directly influences the size of the measurement precision. The neutron source spot monitoring device has important significance in monitoring the neutron source spot in real time in the using process of the neutron source.

At present, there are two ways for measuring the source spot of the high-voltage doubler type D-T neutron source: one is that the vacuum is destroyed after the experiment is finished, the trace size of the target spot is directly measured by a graduated scale, and the source spot size of the neutron source cannot be monitored in real time; the other method is to install a camera near the target in the beam pipeline for real-time monitoring, the method can cause the target structure to be complex, the size to be enlarged and is not beneficial to the accurate measurement of experimental data, in addition, the camera is too close to the target, and a CCD (charge coupled device) is easy to be bombarded by neutrons to cause damage, and the CCD needs to be replaced frequently. For a portable neutron source, the existing measurement method is to perform associated measurement by an alpha point detector and a neutron linear array detector, the measurement method can only measure the one-dimensional size, namely the linear size, of a neutron source spot, and cannot reflect the shape of the whole neutron source spot, and in addition, the measurement method cannot reflect the relative position of the neutron source spot on a target surface.

Disclosure of Invention

In order to solve the problem that the size and the position of a source spot of a neutron source cannot be monitored in the using process of a D-T neutron source, the method is used for monitoring the two-dimensional size of the source spot of the neutron source and the relative position of the source spot and a target surface in real time by utilizing an alpha array detector to image the source spot based on the incidence relation between space and time of D-T source neutrons and alpha particles.

In order to achieve the above purpose, the technical scheme adopted by the invention is a device for measuring the size of a D-T neutron source spot, which is used for measuring the size of the neutron source spot generated on a tritium target arranged in a target head chamber, wherein the target head chamber is internally in a vacuum environment, and the neutron source spot is generated by bombarding the tritium target by an ion beam emitted by a neutron source.

Further, the neutron detection device is a neutron detector powered by a second power supply, and the distance from the neutron detector to the center of the tritium target is 2.5 m; the neutron detector is connected with the data acquisition and analysis system; the first analog signal is obtained by the neutron detector and comprises a neutron analog signal and a gamma particle analog signal.

Further, the neutron detector has n/gamma discrimination capability.

Further, the neutron detector is a combination of a plastic flash detector and a photomultiplier tube; the second power supply is used for supplying power to the photomultiplier tube.

Further, in the present invention,

the associated alpha detection system comprises a beam limiting flange, a light-proof breathable sponge, a light isolation layer, a scintillator, a vacuum isolation layer, a position-sensitive photomultiplier array, a voltage division circuit and a first power supply which are sequentially connected in series, wherein the voltage division circuit is connected with the data acquisition and analysis system; the tritium target and the scintillator form an angle of 45 degrees;

the associated alpha detection system is communicated with the target head chamber and is positioned in vacuum, the scintillator can see the whole target surface of the tritium target, and the distance from the front surface of the scintillator to the center of the target surface of the tritium target is 5 cm.

Further, in the present invention,

the beam limiting flange is used for sealing the associated alpha detection system on the target head chamber, and the light isolation layer is pressed on the surface of the scintillator through a light-proof breathable sponge; the vacuum isolation layer is connected with the beam limiting flange through a vacuum isolation layer bracket;

the position sensitive photomultiplier array and the voltage division circuit are arranged in a shielding box; the top end of the shielding box is connected with the vacuum isolation layer bracket through a bolt, so that the position sensitive photomultiplier array is connected with the vacuum isolation layer; the tail end of the shielding box is provided with a data output interface and a power supply input interface, the data output interface is used for connecting the voltage division circuit with the data acquisition and analysis system, and the power supply input interface is used for connecting the voltage division circuit with the first power supply;

one surface of the vacuum isolation layer is optically coupled with the position sensitive photomultiplier array, and the other surface of the vacuum isolation layer is optically coupled with the scintillator;

the space between the shielding box and the vacuum isolation layer, the space between the vacuum isolation layer and the beam limiting flange and the space between the beam limiting flange and the target head chamber are all fixed through bolts;

the vacuum isolation layer and the beam limiting flange are sealed through a sealing ring, and the beam limiting flange and the target head cavity are sealed through the sealing ring.

Further, in the present invention,

the vacuum isolation layer is made of sapphire glass;

the light isolation layer is made of Al foil and is used for preventing deuterium particles scattered by the tritium target and light of the tritium target from generating interference signals on the scintillator; the side end of the optical isolation layer is grounded with the beam limiting flange through a metal elastic sheet;

the shielding box is made of aluminum;

the vacuum isolation layer bracket is made of titanium steel;

the scintillator is coupled with the vacuum isolation layer through high-viscosity optical silicone grease;

the vacuum isolation layer is coupled with the position sensitive type photomultiplier array through high-viscosity optical silicone grease, and the periphery of the position of the vacuum isolation layer coupled with the position sensitive type photomultiplier array is sealed by a black adhesive tape;

the position sensitive type photomultiplier array adopts a Si-PM array, the rear end of the Si-PM array is connected with the voltage division circuit, and the voltage division circuit is used for dividing the amplitude of the alpha particle analog signal acquired by the associated alpha detection system into an A path analog signal, a B path analog signal, a C path analog signal and a D path analog signal to form the second analog signal.

Further, in the present invention,

the data acquisition and analysis system comprises a digitizer connected with the neutron detector and the voltage division circuit, and a computer connected with the digitizer;

the digitizer is a multi-channel digitizer and is used for acquiring the first analog signal measured by the neutron detection device and the second analog signal measured by the associated alpha detection system, performing A/D conversion on the first analog signal and the second analog signal to obtain a corresponding first digital signal and a corresponding second digital signal, and inputting the first digital signal and the second digital signal into the computer; the first digital signal comprises a neutron digital signal and a gamma particle digital signal; the second digital signal is an alpha particle digital signal and comprises an A path digital signal, a B path digital signal, a C path digital signal and a D path digital signal;

the data processing program in the computer carries out n/gamma pulse shape discrimination on the first digital signal, selects the neutron digital signal, and then carries out the association time coincidence with the alpha particle digital signal, thereby selecting the alpha particle digital signal associated with the neutron digital signal, and simultaneously carries out the position reconstruction of the alpha particle acquired by the associated alpha detection system, thereby acquiring the position information of the alpha particle associated with the neutron digital signal; and after the alpha particle image is obtained, obtaining an image of the source spot of the neutron source according to the position relation between the neutron detector and the associated alpha detection system.

The invention also provides a method for measuring the size of the source spot of the D-T neutron source, which is used for the device for measuring the size of the source spot of the D-T neutron source, and comprises the following steps:

step S1, vacuumizing the target head chamber, and bombarding the tritium target by using the neutron source;

step S2, the neutron detector obtains the first analog signal, and the associated alpha detection system obtains the second analog signal;

step S3, the digitizer collects the first analog signal and the second analog signal, performs a/D conversion on the first analog signal and the second analog signal to obtain a corresponding first digital signal and a corresponding second digital signal, and inputs the first digital signal and the second digital signal into the computer;

the first analog signal comprises the neutron analog signal and the gamma particle analog signal;

the second analog signal is an analog signal of the alpha particle and comprises the path A analog signal, the path B analog signal, the path C analog signal and the path D analog signal;

the first digital signal comprises the neutron digital signal and the gamma particle digital signal;

the second digital signal is the alpha-particle digital signal and comprises the A-path digital signal, the B-path digital signal, the C-path digital signal and the D-path digital signal;

step S4, the data processing program in the computer performs n/γ pulse shape discrimination on the first digital signal, selects the neutron digital signal, and performs the association time matching with the second digital signal, thereby selecting the alpha particle digital signal in the second digital signal associated with the neutron digital signal, and performs the position reconstruction of the alpha particle to obtain the position information of the associated alpha particle; and acquiring the alpha particle image after accumulation for a period of time, and then obtaining the image of the source spot of the neutron source according to the position relation between the neutron detector and the associated alpha detection system.

Further, in the present invention,

in step S4, the neutron digital signal selected after the n/γ pulse shape discrimination is subjected to constant ratio timing to generate a door opening signal; the second digital signal generates a door closing signal through constant ratio timing;

the door opening signal and the door closing signal are subjected to flight time measurement, an n-alpha coincidence time window is selected from a flight time spectrum, and the n-alpha coincidence time window is 5ns, so that the alpha particle digital signal related to the neutron digital signal is selected;

then, obtaining the x-axis coordinate and the y-axis coordinate of the alpha particle signal according to a second formula and a third formula for the selected A path digital signal, B path digital signal, C path digital signal and D path digital signal of the alpha particle digital signal, thereby realizing the position reconstruction of the alpha particle and obtaining the alpha particle image;

then obtaining a real-time image of the source spot of the neutron source through geometric relation conversion according to a first formula;

x is (A-B)/(A + B) second formula

Third formula of y ═ C-D)/(C + D)

x represents the x-axis coordinate;

y represents a y-axis coordinate;

a represents the A-path digital signal;

b represents the B-path digital signal;

c represents the C-path digital signal;

d represents the D-path digital signal;

φ_trepresenting a diameter of the source spot;

φ_αrepresenting the size of the alpha particle image measured on the correlation α detection system;

φ_nrepresents a diameter of the neutron detector;

l represents the distance from the neutron detector to the center point of the tritium target;

l represents the distance from the center of the scintillator in the correlated alpha detection system to the center point of the tritium target.

The invention has the beneficial effects that:

1. the invention adopts the neutron detector 15 with fast time response, small size and n/gamma discrimination capability, and the fast time response can ensure the accuracy of selecting alpha events; the small size facilitates accurate measurement of the size of the source spot 12; the n/gamma discrimination is beneficial to eliminating the interference of the tritium target 13 and the gamma signal in the environment.

2. The invention adopts the associated alpha detection system 2 with fast time response and high position resolution capability, wherein the fast time response is used for accurately timing and eliminating the interference of scattered neutrons; the high resolution of the area array detector is beneficial to ensuring the imaging accuracy of the neutron source spot 12.

3. The invention directly uses the multi-channel digitizer 16 to collect data of each channel, and is simpler and more portable compared with the traditional case-electronics plug-in combination form.

4. The data signals of the multi-channel digitizer 16 are directly transmitted into the computer 17, and the screening of the first digital signals and the second digital signals and the position reconstruction of alpha particles are directly realized through a data processing program, so that the real-time imaging of the alpha particle image 11 is realized.

5. The invention uses a single neutron detector 15 to detect the direct-through neutrons to select the associated alpha particles, can simplify the whole neutron source spot measuring device, and can be carried out when the physical experiment is not influenced.

6. The method can obtain the intensity distribution of the neutron source spot 12, and truly and accurately reflect the information of the neutron source.

7. The method measures the position of the alpha particle associated with the direct-through neutron in real time, and establishes the corresponding relation with time, so that the corresponding relation with the size and the shape of the neutron source spot 12 is established, and the size and the shape change of the neutron source spot 12 can be reflected in real time.

8. The invention reflects the change of the neutron source spot 12 in the space position along with the time by showing the relative position change of the alpha particle image 11 in the imaging area in real time.

9. The invention can reflect the bunching condition of the accelerated D + beam (the beam which is led out by the neutron source and bombards the tritium target 13) in real time by monitoring the shape change of the neutron source spot 12 in real time, and can be used as reference for beam bunching adjustment.

Drawings

FIG. 1 is a schematic diagram of an apparatus for measuring source spot size of a D-T neutron source according to an embodiment of the present invention;

FIG. 2 is a schematic flow chart of a method for measuring the source spot size of a D-T neutron source according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of the data processing flow in step S4 of the method for measuring the source spot size of the D-T neutron source according to the embodiment of the invention,

in fig. 2 and 3:

n/gamma: the first digital signal (including the neutron digital signal and the gamma particle digital signal) before the n/gamma pulse shape discrimination is not performed,

PSD: the shape of the n/gamma pulse is discriminated,

n: the selected neutron digital signals are selected out,

α all: the second digital signal (i.e. the alpha particle digital signal),

TOF: the time-of-flight measurements are taken,

α sel: the alpha particle digital signals associated with the selected neutron digital signals,

α pos: the image of the alpha particles 11 is,

s pos: an image of the source spot 12;

FIG. 4 is a measurement result of the neutron source spot 12 under the focusing condition (coordinates in the figure represent 0.25mm per grid) obtained by the device and the method for measuring the dimension of the D-T neutron source spot according to the embodiment of the invention;

FIG. 5 is a measurement result of the neutron source spot 12 under defocused condition (coordinates in the figure represent 0.25mm per grid) obtained by the device and the method for measuring the dimension of the D-T neutron source spot according to the embodiment of the invention;

in the figure: the method comprises the following steps of 1-neutron detection device, 2-associated alpha detection system, 3-data acquisition and analysis system, 4-beam limiting flange, 5-light-proof breathable sponge, 6-scintillator, 7-vacuum isolation layer, 8-position sensitive photomultiplier array, 9-voltage division circuit, 10-first power supply, 11-alpha particle image, 12-neutron source spot, 13-tritium target, 14-second power supply, 15-neutron detector (with n/gamma discrimination capability), 16-digitizer, 17-computer, 18-target head chamber, 19-flight time switch (located in the computer 17), 20-alpha particle position reconstruction (located in the computer 17), and 21-obtaining image of the neutron source spot 12.

Detailed Description

The invention is further described below with reference to the figures and examples.

As shown in fig. 1, the device for measuring the size of a D-T neutron source spot provided by the present invention is used for measuring the size of a neutron source spot 12 generated on a tritium target 13 disposed in a target chamber 18, the inside of the target chamber 18 is a vacuum environment, the neutron source spot 12 is generated by bombarding the tritium target 13 with an ion beam emitted by a neutron source, the device includes an associated α detection system 2 hermetically disposed on the target chamber 18, a neutron detection device 1 disposed opposite to the associated α detection system 2 and located outside the target chamber 18, and a data acquisition and analysis system 3 for performing association time matching on a first analog signal measured by the neutron detection device 1 and a second analog signal measured by the associated α detection system 2 to obtain the size of the neutron source spot 12 of the neutron source.

The neutron detection device 1 is a neutron detector 15 powered by a second power supply 14 (high-voltage power supply), and the distance from the neutron detector 15 to the center of the tritium target 13 is 2.5m (correlation range); the neutron detector 15 is connected with the data acquisition and analysis system 3; the first analog signal is obtained by the neutron detector 15 and includes a neutron analog signal and a gamma particle analog signal.

Time response of neutron detector 15<1ns, diameter<5cm, n/gamma discrimination, a supply voltage of-1350V of the second power supply 14, and a neutron source intensity of 1 × 10⁸under the intensity of n/s, the neutron detector 15 is placed in the correlation range of 2.5m from the center of the tritium target 13, and under the condition that the detection efficiency of the neutron detector 15 is 10%, the n- α coincidence counting rate is about 125 n/s.

The neutron detector 15 is a combination of a plastic flash detector and a photomultiplier, the plastic flash detector is cylindrical, and the size of the plastic flash detector is phi 1 inch multiplied by 2 inches (the model is EJ 299-33-A); a second power supply 14 is used to power the photomultiplier tubes.

The associated alpha detection system 2 comprises a beam limiting flange 4, a light-proof breathable sponge 5, a light isolation layer, a scintillator 6, a vacuum isolation layer 7, a position sensitive photomultiplier array 8, a voltage division circuit 9 and a first power supply 10 which are sequentially connected in series, wherein the voltage division circuit 9 is connected with the data acquisition and analysis system 3; the tritium target 13 and the scintillator 6 form an angle of 45 degrees;

the associated alpha detection system 2 is communicated with the target head chamber 18 and is positioned in vacuum, the scintillator 6 can see the whole target surface of the tritium target 13, and the front surface of the scintillator 6 is 5cm away from the center of the target surface of the tritium target 13.

The beam limiting flange 4 is used for hermetically arranging the associated alpha detection system 2 on the target head cavity 18 through screw fixation, and the light isolation layer is tightly pressed on the surface of the scintillator 6 through the light-proof breathable sponge 5; the vacuum isolation layer 7 is connected with the beam limiting flange 4 through a vacuum isolation layer bracket;

the position sensitive photomultiplier array 8 and the voltage division circuit 9 are arranged in the shielding box through bolts; the top end of the shielding box is connected with the vacuum isolation layer bracket through a bolt, so that the connection between the position sensitive photomultiplier array 8 and the vacuum isolation layer 7 is realized; the tail end of the shielding box is provided with a data output interface and a power supply input interface, the data output interface is used for connecting the voltage division circuit 9 with the data acquisition and analysis system 3, and the power supply input interface is used for connecting the voltage division circuit 9 with the first power supply 10;

one surface of the vacuum isolation layer 7 is optically coupled with a position sensitive photomultiplier array 8 in the shielding box, and the other surface is optically coupled with the scintillator 6;

the space between the shielding box and the vacuum isolation layer 7, the space between the vacuum isolation layer 7 and the beam limiting flange 4, and the space between the beam limiting flange 4 and the target head chamber 18 are all fixed through bolts;

the vacuum isolation layer 7 and the beam limiting flange 4 are sealed through a sealing ring, and the beam limiting flange 4 and the target head cavity 18 are sealed through a sealing ring.

The diameter of the beam-limiting flange 4 is 90mm, the diameter of the central hole is 20mm, and the material is titanium steel;

the vacuum isolation layer 7 is made of sapphire glass or quartz glass with the thickness of 2.5mm, so that enough mechanical strength can be ensured to isolate vacuum, and the light transmittance of the scintillator 6 is ensured to be more than 95%;

the light isolation layer adopts two layers of Al foils with the thickness of 800nm and is used for preventing deuterium particles scattered by the tritium target 13 and light of the tritium target 13 from generating interference signals on the scintillator 6; the side end of the optical isolation layer is grounded with the beam limiting flange 4 through a metal elastic sheet, so that the influence of charge accumulation on the measurement of the size of the neutron source spot 12 is avoided; the light isolation layer is fixed on the surface of the scintillator 6 through the light-proof breathable sponge 5, so that the light isolation layer is prevented from being broken in the vacuumizing process of the target head cavity 18 while the light-proof effect is realized;

the shielding box is made of aluminum;

the vacuum isolation layer bracket is made of titanium steel so as to ensure enough mechanical strength;

the scintillator 6 is a plastic scintillator (EJ-228 type) 50 μm thick, 50mm × 50mm × 1mm in size, and is coupled with the vacuum insulation layer 7 through a high-viscosity optical silicone grease (Q2-3067);

the vacuum isolation layer 7 is coupled with the position-sensitive photomultiplier array 8 through high-viscosity optical silicone grease (Q2-3067), and the periphery of the position where the vacuum isolation layer 7 is coupled with the position-sensitive photomultiplier array 8 is sealed by a black adhesive tape, so that on one hand, light can be prevented, and on the other hand, air can be prevented from entering bubbles to generate, and light transmission is not influenced;

the position-sensitive photomultiplier array 8 adopts a 16 x 16 Si-PM array, the size of a single Si-PM channel in the Si-PM array is 3mm x 3mm, each Si-PM channel consists of 3200 units, and the size of each unit is 60 mu m x 60 mu m; the rear end of the Si-PM array is connected to a voltage dividing circuit 9(DPC voltage dividing circuit) for dividing the amplitude of the analog signal of the α particle acquired by the associated α detection system 2 to the a-channel analog signal, the B-channel analog signal, the C-channel analog signal, and the D-channel analog signal to form a second analog signal (i.e., the second analog signal includes the a-channel analog signal, the B-channel analog signal, the C-channel analog signal, and the D-channel analog signal). (the type of the alpha detection system adopted by the associated alpha detection system 2 comprises a semiconductor area array detector, an area array detector coupled by a scintillator and a PMT, an area array detector coupled by the scintillator and Si-PM and a SiC area array detector; in the technical scheme of the application, the alpha detection system adopts a Si-PM coupled area array detector.)

The data acquisition and analysis system 3 comprises a digitizer 16 connected with the neutron detector 15 and the voltage division circuit 9, and further comprises a computer 17 connected with the digitizer 16;

the digitizer 16 is a multi-channel digitizer (model number is DT5730) and is configured to collect a first analog signal measured by the neutron detection device 1 and a second analog signal measured by the associated α detection system 2, perform a/D conversion on the first analog signal and the second analog signal to obtain a corresponding first digital signal and a corresponding second digital signal, and input the first digital signal and the second digital signal to the computer 17; the first digital signal comprises a neutron digital signal and a gamma particle digital signal; the second digital signal is an alpha particle digital signal and comprises an A path digital signal, a B path digital signal, a C path digital signal and a D path digital signal;

a data processing program (written by LabWindows) in the computer 17 carries out n/gamma pulse shape discrimination on the first digital signal (n represents a neutron), selects a neutron digital signal, and then carries out association time coincidence with an alpha particle digital signal, thereby selecting an alpha particle digital signal associated with the neutron digital signal, and simultaneously carries out position reconstruction of alpha particles acquired by the associated alpha detection system 2, thereby acquiring position information of the alpha particles associated with the neutron digital signal; after a period of time (several minutes) accumulation, an alpha particle image 11 is obtained, and then an image of the neutron source spot 12 is obtained according to the position relationship between the neutron detector 15 and the associated alpha detection system 2.

The invention also provides a method for measuring the size of the D-T neutron source spot (see the flow chart in figure 2) for the device for measuring the size of the D-T neutron source spot, which utilizes the characteristics that neutrons and alpha particles are simultaneously generated and opposite in direction in the D (T, n) He fusion process, utilizes an alpha position sensitive detector with ultrafast time resolution to measure alpha in the fusion process, utilizes the neutron signals of a small-size neutron detector in an alpha correlation angle to perform time coincidence, can obtain a two-dimensional image of the correlation alpha, and has geometric correspondence between the shape and the size of the image and the shape and the size of the neutron source spot, thereby realizing the accurate monitoring of the size of the neutron source spot, and the method comprises the following steps:

step S1, evacuating the target chamber 18 (10)^-4Pa), setting the intensity of the neutron source to 1 × 10⁸n/s, a neutron source is used for bombarding the tritium target 13, the neutron detection device 1 is arranged in a correlation range which can be detected by the correlation α detection system 2, and the distance can be freely adjusted according to the neutron counting rate of the neutron detection device 1 and the required imaging time;

step S2, the neutron detector 15 acquires a first analog signal, and the associated α detection system 2 acquires a second analog signal;

step S3, the digitizer 16 collects the first analog signal and the second analog signal, and performs a/D conversion on the first analog signal and the second analog signal to obtain a corresponding first digital signal and a second digital signal, and inputs the first digital signal and the second digital signal into the computer 17;

the first analog signal comprises a neutron analog signal and a gamma particle analog signal;

the second analog signal is an analog signal of alpha particles and comprises an A-path analog signal, a B-path analog signal, a C-path analog signal and a D-path analog signal;

the first digital signal comprises a neutron digital signal and a gamma particle digital signal;

the second digital signal is an alpha particle digital signal and comprises an A path digital signal, a B path digital signal, a C path digital signal and a D path digital signal;

step S4, the data processing program in the computer 17 performs n/γ pulse shape discrimination on the first digital signal, selects the neutron digital signal, and performs association time coincidence with the second digital signal, thereby selecting the alpha particle digital signal in the second digital signal associated with the neutron digital signal, and simultaneously performs position reconstruction of the alpha particle to obtain the position information of the associated alpha particle; after a period of time accumulation, an alpha particle image 11 is obtained, and then an image of the neutron source spot 12 is obtained according to the position relationship between the neutron detector 15 and the associated alpha detection system 2.

In the specific data processing flow (shown in fig. 3) of step S4, the neutron digital signal selected after the n/γ Pulse Shape Discrimination (PSD) is subjected to constant ratio timing (CFD) to generate a door opening signal; the second digital signal generates a door closing signal through constant ratio timing (CFD); (n/gamma pulse shape discrimination can be realized by external electronic equipment, or can be directly acquired by a digitizer, PSD is carried out at a software end, n signals are selected (the n signals are neutron digital signals), taking a digitizer DT5730 as an example, the n/gamma signals detected by the neutron detection device 1 enter the DT5730 to record waveform information and time information (the n/gamma signals refer to first digital signals before n/gamma pulse shape discrimination is not carried out and comprise the n signals and the gamma signals, the gamma signals refer to gamma particle digital signals), long window integration time is set to be 200ns by utilizing the characteristic that the n signals and the gamma signals have different slow components, short window integration time is set to be 40ns, a PSD graph can be drawn by the signal (long window integration-short window integration)/(long window integration), and experiments adopt the ratio value of more than 0.15 to select clean neutron digital signals).

The door opening signal and the door closing signal (respectively enter a flight time switch 19) are subjected to time of flight (TOF) measurement, an n-alpha coincidence time window is selected on a flight time spectrum, and the n-alpha coincidence time window is 5ns, so that alpha particle digital signals related to the neutron digital signals are selected;

then, obtaining the x-axis coordinate and the y-axis coordinate of the alpha particle signal according to a second formula and a third formula for the A path digital signal, the B path digital signal, the C path digital signal and the D path digital signal of the selected alpha particle digital signal, thereby realizing the position reconstruction of alpha particles and obtaining an alpha particle image 11;

then, obtaining a real-time image of the neutron source spot 12 through geometric relation conversion according to a first formula, thereby realizing real-time measurement of the neutron source spot 12;

x is A-B/A + B second formula

y ═ C-D/C + D third formula

x represents the x-axis coordinate;

y represents a y-axis coordinate;

a represents a digital signal of A path;

b represents a B-path digital signal;

c represents a C-path digital signal;

d represents a D-path digital signal;

(A, B, C, D is the charge integration of the signal)

φ_tRepresents the diameter of the source spot 12;

φ_αrepresents the size of the alpha particle image 11 measured on the correlation α detection system 2;

φ_nrepresents the diameter of the neutron detector 15 (i.e., the effective cross-sectional dimension of the neutron detector 15);

l represents the distance from the neutron detector 15 to the center point of the tritium target 13;

l represents the distance from the center of the scintillator 6 in the correlation alpha detection system 2 to the center point of the tritium target 13.

The device according to the present invention is not limited to the embodiments described in the specific embodiments, and those skilled in the art can derive other embodiments according to the technical solutions of the present invention, and also belong to the technical innovation scope of the present invention.