A device and method for measuring position resolution of a drift tube detector

Abstract

The present invention discloses a device and method for measuring the position resolution of a drift tube detector. The device comprises: a beta radiation source and a plastic scintillator fixed on the same bracket, a drift tube detector is arranged between the beta radiation source and the plastic scintillator, a row of collimation holes are drilled on the collimator of the beta radiation source and a slit S is arranged, and a slit D is arranged in front of the plastic scintillator, wherein the positions of the beta radiation source, the drift tube detector and the plastic scintillator are positioned by laser collimation, and a radiation source shield is arranged outside the beta radiation source. The present invention uses beta rays to measure the position resolution of the drift tube detector, improves the collimation of the rays by setting the collimation holes and the slits, fixes the ray emission, the collimator and the receiver on the same stand, ensures the positioning accuracy, optimizes the electronic circuit parameters, improves the time accuracy, and obtains the corresponding position resolution by measuring the dispersion of the drift time.

Description

Technical Field

[0001] The invention relates to a drift tube detector position resolution, and in particular to a device and method for measuring the drift tube detector position resolution. Background Art

[0002] Cosmic ray muon imaging technology is a new type of non-destructive imaging technology developed in recent years. It uses natural cosmic rays as radiation sources, avoiding the radiation effects of artificial radiation sources on the inspected objects and operators. In addition, cosmic ray muons are high-energy charged particles with an average energy of 3-4 GeV at sea level. They have strong penetrating power and are relatively sensitive to high atomic number (high Z) materials. These characteristics make this technology advantageous in non-destructive imaging of heavy nuclear materials, and have broad application prospects in the fields of nuclear security, nuclear waste measurement, and treaty verification.

[0003] The principle of cosmic ray μ imaging is to detect the material (atomic number Z) by measuring the deflection angle of cosmic ray μ passing through matter, such as Figure 1 The simulation calculation of the standard deviation of the scattering angle of muons penetrating 10 cm of different materials is shown, and the different deflection angles of muons when they pass through 10 cm of different materials are listed. The measurement of the deflection angle is obtained by measuring the muon track, so the resolution of the atomic number Z depends on the position resolution of the cosmic ray μ track by the position sensitive detector. Several common position sensitive detectors include drift tube (DT), cathode strip chamber (CSC), narrow gap chamber (TGC), impedance plate chamber (RPC), multi-gap impedance plate chamber (MRPC), gas multiplier (GEM), etc. Among these detectors, the drift tube detector (DT) has the best position resolution, and the precision drift tube position sensitive detector is the best choice for carrying out cosmic ray μ imaging technology. Summary of the invention

[0004] In view of the problem that the position resolution of the drift tube cannot be measured in the prior art, the purpose of the present invention is to provide a device and method for measuring the position resolution of a drift tube detector, which improves the collimation of rays, ensures positioning accuracy, optimizes electronic circuit parameters, and improves time accuracy.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A device for measuring the position resolution of a drift tube detector, comprising: a β radiation source and a plastic scintillator fixed on the same bracket, a drift tube detector arranged between the β radiation source and the plastic scintillator, a row of collimation holes drilled on the collimator of the β radiation source and a slit S, a slit D arranged in front of the plastic scintillator, wherein the positions of the β radiation source, the drift tube detector and the plastic scintillator are positioned by laser collimation, and a radiation source shield is arranged outside the β radiation source;

[0007] The beta rays generated by the beta radiation source are incident through the collimator in a direction perpendicular to the radial direction of the drift tube detector, and pass through the slit S, the drift tube detector, and the slit D respectively to reach the plastic scintillator, and a pulse signal is generated on the anode of the drift tube detector and the plastic scintillator respectively. The drift time of the drift tube detector is obtained by measuring the time difference between the two pulse signals, and the time dispersion is obtained based on the drift time measured multiple times at different positions, and then converted to obtain the corresponding position resolution.

[0008] Further, in the measuring device as described above, the pulse signal generated by the plastic scintillator is measured and amplified by a photomultiplier tube and then transmitted to a time-to-digital converter;

[0009] The pulse signal generated by the anode of the drift tube detector is transmitted to the time-to-digital converter after preamplification, threshold discrimination and conversion;

[0010] The time difference between the two pulse signals is measured by the time-to-digital converter to obtain the drift time of the drift tube detector.

[0011] Furthermore, the measurement device as described above obtains time dispersion based on drift times measured multiple times at different positions, and then converts it into corresponding position resolution, including:

[0012] The frequency distribution of drift time measured multiple times at different locations was Gaussian fitted to obtain the mean value and its time dispersion;

[0013] The average value is fitted with a straight line to obtain the corresponding relationship between drift time and distance, i.e. the slope, and the corresponding position resolution σ0 is obtained by converting the time dispersion;

[0014] The actual value of the position resolution σ is obtained by eliminating the systematic error of the measurement:

[0015] σ=(σ0 2 -s 2 -d 2 ) 1 / 2

[0016] Wherein, s is the width of the slit S, and d is the width of the slit D.

[0017] Furthermore, in the measuring device as described above, the thickness of the collimator is 20 mm, the diameter of the collimating aperture is 1 mm, the width of the slit S is 0.4 mm, the width of the slit D is 0.4 mm, and the slit S and the slit D are made of 2 mm thick aluminum plates.

[0018] A method for measuring the position resolution of a drift tube detector, comprising:

[0019] (1) The beta ray generated by the beta radiation source is incident through the collimator in a direction perpendicular to the radial direction of the drift tube detector, passes through the slit S, the drift tube detector, and the slit D respectively to reach the plastic scintillator, and generates a pulse signal on the anode of the drift tube detector and the plastic scintillator respectively;

[0020] (2) obtaining the drift time of the drift tube detector by measuring the time difference between the two pulse signals;

[0021] (3) The time dispersion is obtained based on the drift time of multiple measurements at different positions, and then converted into the corresponding position resolution.

[0022] Further, in the above-mentioned measuring method, step (2) comprises:

[0023] The pulse signal generated by the plastic scintillator is measured and amplified by a photomultiplier tube and then transmitted to a time-to-digital converter;

[0024] The pulse signal generated by the anode of the drift tube detector is transmitted to the time-to-digital converter after preamplification, threshold discrimination and conversion;

[0025] The time difference between the two pulse signals is measured by the time-to-digital converter to obtain the drift time of the drift tube detector.

[0026] Further, in the measuring device as described above, step (3) comprises:

[0027] The frequency distribution of drift time measured multiple times at different locations was Gaussian fitted to obtain the mean value and its time dispersion;

[0028] The average value is fitted with a straight line to obtain the corresponding relationship between drift time and distance, i.e. the slope, and the corresponding position resolution σ0 is obtained by converting the time dispersion;

[0029] The actual value of the position resolution σ is obtained by eliminating the systematic error of the measurement:

[0030] σ=(σ0 2 -s 2 -d 2 ) 1 / 2

[0031] Wherein, s is the width of the slit S, and d is the width of the slit D.

[0032] Further, according to the measurement method described above, the thickness of the collimator is 20 mm, the diameter of the collimating aperture is 1 mm, the width of the slit S is 0.4 mm, the width of the slit D is 0.4 mm, and the slit S and the slit D are made of 2 mm thick aluminum plate.

[0033] The beneficial effects of the present invention are as follows: the present invention uses beta rays to measure the position resolution of a drift tube detector, improves the collimation of the rays by setting collimation holes and slits, fixes the ray emission, collimator and receiver on the same stand, ensures positioning accuracy, optimizes electronic circuit parameters, improves time accuracy, and obtains the corresponding position resolution by measuring the dispersion of drift time. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a table for simulating and calculating the standard deviation of scattering angles of different materials for muons penetrating 10 cm provided in an embodiment of the present invention;

[0035] Figure 2 A structural diagram of a drift tube provided in an embodiment of the present invention;

[0036] Figure 3 A schematic diagram of electron drift in a drift tube provided in an embodiment of the present invention;

[0037] Figure 4 A schematic diagram of the structure of a device for measuring the position resolution of a drift tube detector provided in an embodiment of the present invention;

[0038] Figure 5 A signal measurement timing diagram provided in an embodiment of the present invention;

[0039] Figure 6 The present invention is a flowchart of a method for measuring the position resolution of a drift tube detector provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved more clearly, the technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] The main basis for using cosmic ray muons to image objects is the different deflection angles of muons in nuclear materials. The core is to accurately locate the tracks of muons. The position resolution of the drift tube detector directly affects the measured tracks, and thus affects the imaging quality. Therefore, the measurement of the drift tube position resolution is an important technical indicator of the final imaging quality. 2The position and direction of the incident light on the detector are close to random, and it is not easy to get the accurate direction and position directly, so it is necessary to use a charged particle with a known incident direction and energy to replace it for measurement. β rays are also charged particles, and β rays emitted by Sr-90 radiation sources can be used to replace muons to establish a set of drift tube position resolution measurement devices and methods.

[0042] like Figure 2 As shown, the drift tube is composed of an outer aluminum tube 2, an inner gold-plated rhenium tungsten wire 3 and a number of connecting components 1. The middle anode wire 3 is a gold-plated rhenium tungsten wire with a diameter of about 30 μm. The tube is filled with a mixture of Ar and CO2, and the gas pressure is 2-3 atmospheres. The middle anode wire needs to be added with a high voltage of 2000-3000V.

[0043] like Figure 3 As shown, muons are incident into the drift tube to ionize the gas, and electrons drift toward the anode wire 3 under the action of the high voltage electric field. The shortest time for the electrons generated by ionization to drift from the original position to the anode wire, i.e., the drift time, corresponds to the shortest radial distance r between the muon track and the central wire. The relationship between the drift distance and time can be calibrated experimentally, so the position of the muon incident into the drift tube is obtained by measuring the drift time of the original electrons. The position resolution of the drift tube is also obtained by measuring the dispersion of the drift time.

[0044] The embodiment of the present invention provides a device for measuring the position resolution of a drift tube detector, such as Figure 4 As shown, the measuring device comprises: a β radiation source 10 and a plastic scintillator 5 fixed on the same bracket, a drift tube detector 7 is arranged between the β radiation source 10 and the plastic scintillator 5, a row of collimation holes are drilled on the collimator 9 of the β radiation source 10 and a slit S 8 is arranged, and a slit D6 is arranged in front of the plastic scintillator 5, wherein the positions of the β radiation source 10, the drift tube detector 7 and the plastic scintillator 5 are positioned by laser collimation, and a radiation source shield 11 is arranged outside the β radiation source 10.

[0045] The beta rays generated by the beta radiation source 10 are incident through the collimator 9 in a direction perpendicular to the radial direction of the drift tube detector 7, and pass through the slit S8, the drift tube detector 7, and the slit D6 to reach the plastic scintillator 5, respectively, and a pulse signal is generated on the anode of the drift tube detector 7 and the plastic scintillator 5, respectively. The drift time of the drift tube detector 7 is obtained by measuring the time difference between the two pulse signals, and the time dispersion is obtained based on the drift time measured multiple times at different positions, and then converted to obtain the corresponding position resolution.

[0046] Specifically, the pulse signal generated by the plastic scintillator is measured and amplified by a photomultiplier tube and then transmitted to a time digital converter; the pulse signal generated by the anode of the drift tube detector is pre-amplified, threshold-identified and converted and then transmitted to the time digital converter; the time difference between the two pulse signals is measured by the time digital converter to obtain the drift time of the drift tube detector. The light signal of the plastic scintillator is measured and amplified by a photomultiplier tube and then transmitted to the TDC (time digital converter). The pulse signal of the drift tube anode wire is pre-amplified, threshold-identified and converted and then transmitted to the TDC for collection. The TDC performs time matching on the two signals and obtains the time difference, i.e., the drift time. Figure 5 . Figure 5 It is explained that different incident positions make the drift time of muons different T1 and T2, and thus the measured signals have a time sequence. By changing the incident position of the radiation source, the drift time of different incident positions is measured, that is, the relationship between drift time and distance. The circuit delay and cable delay of the two signals are corrected by the pulse generator.

[0047] Specifically, the time dispersion is obtained based on the drift time measured multiple times at different positions, and then converted to the corresponding position resolution, including:

[0048] The frequency distribution of drift time measured multiple times at different positions is Gaussian fitted to obtain the average value and its time dispersion; the average value is linearly fitted to obtain the corresponding relationship between drift time and distance, i.e. the slope, and the corresponding position resolution σ0 is obtained by converting the time dispersion; the systematic error of the measurement is eliminated by the following formula to obtain the actual value of the position resolution σ:

[0049] σ=(σ0 2 -s 2 -d 2 ) 1 / 2

[0050] Wherein, s is the width of the slit S, and d is the width of the slit D.

[0051] The frequency distribution of drift time values ​​measured multiple times at different locations is Gaussian fitted to obtain the measured average value Xc and its time dispersion σ T , a straight line fitting is performed on the average value to obtain the corresponding relationship (slope) between drift time and distance, and thus the corresponding position resolution σ0 is converted from the measured time dispersion (resolution).

[0052] Specifically, the thickness of the collimator can be set to 20 mm, the diameter of the collimating aperture can be set to 1 mm, the width of the slit S can be set to 0.4 mm, the width of the slit D can be set to 0.4 mm, and the slit S and the slit D can be made of 2 mm thick aluminum plate.

[0053] The position resolution (drift time dispersion) of the drift tube itself is affected by multiple factors such as anode voltage, gas filling pressure, gas ratio, temperature, etc. When these factors remain constant, the measurement error mainly depends on the position accuracy and time measurement accuracy. In order to increase the collimation of the incident rays, a row of 1mm collimation holes is drilled on the collimator 9 (20mm thick) of the Sr-90 source and a 0.4mm wide slit S 8 is added to improve the collimation; a 0.4mm slit D 6 is also added in front of the plastic scintillator to improve the spatial measurement accuracy. Since the penetration ability of β rays is very weak, a 2mm thick aluminum plate can be used for the slit.

[0054] In order to ensure the positioning accuracy, the β radiation source and shield, collimator, slit, plastic flash, and photomultiplier tube are fixed on a C-shaped bracket. The position of the β radiation source can be moved by a five-dimensional optical platform, and the incident position of the radiation source is adjusted by laser alignment to ensure the accuracy of the measurement position. A fast-response photomultiplier tube is used to measure the plastic flash signal, with a rise time of about 0.7ns. The preamplifier signal rise time of the drift tube signal is about 15ns, and the accuracy of the TDC synchronous clock is less than 100ps, thus ensuring that the time measurement accuracy can be controlled at the ns level (~30μm). Ultimately, the measurement accuracy (systematic error) mainly comes from the slit width (200~400μm) before the source and the plastic flash. After eliminating the systematic error of the measurement through the following formula, the actual value of the resolution σ can be obtained, σ=(σ0 2 -s 2 -d 2 ) 1 / 2 , where s is the width of slit S and d is the width of slit D.

[0055] For example, the measuring device of the present invention is composed of a β radiation source 10, a radiation source shield 11, a collimator 9, a slit S 8, a drift tube 7 (drift tube detector), a slit D6, a plastic scintillator 5, and a photomultiplier tube 4. Figure 4. Sr-90 source is used as a substitute source for muon rays. Sr-90 produces beta rays with a maximum of 2.28MeV. The collimation of the collimator 9 is achieved through a row of 1mm collimation holes, and a 0.4mm slit S 8 is added on it to improve the collimation effect; a 0.4mm slit D6 is also added in front of the plastic scintillator to improve the collimation effect. The double-layer slit design can improve the collimation effect of beta rays. Since the penetration ability of beta rays is very weak, the slits S8 and D6 are made of 2mm thick aluminum plates, and the width of the slits can be adjusted manually according to the actual amount of incident beta rays. The β ray is incident in a direction perpendicular to the radial direction of the drift tube 7, passes through the collimator 9, the slit S8, the drift tube 7, the slit D6 and reaches the plastic scintillator 5, and generates a fluorescence signal on the drift tube anode 3 and the plastic scintillator 5 respectively. The light signal of the plastic scintillator is measured and amplified by the photomultiplier tube and transmitted to the TDC (time digital converter). The pulse signal of the drift tube anode wire is also transmitted to the TDC for collection after pre-amplification, threshold discrimination and conversion. The time information of the two signals is read out by the TDC, and it is considered to be a valid signal only if it meets a certain logical relationship. The arrival time of the drift tube signal minus the arrival time of the plastic scintillator is obtained to obtain the drift time of the detector. Because the drift time of the drift tube is basically linear with the incident position, the incident position is obtained by obtaining the drift time. In other words, the corresponding position resolution can be obtained by measuring the time dispersion of the drift tube signal, and the two signals are time-matched to obtain the time difference, that is, the drift time.

[0056] The device of the present invention is used to measure the position resolution of the drift tube detector using β rays. The collimation of the rays is improved by setting collimation holes and slits. The ray emission, collimator and receiver are all fixed on the same stand to ensure positioning accuracy, optimize electronic circuit parameters, improve time accuracy, and obtain the corresponding position resolution by measuring the dispersion of drift time.

[0057] According to another aspect of an embodiment of the present invention, a method for measuring the position resolution of a drift tube detector is also provided, which is applied to the aforementioned device for measuring the position resolution of a drift tube detector. Figure 6 As shown, including:

[0058] The beta rays generated by the S100 and beta radiation sources are incident through the collimator in a direction perpendicular to the radial direction of the drift tube detector, and pass through the slit S, the drift tube detector, and the slit D respectively to reach the plastic scintillator, generating a pulse signal on the anode of the drift tube detector and the plastic scintillator respectively.

[0059] Specifically, the thickness of the collimator can be set to 20 mm, the diameter of the collimating aperture can be set to 1 mm, the width of the slit S can be set to 0.4 mm, the width of the slit D can be set to 0.4 mm, and the slit S and the slit D can be made of 2 mm thick aluminum plate.

[0060] S200 , obtaining the drift time of the drift tube detector by measuring the time difference between the two pulse signals.

[0061] Specifically, step S200 includes: the pulse signal generated by the plastic scintillator is measured and amplified by a photomultiplier tube and then transmitted to a time digital converter; the pulse signal generated by the anode of the drift tube detector is pre-amplified, threshold-identified and converted and then transmitted to the time digital converter; the time difference between the two pulse signals is measured by the time digital converter to obtain the drift time of the drift tube detector.

[0062] S300, obtaining time dispersion based on drift times measured multiple times at different positions, and then converting to obtain corresponding position resolution.

[0063] Specifically, step S300 includes: performing Gaussian fitting on the frequency distribution of drift time measured multiple times at different positions to obtain an average value and its time dispersion; performing linear fitting on the average value to obtain the corresponding relationship between drift time and distance, i.e., the slope, and converting the time dispersion to obtain the corresponding position resolution σ0; eliminating the systematic error of the measurement by the following formula to obtain the actual value σ of the position resolution:

[0064] σ=(σ0 2 -s 2 -d 2 ) 1 / 2

[0065] Wherein, s is the width of the slit S, and d is the width of the slit D.

[0066] By adopting the method of the present invention, the position resolution of the drift tube detector is measured by using β rays, the collimation of the rays is improved by setting collimation holes and slits, and the ray emission, collimator and receiver are all fixed on the same stand to ensure positioning accuracy, optimize electronic circuit parameters, improve time accuracy, and obtain the corresponding position resolution by measuring the dispersion of drift time.

[0067] It should be noted that the measuring method of the present invention and the aforementioned measuring device belong to the same inventive concept, and the specific implementation mode and technical solution will not be repeated here.

[0068] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A device for measuring the position resolution of a drift tube detector, characterized in that: include: A beta radiation source and a plastic scintillator fixed on the same bracket, a drift tube detector is arranged between the beta radiation source and the plastic scintillator, a row of collimation holes and a slit S are drilled on the collimator of the beta radiation source, and a slit D is arranged in front of the plastic scintillator, wherein the positions of the beta radiation source, the drift tube detector and the plastic scintillator are positioned by laser collimation, and a radiation source shield is arranged outside the beta radiation source; The beta ray generated by the beta radiation source is incident through the collimator in a direction perpendicular to the radial direction of the drift tube detector, passes through the slit S, the drift tube detector, and the slit D respectively to reach the plastic scintillator, and a pulse signal is generated on the anode of the drift tube detector and the plastic scintillator respectively, and the drift time of the drift tube detector is obtained by measuring the time difference between the two pulse signals, and the time dispersion is obtained based on the drift time measured multiple times at different positions, and then converted to obtain the corresponding position resolution, including: The frequency distribution of drift time measured multiple times at different locations was Gaussian fitted to obtain the mean value and its time dispersion; The average value is fitted with a straight line to obtain the corresponding relationship between drift time and distance, i.e. the slope, and the corresponding position resolution σ0 is obtained by converting the time dispersion; The actual value of the position resolution σ is obtained by eliminating the systematic error of the measurement: σ=(σ0 2 -s 2 -d 2 ) 1 / 2 Wherein, s is the width of the slit S, and d is the width of the slit D.

2. The measuring device according to claim 1, characterized in that The pulse signal generated by the plastic scintillator is measured and amplified by a photomultiplier tube and then transmitted to a time-to-digital converter; The pulse signal generated by the anode of the drift tube detector is transmitted to the time-to-digital converter after preamplification, threshold discrimination and conversion; The time difference between the two pulse signals is measured by the time-to-digital converter to obtain the drift time of the drift tube detector.

3. The measuring device according to any one of claims 1 to 2, characterized in that: The thickness of the collimator is 20 mm, the diameter of the collimating aperture is 1 mm, the width of the slit S is 0.4 mm, the width of the slit D is 0.4 mm, and the slit S and the slit D are made of 2 mm thick aluminum plates.

4. A method for measuring the position resolution of a drift tube detector, applied to the measuring device according to any one of claims 1 to 3, characterized in that: include: (1) The beta ray generated by the beta radiation source is incident through the collimator in a direction perpendicular to the radial direction of the drift tube detector, passes through the slit S, the drift tube detector, and the slit D respectively to reach the plastic scintillator, and generates a pulse signal on the anode of the drift tube detector and the plastic scintillator respectively; (2) obtaining the drift time of the drift tube detector by measuring the time difference between the two pulse signals; (3) The time dispersion is obtained based on the drift time of multiple measurements at different positions, and then converted into the corresponding position resolution.

5. The measuring method according to claim 4, characterized in that: Step (2) comprises: The pulse signal generated by the plastic scintillator is measured and amplified by a photomultiplier tube and then transmitted to a time-to-digital converter; The pulse signal generated by the anode of the drift tube detector is transmitted to the time-to-digital converter after preamplification, threshold discrimination and conversion; The time difference between the two pulse signals is measured by the time-to-digital converter to obtain the drift time of the drift tube detector.

6. The measuring method according to claim 4, characterized in that: Step (3) includes: The frequency distribution of drift time measured multiple times at different locations was Gaussian fitted to obtain the mean value and its time dispersion; The average value is fitted with a straight line to obtain the corresponding relationship between drift time and distance, i.e. the slope, and the corresponding position resolution σ0 is obtained by converting the time dispersion; The actual value of the position resolution σ is obtained by eliminating the systematic error of the measurement: σ=(σ0 2 -s 2 -d 2 ) 1 / 2 Wherein, s is the width of the slit S, and d is the width of the slit D.

7. The measuring method according to any one of claims 4 to 6, characterized in that: The thickness of the collimator is 20 mm, the diameter of the collimating aperture is 1 mm, the width of the slit S is 0.4 mm, the width of the slit D is 0.4 mm, and the slit S and the slit D are made of 2 mm thick aluminum plates.

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