A system and method for measuring the precision of x-ray detector photon time-of-arrival stamps

Abstract

The present application relates to a kind of X-ray detector photon arrival time mark precision measurement system and method.The present application system includes: signal generator, pulse X-ray generator, X-ray detector to be measured, time mark photon counter and processing module deployed on host computer constitute;Wherein, the signal generator is used to generate pulse signal, and respectively give pulse X-ray generator and time mark photon counter;The pulse X-ray generator is used to generate X-ray photon according to pulse signal;The X-ray detector to be measured is used to accept X-ray photon, and X-ray photon is converted into electric pulse, and is output to time mark photon counter;The time mark photon counter is used to time mark when receiving electric pulse electric pulse, and obtain the time interval between receiving pulse signal and electric pulse;The processing module is used to process time interval and obtain the time mark precision of X-ray detector to be measured.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of X-ray pulsar navigation, in particular to an X-ray photon arrival time mark precision measurement system for X-ray detectors, which is suitable for measuring and evaluating the time mark precision of various X-ray single photon detectors, and in particular to an X-ray detector photon arrival time mark precision measurement system and method. BACKGROUND

[0002] X-ray pulsar navigation is a new strategic navigation technology. Pulsar navigation uses a pulsar with a stable self-rotation period as a navigation beacon, has the characteristics of not being limited by ground equipment or fixed beacon field of view, can reduce the burden of ground navigation support equipment, improve the system anti-interference ability, realize the backup of existing near-earth navigation systems, and help to improve the autonomous navigation function of spacecraft. With the continuous deepening of human activities into the universe, pulsar navigation is becoming indispensable.

[0003] In an X-ray pulsar navigation system, an X-ray single photon detector is one of the key components of the navigation system, which is used to receive and record the X-ray pulse arrival time (TOA) of a pulsar. The higher the arrival time precision of a single photon measured by the detector, the more accurate the pulse phase difference obtained after period folding processing, and thus the higher the navigation positioning precision. Therefore, the X-ray single photon detector used for pulsar navigation needs to calibrate its time mark precision for detector selection and system navigation precision evaluation.

[0004] Currently, there is still a lack of a general, complete, and high-precision X-ray detector photon arrival time mark precision measurement system internationally. NASA Goddard Flight Center has designed and developed a system composed of a pulsed X-ray source based on LED ultraviolet lamp modulation and an oscilloscope for detector TOA calibration and testing, in which the LED is used to control the timing output of the X-ray, and the oscilloscope is used to capture the time delay of the detector output signal and the LED trigger signal. However, the pulse width of the LED is as high as 20 ns, resulting in an X-ray arrival time precision error greater than 20 ns. Moreover, the time delay displayed by the oscilloscope is read out through the waveform, which is relatively low in precision and efficiency. Therefore, the existing TOA mark precision measurement system has limitations such as limited measurement precision and low measurement efficiency. SUMMARY

[0005] The present application aims to overcome the limitations of the existing TOA mark precision measurement system, such as limited measurement precision and low measurement efficiency. To achieve the above-mentioned purpose, the present application realizes the following technical solutions.

[0006] The application provides an X-ray detector photon arrival time mark precision measurement system, characterized in that the system comprises a signal generator, a pulsed X-ray generator, a to-be-measured X-ray detector, a time mark photon counter and a processing module arranged on an upper computer.

[0007] The signal generator is used for generating a pulse signal and transmitting the pulse signal to the pulsed X-ray generator and the time mark photon counter respectively.

[0008] The pulsed X-ray generator is used for generating X-ray photons according to the pulse signal.

[0009] The to-be-measured X-ray detector is used for accepting the X-ray photons and converting the X-ray photons into an electric pulse and outputting the electric pulse to the time mark photon counter.

[0010] The time mark photon counter is used for performing time marking on the electric pulse when the electric pulse is received and obtaining a time interval between the received pulse signal and the electric pulse.

[0011] The processing module is used for processing the time interval to obtain the time mark precision of the to-be-measured X-ray detector.

[0012] As one of the improvements of the above technical solution, the pulse signal is a square wave or a triangular wave; the frequency of the pulse signal is 1 MHz-100 MHz, the width of the pulse signal is 1 ns-50 ns, and the amplitude variation range of the pulse signal covers-1 V to +0.5 V.

[0013] As one of the improvements of the above technical solution, the pulsed X-ray generator is an X-ray source with a multi-stage electrostatic focusing system.

[0014] The electrode of the pulsed X-ray generator comprises a cathode, a modulation electrode, three focusing electrodes and an anode.

[0015] The cathode comprises a filament and is used for heating the filament to generate electrons after electrification.

[0016] The modulation electrode is used for controlling electron passing or inhibiting electron passing.

[0017] The three focusing electrodes are used for focusing the electrons to form an electron beam.

[0018] The anode is provided with a target material and is used for generating X-ray photons through bremsstrahlung mechanism when the electron beam is incident on the target material.

[0019] As one of the improvements of the above technical solution, the modulation electrode is used for controlling electron passing or inhibiting electron passing and specifically comprises the following steps.

[0020] When the voltage of the modulation electrode is a positive voltage, the modulation electrode controls electron passing.

[0021] When the modulation electrode voltage is a negative voltage, the modulation electrode suppresses the passage of electrons.

[0022] As one of the improvements of the above technical solutions, the voltage of each focusing electrode is tens of volts to thousands of volts, which is determined according to the size and spacing of each electrode; the anode is connected to a positive high voltage, and the voltage is 5kV-50kV, which is determined according to the required energy of X-ray photons.

[0023] As one of the improvements of the above technical solutions, the energy response range of the X-ray single photon detected by the X-ray detector under test is several keV to tens of keV.

[0024] As one of the improvements of the above technical solutions, the time-marked photon counter comprises a first input end and a second input end; wherein the first input end is used to receive a pulse signal from a signal generator; and the second input end is used to receive an electric pulse output by the X-ray detector under test.

[0025] The first input end is triggered by a rising edge, and the trigger level is set according to the pulse signal output by the signal generator;

[0026] The second input end sets the trigger mode and trigger threshold according to the pulse waveform and amplitude of the electric pulse output by the X-ray detector under test.

[0027] As one of the improvements of the above technical solutions, the time-marked photon counter further comprises a timer.

[0028] The time-marked photon counter is used to obtain the time interval between the received pulse signal and the electric pulse, and specifically comprises:

[0029] When the first input end receives each pulse signal, the timer starts timing, and each time the second input end receives an electric pulse output by the X-ray detector under test before the next pulse signal arrives at the first input end, the timer records the time interval;

[0030] For the time interval recorded by the timer, if there is no photon signal in the detection period, there is no time interval in the detection period; if the detection period includes multiple X-ray photons, only the time interval of the first X-ray photon is taken; and the detection period is the time between two adjacent pulse signals received by the first input end.

[0031] As one of the improvements of the above technical solutions, the processing process of the processing module specifically comprises:

[0032] Sort the sizes of the time intervals;

[0033] Set each time interval interval, respectively, the number of each interval in accordance with the interval requirements of the time interval statistics, and generate a statistical chart;

[0034] The statistical chart is fitted to obtain a Gaussian distribution curve, and the standard deviation of the curve is obtained; the standard deviation of the curve is the time mark precision of the X-ray detector to be measured.

[0035] The application also provides an X-ray detector photon arrival time precision measurement method based on the system.

[0036] Step 1) Set the anode, focusing pole and cathode filament voltage of the pulse X-ray generator, and turn on the pulse X-ray generator;

[0037] Step 2) Set the pulse shape, frequency, amplitude and width of the pulse signal of the signal generator, and generate a pulse signal through the signal generator;

[0038] Step 3) Turn on the X-ray detector to be measured;

[0039] Step 4) Start the time mark photon counter, time mark the electric pulse through the time mark photon counter, and obtain the time interval between the received pulse signal and the electric pulse;

[0040] Step 5) Save and transmit the time interval to the host computer processing module;

[0041] Step 6) In the host computer processing module, the detected time interval is statistically plotted to obtain a statistical chart, and the statistical chart is fitted to obtain a Gaussian distribution curve, and then the standard deviation of the Gaussian distribution curve, i.e. the time mark precision of the X-ray detector to be measured.

[0042] Compared with the prior art, the application has the following advantages:

[0043] The pulse X-ray generator has high frequency response, can generate nanosecond-level extremely narrow X-ray pulses, and the time mark photon counter has high measurement precision, so that the overall measurement system is convenient to use, fast in measurement speed and high in measurement precision, and can meet the measurement requirements of the time mark precision of the X-ray detector. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is an X-ray photon arrival time precision measurement system structure diagram;

[0045] Figure 2 is a time mark photon counter measurement pulse time interval schematic diagram;

[0046] Fig. 3(a) is a histogram of a certain X-ray detector photon sequence, and Fig. 3(b) is a fitted Gaussian distribution diagram. DETAILED DESCRIPTION

[0047] The present application provides an X-ray detector photon arrival time mark precision measurement system, which comprises a pulsed X-ray generator, a signal generator, a to-be-tested X-ray detector, a time-marked photon counter and a data acquisition and analysis computer.

[0048] The technical solutions provided by the present application are further described below in combination with examples.

[0049] Example 1

[0050] As shown in Figure 1 Fig. 1, the present application provides an X-ray detector photon arrival time mark precision measurement system, which comprises a pulsed X-ray generator, a signal generator, a to-be-tested X-ray detector, a time-marked photon counter and a data acquisition and analysis computer.

[0051] The pulsed X-ray generator is an X-ray source with a multi-stage electrostatic focusing system, specifically comprising six electrodes, i.e. a cathode, a modulation electrode, three focusing electrodes and an anode. After the cathode filament is heated by being electrified, electrons are emitted. When the voltage of the modulation electrode is positive, the electrons can pass through the modulation electrode, are accelerated by the high voltage of the focusing electrodes and the anode, and are incident on the anode target to generate X-rays by the bremsstrahlung mechanism. When the voltage of the modulation electrode is negative, the electric field inhibits the electrons from passing through the modulation electrode, so that no X-rays are generated. The three focusing electrodes focus the electron beam to form a micro-focus X-ray source. The voltage of the focusing electrodes generally varies from several tens of volts to several thousand volts, and is specifically determined according to the size and spacing of the six electrodes. The anode is connected to a positive high voltage, and the voltage is 5kV-50kV, which is determined according to the energy of the required X-rays. The electron cut-off voltage of the present pulsed X-ray generator is below -1V, and the voltage is above +0.5V when turned on, which can quickly excite X-ray photon generation. The present application is a low-voltage controlled pulsed X-ray generator.

[0052] The signal generator generates high-frequency pulses, which are applied to the modulation electrode of the pulsed X-ray generator and the trigger end of the time-tagged photon counter at the same time. Generally, square wave or triangular wave pulses are required, with positive pulse amplitude higher than +0.5 V and negative pulse amplitude lower than -1 V. The signal generator can generate pulses with a frequency of more than 1 MHz and a pulse width of less than 10 ns. When the pulse amplitude is higher than 0.5 V, the pulsed X-ray generator generates X-rays, and when the pulse amplitude is lower than -1 V, the pulsed X-ray generator has no X-ray output.

[0053] The to-be-tested X-ray detector can detect X-ray single photons and has an energy response range of several keV to several tens of keV. After receiving a single photon from the pulsed X-ray generator, the to-be-tested X-ray detector can quickly convert into an electrical pulse output with a pulse amplitude of more than 20 mV. The to-be-tested X-ray detector is generally placed in front of the X-ray signal generator, within a distance of about 20 cm from the X-ray output end. The distance depends on whether the X-rays from the pulsed X-ray generator can be detected.

[0054] The time-tagged photon counter includes two input ends (a first input end CH1 and a second input end CH2), one end receiving a pulse reference signal (CH1) from the signal generator, and the other end receiving an output signal (CH2) of the to-be-tested X-ray detector. The pulse reference signal trigger end is selected to trigger the rising edge, and the time-tagged photon counter starts the internal timer immediately after being triggered. When the output signal of the to-be-tested X-ray detector is received, the timer stops timing and stores the ΔT digitally, with a time accuracy of better than 1 ns. At the same time, when the time-tagged photon counter receives the output signal from the to-be-tested detector, it immediately marks it with a high-precision time stamp, with a time accuracy of better than 1 ns. In this way, the signal from the pulsed X-ray generator is stored, including two important time information: ΔT and high-precision time stamp.

[0055] The time-tagged photon counter sorts and stores the detected X-ray single photons in time sequence, and uploads them to a data acquisition and analysis computer. The computer generates a histogram from the collected photon sequence, and the standard deviation of the fitted histogram is the time-tagging accuracy of the to-be-tested X-ray detector.

[0056] Embodiment 2

[0057] The embodiment 2 of the present application provides a measurement method of an X-ray detector photon arrival time accuracy measurement system, including the following steps:

[0058] Step 1), set the anode, focusing electrode and filament voltage of the pulsed X-ray generator, and start the pulsed X-ray generator.

[0059] Step 2), using a signal generator to set the positive pulse voltage applied to the pulse X-ray generator modulation pole, the frequency is self-defined, the pulse width is set to a narrow pulse of about 10 ns, the amplitude is set to vary in the range of -1V~+0.5V, and generally -3V~+3V. It is narrow to ensure that the distribution of X-ray photon emission time is as concentrated as possible in the extremely short time when the pulse X-ray generator is turned on, and to avoid the distribution of photon emission time from interfering with the measurement.

[0060] Step 3), the X-ray detector to be measured is placed within 20 cm in front of the anode of the pulse X-ray generator, and the output end is connected to the CH2 input end of the time-tagged photon counter. The X-ray detector to be measured is turned on.

[0061] Step 4), start the time-tagged photon counter, set appropriate measurement parameters in the computer control program, including trigger end (CH1) pulse reference signal trigger mode selection rising edge, and trigger level according to the pulse output by the signal generator; receive the output signal end (CH2) of the X-ray detector to be measured, select the trigger mode and trigger threshold according to the output pulse waveform and amplitude of the X-ray detector to be measured, and the trigger threshold is generally higher than 10 mV.

[0062] Step 5), the time-tagged photon counter measures the time interval between the pulse reference signal of the signal generator and the output signal of the X-ray detector to be measured, and marks the time stamp of the detected X-ray photons. The detection data is saved to a txt file or binary text file.

[0063] Step 6), upload the detection data to the data acquisition and analysis computer, and use MATLAB or other software to statistically plot the detected photon sequence file, which will obtain a statistical graph of approximately Gaussian distribution, and fit the standard deviation of the Gaussian distribution, thereby obtaining the time measurement accuracy of the X-ray detector to be measured.

[0064] The measurement mode of the time-tagged photon counter in the system of the present application and the measurement result data are further described below.

[0065] In step 5), the schematic diagram of the time-tagged photon counter measuring the relative time Δt is as shown in Figure 2 The CH1 channel inputs the pulse reference signal of the signal generator, and every two adjacent signals are a detection period. The CH2 channel inputs the photon signal received by the X-ray detector to be measured. The instrument will measure and record the relative time interval Δt1, Δt2, etc. between the two. There may be no photon signal in some detection periods, such as Figure 2 No photon is detected in the third detection period in

[0066] After the measurement experiment of the X-ray detector is performed by using the system in step 6), the detected photon sequence file is statistically plotted, and an approximately Gaussian distribution statistical histogram and a fitted Gaussian distribution are obtained as shown in FIG. 3(a) and FIG. 3(b), wherein FIG. 3(a) is a histogram of the photon sequence collected by the X-ray detector, and FIG. 3(b) is a fitted Gaussian distribution graph. The photon arrival time accuracy of the X-ray detector is the standard deviation of the Gaussian distribution.

[0067] As can be seen from the above detailed description of the present application, the measurement system of the present application is convenient to use, the measurement method of the present application is fast, and the measurement accuracy is high, and the time mark accuracy of the X-ray detector can be accurately measured.

[0068] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. An X-ray detector photon time of arrival marking precision measurement system, characterized in that, The system comprises a signal generator, a pulsed X-ray generator, a to-be-tested X-ray detector, a time-marked photon counter and a processing module arranged on a host computer. The signal generator is configured to generate a pulse signal and transmit the pulse signal to the pulsed X-ray generator and the time-marked photon counter respectively. The pulsed X-ray generator is configured to generate X-ray photons according to the pulse signal. The to-be-tested X-ray detector is configured to receive the X-ray photons and convert the X-ray photons into an electric pulse and output the electric pulse to the time-marked photon counter. The time-marked photon counter is configured to time mark the electric pulse when the electric pulse is received and obtain a time interval between the received pulse signal and the electric pulse. The processing module is configured to process the time interval to obtain time-marking precision of the to-be-tested X-ray detector. The time-marked photon counter comprises a first input end and a second input end. The first input end is configured to receive the pulse signal from the signal generator. The second input end is configured to receive the electric pulse output by the to-be-tested X-ray detector.

2. The X-ray detector photon time of arrival marker precision measurement system of claim 1, wherein, The first input end is triggered by a rising edge and the trigger level is set according to the pulse signal output by the signal generator.

3. The X-ray detector photon time of arrival marker precision measurement system of claim 1, wherein, The second input end sets the trigger mode and the trigger threshold according to the pulse waveform and amplitude of the electric pulse output by the to-be-tested X-ray detector. The pulse signal is a square wave or a triangular wave. The frequency of the pulse signal is 1 MHz to 100 MHz. The width of the pulse signal is 1 ns to 50 ns. The amplitude of the pulse signal ranges from -1 V to +0.5 V. The pulsed X-ray generator is an X-ray source with a multi-stage electrostatic focusing system.

4. The X-ray detector photon time of arrival marker precision measurement system of claim 3, wherein, The electrode of the pulsed X-ray generator comprises a cathode, a modulation electrode, three focusing electrodes and an anode. The cathode comprises a filament and is configured to heat the filament to generate electrons after being powered on. The modulation electrode is configured to control the passage of electrons or inhibit the passage of electrons.

5. The X-ray detector photon time of arrival marker precision measurement system of claim 3, wherein, The three focusing electrodes are configured to focus the electrons to form a focused electron beam.

6. The X-ray detector photon time of arrival marker precision measurement system of claim 1, wherein, The anode is provided with a target material and is configured to accelerate the electrons and generate X-ray photons by bremsstrahlung mechanism when the electron beam is incident on the target material.

7. The X-ray detector photon time of arrival marker precision measurement system of claim 1, wherein, The modulation electrode is configured to control the passage of electrons or inhibit the passage of electrons. When the voltage of the modulation electrode is positive, the modulation electrode controls the passage of electrons. When the voltage of the modulation electrode is negative, the modulation electrode inhibits the passage of electrons. The voltage of each focusing electrode is tens of volts to several thousand volts and is determined according to the size and spacing of each electrode. The anode is connected to a positive high voltage with a voltage of 5 kV to 50 kV and is determined according to the energy of the required X-ray photons. The energy response range of the to-be-tested X-ray detector for detecting X-ray single photons is several keV to several tens of keV. The time-marked photon counter further comprises a timer. The time-marked photon counter is configured to obtain the time interval between the received pulse signal and the electric pulse. When the first input end receives each pulse signal, the timer starts timing. Before the next pulse signal arrives at the first input end, the timer records the time interval each time the second input end receives the electric pulse output by the to-be-tested X-ray detector. If there is no photon signal in the detection period, the detection period has no time interval; if the detection period includes multiple X-ray photons, only the time interval of the first X-ray photon is taken; the detection period is the time between two adjacent pulse signals received by the first input.

8. The X-ray detector photon time of arrival marker precision measurement system of claim 1, wherein, The processing process of the processing module specifically includes: Sort the time intervals according to their sizes; Set the time interval intervals, respectively count the number of time intervals meeting the interval requirements in each interval, and generate a statistical chart; Fit the statistical chart to obtain a Gaussian distribution curve, and further obtain the standard deviation of the curve; the standard deviation of the curve is the time mark precision of the X-ray detector to be measured.

9. An X-ray detector photon arrival time precision measurement method based on the system of any one of claims 1-8, the method comprising the following steps: Step 1) Set the anode, focusing pole and cathode filament voltage of the pulsed X-ray generator, and turn on the pulsed X-ray generator; Step 2) Set the pulse shape, frequency, amplitude and width of the pulse signal of the signal generator, and generate a pulse signal through the signal generator; Step 3) Turn on the X-ray detector to be measured; Step 4) Start the time-marking photon counter, time-mark the electrical pulse through the time-marking photon counter, and obtain the time interval between the received pulse signal and the electrical pulse; Step 5) Save the time interval and transmit it to the processing module of the host computer; Step 6) In the processing module, the detected time intervals are statistically plotted to obtain a statistical chart, and the statistical chart is fitted to obtain a Gaussian distribution curve, and further obtain the standard deviation of the Gaussian distribution curve, which is the time mark precision of the X-ray detector to be measured.

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