CN115032679A - Two-dimensional positron annihilation lifetime spectrum measuring method and system - Google Patents
Two-dimensional positron annihilation lifetime spectrum measuring method and system Download PDFInfo
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Abstract
The disclosure relates to a method and a system for measuring a two-dimensional positron annihilation lifetime spectrum, and relates to the technical field of nuclear spectroscopy and nuclear detection. The method comprises the steps of detecting first stop time and second stop time of two annihilation gamma photons generated reversely when positron annihilation occurs in an annihilation sample, calculating the first life value and the second life value with the start time of the gamma photons generated by radioactive source decay, and carrying out two-dimensional statistics on the first life value and the second life value to obtain a two-dimensional positron annihilation life spectrum of the positron annihilation in the sample to be detected. According to the method, two annihilation gamma photons generated by one annihilation case are counted, so that background counting can be effectively eliminated, the peak-to-valley ratio of a life spectrum is improved, the utilization rate of annihilation gamma photon information in the annihilation case can be improved, and the time resolution of measurement is improved.
Description
Technical Field
The disclosure relates to the technical field of nuclear spectroscopy and nuclear detection, in particular to a two-dimensional positron annihilation lifetime spectrum measuring method and system.
Background
Positron Annihilation Lifetime Spectrum (PALS) measurement is a measurement method that characterizes the type and number of material defects by measuring the Annihilation Lifetime of a Positron in a material. The radioactive source emits initial gamma photons with specific energy when decaying to release positrons, the positrons can generate two annihilation gamma photons with specific energy when annihilation occurs, so that energy signals of the initial gamma photons and the annihilation gamma photons can be detected in measurement, and annihilation life time from generation to annihilation of the positrons is obtained according to time difference between the energy signals.
At present, in positron annihilation lifetime spectrum measurement, two detectors are generally adopted to respectively detect the occurrence time of an energy signal of an initial gamma photon as the initial time of positron generation, detect the occurrence time of an annihilation gamma photon as the stop time of positron generation, and count the annihilation lifetime of the positron according to the initial time and the stop time.
The peak-to-valley ratio is an important index for measuring the measurement accuracy of the positron annihilation lifetime spectrum. However, in the measurement of the above scheme, it may be difficult to distinguish partial background counts, so that the peak-to-valley ratio of the obtained positron annihilation lifetime spectrum needs to be improved. In addition, the problem of low utilization rate of annihilation gamma photon information exists when the generation time of an annihilation gamma photon is detected as the stop time, so that the time resolution of measurement in the scheme is also to be improved.
It is to be noted that the information disclosed in the above background section is only for enhancement of understanding of the background of the present disclosure, and thus may include information that does not constitute prior art known to those of ordinary skill in the art.
Disclosure of Invention
The invention aims to provide a two-dimensional positron annihilation life spectrum measuring method and a system, wherein the method is used for respectively detecting two annihilation gamma photons generated by positron annihilation reversal at a first side and a second side opposite to a sample to be measured in the measuring process, so that back counting in the measurement can be effectively eliminated, and the peak-to-valley ratio is further improved; and annihilation gamma photon information is more fully utilized, and the time resolution of measurement is improved, so that the measurement precision of the positron annihilation lifetime spectrum is improved.
According to a first aspect of the present disclosure, there is provided a two-dimensional positron annihilation lifetime spectroscopy measurement method, which may include:
detecting the starting time of a radioactive source generating a first energy signal by decay, wherein the energy threshold of the first energy signal is set according to the energy of the starting gamma photon generated by the radioactive source by decay;
detecting a first stop time of a first side of a sample to be detected for generating a second energy signal, and detecting a second stop time of a second side of the sample to be detected for generating a third energy signal, wherein energy thresholds of the second energy signal and the third energy signal are set according to energy of annihilation gamma photons generated by positron annihilation, and the first side is opposite to the second side;
under the condition that the first stop time meets the first recording condition, calculating to obtain a first life value according to the starting time and the first stop time;
under the condition that the second stop time meets the second recording condition, calculating according to the starting time and the second stop time to obtain a second life value;
and under the condition of obtaining the first life value and the second life value, performing two-dimensional statistics on the first life value and the second life value to obtain a two-dimensional positron annihilation life spectrum.
Optionally, the first recording condition includes that the start time and the first stop time are obtained within a first preset time window.
Optionally, the second recording condition includes that the start time and the second stop time are obtained within a second preset time window.
Optionally, in a case that the first lifetime value and the second lifetime value are obtained, performing two-dimensional statistics on the first lifetime value and the second lifetime value to obtain a two-dimensional positron annihilation lifetime spectrum, including:
under the condition of obtaining a first life value and a second life value, performing two-dimensional statistics by taking the first life value as a horizontal axis and the second life value as a vertical axis;
and under the condition that the difference value of the first life value and the second life value is smaller than the preset time difference, obtaining a two-dimensional positron annihilation life spectrum according to the first life value and the second life value.
Optionally, the first stop time corresponds to a first time resolution, the second stop time corresponds to a second time resolution, and a ratio of the first time resolution to the second time resolution is smaller than
According to a second aspect of the present disclosure, there is provided a two-dimensional positron annihilation lifetime spectroscopy measurement system, which may include:
the starting time recording module is used for detecting the starting time of a first energy signal generated by the decay of the radioactive source, and the energy threshold of the first energy signal is set according to the energy of the starting gamma photon generated by the decay of the radioactive source;
the first stop time recording module is used for detecting the first stop time of a second energy signal generated by the first side of the sample to be detected, and the energy threshold of the second energy signal is set according to the energy of annihilation gamma photons generated by positron annihilation;
the second stop time recording module is used for detecting the second stop time of a second side of the sample to be detected for generating a third energy signal, the energy threshold of the third energy signal is set according to the energy of annihilation gamma photons generated by positron annihilation, and the first side is opposite to the second side;
the service life value calculating module is used for calculating and obtaining a first service life value according to the starting time and the first stopping time under the condition that the first stopping time meets the first recording condition;
the life value calculating module is further used for calculating and obtaining a second life value according to the starting time and the second stopping time under the condition that the second stopping time meets the second recording condition;
and the two-dimensional life spectrum counting module is used for performing two-dimensional counting on the first life value and the second life value under the condition of obtaining the first life value and the second life value to obtain a two-dimensional positron annihilation life spectrum.
Optionally, the first stop time recording module includes:
a first stop detector for detecting a second energy signal at a first side of the sample to be measured;
a first time extraction unit, for extracting the occurrence time of the second energy signal to obtain a first stop time when the second energy signal reaches 0.511 MeV;
optionally, the second stop time recording module includes:
the second stop detector is used for detecting a third energy signal of the second side of the sample to be detected;
and the second time extraction unit is used for extracting the occurrence time of the third energy signal to obtain a second stop time under the condition that the third energy signal reaches 0.511 MeV.
Optionally, the first stop time recording module corresponds to a first time resolution, the second stop time recording module corresponds to a second time resolution, and a ratio of the first time resolution to the second time resolution is smaller than
Optionally, the two-dimensional lifetime spectrum statistics module comprises:
the service life counting unit is used for carrying out two-dimensional counting by taking the first service life as a horizontal axis and the second service life as a vertical axis under the condition of obtaining the first service life and the second service life;
and the service life value extraction unit is used for obtaining a two-dimensional positron annihilation service life spectrum according to the first service life value and the second service life value when the difference value of the first service life value and the second service life value is smaller than the preset time difference.
Optionally, the first recording condition includes that the start time and the first stop time are obtained within a first preset time window.
Optionally, the second recording condition includes that the start time and the second stop time are obtained within a second preset time window.
Optionally, the start time recording module includes:
the initial detector is used for detecting a first energy signal of the radioactive source;
and a third time extraction unit for extracting the occurrence time of the first energy signal to obtain a start time in the case where the first energy signal reaches 1.28 MeV.
According to a third aspect of the present disclosure, there is provided a computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements the method of the first aspect described above.
According to a fourth aspect of the present disclosure, there is provided an electronic device comprising:
a processor; and
a memory for storing executable instructions of the processor;
wherein the processor is configured to implement the method of the first aspect described above via execution of the executable instructions.
The two-dimensional positron annihilation lifetime spectrum measuring method provided by the disclosure detects the starting time of a radioactive source generating a first energy signal, the first stopping time of a first side of a sample to be measured generating a second energy signal, and the second stopping time of a second side of the sample to be measured generating a third energy signal, wherein the energy threshold of the first energy signal is set according to the energy of the starting gamma photon generated by the radioactive source decay, the energy thresholds of the second energy signal and the third energy signal are set according to the energy of an annihilation gamma photon generated by positron annihilation, and the first side is opposite to the second side; under the condition that the acquisition of the first stop time accords with the first recording condition, calculating a first life value according to the start time and the first stop time, and under the condition that the acquisition of the second stop time accords with the second recording condition, calculating a second life value according to the start time and the second stop time; and performing two-dimensional statistics on the first life value and the second life value to obtain a two-dimensional positron annihilation life spectrum of the positron annihilation in the sample to be detected.
According to the two-dimensional positron annihilation life spectrum measuring method, two annihilation gamma photons generated by an annihilation case are respectively detected once in the measuring process, the respective first stop time and second stop time are obtained, two-dimensional statistics is carried out on the life of the annihilation case according to the first stop time and the second stop time, so that background counting in the measuring process can be effectively eliminated, accidental introduction of error cases is reduced, and the peak-to-valley ratio is further improved; moreover, the utilization rate of annihilation gamma photon information can be improved, and the time resolution of measurement is improved. The method effectively improves the measurement precision of the annihilation life of the positron on the basis of improving the peak-to-valley ratio and the time resolution.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and together with the description, serve to explain the principles of the disclosure. It is to be understood that the drawings in the following description are merely exemplary of the disclosure, and that other drawings may be derived from those drawings by one of ordinary skill in the art without the exercise of inventive faculty.
Fig. 1 illustrates a schematic structure of a conventional positron annihilation lifetime spectrum measurement system.
Figure 2 illustrates a schematic diagram of a conventional positron annihilation lifetime spectrum.
Fig. 3 illustrates a flow chart of a two-dimensional positron annihilation lifetime spectroscopy measurement method in an embodiment of the disclosure.
Fig. 4 illustrates a flow chart of a statistical two-dimensional positron annihilation lifetime spectrum in an embodiment of the disclosure.
Figure 5 illustrates a schematic diagram of a two-dimensional positron annihilation lifetime spectrum in accordance with an embodiment of the disclosure.
Fig. 6 illustrates a schematic diagram of annihilation lifetime diagonalization processing in an embodiment of the disclosure.
Fig. 7 illustrates one of the structural schematic diagrams of a two-dimensional positron annihilation lifetime spectroscopy measurement system in an embodiment of the disclosure.
Fig. 8 illustrates one of the structural schematic diagrams of a two-dimensional positron annihilation lifetime spectroscopy measurement system in an embodiment of the disclosure.
Fig. 9 illustrates a schematic structural diagram of an electronic device according to an embodiment of the present disclosure.
Detailed Description
Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the subject matter of the present disclosure can be practiced without one or more of the specific details, or with other methods, components, devices, steps, and the like. In other instances, well-known technical solutions have not been shown or described in detail to avoid obscuring aspects of the present disclosure.
Furthermore, the drawings are merely schematic illustrations of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and a repetitive description thereof will be omitted. Some of the block diagrams shown in the figures are functional entities and do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented in the form of software, or in one or more hardware modules or integrated circuits, or in different networks and/or processor devices and/or microcontroller devices.
Positrons are antiparticles of electrons and annihilate upon contact with an extra-nuclear electron of an atom in a substance and produce two gamma photons of opposite energy of 0.511MeV, with the annihilation lifetime τ of the positron being directly related to the electron density at the site where the annihilation occurred. Since a vacancy-type defect in a substance is generally electronegative due to a loss of atomic mass and is more likely to capture positrons, and the electron density at the defect is generally lower than that of the substrate, the annihilation lifetime of positrons at the defect of the substance is longer than that of the substrate. In general, different components of the annihilation lifetime can characterize different types of defects, the intensity of the annihilation lifetime of different components can characterize the number of different types of defects, and the type and number of defects in a substance can be characterized by measuring the annihilation lifetime of a positron in the substance.
Fig. 1 illustrates a schematic structural diagram of a conventional positron annihilation lifetime spectrum measurement system 100, as shown in fig. 1, the conventional PALS measurement system generally comprises a radiation source, a sample to be measured, a start detector 110, a stop detector 120, a start time extraction unit 130, a stop time extraction unit 140, a time difference calculation unit 150, and a statistic unit 160, the radiation source is usually used 22 The source of the Na radioactive source, 22 na, while decaying to produce positrons, concomitantly emits an initial gamma photon of 1.28MeV energy, and thus can detect the gamma photon energy signal of 1.28MeV as the initial signal for annihilation. The start detector 110 detects a start gamma photon signal of 1.28MeV, the stop detector 120 detects an annihilation gamma photon signal of 0.511MeV, and the start time of the start gamma photon signal and the stop time of the annihilation gamma photon signal are respectively extracted by the start time extraction unit 130 and the stop time extraction unit 140, respectively, and the time difference calculation unit 150 can calculate the annihilation lifetime of the positron according to the start time and the stop time, and the annihilation lifetime of the positron is counted in the counting unit 160 to obtain the conventional positron annihilationLife spectrogram.
It can be seen that, in the conventional positron annihilation lifetime spectrum measurement system 100, the stop detector 120 is adopted to detect an annihilation gamma photon, and the utilization rate of annihilation gamma photon information in an annihilation case is low, so that the time resolution of measurement is affected, and the measurement accuracy is affected.
Figure 2 illustrates a schematic diagram of a conventional positron annihilation lifetime spectrum, shown in figure 2, with the positron annihilation lifetime measured from channel 1(channel1) counted in one dimension on the horizontal axis and Normalized (Normalized N) counts of different lifetime values on the vertical axis. At this time, the positron annihilation lifetime spectrum f (t) can be represented by the following formula (1):
wherein, L (t) is an ideal positron annihilation lifetime spectrum function, R (t) is a system time resolution, and B is a background.
Further, the ideal positron lifetime spectrum function l (t) is a superposition of multi-exponential functions, and can be represented by the following formula (2):
wherein N is the lifetime component fraction of positron annihilation in the sample to be detected, and N 0 Is the total intensity of the positron lifetime spectrum, I i Is the relative intensity of the ith lifetime component, τ i The lifetime value of the i-th lifetime component.
As can be seen from the above, the background B is also an important factor affecting the measurement accuracy of the conventional positron annihilation lifetime spectrum.
The embodiment of the disclosure provides a two-dimensional positron annihilation lifetime spectrum measuring method, which includes the steps of obtaining the starting time of a radioactive source generating a starting gamma photon through decay, and obtaining a first stop time and a second stop time of two annihilation gamma photons reversely generated during positron annihilation on two opposite sides of a sample to be measured, so as to obtain a first lifetime value and a second lifetime value; and then, through carrying out two-dimensional statistics on the first service life value and the second service life value which accord with the preset recording condition, a large number of back-bottom counts can be effectively eliminated, the peak-to-valley ratio of the spectrogram is further improved, annihilation gamma photon information is fully utilized, the time resolution is further improved, and the spectrogram measurement precision is effectively improved.
The embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.
Fig. 3 illustrates a flow chart of a method for measuring a two-dimensional positron annihilation lifetime spectrum according to an embodiment of the disclosure. The method is applied to a two-dimensional positron annihilation lifetime spectrum measurement system, and the system can be integrated on electronic equipment such as a notebook, a desktop computer and the like. The method includes steps 310 to 350 as follows.
Among other things, measurement of positron annihilation lifetime spectra is generally based on the beta of the radioisotope + Decay to produce positrons, commonly used in measurements 22 Na is used as a radioactive source and can release positrons with the kinetic energy of 0-0.545 MeV. When the radioactive source decays to generate positrons, initial gamma photons are generated in a cascade mode, and therefore the generation time of the initial gamma photons can be used as the initial time of the radioactive source decaying to generate positrons. The initial gamma photons released as a result of decay of the radioactive source have a specific energy, e.g. 22 Na cascades to generate an initial gamma photon of 1.28MeV when releasing a positron, so that a corresponding energy threshold can be set according to the specific energy, and the occurrence time when the detected first energy signal reaches the energy threshold is taken as the generation time of the positron to obtain an initial time which is taken as the starting point of the positron annihilation lifetime statistics.
Step 320, detecting a first stop time of a first side of the sample to be detected generating a second energy signal, and detecting a second stop time of a second side of the sample to be detected generating a third energy signal, wherein energy thresholds of the second energy signal and the third energy signal are set according to energy of annihilation gamma photons generated by positron annihilation, and the first side is opposite to the second side.
Wherein, when the positron annihilates in a sample to be measured, the positron will usually be reversely converted to generate two annihilation gamma photons with specific energy. Therefore, a second energy signal and a third energy signal can be respectively detected on a first side and a second side of the sample to be detected, wherein the first side and the second side are opposite sides of the sample to be detected, and energy thresholds of the second energy signal and the third energy signal are set according to the energy of the annihilation gamma photon, so that the occurrence time of the detected second energy signal reaching the energy threshold is taken as the generation time of the annihilation gamma photon to obtain a first stop time; the time of occurrence of the detected third energy signal reaching the energy threshold is taken as the time of generation of another annihilation gamma photon, and a second stop time is obtained as the end of the positron annihilation lifetime statistic.
The annihilation life time of the positron is the time difference from the positron released by decay of a radioactive source to annihilation of the positron, the annihilation case starts from the generation identifier of the initial gamma photon and stops from the generation identifier of the annihilation gamma photon, and therefore the annihilation life time of the positron can be identified by the time difference from the initial time to the first stop time.
In the embodiment of the present disclosure, after obtaining the start time, the first life value may be calculated according to the start time and the first stop time when the first stop time meets the first recording condition. The first recording condition is used for screening the first stop time to reduce the introduction of error cases caused by other signal interference, and the first recording condition can be set according to the annihilation lifetime range of the positron or the known error range of a measuring instrument. When the first stop time does not meet the first recording condition, the counting of the next annihilation instance may be directly performed, or data such as the current start time and the first stop time may be marked or discarded.
And 340, calculating to obtain a second life value according to the starting time and the second stopping time under the condition that the second stopping time meets the second recording condition.
The calculation of the second stop time, the second recording condition and the second lifetime value may be referred to the calculation of the first stop time, the first recording condition and the first lifetime value in step 330, and is not repeated herein for avoiding repetition.
Because positron annihilation generally releases two annihilation gamma photons in opposite directions simultaneously, the two annihilation gamma photons are detected separately in the embodiments of the disclosure, and two lifetime values, namely, a first lifetime value and a second lifetime value, can be obtained for the same annihilation instance. During the measurement process, the calculation of each lifetime value needs to meet the first recording condition and the second recording condition respectively, so that the annihilation gamma photon information can be more fully utilized.
And 350, performing two-dimensional statistics on the first life value and the second life value under the condition of obtaining the first life value and the second life value to obtain a two-dimensional positron annihilation life spectrum.
In steps 310-340, a first life time value and a second life time value of an annihilation case are respectively collected, and two-dimensional statistics is carried out under the condition that the first life time value and the second life time value are both counted, so that a two-dimensional positron annihilation life spectrum is obtained. When the first life time value and the second life time value are not obtained, the count of the annihilation case may be wrong if the corresponding first stop time and the corresponding second stop time do not meet the recording conditions, and therefore the annihilation case is not counted, a large number of background counts can be eliminated from the obtained two-dimensional positron annihilation life spectrum, the peak-to-valley ratio of the spectrum is further improved, and the measurement accuracy is ensured.
In a method embodiment of the present disclosure, the first recording condition includes that the start time and the first stop time are obtained within a first preset time window.
In the embodiment of the present disclosure, since the annihilation lifetime of the positron is generally distributed in a certain range, a first preset time window is set in the first recording condition, and the first preset time window is used to determine whether the acquisition time of the acquisition start time and the acquisition time of the first stop time are within a statistical range of the annihilation lifetime, so as to exclude an error case. Alternatively, the timing is started when the starting time is obtained, and the first stopping time is determined to meet the first recording condition when the first stopping time is obtained in the first preset time window; the starting time and the first stopping time may also be continuously acquired, and when the acquisition time interval between the starting time and the first stopping time is smaller than the first time window, it is determined that the first stopping time meets the first recording condition, which is not limited in this disclosure.
In one method embodiment of the present disclosure, the first predetermined time window is 100 nanoseconds.
The first preset time window can be set to be 100 nanoseconds, namely, timing is started when the starting time is obtained, and whether first stop time is obtained or not before the timing is accumulated for 100 nanoseconds is judged; or continuously acquiring the starting time and the first stopping time, and judging whether the acquisition time interval of the starting time and the first stopping time is less than or equal to 100 nanoseconds or not. The 100 ns in the present disclosure is only used as an example, and those skilled in the art can adjust the range of the first preset time window according to the actual measurement condition and the application requirement, and the present disclosure does not specifically limit this.
In a method embodiment of the present disclosure, the second recording condition includes that the start time and the second stop time are obtained within a second preset time window.
In the embodiment of the present disclosure, the second recording condition and the second preset time window may refer to the related description of the first recording condition and the first preset time window, and are not repeated herein for avoiding repetition.
In one method embodiment of the present disclosure, the second preset time window is 100 nanoseconds.
In the embodiments of the present disclosure, the second predetermined time window may refer to the related description of the first predetermined time window, and is not repeated herein for avoiding repetition.
Fig. 4 illustrates a flow chart of a statistical two-dimensional positron annihilation lifetime spectrum in an embodiment of the disclosure. In one embodiment of the present disclosure, as shown in fig. 4, the step 340 specifically includes the following steps 441 to 442.
And step 441, performing two-dimensional statistics by taking the first life value as a horizontal axis and the second life value as a vertical axis under the condition of obtaining the first life value and the second life value.
In the case where both the first lifetime value and the second lifetime value are counted, it is considered that the first lifetime value and the second lifetime value correspond to the same annihilation case, and in this case, two-dimensional statistics may be performed with the first lifetime value as a horizontal axis and the second lifetime value as a vertical axis. Because two annihilation gamma photons are generally generated by simultaneously inverting at the time of positron annihilation, the first lifetime value and the second lifetime value of the same annihilation instance are generally distributed intensively in a region with a slope of 1 in two-dimensional statistics, and thus the recorded first lifetime value and the recorded second lifetime value can be further screened through the two-dimensional statistics to obtain a count of valid annihilation instances.
And 442, under the condition that the difference value of the first life span value and the second life span value is smaller than the preset time difference, obtaining a two-dimensional positron annihilation life span spectrum according to the first life span value and the second life span value.
In the embodiment of the present disclosure, the first lifetime value and the second lifetime value of the two-dimensional statistics may be further filtered according to the difference value, so as to exclude the background count which is recorded by accident. In one-dimensional statistics of positron annihilation lifetimes, only one lifetime value corresponding to an annihilation gamma photon is counted for each annihilation instance, and therefore coincidence of an onset gamma photon and an annihilation gamma photon occurring in an occasional case cannot be excluded, resulting in that the count including the onset gamma photon and the annihilation gamma photon of different annihilation instances is occasionally counted by coincidence judgment. In the present disclosure, a first lifetime value and a second lifetime value corresponding to two annihilation gamma photons are respectively counted for each annihilation instance, and since the first lifetime value and the second lifetime value should be theoretically the same, a difference should be within a certain range in actual measurement. Therefore, whether the difference value of the first service life value and the second service life value of the same positron is smaller than the preset time difference or not is used for screening, accidental background in a spectrogram can be further eliminated, the peak-to-valley ratio is further improved, and the accuracy of spectrogram measurement is guaranteed.
The preset time difference can be adjusted according to a measurement object, a measurement condition, a measurement result, a measurement requirement and the like, and different preset time differences can be selected according to the type and the state of a sample to be measured, the precision of a measurement system, the distribution condition of the first life value and the second life value in an area with a slope of 1 in two-dimensional statistics and the like in actual measurement.
Fig. 5 is a schematic diagram illustrating a two-dimensional positron annihilation lifetime spectrum in an embodiment of the disclosure, where a first lifetime value is obtained through a channel a (channel a) and a second lifetime value is obtained through a channel b (channel b), and then two-dimensional statistics is performed by taking the first lifetime value as a horizontal axis and the second lifetime value as a vertical axis, and using Counts (Counts) of different color indicating lifetime values of different sizes, as shown in fig. 5. It can be seen that the first lifetime value and the second lifetime value are distributed in a concentrated manner in the direction of a straight line with a slope of 1 in two-dimensional statistics, so that the concentrated distribution area of the first lifetime value and the second lifetime value can be divided by the straight line with the slope of 1 on the horizontal axis and the vertical axis, and dispersed and accidental background counting is eliminated.
Taking the area 510 as an example, the preset time difference is expressed as an intercept of the boundary of the area 510 on the horizontal axis and the vertical axis, the track width of the horizontal axis and the vertical axis is 10 picoseconds, the preset time difference is 500 picoseconds, and the intercept of the two boundaries of the area 510 on the horizontal axis and the vertical axis is 50 tracks, so that only the count that the difference between the first life value and the second life value is less than 500 picoseconds is included in the area 510.
In the embodiment of the present disclosure, 500 picoseconds is only used as an example, and a person skilled in the art may adaptively select the preset time difference in the actual measurement, for example, the preset time difference may be determined according to the type and property of the sample to be measured, the precision of the measurement system, and the like before the measurement, or the preset time difference may be determined according to the distribution of the first life value and the second life value in the two-dimensional statistics, the data amount of the measurement data, the precision requirement, and the like after the first life value and the second life value are obtained by the measurement, and the present disclosure is not limited specifically herein.
In one embodiment of the present disclosure, the first stop time corresponds to a first time resolution, the second stop time corresponds to a second time resolution, and a ratio of the first time resolution to the second time resolution is smaller than
The ratio of the first time resolution to the second time resolution includes a first ratio of the first time resolution to the second time resolution and a second ratio of the second time resolution to the first time resolution. In an embodiment of the present disclosure, the first ratio is less than
And the second ratio is less than
Time Resolution (TR) is an index for measuring the ability to distinguish different events in a Time dimension during measurement, and is also one of important factors influencing the measurement accuracy of the positron annihilation lifetime spectrum, and an observed value of the annihilation lifetime during measurement can be expressed by the following formula (3):
T＝τ+δ＝τ+δ start +δ stop (3)
wherein T is the measured annihilation lifetime value, tau is the ideal annihilation lifetime value, delta is the lifetime value deviation caused by the system time resolution, delta start Deviation of the start time, delta, due to the resolution of the start time stop The deviation of the stop time caused by the stop time resolution.
On the basis of this, the system time resolution TR is changed from the starting time resolution TR start And stopping the time resolution TR stop And (4) forming. The time-resolved function can be regarded as a single gaussian function, and the system time-resolved function can be expressed as the following equation (4):
the starting time-resolved function can be expressed as the following equation (5):
the stop time resolution function can be expressed as the following equation (6):
wherein, the sigma is the standard deviation of the time resolution function of the system, and the sigma is start Is the standard deviation, σ, of the initial time-resolved function stop Is the standard deviation of the stopping time-resolved function. The time resolution of the system is TR 2.355 σ, the starting time resolution TR start ＝2.355σ start And stop time resolution TR stop ＝2.3556 stop And the system time resolution is satisfied
Thus, the lifetime component of positron annihilation can be derived from the positron annihilation lifetime spectrum f (t) deconvolution system time-resolved function r (t).
In the disclosed embodiment, the first life values T are collected separately 1 A second life value T 2 And performing two-dimensional statistics to obtain a two-dimensional positron annihilation lifetime spectrum. In an ideal situation, if the time resolution does not exist in the measurement, the first lifetime value and the second lifetime value in the two-dimensional positron annihilation lifetime spectrum are all distributed on the straight line T 2 ＝T 1 C, removing; and in the case where there is a time resolution, the first lifetime value may be expressed by the following equation (7):
T 1 ＝τ+δ 1 ＝τ+δ start +δ stop1 (7)
the second life value may be expressed by the following formula (8):
T 2 ＝τ+δ 2 ＝τ+δ start +δ stop2 (8)
on this basis, the annihilation lifetime τ of the positron can be expressed by the following formula (9):
wherein, delta stop1 Is a first time resolution TR corresponding to a first stop time stop1 Resulting in a deviation of the lifetime, δ stop2 Is a second time resolution TR corresponding to a second stop time stop2 Resulting in a deviation of the lifetime, δ start To start time resolution TR start Resulting in a deviation in lifetime. Delta. for the preparation of a coating start 、δ stop1 And delta stop2 Satisfying the gaussian distribution, the time resolution corresponding to the channel for measuring the first lifetime value can be expressed by the following formula (10):
the time resolution corresponding to the channel for measuring the second lifetime value may be expressed by the following equation (11):
fig. 6 illustrates a schematic diagram of annihilation lifetime diagonalization processing in an embodiment of the present disclosure, and as shown in fig. 6, in a two-dimensional positron annihilation lifetime spectrum, annihilation lifetimes τ are distributed in an elliptical region 610 due to the influence of temporal resolution. The annihilation lifetime τ in the elliptical region 610 is diagonalized, i.e., is
As a measure of annihilation lifetime, the deviation is
The time resolution TR of the two-dimensional positron annihilation lifetime spectrum can be expressed as the following equation (12):
on the basis of this, TR is enabled<TR 1 And TR<TR 2 If true, the following formula (13) is given:
At a first time resolution TR, as shown in equation (13) stop1 With a second time resolution TR stop2 Is less than
In the case of (2), the time resolution TR of the two-dimensional positron annihilation lifetime spectrum is less than the time resolution TR corresponding to the channel measuring the first lifetime value 1 Time resolution TR corresponding to the channel also being less than the second life value 2 The measurement accuracy of the two-dimensional positron annihilation lifetime spectrum is further improved on the basis of the positron annihilation lifetime spectrum of any single channel.
The two-dimensional positron annihilation lifetime spectrum measuring method provided by the disclosure detects the starting time of a radioactive source generating a first energy signal, the first stopping time of a first side of a sample to be measured generating a second energy signal, and the second stopping time of a second side of the sample to be measured generating a third energy signal, wherein the energy threshold of the first energy signal is set according to the energy of the starting gamma photon generated by the radioactive source decay, the energy thresholds of the second energy signal and the third energy signal are set according to the energy of an annihilation gamma photon generated by positron annihilation, and the first side is opposite to the second side; under the condition that the acquisition of the first stop time accords with the first recording condition, calculating a first life value according to the start time and the first stop time, and under the condition that the acquisition of the second stop time accords with the second recording condition, calculating a second life value according to the start time and the second stop time; and performing two-dimensional statistics on the first life value and the second life value to obtain a two-dimensional positron annihilation life spectrum of the positron annihilation in the sample to be detected.
According to the two-dimensional positron annihilation life spectrum measuring method, two annihilation gamma photons generated by an annihilation case are respectively detected once in the measuring process, the respective first stop time and second stop time are obtained, two-dimensional statistics is carried out on the life of the annihilation case according to the first stop time and the second stop time, so that background counting in the measuring process can be effectively eliminated, accidental introduction of error cases is reduced, and the peak-to-valley ratio is further improved; moreover, the utilization rate of annihilation gamma photon information can be improved, and the time resolution of measurement is improved. The method effectively improves the measurement precision of the annihilation life of the positron on the basis of improving the peak-to-valley ratio and the time resolution.
The following are embodiments of the disclosed system that may be used to perform embodiments of the disclosed method. For details not disclosed in the system example of the apparatus of the present disclosure, refer to the method example of the present disclosure.
Fig. 7 illustrates one of the structural schematic diagrams of a two-dimensional positron annihilation lifetime spectroscopy measurement system 700 in an embodiment of the disclosure, which, as shown in fig. 7, may include:
and a start time recording module 710 for detecting a start time of the radioactive source decay to generate a first energy signal, wherein an energy threshold of the first energy signal is set according to an energy of a start gamma photon generated by the radioactive source decay.
And the first stop time recording module 720 is used for detecting the first stop time of the first side of the sample to be detected for generating the second energy signal, and the energy threshold of the second energy signal is set according to the energy of the annihilation gamma photon generated by positron annihilation.
And a second stop time recording module 730, configured to detect a second stop time at which a second side of the sample to be detected generates a third energy signal, where an energy threshold of the third energy signal is set according to energy of annihilation gamma photons generated by positron annihilation, and the first side is opposite to the second side.
The life value calculating module 740 is configured to calculate a first life value according to the start time and the first stop time when the first stop time meets the first recording condition.
The lifetime value calculating module 740 is further configured to calculate a second lifetime value according to the start time and the second stop time when the second stop time meets the second recording condition.
And a two-dimensional lifetime spectrum statistics module 750, configured to perform two-dimensional statistics on the first lifetime value and the second lifetime value to obtain a two-dimensional positron annihilation lifetime spectrum, when the first lifetime value and the second lifetime value are obtained.
The two-dimensional positron annihilation lifetime spectrum measuring system provided by the present disclosure detects a start time when a radioactive source decays to generate a first energy signal, a first stop time when a first side of a sample to be measured generates a second energy signal, and a second stop time when a second side of the sample to be measured generates a third energy signal, wherein an energy threshold of the first energy signal is set according to an energy of a start gamma photon generated by the radioactive source decaying, and energy thresholds of the second energy signal and the third energy signal are set according to an energy of an annihilation gamma photon generated by positron annihilation, and the first side is opposite to the second side; under the condition that the acquisition of the first stop time meets a first recording condition, calculating a first life value according to the start time and the first stop time, and under the condition that the acquisition of the second stop time meets a second recording condition, calculating a second life value according to the start time and the second stop time; and then carrying out two-dimensional statistics on the first life value and the second life value so as to obtain a two-dimensional positron annihilation life spectrum of the positron annihilation in the sample to be detected.
According to the two-dimensional positron annihilation life spectrum measuring system, two annihilation gamma photons generated by an annihilation case are respectively detected once in the measuring process, the respective first stop time and second stop time are obtained, two-dimensional statistics is carried out on the life of the annihilation case according to the first stop time and the second stop time, so that background counting in the measuring process can be effectively eliminated, accidental introduction of error cases is reduced, and the peak-to-valley ratio is further improved; moreover, the utilization rate of annihilation gamma photon information can be improved, and the time resolution of measurement is improved. The system effectively improves the measurement precision of the annihilation life of the positron on the basis of improving the peak-to-valley ratio and the time resolution.
Fig. 8 illustrates a second structural schematic diagram of a two-dimensional positron annihilation lifetime spectrum measurement system 800 in an embodiment of the disclosure, as shown in fig. 8, the system may include a start time recording module 810, a first stop time recording module 820, a second stop time recording module 830, a lifetime value calculating module 840, and a two-dimensional lifetime spectrum statistical module 850;
in one embodiment of the present disclosure, the first stop time recording module 820 includes:
a first stop detector 821 for detecting a second energy signal at the first side of the sample to be measured;
a first time extracting unit 822, configured to extract an occurrence time of the second energy signal to obtain a first stop time when the second energy signal reaches 0.511 MeV.
In a system implementation manner of the present disclosure, the second stop time recording module 830 includes:
a second stop detector 831 for detecting a third energy signal at the second side of the sample to be measured;
and a second time extraction unit 832 for extracting the occurrence time of the third energy signal to obtain a second stop time, in case the third energy signal reaches 0.511 MeV.
The first stop detector 821 and the second stop detector 831 are disposed on opposite sides of the sample to be measured, and may be arranged oppositely at an angle of 180 ° on both sides of the sample to be measured, for example, to respectively detect two annihilation gamma photons generated in the sample after positron annihilation and in the opposite direction.
In one system embodiment of the present disclosure, the first stop time recording module 820 corresponds to a first time resolution, the second stop time recording module 830 corresponds to a second time resolution, and a ratio of the first time resolution to the second time resolution is less than √ 3.
In a system embodiment of the present disclosure, the two-dimensional lifetime spectrum statistics module 850 includes:
a lifetime value counting unit 851, configured to perform two-dimensional counting with the first lifetime value as a horizontal axis and the second lifetime value as a vertical axis when the first lifetime value and the second lifetime value are obtained;
a lifetime value extracting unit 852 is configured to obtain a two-dimensional positron annihilation lifetime spectrum according to the first lifetime value and the second lifetime value when a difference between the first lifetime value and the second lifetime value is smaller than a preset time difference.
In a system embodiment of the present disclosure, the first recording condition includes that the start time and the first stop time are obtained within a first preset time window.
In a system embodiment of the present disclosure, the second recording condition includes that the start time and the second stop time are obtained within a second preset time window.
In one embodiment of the present disclosure, the start time recording module 810 includes:
a start detector 811 for detecting a first energy signal of the radiation source;
a third time extraction unit 812 for extracting the occurrence time of the first energy signal to obtain the start time in case that the first energy signal reaches 1.28 MeV.
In one embodiment of the present disclosure, the lifetime value calculating module 840 includes:
a first time difference calculation unit 841, configured to calculate and obtain a first life value according to the start time and the first stop time when the first stop time meets the first recording condition;
the second time difference calculation unit 842 is configured to calculate a second lifetime value according to the start time and the second stop time when the second stop time meets the second recording condition.
It should be noted that although in the above detailed description several modules or units of the device for action execution are mentioned, such a division is not mandatory. Indeed, the features and functionality of two or more modules or units described above may be embodied in one module or unit, according to embodiments of the present disclosure. Conversely, the features and functions of one module or unit described above may be further divided into embodiments by a plurality of modules or units.
Moreover, although the steps of the methods of the present disclosure are depicted in the drawings in a particular order, this does not require or imply that the steps must be performed in this particular order, or that all of the depicted steps must be performed, to achieve desirable results. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step execution, and/or one step broken down into multiple step executions, etc.
Through the above description of the embodiments, those skilled in the art will readily understand that the exemplary embodiments described herein may be implemented by software, or by software in combination with necessary hardware. Therefore, the technical solution according to the embodiments of the present disclosure may be embodied in the form of a software product, which may be stored in a non-volatile storage medium (which may be a CD-ROM, a usb disk, a removable hard disk, etc.) or on a network, and includes several instructions to enable a computing device (which may be a personal computer, a server, a mobile terminal, or a network device, etc.) to execute the method according to the embodiments of the present disclosure.
In an exemplary embodiment of the present disclosure, an electronic device capable of implementing the above method is also provided.
As will be appreciated by one skilled in the art, aspects of the present disclosure may be embodied as a system, method or program product. Accordingly, various aspects of the present disclosure may be embodied in the form of: an entirely hardware embodiment, an entirely software embodiment (including firmware, microcode, etc.) or an embodiment combining hardware and software aspects that may all generally be referred to herein as a "circuit," module "or" system.
An electronic device 900 according to this embodiment of the disclosure is described below with reference to fig. 9. The electronic device 900 shown in fig. 9 is only an example and should not bring any limitations to the functionality and scope of use of the embodiments of the present disclosure.
As shown in fig. 9, the electronic device 900 is embodied in the form of a general purpose computing device. Components of electronic device 900 may include, but are not limited to: the at least one processing unit 910, the at least one memory unit 920, and a bus 930 that couples various system components including the memory unit 920 and the processing unit 910.
Where the storage unit stores program code, the program code may be executed by the processing unit 910 to cause the processing unit 910 to perform the steps according to various exemplary embodiments of the present disclosure described in the above-mentioned "exemplary methods" section of this specification.
The storage unit 920 may include a readable medium in the form of a volatile storage unit, such as a random access storage unit (RAM)9201 and/or a cache storage unit 9202, and may further include a read only storage unit (ROM) 9203.
The electronic device 900 may also communicate with one or more external devices 900 (e.g., keyboard, pointing device, bluetooth device, etc.), with one or more devices that enable a user to interact with the electronic device 900, and/or with any devices (e.g., router, modem, etc.) that enable the electronic device 900 to communicate with one or more other computing devices. Such communication may occur through the display unit 940 and an input/output (I/O) interface 950 connected to the display unit 940. Also, the electronic device 900 may communicate with one or more networks (e.g., a Local Area Network (LAN), a Wide Area Network (WAN) and/or a public network, such as the Internet) via the network adapter 960. As shown, the network adapter 960 communicates with the other modules of the electronic device 900 via the bus 930. It should be appreciated that although not shown in the figures, other hardware and/or software modules may be used in conjunction with the electronic device 900, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems, among others.
Through the above description of the embodiments, those skilled in the art will readily understand that the exemplary embodiments described herein may be implemented by software, or by software in combination with necessary hardware. Therefore, the technical solution according to the embodiments of the present disclosure may be embodied in the form of a software product, which may be stored in a non-volatile storage medium (which may be a CD-ROM, a usb disk, a removable hard disk, etc.) or on a network, and includes several instructions to enable a computing device (which may be a personal computer, a server, a terminal device, or a network device, etc.) to execute the method according to the embodiments of the present disclosure.
In an exemplary embodiment of the present disclosure, there is also provided a computer readable storage medium having stored thereon a program product capable of implementing the above-described method of the present specification. In some possible embodiments, various aspects of the disclosure may also be implemented in the form of a program product comprising program code for causing a terminal device to perform the steps according to various exemplary embodiments of the disclosure described in the above-mentioned "exemplary methods" section of this specification, when the program product is run on the terminal device.
In an embodiment of the present disclosure, there is also provided a program product for implementing the above method, which may employ a portable compact disc read only memory (CD-ROM) and include program code, and may be run on a terminal device, such as a personal computer. However, the program product of the present disclosure is not limited thereto, and in this document, a readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
The program product may employ any combination of one or more readable media. The readable medium may be a readable signal medium or a readable storage medium. The readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the foregoing. More specific examples (a non-exhaustive list) of the readable storage medium include: an electrical connection having one or more wires, a portable disk, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.
A computer readable signal medium may include a propagated data signal with readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated data signal may take many forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A readable signal medium may also be any readable medium that is not a readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.
Program code embodied on a readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.
Program code for carrying out operations for the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, C + + or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computing device, partly on the user's device, as a stand-alone software package, partly on the user's computing device and partly on a remote computing device, or entirely on the remote computing device or server. In the case of a remote computing device, the remote computing device may be connected to the user computing device through any kind of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or may be connected to an external computing device (e.g., through the internet using an internet service provider).
Furthermore, the above-described figures are merely schematic illustrations of processes included in methods according to exemplary embodiments of the present disclosure, and are not intended to be limiting. It will be readily understood that the processes shown in the above figures are not intended to indicate or limit the chronological order of the processes. In addition, it is also readily understood that these processes may be performed synchronously or asynchronously, e.g., in multiple modules.
Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This application is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice in the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.
Claims (10)
1. A two-dimensional positron annihilation lifetime spectroscopy measurement method, the method comprising:
detecting a starting time of a radioactive source decay to generate a first energy signal, wherein an energy threshold of the first energy signal is set according to energy of a starting gamma photon generated by the radioactive source decay;
detecting a first stop time of a first side of a sample to be detected for generating a second energy signal, and detecting a second stop time of a second side of the sample to be detected for generating a third energy signal, wherein energy thresholds of the second energy signal and the third energy signal are set according to energy of annihilation gamma photons generated by positron annihilation, and the first side is opposite to the second side;
under the condition that the first stop time meets a first recording condition, calculating according to the starting time and the first stop time to obtain a first life value;
under the condition that the second stop time meets a second recording condition, calculating according to the starting time and the second stop time to obtain a second life value;
and under the condition of obtaining the first life value and the second life value, performing two-dimensional statistics on the first life value and the second life value to obtain a two-dimensional positron annihilation life spectrum.
2. The method according to claim 1, wherein the first recording condition includes:
the starting time and the first stopping time are obtained in a first preset time window;
the second recording condition includes:
and the starting time and the second stopping time are obtained in a second preset time window.
3. The method of claim 1, wherein the obtaining of the two-dimensional positron annihilation lifetime spectrum by performing two-dimensional statistics on the first lifetime value and the second lifetime value when obtaining the first lifetime value and the second lifetime value comprises:
under the condition of obtaining the first life value and the second life value, performing two-dimensional statistics by taking the first life value as a horizontal axis and the second life value as a vertical axis;
and under the condition that the difference value of the first life value and the second life value is smaller than a preset time difference, obtaining the two-dimensional positron annihilation life spectrum according to the first life value and the second life value.
4. The method according to claim 1, characterized in that said first stop time corresponds to a first temporal resolution and said second stop time corresponds to a second temporal resolution, the ratio between said first temporal resolution and said second temporal resolution being less than √ 3.
5. A two-dimensional positron annihilation lifetime spectroscopy measurement system, the system comprising:
the starting time recording module is used for detecting the starting time of a first energy signal generated by the decay of a radioactive source, and the energy threshold of the first energy signal is set according to the energy of the starting gamma photon generated by the decay of the radioactive source;
the first stop time recording module is used for detecting the first stop time of a second energy signal generated by the first side of the sample to be detected, and the energy threshold of the second energy signal is set according to the energy of annihilation gamma photons generated by positron annihilation;
the second stop time recording module is used for detecting a second stop time of a second side of the sample to be detected for generating a third energy signal, an energy threshold of the third energy signal is set according to energy of annihilation gamma photons generated by positron annihilation, and the first side is opposite to the second side;
the life value calculating module is used for calculating and obtaining a first life value according to the starting time and the first stopping time under the condition that the first stopping time meets a first recording condition;
the life value calculating module is further used for calculating to obtain a second life value according to the starting time and the second stopping time under the condition that the second stopping time meets a second recording condition;
and the two-dimensional life spectrum counting module is used for performing two-dimensional counting on the first life value and the second life value under the condition of obtaining the first life value and the second life value to obtain a two-dimensional positron annihilation life spectrum.
6. The system of claim 5, wherein the first stop time recording module comprises:
the first stop detector is used for detecting a second energy signal of the first side of the sample to be detected;
a first time extraction unit, configured to extract an occurrence time of the second energy signal to obtain a first stop time when the second energy signal reaches 0.511 MeV;
the second stop time recording module includes:
a second stop detector for detecting a third energy signal at a second side of the sample to be tested;
a second time extraction unit, configured to extract an occurrence time of the third energy signal to obtain a second stop time when the third energy signal reaches 0.511 MeV.
7. The system of claim 5, wherein the first stop time recording module corresponds to a first time resolution and the second stop time recording module corresponds to a second time resolution, and wherein a ratio of the first time resolution to the second time resolution is less than
8. The system of claim 5, wherein the two-dimensional lifetime spectrum statistics module comprises:
the service life value counting unit is used for carrying out two-dimensional statistics by taking the first service life value as a horizontal axis and the second service life value as a vertical axis under the condition of obtaining the first service life value and the second service life value;
and a lifetime value extraction unit, configured to obtain the two-dimensional positron annihilation lifetime spectrum according to the first lifetime value and the second lifetime value when a difference between the first lifetime value and the second lifetime value is smaller than a preset time difference.
9. The system according to claim 5, wherein the first recording condition includes:
the starting time and the first stopping time are obtained in a first preset time window;
the second recording condition includes:
and the starting time and the second stopping time are obtained in a second preset time window.
10. The system of claim 5, wherein the start time recording module comprises:
a start detector for detecting the first energy signal of the radiation source;
a third time extraction unit, configured to extract an occurrence time of the first energy signal to obtain a start time when the first energy signal reaches 1.28 MeV.
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