CN108107465B - Positron annihilation lifetime spectrum measuring method and system - Google Patents
Positron annihilation lifetime spectrum measuring method and system Download PDFInfo
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Abstract
The disclosure relates to the technical field of nuclear spectroscopy and discloses a positron annihilation lifetime spectrum measuring method. The method comprises the following steps: receiving a first judging signal and a second judging signal, and judging by amplitude values to obtain a first initial signal and a second initial signal; carrying out OR operation on the first initial signal and the second initial signal to generate a trigger signal; receiving a first detection signal and a second detection signal within a set time in response to a trigger signal; judging the matching conditions of the amplitude of the first detection signal and the amplitude of the second detection signal with the first amplitude and the second amplitude to obtain a first judgment result and a second judgment result, and calculating a first time difference and a second time difference between the first detection signal and the second detection signal; and counting the first time difference according to the first judgment result to obtain a first life map, counting the second time difference according to the second judgment result to obtain a second life map, and superposing the first life map and the second life map to obtain a positron annihilation life map. The method improves the utilization rate of the detection signal.
Description
Technical Field
The disclosure relates to the technical field of nuclear spectroscopy and nuclear detection, in particular to a positron annihilation lifetime spectrum measuring method and a positron annihilation lifetime spectrum measuring system.
Background
The positron annihilation measurement technology provides a unique nondestructive characterization method for researching the internal microstructure of the material, wherein the most common and characteristic positron annihilation lifetime spectrum measurement technology can not only judgeThe type and size of defects in the material are broken and the relative concentration of different defects can be measured. Referring to a structural schematic diagram of a positron annihilation lifetime spectrum measuring instrument shown in FIG. 1; positron annihilation lifetime spectroscopy instruments (hereinafter referred to as spectrometers) typically use two bafs2The detectors being respectively the starting probe (corresponding detection)22Na-emitted 1.28MeV cascade gamma signals) and a termination probe (corresponding to 0.511MeV annihilation gamma signals emitted after positron annihilation is detected), respectively outputting time signals of 1.28MeV gamma photons and time signals of 0.511MeV gamma photons through energy threshold selection and constant ratio timing differential discriminator (CFDD), converting the time difference of the two signals (wherein, the termination signal is output in a delayed manner) into amplitude values through a Time Amplitude Converter (TAC) and entering a multichannel analyzer (MCA), and acquiring spectra by using corresponding data collection software on a terminal (PC) to obtain a positron annihilation life diagram.
The main parameters characterizing the performance of the positron annihilation lifetime spectrum measuring instrument have two parameters of time resolution and effective coincidence counting rate. The performance of the gamma detector is the primary factor limiting the quality of these two parameters. In order to obtain higher time resolution, plastic scintillators with shorter luminescence decay constant are mostly used in early laboratories, and scintillation detectors are formed by coupling the plastic scintillators with photomultiplier tubes with faster time response. However, since the density of the plastic scintillator is low, the detection efficiency of the gamma ray is low, so that the coincidence counting rate of the measuring system is low, and a long measuring time is required to ensure sufficient statistical counting requirements. BaF is commonly adopted in laboratories in recent years2(barium fluoride) crystals replace plastic scintillators. BaF2The (barium fluoride) scintillator has a light-emitting component with a shorter attenuation constant, is high in density and atomic number, and a scintillation detector consisting of the (barium fluoride) scintillator and a photomultiplier can effectively improve the coincidence counting rate of the spectrometer while ensuring the high time resolution of the spectrometer.
In addition to optimizing the performance of the detector, under the requirement of ensuring high time resolution of positron annihilation lifetime measurement, in order to further improve the effective coincidence counting rate, a method for improving the intensity of a positron radiation source can be adopted, however, the increase of accidental coincidence background components is caused, the dead time of a measurement system is increased, the shape of a time-resolved response function is influenced to a certain extent, and the distortion of an actual measurement spectrum is caused.
The detection efficiency of two scintillation detectors in a positron annihilation lifetime spectrum measuring instrument is a key factor for improving the final coincidence counting rate of a spectrometer. In a conventional measurement system, whether the signal detected by the detector is a 1.28MeV gamma signal or a 0.511MeV gamma signal is determined by energy selection (energy window), and a corresponding start signal detector and end signal detector are artificially defined, and whether the same annihilation event occurs is determined both in energy and time by using fast-fast or fast-slow coincidence.
For each positron annihilation instance, the probability of detecting a 1.28MeV start time signal is identical for both detectors in the measurement system (and similarly, the probability of detecting an annihilation gamma 0.511MeV stop time signal is identical). There is no difference in principle between the two detectors, and either detector can detect the two gamma photon signals, and can be used as both the start signal detector and the stop signal detector. Whether a detector is a start time detector or a stop time detector depends entirely on the choice of the electronic system for the energy window of the pulse signal. That is, one detector is artificially defined as a start time detector and the other as a stop time detector as required by the selection of the signal energy window. Therefore, when the detector used as the detection stop signal detects a start time signal, it becomes an invalid case due to the requirement of the selection of the energy window, and vice versa. It can be seen that at least half of the valid positron annihilation instances are not acquired due to the requirements of the detector energy window selection.
Therefore, it is necessary to develop a new positron annihilation lifetime spectrum measurement method and a new positron annihilation lifetime spectrum measurement system.
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
An object of the present disclosure is to provide a positron annihilation lifetime spectrum measurement method and a positron annihilation lifetime spectrum measurement system, thereby overcoming, at least to some extent, one or more of the problems due to the limitations and disadvantages of the related art.
According to an aspect of the present disclosure, there is provided a positron annihilation lifetime spectroscopy measurement method including:
receiving a first judgment signal and obtaining a first initial signal through amplitude judgment, and receiving a second judgment signal and obtaining a second initial signal through amplitude judgment;
performing an OR operation on the first starting signal and the second starting signal to generate a trigger signal;
responding to the trigger signal, and receiving a first detection signal and a second detection signal within a set time;
judging the matching conditions of the amplitude of the first detection signal and the amplitude of the second detection signal with the first amplitude and the second amplitude to obtain a first judgment result and a second judgment result, and calculating a first time difference and a second time difference between the first detection signal and the second detection signal;
and counting the first time difference according to the first judgment result to obtain a first life map, counting the second time difference according to the second judgment result to obtain a second life map, and superposing the first life map and the second life map to obtain a positron annihilation life map.
In an exemplary embodiment of the present disclosure, superimposing the first life map and the second life map comprises:
coinciding a zero time of the first lifetime map with a zero time of the second lifetime map;
and sequentially and correspondingly adding the statistical counts in the plurality of same time intervals of the first life map with the statistical counts in the corresponding plurality of same time intervals of the second life map.
In an exemplary embodiment of the present disclosure, matching conditions between the amplitudes of the first and second detection signals and the first and second amplitudes are determined to obtain first and second determination results, and a first and second time difference between the first and second detection signals is calculated; the method comprises the following steps:
obtaining a first judgment result when the amplitude of the first detection signal is the first amplitude and the amplitude of the second detection signal is the second amplitude, and obtaining a second judgment result when the amplitude of the first detection signal is the second amplitude and the amplitude of the second detection signal is the first amplitude;
and calculating the time difference from the second detection signal to the first detection signal according to the first judgment result to obtain the first time difference, and calculating the time difference from the first detection signal to the second detection signal according to the second judgment result to obtain the second time difference.
In an exemplary embodiment of the disclosure, the first probe signal and the first decision signal are obtained by a first splitter splitting a first measurement signal into two paths, and the second probe signal and the second decision signal are obtained by a second splitter splitting a second measurement signal into two paths.
In an exemplary embodiment of the present disclosure, the first measurement signal is generated by a first detector detecting a first gamma photon and the second measurement signal is generated by a second detector detecting a second gamma photon;
the distance between the first detector and a sample to be detected is the same as the distance between the second detector and the sample to be detected, and the first detector and the second detector are arranged at a set angle with the sample to be detected.
According to an aspect of the present disclosure, there is provided a positron annihilation lifetime spectroscopy measurement system comprising:
the starting signal generating unit is used for receiving the first judging and selecting signal and obtaining a first starting signal through amplitude judgment, and receiving the second judging and selecting signal and obtaining a second starting signal through amplitude judgment;
the trigger signal generating unit is used for carrying out OR operation on the first starting signal and the second starting signal to generate a trigger signal;
the receiving unit is used for responding to the trigger signal and receiving a first detection signal and a second detection signal within set time;
the waveform analysis unit is used for judging the matching conditions of the amplitude of the first detection signal and the amplitude of the second detection signal with the first amplitude and the second amplitude to obtain a first judgment result and a second judgment result, and calculating a first time difference and a second time difference between the first detection signal and the second detection signal;
and the map processing unit is used for obtaining a first life map according to the first judgment result and the first time difference, obtaining a second life map according to the second judgment result and the second time difference, and superposing the first life map and the second life map to obtain a positron annihilation life map.
In an exemplary embodiment of the present disclosure, superimposing the first life map and the second life map comprises:
coinciding a zero time of the first lifetime map with a zero time of the second lifetime map;
and sequentially and correspondingly adding the statistical counts in the plurality of same time intervals of the first life map with the statistical counts in the corresponding plurality of same time intervals of the second life map.
In an exemplary embodiment of the present disclosure, matching conditions between the amplitudes of the first and second detection signals and the first and second amplitudes are determined to obtain first and second determination results, and a first and second time difference between the first and second detection signals is calculated; the method comprises the following steps:
obtaining a first judgment result when the amplitude of the first detection signal is the first amplitude and the amplitude of the second detection signal is the second amplitude, and obtaining a second judgment result when the amplitude of the first detection signal is the second amplitude and the amplitude of the second detection signal is the first amplitude;
and calculating the time difference from the second detection signal to the first detection signal according to the first judgment result to obtain the first time difference, and calculating the time difference from the first detection signal to the second detection signal according to the second judgment result to obtain the second time difference.
In an exemplary embodiment of the present disclosure, the positron annihilation lifetime spectroscopy measurement system further comprises:
the first splitter is used for splitting a first measurement signal into two paths to obtain the first detection signal and the first judgment and selection signal;
and the second splitter is used for splitting a second measurement signal into two paths to obtain the second detection signal and the second judgment signal.
In an exemplary embodiment of the present disclosure, the positron annihilation lifetime spectroscopy measurement system further comprises:
a first detector for generating the first measurement signal upon detection of a first gamma photon;
a second detector for generating the second measurement signal upon detection of a second gamma photon;
the distance between the first detector and a sample to be detected is the same as the distance between the second detector and the sample to be detected, and the first detector and the second detector are arranged at a set angle with the sample to be detected.
The positron annihilation lifetime spectrum measuring method and the positron annihilation lifetime spectrum measuring system receive a first detection signal and a second detection signal within a set time, judge matching conditions of an amplitude of the first detection signal and an amplitude of the second detection signal with the first amplitude and the second amplitude to obtain a first judgment result and a second judgment result, calculate a first time difference and a second time difference between the first detection signal and the second detection signal, obtain a first lifetime map according to the first judgment result and the first time difference, obtain a second lifetime map according to the second judgment result and the second time difference, and then superimpose the first lifetime map and the second lifetime map to obtain a positron annihilation lifetime spectrum. On one hand, a certain detector is not limited to be an initial detector, but a detector to which the initial signal belongs is screened out through OR operation of the initial signal, and then a first judgment result and a second judgment result are obtained through amplitude matching judgment, so that more effective positron annihilation cases can be collected, and the utilization rate of the detection signal is improved. On the other hand, the detection signal is fully utilized, the acquisition time of the positron life spectrum can be reduced, and the experimental efficiency is improved; the intensity of the positron emission source can be reduced, and the increase of accidental coincidence background components caused by high intensity of a positive electron source and the influence on the shape of a time-resolved response function are avoided.
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 schematically shows a structure diagram of a positron annihilation lifetime spectrum measuring instrument in the related art.
Figure 2 schematically illustrates a flow diagram of an example embodiment of a positron annihilation lifetime spectroscopy measurement method of the present disclosure.
Fig. 3 schematically shows a logic diagram of two independent time difference measurement units of an example embodiment of the positron annihilation lifetime spectroscopy measurement method of the present disclosure.
Fig. 4 schematically shows two positron annihilation lifetime spectra and their superimposed spectra measured by the positron annihilation lifetime spectrum measurement method of the present disclosure.
Fig. 5 schematically shows a block diagram of the structure of the positron annihilation lifetime spectrum measurement system of the present disclosure.
Figure 6 schematically illustrates a block diagram of an example embodiment of a positron annihilation lifetime spectroscopy measurement system of the present disclosure.
In the figure:
1. a start signal generation unit; 2. a trigger signal generation unit; 3. a receiving unit; 4. a waveform analyzing unit; 5. an atlas handling unit; 6. a second detector; 7. a high voltage power supply; 8. a first splitter; 9. a second splitter; 10. a first constant ratio timing discriminator; 11. a second constant ratio timing discriminator; 12. a delay unit; 13. a digital oscilloscope; 14.22na radioactive source and test sample; 15. a first detector.
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 thus their repetitive description 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.
First, a positron annihilation lifetime spectrum measuring method is provided in the present exemplary embodiment, and referring to a flowchart of an exemplary embodiment of the positron annihilation lifetime spectrum measuring method shown in fig. 2, the positron annihilation lifetime spectrum measuring method may include the following steps:
and step S10, receiving the first judging signal, obtaining a first initial signal through amplitude judgment, receiving the second judging signal, and obtaining a second initial signal through amplitude judgment.
Step S20, performing an or operation on the first start signal and the second start signal to generate a trigger signal.
And step S30, responding to the trigger signal, and receiving the first detection signal and the second detection signal within a set time.
Step S40, determining matching conditions between the amplitudes of the first and second detection signals and the first and second amplitudes to obtain first and second determination results, and calculating first and second time differences between the first and second detection signals.
Step S50, obtaining a first lifetime map by counting the first time difference according to the first determination result, obtaining a second lifetime map by counting the second time difference according to the second determination result, and superimposing the first lifetime map and the second lifetime map to obtain a positron annihilation lifetime map.
According to the positron annihilation lifetime spectrum measuring method in the exemplary embodiment, on one hand, a certain detector is not limited to be an initial detector, but a detector to which the initial signal belongs is screened out through or operation of the initial signal, and then a first judgment result and a second judgment result are obtained through amplitude matching judgment, so that more effective positron annihilation cases can be collected, and the utilization rate of detection signals is improved. On the other hand, the detection signal is fully utilized, the acquisition time of the positron life spectrum can be reduced, and the experimental efficiency is improved; the intensity of the positron emission source can be reduced, and the increase of accidental coincidence background components caused by high intensity of a positive electron source and the influence on the shape of a time-resolved response function are avoided.
Next, the positron annihilation lifetime spectrum measuring method in the present exemplary embodiment will be further described.
And step S10, receiving the first judging signal, obtaining a first initial signal through amplitude judgment, receiving the second judging signal, and obtaining a second initial signal through amplitude judgment.
The distance between the first detector 15 and the sample to be detected is the same as the distance between the second detector 6 and the sample to be detected, and the first detector and the second detector are arranged at a set angle with the sample to be detected. In the present exemplary embodiment, the first detector 15 and the second detector 6 are disposed on opposite sides of the sample to be measured, i.e., the angle formed by the first detector and the second detector and the sample to be measured is 180 degrees. Of course, in other exemplary embodiments of the present invention, the angle formed by the first detector and the second detector and the sample to be measured may be various angles, such as 90 degrees, 120 degrees, and 60 degrees, which are not limited herein.
The first detector 15 detects first gamma photons to generate a first measurement signal and the second detector 6 detects second gamma photons to generate a second measurement signal. Then, the first splitter 8 divides the first measurement signal into two paths to obtain a first detection signal and a first judgment signal, and the first judgment signal discriminates a first initial signal through a first constant ratio timing discriminator 10; the second splitter 9 divides the second measurement signal into two paths to obtain a second detection signal and a second decision signal, wherein the second decision signal discriminates the second start signal through a second constant ratio timing discriminator 11. The amplitude and the shape of the first detection signal and the first judging and selecting signal are the same, and the amplitude and the shape of the second detection signal and the second judging and selecting signal are the same; the first detection signal and the second decision signal may be further amplified by an amplifier having a certain amplification factor before entering into the receiving or the decision, respectively. In this exemplary embodiment, the amplitude of the amplitude discrimination may be 1.28MeV energy window, that is, a signal having an amplitude within 1.28MeV energy window in the first discrimination signal is output as the first start signal, and a signal having an amplitude within 1.28MeV energy window in the second discrimination signal is output as the second start signal.
In step S20, the first start signal and the second start signal are ored to generate a trigger signal.
In the present exemplary embodiment, the operation is an or operation. The first start signal and the second start signal are unlikely to be generated at the same time, and the trigger signal generating unit 2 performs an or operation to output the trigger signal after receiving the first start signal and the second start signal, that is, the trigger signal generating unit 2 outputs the trigger signal after receiving the first start signal or the second start signal. The first start signal and the second start signal are both signals of 1.28MeV gamma photons. After such a logical or operation, only one signal of a detected 1.28MeV gamma photon (onset time) triggers data acquisition as a valid positron annihilation event, regardless of the detector. Of course, it will be understood by those skilled in the art that the first start signal or the second start signal need not be subjected to a logical or operation, and the trigger signal may be generated as long as one of the first start signal and the second start signal is received.
In step S30, the first probe signal and the second probe signal are received within a set time in response to the trigger signal.
In the present exemplary embodiment, the set time is an acquisition time window, which is set to about 200ns, and can meet the requirement of most positron lifetime measurements. The trigger signal generated based on the first start signal is responsive to receive the first detection signal having the first amplitude and the second detection signal having the second amplitude, and the trigger signal generated based on the second start signal is responsive to receive the second detection signal having the first amplitude and the first detection signal having the second amplitude. The first detection signals may comprise signals of 1.28MeV gamma photons and 0.511MeV annihilation gamma photon signals, and the second detection signals may also comprise signals of 1.28MeV gamma photons and 0.511MeV annihilation gamma photon signals. And after receiving the trigger signal, starting the receiving channels to receive the first detection signal and the second detection signal, timing simultaneously, and receiving the first detection signal and the second detection signal through the two receiving channels in the acquisition time window, namely receiving the first detection signal through the first channel and receiving the second detection signal through the second channel. In addition, the set time may also be set to a time period greater than or less than 200 ns.
In step S40, the amplitude of the first detection signal and the amplitude of the second detection signal are determined to match the first amplitude and the second amplitude to obtain a first determination result and a second determination result, and a first time difference and a second time difference between the first detection signal and the second detection signal are calculated.
In the present exemplary embodiment, the amplitude is a first amplitude within a 1.28MeV energy window and the amplitude is a second amplitude within a 0.511MeV energy window. The first time difference is a time difference between a first detection signal having a first amplitude and a second detection signal having a second amplitude. The second time difference is a time difference between the second detection signal having the first amplitude and the first detection signal having the second amplitude.
Reference is made to the logic diagram of two separate time difference measurement units of an exemplary embodiment of a positron annihilation lifetime spectroscopy measurement method shown in figure 3.
As shown in part (a), when the amplitude of the first detection signal is the first amplitude (1.28MeV) and the amplitude of the second detection signal is the second amplitude (0.511MeV), a first determination result is obtained, which indicates that the first detection signal received through the first channel is a start signal, the first detector 15 is a start detector, the second detection signal received through the second channel is an end signal, and the second detector 6 is an end detector. At this time, the time difference Δ t between the first detection signal and the second detection signal may be calculated1I.e. Δ t1＝t2-t1The time difference is a lifetime value of a positron.
In the drawings(b) Partially, when the amplitude of the first detection signal is the second amplitude (0.511MeV) and the amplitude of the second detection signal is the first amplitude (1.28MeV), a second determination result is obtained, which indicates that the first detection signal received through the first channel is an end signal, the first detector 15 is an end detector, the second detection signal received through the second channel is a start signal, and the second detector 6 is a start detector. At this time, the time difference Δ t between the first detection signal and the second detection signal may be calculated2I.e. Δ t2＝t1-t2The time difference is the lifetime value of another positron.
Of course, there may be a case where the first probe signal received only through the first channel at a set time is not received through the second channel, and there may be a case where the second probe signal received only through the second channel at a set time is not received through the first channel. Both cases are invalid events, with no output, and no statistical count of the event. Other instances of invalidating events of the present disclosure may be readily envisioned by those skilled in the art and are not described in further detail herein.
In step S50, a first lifetime map is obtained by counting the first time difference according to the first determination result, a second lifetime map is obtained by counting the second time difference according to the second determination result, and the first lifetime map and the second lifetime map are superimposed to obtain a positron annihilation lifetime map.
And counting the lifetime value of the positron to obtain a positron annihilation lifetime spectrum.
In the exemplary embodiment, the first lifetime map is a statistic of lifetime values of positrons having a first determination result, i.e., the amplitude of the first detection signal is a first amplitude (within 1.28MeV energy window) and the amplitude of the second detection signal is a second amplitude (within 0.511 mv energy window)eWithin the V-energy window). The second lifetime map is the statistic of the lifetime value of the positron with the second judgment result, and the second judgment result is the second judgment resultThe detection signal has an amplitude of a first amplitude (amplitude within a 1.28MeV energy window) and the first detection signal has an amplitude of a second amplitude (amplitude within a 0.511MeV energy window).
Referring to two positron annihilation lifetime spectra and their superimposed spectra shown in fig. 4, in the present example embodiment, the first lifetime map and second lifetime map superimposing method may include: firstly, coinciding the zero time of the first life map with the zero time of the second life map; and then, correspondingly adding the statistical counts in the same time intervals of the first life map and the statistical counts in the same time intervals of the second life map in sequence. The time interval may be a track width of the lifetime spectrum, the track width of the lifetime spectrum may be several tens of ps, and theoretically, the smaller the track width, the more accurate the lifetime spectrum is obtained. In the present exemplary embodiment, the time interval may be 50ps, that is, the positron annihilation lifetime spectrum may be obtained by correspondingly adding the statistical counts of the first lifetime spectrum and the statistical counts of the second lifetime spectrum in a plurality of time intervals, such as 0 to-50 ps, 0 to 50ps, 50ps to 100ps, 100ps to 150ps, 150ps to 200ps, and the like. For example, the statistical counts of the first lifetime map in three identical time intervals of 0 to-50 ps, 0 to 50ps, and 50ps to 100ps are 8000, 9000, and 12000, respectively, the statistical counts of the second lifetime map in three identical time intervals of 0 to-50 ps, 0 to 50ps, and 50ps to 100ps are 8500, 9200, and 11800, respectively, and the statistical counts of the positron annihilation lifetime map calculated in three identical time intervals of 0 to-50 ps, 0 to 50ps, and 50ps to 100ps are 8000+8500, 16500, 9000+9200, and 12000+11800, 23800. Of course, in other example embodiments of the present disclosure, the time intervals may also coincide at multiple times of 1ns, 2ns, and so on, and multiple times of 20ps, 30ps, 60pns, and so on may also be selected as the time intervals.
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.
Further, the present exemplary embodiment also provides a positron annihilation lifetime spectrum measurement system corresponding to the above-described positron annihilation lifetime spectrum measurement method. Referring to a block diagram of an exemplary embodiment of a positron annihilation lifetime spectrum measurement system shown in fig. 5, the positron annihilation lifetime spectrum measurement system may include a start signal generating unit 1, a trigger signal generating unit 2, a receiving unit 3, a waveform analyzing unit 4, a map processing unit 5, and the like.
The start signal generating unit 1 may be configured to receive the first selection signal and obtain a first start signal through amplitude determination, and to receive the second selection signal and obtain a second start signal through amplitude determination.
The trigger signal generating unit 2 may be configured to perform an or operation on the first start signal and the second start signal to generate a trigger signal.
The receiving unit 3 may be configured to receive the first probe signal and the second probe signal within a set time in response to the trigger signal.
The waveform analyzing unit 4 may be configured to determine matching situations between the amplitudes of the first detection signal and the second detection signal and the first amplitude and the second amplitude to obtain a first determination result and a second determination result, and calculate a first time difference and a second time difference between the first detection signal and the second detection signal.
The map processing unit 5 may be configured to obtain a first lifetime map according to the first determination result and statistics of the first time difference, obtain a second lifetime map according to the second determination result and statistics of the second time difference, and superimpose the first lifetime map and the second lifetime map to obtain a positron annihilation lifetime map.
In this example embodiment, superimposing the first lifetime map and the second lifetime map may include:
coinciding a zero time of the first lifetime map with a zero time of the second lifetime map;
and sequentially and correspondingly adding the statistical counts in the plurality of same time intervals of the first life map with the statistical counts in the corresponding plurality of same time intervals of the second life map.
In the present exemplary embodiment, the matching between the amplitude of the first detection signal and the amplitude of the second detection signal and the first amplitude and the second amplitude is determined to obtain a first determination result and a second determination result, and a first time difference and a second time difference between the first detection signal and the second detection signal are calculated; the method can comprise the following steps:
obtaining a first judgment result when the amplitude of the first detection signal is the first amplitude and the amplitude of the second detection signal is the second amplitude, and obtaining a second judgment result when the amplitude of the first detection signal is the second amplitude and the amplitude of the second detection signal is the first amplitude; and calculating the time difference from the second detection signal to the first detection signal according to the first judgment result to obtain the first time difference, and calculating the time difference from the first detection signal to the second detection signal according to the second judgment result to obtain the second time difference.
In the present exemplary embodiment, the positron annihilation lifetime spectrum measurement system may further include a first splitter 8 and a second splitter 9, and so on; the first splitter 8 may be configured to split the first measurement signal to generate the first detection signal and the first decision signal; the second splitter 9 may be configured to split the second measurement signal to generate the second detection signal and the second decision signal. The start signal generation unit 1 may include a first constant ratio timing discriminator 10 and a second constant ratio timing discriminator 11. The first constant ratio timing discriminator 10 may be configured to discriminate the first discrimination signal amplitude to generate a first start signal; the second constant ratio timing discriminator 11 may be configured to discriminate the second discrimination signal amplitude to generate a second start signal.
In the present exemplary embodiment, the positron annihilation lifetime spectrum measurement system may further include a first detector 15 and a second detector 6, and so on; the first detector 15 may be used to generate the first measurement signal when a first gamma photon is detected; a second detector 6 may be used to generate the second measurement signal when a second gamma photon is detected; the distance between the first detector 15 and the sample to be detected is the same as the distance between the second detector 6 and the sample to be detected, and the first detector 15 and the second detector 6 and the sample to be detected are set at a set angle.
Referring to figure 6, a block diagram of an exemplary embodiment of a positron annihilation lifetime spectroscopy measurement system is shown. In the present exemplary embodiment, a film encapsulated by Kapton film is used22Na positron emission source, the radioactivity of which is about 10 mu Ci, and the test sample is pure iron material. Two identical samples tightly clamping radioactive source to form a sandwich structure22Na radioactive source and test sample 14. The first detector 15 and the second detector 6 are both barium fluoride detectors, the crystal size of barium fluoride is phi 30 multiplied by 20, the model of a photomultiplier is Hamamatsu R3377, and the high-voltage power supply 7 can provide-1700V voltage.
In the present exemplary embodiment, the start signal generation unit 1 may include a first constant ratio timing discriminator 10 and a second constant ratio timing discriminator 11. The trigger signal generation unit 2 is a nuclear electronics plug-in ORTEC 418A. The functions of the receiving unit 3, the waveform analyzing unit 4 and the atlas handling unit 5 are all realized by a digital oscilloscope 13.
In the present exemplary embodiment, the positron annihilation lifetime spectrum measurement system may further include two delay units 12, and the two delay units 12 are electrically connected between the first splitter 8 and the receiving unit (i.e., the digital oscilloscope 13) and between the second splitter 9 and the receiving unit (i.e., the digital oscilloscope 13), respectively.
The digital oscilloscope 13 digitally samples the input signal with a sampling rate of 10 GS/s. In an external trigger mode, two waveform timing measurements are set in measurement options of the digital oscilloscope 13 and respectively used as a time difference measurement unit with a first detector 15 as an initial detector, a second detector 6 as an end detector and the second detector 6 as the initial detector, and the first detector 15 as the end detector.
The comparison between the conventional measurement method and the method herein was obtained by counting the time and count rate required for the acquisition of the first lifetime map and the second lifetime map, as shown in table 1:
TABLE 1 full Width at half maximum (FWHM) comparison of count rate and lifetime spectra between conventional measurement methods and the present method
Where FWHM denotes the full width at half maximum of the lifetime spectrum, CH1-start & CH2-stop denotes the first detector 15 acquisition start signal and the second detector 6 acquisition stop signal, and CH2-start & CH1-stop denotes the second detector 6 acquisition start signal and the first detector 15 acquisition stop signal. As can be seen from table 1, the acquisition count rate obtained by the method by simultaneously acquiring two lifetime maps is about twice that of the conventional method, which indicates that the rate of acquiring effective annihilation events is increased by about one time, and the utilization rate of gamma signals of two detectors is greatly increased.
The specific details of each module in the positron annihilation lifetime spectrum measurement system are already described in detail in the corresponding virtual object motion control method, and therefore are not described herein again.
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.
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.
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 within 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 (6)
1. A positron annihilation lifetime spectrum measurement method, comprising:
receiving a first judgment signal and obtaining a first initial signal through amplitude judgment, and receiving a second judgment signal and obtaining a second initial signal through amplitude judgment;
performing an OR operation on the first starting signal and the second starting signal to generate a trigger signal;
responding to the trigger signal, and receiving a first detection signal and a second detection signal within a set time;
judging the matching condition of the amplitude of the first detection signal and the amplitude of the second detection signal with the first amplitude and the second amplitude to obtain a first judgment result and a second judgment result, and calculating a first time difference and a second time difference between the first detection signal and the second detection signal, including: obtaining a first judgment result when the amplitude of the first detection signal is the first amplitude and the amplitude of the second detection signal is the second amplitude, and obtaining a second judgment result when the amplitude of the first detection signal is the second amplitude and the amplitude of the second detection signal is the first amplitude; calculating a time difference from the second detection signal to the first detection signal according to the first judgment result to obtain the first time difference, and calculating a time difference from the first detection signal to the second detection signal according to the second judgment result to obtain the second time difference;
according to the first judgment result and the first time difference, a first life map is obtained, according to the second judgment result and the second time difference, a second life map is obtained, and the first life map and the second life map are superposed to obtain a positron annihilation life map; wherein superimposing the first lifetime map with the second lifetime map comprises:
coinciding a zero time of the first lifetime map with a zero time of the second lifetime map; and sequentially and correspondingly adding the statistical counts in the plurality of same time intervals of the first life map with the statistical counts in the corresponding plurality of same time intervals of the second life map.
2. The positron annihilation lifetime spectrum measuring method of claim 1, wherein the first detection signal and the first decision signal are obtained by a first splitter splitting a first measurement signal into two paths, and the second detection signal and the second decision signal are obtained by a second splitter splitting a second measurement signal into two paths.
3. The positron annihilation lifetime spectroscopy measurement method of claim 2, wherein the first measurement signal is generated by a first detector detecting a first gamma photon and the second measurement signal is generated by a second detector detecting a second gamma photon;
the distance between the first detector and a sample to be detected is the same as the distance between the second detector and the sample to be detected, and the first detector and the second detector are arranged at a set angle with the sample to be detected.
4. A positron annihilation lifetime spectroscopy measurement system, comprising:
the starting signal generating unit is used for receiving the first judging and selecting signal and obtaining a first starting signal through amplitude judgment, and receiving the second judging and selecting signal and obtaining a second starting signal through amplitude judgment;
the trigger signal generating unit is used for carrying out OR operation on the first starting signal and the second starting signal to generate a trigger signal;
the receiving unit is used for responding to the trigger signal and receiving a first detection signal and a second detection signal within set time;
a waveform analysis unit, configured to determine matching conditions between the amplitudes of the first and second detection signals and between the amplitudes of the second and first amplitudes and the second amplitudes to obtain first and second determination results, and calculate first and second time differences between the first and second detection signals, including: obtaining a first judgment result when the amplitude of the first detection signal is the first amplitude and the amplitude of the second detection signal is the second amplitude, and obtaining a second judgment result when the amplitude of the first detection signal is the second amplitude and the amplitude of the second detection signal is the first amplitude;
calculating a time difference from the second detection signal to the first detection signal according to the first judgment result to obtain the first time difference, and calculating a time difference from the first detection signal to the second detection signal according to the second judgment result to obtain the second time difference;
the map processing unit is used for obtaining a first life map according to the first judgment result and the first time difference in a statistical manner, obtaining a second life map according to the second judgment result and the second time difference in a statistical manner, and superposing the first life map and the second life map to obtain a positron annihilation life map; wherein: superimposing the first lifetime map with the second lifetime map, comprising:
coinciding a zero time of the first lifetime map with a zero time of the second lifetime map; and sequentially and correspondingly adding the statistical counts in the plurality of same time intervals of the first life map with the statistical counts in the corresponding plurality of same time intervals of the second life map.
5. The positron annihilation lifetime spectrum measurement system of claim 4, further comprising:
the first splitter is used for splitting a first measurement signal into two paths to obtain the first detection signal and the first judgment and selection signal;
and the second splitter is used for splitting a second measurement signal into two paths to obtain the second detection signal and the second judgment signal.
6. The positron annihilation lifetime spectrum measurement system of claim 5, further comprising:
a first detector for generating the first measurement signal upon detection of a first gamma photon;
a second detector for generating the second measurement signal upon detection of a second gamma photon;
the distance between the first detector and a sample to be detected is the same as the distance between the second detector and the sample to be detected, and the first detector and the second detector are arranged at a set angle with the sample to be detected.
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