阅读说明：本技术 一种数字化反符合多路互为起始正电子湮没寿命谱仪 (Digitized anti-coincidence multi-path interaction-starting positron annihilation life spectrometer ) 是由 董赟 赵秋贺 叶邦角 刘建党 张宏俊 于 2021-08-16 设计创作，主要内容包括：本发明涉及一种数字化反符合多路互为起始正电子湮没寿命谱仪,包括：多路闪烁体探测模块、数字化信号采集模块、计算机终端、样品结构单元；所述多路闪烁体探测模块：包括一路反符合探测器和三路互为起始的符合探测器,都使用光电倍增管和闪烁体；其中,所述一路反符合探测器,采用一个塑料闪烁体用硅油耦合一个光电倍增管PMT0,在所述闪烁体上设置样品结构单元；所述反符合探测器用于探测正电子信号；所述三路互为起始的符合探测器结构相同,均采用1个闪烁体耦合1个光电倍增管作为符合探测器,且三者互为直角放置,光电倍增管PMT1-3每一个均能探测起始或终止γ光子信号；使用数字采集卡采集信号由计算机终端在线处理信号得到正确的寿命谱。(The invention relates to a digitalized anti-coincidence multi-path interaction-initial positron annihilation life spectrometer, which comprises: the device comprises a multi-path scintillator detection module, a digital signal acquisition module, a computer terminal and a sample structure unit; the multi-path scintillator detection module: the device comprises a one-way anti-coincidence detector and three-way mutual-starting coincidence detectors, wherein both the one-way anti-coincidence detector and the three-way mutual-starting coincidence detector use a photomultiplier tube and a scintillator; the anti-coincidence detector adopts a plastic scintillator and is coupled with a photomultiplier PMT0 by silicon oil, and a sample structure unit is arranged on the scintillator; the anti-coincidence detector is used for detecting a positron signal; the three paths of mutually-started coincidence detectors have the same structure, 1 scintillator is coupled with 1 photomultiplier tube to serve as the coincidence detector, the three paths of mutually-started coincidence detectors are arranged at right angles, and each photomultiplier tube PMT1-3 can detect a start gamma photon signal or an end gamma photon signal; the digital acquisition card is used for acquiring signals, and the computer terminal processes the signals on line to obtain a correct life spectrum.)

1. A digitized anti-coincidence multiplexed positron annihilation lifetime spectrometer comprising: the device comprises a multi-path scintillator detection module, a digital signal acquisition module, a computer terminal program and a sample structure unit;

the multi-path scintillator detection module: the device comprises a one-way anti-coincidence detector and three-way mutual-starting coincidence detectors, wherein both the one-way anti-coincidence detector and the three-way mutual-starting coincidence detector use a photomultiplier tube and a scintillator;

the anti-coincidence detector adopts a plastic scintillator and is coupled with a photomultiplier PMT0 by silicon oil, and a sample structure unit is arranged on the scintillator; the anti-coincidence detector is used for detecting a positron signal;

the three paths of mutually-started coincidence detectors have the same structure, 1 scintillator is coupled with 1 photomultiplier PMT 1-PMT 3 to serve as the coincidence detectors, the three paths of mutually-started coincidence detectors are placed at right angles, each detector is provided with working voltage by a high-voltage power supply, each of the photomultiplier PMT1, the photomultiplier PMT2 and the photomultiplier PMT3 can detect a start or stop gamma photon signal, and the photomultiplier PMT0 is only used for detecting a positive electron signal;

and acquiring signals detected by the multi-channel scintillator detection module by using a digital acquisition card, and processing the signals by using a computer terminal program to obtain a correct life spectrum.

2. The positron annihilation lifetime spectrometer of claim 1 wherein three coincident detectors at right angles to each other are spatially distributed in three dimensions, each detector being capable of detecting the onset and the end of an annihilation event, increasing the count rate.

3. The digital anti-coincidence multiplex positron annihilation lifetime spectrometer as claimed in claim 1, wherein said sample structure unit is in close proximity to an anti-coincidence detector, and comprises a scintillator, a radiation source, and a sample, which form a scintillator-radiation source-sample sandwich, said sample structure unit being coupled to a photomultiplier tube via the scintillator.

4. The digitized anti-coincidence multi-path mutual initiation positron annihilation lifetime spectrometer of claim 1, wherein the computer terminal program is used for energy spectrum acquisition, conventional lifetime spectrum acquisition, mutual initiation lifetime spectrum acquisition, and anti-coincidence lifetime spectrum acquisition.

5. The annihilation lifetime spectrometer of claim 1 wherein each of the plurality of detectors detects both an initiation signal and an end signal, converts the detected gamma photon signals to electrical signals via a photomultiplier tube and inputs the electrical signals to the digital acquisition module via a coaxial cable, sets a trigger logic and coincidence time window, selects a 20ns time window, the coincidence logic is when any scintillator channel detects a 1.275MeV gamma photon, any other scintillator channel detects a 511keV gamma photon within 20ns and the anti-coincidence detector does not detect a positron signal, a valid event, and records the event in a predetermined data format.

6. The positron annihilation lifetime spectrometer of claim 1 wherein the coincidence event is determined by fitting or interpolating the signal front edge to determine the time difference and improve timing accuracy, and the lifetime spectrum is obtained by accumulating the time difference into a histogram.

Technical Field

The invention relates to the technical field of positron annihilation lifetime spectrometers, in particular to anti-coincidence and multi-path mutual initiation coincidence technologies.

Background

Positron annihilation lifetime refers to the time elapsed from the generation of a positron to annihilation with an electron. The service life is directly related to the electron density distribution in the substance. When a defect is present in a substance, the annihilation lifetime of the positron at the defect is altered, and the positron annihilation lifetime spectrum is therefore very sensitive to the defect. The type and size information of the defect can be known through the measurement of positron annihilation lifetime spectrum. Positron annihilation lifetime spectrum is widely used in material science as a non-destructive characterization means.

The conventional positron annihilation life spectrometer consists of a scintillation crystal, a photomultiplier, a high-voltage constant-ratio timing discriminator, a fast coincidence circuit, a delayer, a time-amplitude converter, an NIM case, a multi-channel analyzer and a computer. The radioactive source is normally sealed with a Kapton membrane²²Na and forming a sandwich structure of 'sample-source-sample' with the sample to be detected.

Using two scintillator detectors, respectively detecting²²The Na decay releases a gamma photon of 1.275MeV as the start signal and the positron annihilates in the material forming a 511keV gamma photon as the stop signal. After the scintillator detects gamma rays, an electric signal is generated through the photomultiplier, a pulse electric signal enters the constant ratio timing discriminator, the constant ratio timing discriminator discriminates the amplitude of an input signal on one hand, and discriminates and selects the upper threshold and the lower threshold of the amplitude of the input signal on the other hand, and a standard signal determined by a constant ratio timing method is output. Then, dividing the signals into two paths of standard output signals in a constant ratio timing discriminator: one output signal is used for fast coincidence to trigger a gate signal, and the other output signal enters a time-amplitude converter after time delay. After the fast coincidence output gate signal is sent to the time-amplitude converter, the time-amplitude converters of the two paths of standard signals convert the time difference into a signal which is in direct proportion to the amplitude, the amplitude is discriminated by the analog-digital converter or the multiple paths, so that the amplitude signal is converted into a numerical value file to be stored, and finally, a spectrum obtained by accumulating a large number of events is a positron annihilation lifetime spectrum.

The conventional positron annihilation lifetime spectrometer has the disadvantages of low counting rate, long acquisition time, multiple plug-in units, high equipment cost, and harsh requirements of a sample-source-sample sandwich structure, namely two identical samples and the like, which are generally required for each test.

Disclosure of Invention

The invention aims to provide a digitalized anti-coincidence multipath annihilation life spectrometer taking each other as a starting positron, which greatly improves the counting rate of the spectrometer and shortens the measurement time on the premise of basically not influencing time resolution; the spectrometer device is simplified, and the equipment cost is reduced; and a single-side sample is used, so that the sample preparation condition is reduced.

A digitized anti-coincidence multiplexed interaction-initiating positron annihilation lifetime spectrometer comprising: the device comprises a multi-path scintillator detection module, a digital signal acquisition module, a computer terminal and a sample structure unit;

the multi-path scintillator detection module: the device comprises a one-way anti-coincidence detector and three-way mutual-starting coincidence detectors, wherein both the one-way anti-coincidence detector and the three-way mutual-starting coincidence detector use a photomultiplier tube and a scintillator;

the anti-coincidence detector adopts a plastic scintillator and is coupled with a photomultiplier PMT0 by silicon oil, and a sample structure unit is arranged on the scintillator; the anti-coincidence detector is used for detecting a positron signal;

the three paths of mutually-started coincidence detectors have the same structure, 1 scintillator is coupled with 1 photomultiplier PMT 1-PMT 3 to serve as the coincidence detectors, the three paths of mutually-started coincidence detectors are placed at right angles, each detector is provided with working voltage by a high-voltage power supply, each of the photomultiplier PMT1, the photomultiplier PMT2 and the photomultiplier PMT3 can detect a start or stop gamma photon signal, and the photomultiplier PMT0 is only used for detecting a positive electron signal;

and acquiring signals detected by the multi-channel scintillator detection module by using a digital acquisition card, and processing the signals by using a computer terminal to obtain a correct life spectrum.

Furthermore, three paths of coincidence detectors which are mutually starting are distributed in a three-dimensional space in a three-dimensional mode, each detector can detect the starting signal and the ending signal of the annihilation event which are mutually right-angled, and the counting rate is improved.

Furthermore, the sample structure unit is close to the anti-coincidence detector and comprises a scintillator, a radioactive source and a sample, the scintillator, the radioactive source and the sample form a sandwich structure of the scintillator, the radioactive source and the sample, and the sample structure unit is coupled with the photomultiplier through the scintillator.

Further, the computer terminal program is used for energy spectrum acquisition, conventional life spectrum acquisition, mutual initial life spectrum acquisition and anti-coincidence life spectrum acquisition.

Furthermore, each path of the multi-path detector can detect both an initial signal and a termination signal, the detected gamma photon signals are converted into electric signals through a photomultiplier tube and then input into the digital acquisition module through a coaxial cable, triggering logic and a coincidence time window are set, a time window of 20ns is selected, the coincidence logic is that when any scintillator channel detects a gamma photon of 1.275MeV, another scintillator channel detects a gamma photon of 511keV within 20ns and does not detect a positron signal, the event is an effective event, and the event can be recorded according to a preset data format.

Furthermore, the time difference is determined by the signal leading edge in a timing mode through fitting or interpolation of the coincidence events, the timing precision is improved, and the time difference is accumulated to form a histogram, so that the service life spectrum can be obtained.

Compared with the prior art, the invention has the advantages that:

(1) the invention reduces the requirements of test conditions and the preparation cost of samples, and reduces the test conditions by utilizing the anti-coincidence technology. The sample for testing is required to be halved, and the method is very friendly to some samples with difficult preparation.

(2) By utilizing the multi-path mutual initiation coincidence technology, a larger solid angle is covered on the premise of keeping the other performances unchanged, the counting rate is greatly improved, the testing time is greatly reduced, and the method can be applied to scenes needing rapid measurement.

(3) The electronic module has the advantages of simple structure, high integration level, capability of updating logic on line, convenience for data processing and function improvement, and convenience for maintenance and upgrading.

Drawings

FIG. 1 is a schematic diagram of an anti-coincidence multi-path positron annihilation lifetime spectrometer;

FIG. 2 is a positron energy spectrum measured by an anti-coincidence detector;

FIG. 3 shows life spectra before and after anticoincidence;

FIG. 4 is a schematic diagram of a sample structural unit.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention without creative efforts.

The positron annihilation lifetime spectrometer comprises: the device comprises a multi-path scintillator detection module, a digital signal acquisition module, a computer terminal and a sample structure unit;

the multi-path scintillator detection module: including one-way anti-coincidence detectors and multiple-way mutual-initiation coincidence detectors, all using photomultiplier tubes and scintillators.

A high voltage power supply is used to provide a high voltage to each photomultiplier tube.

The single-path anti-coincidence detector is used for detecting positron signals, and the multiple-path mutual initial detectors are used for detecting gamma signals generated by positron annihilation events.

As shown in fig. 1, the positron annihilation lifetime spectrometer of the invention adopts a plastic scintillator coupled with silicone oil and a photomultiplier tube (PMT) as an anti-coincidence detector, and a radioactive source and a single sample (PMT 0 and a hexagon mark at one end in the figure) are placed on the scintillator to form a sample structural unit; as shown in fig. 4, the sample structure unit, in which a scintillator 1, a radiation source 2 and a sample 3 form a sandwich structure of "scintillator-radiation source-sample", is coupled with a photomultiplier through the scintillator.

The other 3 scintillators are coupled with 3 photomultiplier tubes which are mutually arranged at right angles as coincidence detectors (in the figure, PMT1, PMT2 and PMT3 form a solid angle in space and are in a tetrahedral conical structure), the four detectors are as close as possible, and each detector is provided with a high-voltage power supply (HV) for supplying high voltage; PMT1, PMT2, PMT3 may each detect an onset or an end gamma photon signal, PMT0 being used only to detect positron signals.

And a digital acquisition card is used for acquiring signals output by the multi-path scintillator detection module, and the signals are processed on line through a computer terminal to obtain a correct life spectrum.

The positron annihilation life spectrometer has the time resolution same as that of a conventional spectrometer, and the counting rate is about 5 times that of the conventional life spectrometer (double probes).

The principle of the device of the invention is as follows: first, a positive electron source (²²Na) to produce beta⁺Decays, producing positrons and concomitant emission of 1.275MeV gamma photons. On one hand, after being incident into the sample, the positron is annihilated with electrons in the sample to generate a pair of 511keV gamma photons, and scintillation light generated by the gamma photons deposited in the crystal is received by a coupled photomultiplier tube to generate a photoelectric signal. On the other hand, the positron does not annihilate with the material into the scintillator and deposit energy for receipt by the coupled photomultiplier tubes.

Figure 2 is a spectrum of positron energy detected by an anti-coincidence detector.

Each path of the multi-path detector can detect an initial signal and a termination signal, a detected gamma photon signal is converted into an electric signal through a photomultiplier tube and then is input into a high-bandwidth high-sampling-rate digital acquisition module through a coaxial cable, triggering logic and a coincidence time window are set, the time window of 20ns is selected, the coincidence logic is that when any scintillator channel detects 1.275MeV gamma photons, another arbitrary scintillator channel detects 511keV gamma photons within 20ns and does not detect positron signals, the event is an effective event, and the event can be recorded according to a certain data format.

The time difference is determined by the signal front edge in a timing mode through fitting or interpolation of the coincidence events, timing precision is improved, and the time difference is accumulated to form a histogram, so that a service life spectrum can be obtained.

FIG. 3 is a monolithic sample measurement of Yttrium Stabilized Zirconia (YSZ) plotted using circles and straight lines for the spectral patterns of the lifetime spectrum with and without anticoincidence, respectively. The error cases of the unused life spectrum are more, and the spectrum error is obvious; and the measurement result of the lifetime spectrum using the anti-coincidence is completely correct.

In the embodiment of the invention, the solid angle of detection is increased by adopting a design of taking multiple paths as the starting point, and the coincidence events which cannot be recorded by a conventional spectrometer are recorded; a single-chip sample is used, and accidental coincidence events are removed in a reverse coincidence mode, so that the sample preparation requirement is reduced; under the condition of unchanged time resolution, the counting rate is greatly improved, and the measurement time is effectively shortened; greatly simplifying the equipment and reducing the equipment cost.

Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but various changes may be apparent to those skilled in the art, and it is intended that all inventive concepts utilizing the inventive concepts set forth herein be protected without departing from the spirit and scope of the present invention as defined and limited by the appended claims.