Waveform-sampling-based scintillator decay time test method

Abstract

The application discloses a kind of scintillator decay time test methods based on waveform sampling, the steps of test method include: scintillator is coupled to the optical window of photomultiplier tube placed in shielding box, using radioactive source excitation sample, open oscilloscope automatic acquisition not less than 100 pulse signals and transmission to control computer;Pulse waveform data acquired by oscilloscope is handled calculation, obtains the decay time constant corresponding to single pulse data;The above steps are repeated for processing all collected pulse data, obtain decay time constant set;With decay time constant set histogram, data should present normal distribution;Using Gaussian function to the normal distribution is fitted, the decay time value corresponding to the peak obtained is the decay time of the sample.The application can accurately test the decay time of different scintillating materials, especially suitable for high-throughput decay time measurement.

Description

Technical Field

[0001] This invention belongs to the field of nuclear radiation detection technology, and in particular relates to a method for testing the decay time of scintillators based on waveform sampling. Background Technology

[0002] Rare-earth scintillation materials, as the most important component of scintillation materials, have found extensive applications in nuclear medicine imaging, high-energy physics, and military fields, making numerous contributions to national welfare and security. In the field of tumor screening, the most important large-scale medical device, positron emission tomography (PET), utilizes Lu₂SiO₅ / Lu₂. 2-x Y x SiO5 crystal arrays will serve as the core detector. In the field of high-energy physics, tens of thousands of Lu2SiO5 / Lu crystal arrays will be used in the CMS upgrade at CERN. 2-x Y x Constructing a CMS MIP timing detector using SiO5 crystal strips. In summary, the research and production of rare-earth scintillators is a major undertaking related to national economy, people's livelihood, and national defense security. The rapid and accurate characterization and calibration of their scintillation performance are indispensable in the research and production of these materials. For the application of scintillator materials, the three most important performance indicators are: light yield, energy resolution, and decay time. Among these three indicators, decay time testing requires the longest time, the most complex testing process, and has the largest testing error. Applications such as PET or high-energy physics have strict requirements on the decay time of the scintillator materials used. At the same time, these applications require a large number of small-sized samples, and testing the decay time of each sample using existing testing techniques would be unacceptably time-consuming. Therefore, a rapid and accurate method for testing the decay time of scintillators is needed to meet the high-throughput quality evaluation requirements of industrial production. Summary of the Invention

[0003] In view of this, the present invention aims to overcome the shortcomings of the above-mentioned problems in the prior art and proposes a scintillator decay time test method based on waveform sampling, which can accurately test the decay time of different scintillator materials, and is especially suitable for high-throughput decay time testing.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A method for testing the decay time of a scintillator based on waveform sampling, comprising:

[0006] The sample to be tested is irradiated by a radiation source, and the light emitted by the sample after being irradiated by the radiation source is converted into an electrical signal by a photoelectric conversion element.

[0007] An oscilloscope is used to acquire electrical signals, obtain waveform data of voltage pulse signals, and transmit them to a computer for processing.

[0008] The computer performs batch reading and processing of waveform data, takes the average value of the first 100 data points of the waveform as the base, subtracts the base value from the baseline, sets the peak position of the waveform as the coordinate zero point, and the data set from the coordinate zero point onwards is the decay time fitting dataset. The pulse voltage amplitudes at all time acquisition points are added together as the pulse intensity.

[0009] The pulse intensity histogram is displayed to obtain the energy spectrum of the scintillator's emission, as well as the two-dimensional kernel density histogram of pulse intensity versus decay time. Based on the two-dimensional kernel density histogram of pulse intensity versus decay time, the normal distribution of the scintillator's emission decay time is obtained, and the decay time of the peak position is regarded as the accurate value.

[0010] Furthermore, the photoelectric conversion element is a photomultiplier tube or a phototube.

[0011] Furthermore, when using an oscilloscope to acquire electrical signals, select the self-trigger mode, and use electrical signals with amplitudes higher than the preset amplitude as the primary target electrical signal.

[0012] Furthermore, this also includes revising the results:

[0013] All pulse signals output by the computer are analyzed individually, and the obtained decay times are statistically distributed. The statistical values ​​are considered accurate values.

[0014] Furthermore, it also includes coupling the sample under test and the photoelectric conversion element with silicone grease, as well as wrapping a highly reflective layer.

[0015] Furthermore, the radioactive source is a Na-22 standard source.

[0016] Furthermore, this also includes shielding the test samples with strong afterglow before testing.

[0017] Compared with existing technologies, the scintillator decay time testing method based on waveform sampling described in this invention has the following advantages:

[0018] 1. This invention eliminates the error caused by ignoring the inconsistency of the decay time of a single pulse in traditional testing methods, and corrects the test results.

[0019] 2. Compared with traditional testing methods, this invention retains the intensity and decay time information of a single optical pulse, obtains the Gaussian distribution of the decay time of all pulses, and the correlation between decay time and pulse intensity.

[0020] 3. The testing process and results of this invention are accurate and fast. The testing technology provided by this invention has a data repeatability of better than 3% for LSO / LYSO crystal decay time testing, and the error is less than 15% compared with the test results of time-correlated single-photon counting method. The testing time for a single sample is less than 5 minutes, and the data processing time is less than 10 minutes.

[0021] 4. This invention studies the influencing factors of rapid decay time test error and reveals the influencing factors of the half-width at half maximum (WHM) of the decay time distribution spectrum, thereby further improving the accuracy of the test.

[0022] 5. This invention combines single-pulse processing of a large number of scintillation pulses with a large number of decay time distributions. It takes advantage of the fast pulse data collection speed and the high accuracy of decay time obtained by statistical analysis of a large amount of data. As a fast and accurate scintillator decay time test method, it better meets the quality evaluation needs of industrial production in PET applications or high-energy physics applications. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 This is a schematic diagram of the scintillator decay time testing system based on waveform sampling according to the present invention;

[0025] Figure 2 This is a schematic diagram of the scintillator emission spectrum obtained from the decay time test of the LYSO:Ce crystal in Example 1.

[0026] Figure 3 This is a schematic diagram of the two-dimensional histogram distribution of the scintillator emission pulse intensity and decay time obtained in the decay time test of the LYSO:Ce crystal in Example 1.

[0027] Figure 4 This is a schematic diagram of the Gaussian distribution spectrum of the scintillation decay time and the fitting results obtained in the decay time test of the LYSO:Ce crystal in Example 1.

[0028] Figure 5 This is a schematic diagram showing the relationship between the scintillation decay time and the full width at half maximum (FWHM) of the Ce and Ti co-doped LYSO crystal in Example 2 under darkroom conditions.

[0029] Figure 6 This is a schematic diagram showing the relationship between the scintillation decay time and the full width at half maximum (FWHM) of the Ce and Ti co-doped LYSO crystal under sunlight conditions in Example 2.

[0030] Figure 7 This is a schematic diagram showing the relationship between the scintillation decay time and the scintillation pulse intensity obtained in the decay time test of the Ce and Ti co-doped LYSO crystal with strong afterglow under sunlight conditions in Example 3.

[0031] Figure 8 This is a schematic diagram of exponential fitting of the normalized superimposed average value of all scintillation pulse intensities obtained in the decay time test of the LYSO:Ce crystal in Example 6.

[0032] Figure 9 This is a schematic diagram of the scintillator emission spectrum obtained in the decay time test of the BGO crystal in Example 7;

[0033] Figure 10 This is a schematic diagram showing the relationship between the scintillation decay time and the full width at half maximum (FWHM) and the scintillation pulse intensity obtained in the decay time test of the BGO crystal in Example 7. Detailed Implementation

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0035] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0036] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0038] like Figure 1-10 As shown, the present invention provides a method for testing the decay time of a scintillator based on waveform sampling, comprising:

[0039] A waveform sampling-based scintillator decay time testing system was constructed, including a radiation source, a sample under test, an oscilloscope, and a computer. The testing system was used to perform tests, including:

[0040] The sample to be tested is irradiated by a radiation source, and the light emitted by the sample after being irradiated by the radiation source is converted into an electrical signal by a photoelectric conversion element.

[0041] An oscilloscope is used to acquire electrical signals, obtain waveform data of voltage pulse signals, and transmit them to a computer for processing.

[0042] The computer performs batch reading and processing of waveform data, takes the average value of the first 100 data points of the waveform as the base, subtracts the base value from the baseline, sets the peak position of the waveform as the coordinate zero point, and the data set from the coordinate zero point onwards is the decay time fitting dataset. The pulse voltage amplitudes at all time acquisition points are added together as the pulse intensity.

[0043] The pulse intensity histogram is displayed to obtain the energy spectrum of the scintillator's emission, as well as the two-dimensional kernel density histogram of pulse intensity versus decay time. Based on the two-dimensional kernel density histogram of pulse intensity versus decay time, the normal distribution of the scintillator's emission decay time is obtained, and the decay time of the peak position is regarded as the accurate value.

[0044] In this invention, the decay time testing method involves the interpretation of a large number of pulse spectra, and the statistical error of the test is inversely correlated with the number of pulse spectra. To improve testing accuracy, as much pulse data as possible needs to be collected and processed, which raises the issue of computational efficiency. For a decay time on the order of hundreds of nanoseconds, the data size of a single pulse is on the order of hundreds of kilobytes. To ensure sufficient testing accuracy, the total data for a single sample is in the range of hundreds of megabytes to several gigabytes.

[0045] In this invention, a kernel density histogram distribution correlated with pulse intensity and decay time in two dimensions is constructed. The optical decay times at different pulse intensities are automatically screened and fitted with a normal distribution to obtain decay time values ​​and half-width at half-maximum (HWHM) for different pulse intensities. This process reveals the influencing factors of the spectral width of the scintillation decay time distribution, providing new parameters for characterizing the performance of scintillation materials. The decay times obtained by exponential fitting of a large number of single-pulse spectra exhibit a Gaussian distribution. It was found that the HWHM of this Gaussian distribution is sample-dependent. Test results of the decay times of LYSO crystal samples of the same size but with different doping levels show that this HWHM is a sample-dependent parameter. This HWHM directly affects the accuracy of decay time testing; a smaller HWHM indicates higher accuracy in decay time testing.

[0046] Specifically, the photoelectric conversion element is a photomultiplier tube or a phototube.

[0047] In this invention, the photomultiplier tube is the R2059 model manufactured by Hamamatsu Corporation, with a response wavelength of 160-650 nm, a rise time of approximately 1.3 ns, a wide spectral response range, and high acquisition efficiency and gain. It is recommended that the negative high voltage applied to the photomultiplier tube (for the R2059) base be in the range of 1600V to 2000V. If the sample under test emits weak light, a higher voltage can be applied.

[0048] Specifically, when using an oscilloscope to acquire electrical signals, select the self-trigger mode, and use electrical signals with an amplitude higher than the preset amplitude as the primary target electrical signal.

[0049] In this invention, the oscilloscope is a Lecroy WaveRUNNER 8104, which has a 1GHz bandwidth, 4 channels, and a sampling rate of up to 20GS / s on 2Ch, enabling more accurate data acquisition. Appropriate oscilloscope signal parameters are set: impedance matching is 50 ohms.

[0050] In this invention, the self-triggering mode enables faster pulse spectrum acquisition, higher testing efficiency, and improved testing accuracy.

[0051] Specifically, this also includes correcting the results:

[0052] All pulse signals output by the computer are analyzed individually, and the obtained decay times are statistically distributed. The statistical values ​​are considered accurate values.

[0053] Specifically, this also includes coupling the sample under test and the photoelectric conversion element with silicone grease, as well as wrapping them with a highly reflective layer to achieve higher testing accuracy.

[0054] In this invention, the sample to be tested is placed in a metal shielded box that can isolate external interference signals, and the excitation source is a Na-22 standard source.

[0055] Specifically, this also includes shielding the test sample with strong afterglow before testing to reduce errors, obtain the minimum decay time half-width, and higher test accuracy.

[0056] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the following examples.

[0057] Example 1 (Decay time test of LYSO:Ce crystal)

[0058] The LYSO:Ce sample crystal (15×15×2.3mm) was coupled to the PMT via silicone oil, covered with a reflective layer, and a Na-22 standard source was placed. The negative high voltage on the photomultiplier tube R2059 was 1800V. The signal parameters of the Lecroy WaveRUNNER 8104 oscilloscope were set as follows: impedance matching 50 ohms, sampling rate 10GS / s, trigger condition: self-triggered, trigger mode: edge-triggered. The collected 100,000 waveform data were processed by computer programming.

[0059] Example 2 (Decay time test of LYSO:Ce and Ti crystals under different preparation conditions)

[0060] Ce and Ti co-doped LYSO sample crystals (15×15×2.3mm) were placed in sunlight and darkroom environments, respectively, and coupled to a PMT via silicone oil. A reflective layer was then placed on top, and a Na-22 standard source was placed. The negative high voltage on the photomultiplier tube R2059 was 1700V. The signal parameters of the Lecroy WaveRUNNER 8104 oscilloscope were set as follows: impedance matching 50 ohms, sampling rate 10GS / s, trigger condition: self-triggered, trigger mode: edge-triggered. The computer program processed the collected 200,000 waveform data and calculated the emission decay time and half-width at ten different pulse intensities.

[0061] Example 3 (Decay time test of LYSO:Ce and Ti crystals with strong afterglow)

[0062] A Ce and Ti co-doped LYSO sample (15×15×2.3mm) with strong afterglow was placed in sunlight and coupled to a PMT via silicone oil. A reflective layer was then placed on top, and a Na-22 standard source was placed. The negative high voltage on the photomultiplier tube R2059 was 1700V. The signal parameters of the Lecroy WaveRUNNER 8104 oscilloscope were set as follows: impedance matching 50 ohms, sampling rate 10GS / s, trigger condition: self-triggered, trigger mode: edge-triggered. The computer program processed the collected 200,000 waveform data and calculated the emission decay time at ten different pulse intensities.

[0063] Example 4 (Decay time test of LYSO:Ce crystals with different Ti doping concentrations)

[0064] LYSO:Ce sample crystals (15×15×2.3mm) with Ti co-doped concentrations of 0.01%, 0.05%, 0.1%, and 0.25% were coupled to a PMT via silicone oil, covered with a reflective layer, and a Na-22 standard source was placed. A negative high voltage of 1700V was applied to the photomultiplier tube R2059. The signal parameters of the Lecroy WaveRUNNER 8104 oscilloscope were set as follows: impedance matching 50 ohms, sampling rate 10GS / s, trigger condition: self-triggered, trigger mode: edge-triggered. 200,000 waveform data points were acquired for each sample. The relevant results are summarized in Table 1.

[0065] Table 1

[0066]

[0067] Example 5 (Decay time test of LYSO:Ce crystals with different Ca doping concentrations)

[0068] LYSO:Ce sample crystals (10×10×2mm) with Ca co-doped concentrations of 0%, 0.1%, 0.2%, 0.3%, and 0.4% were coupled to a PMT via silicone oil, covered with a reflective layer, and a Na-22 standard source was placed. A negative high voltage of 1700V was applied to the photomultiplier tube R2059. The signal parameters of the Lecroy WaveRUNNER 8104 oscilloscope were set as follows: impedance matching 50 ohms, sampling rate 10GS / s, trigger condition: self-triggered, trigger mode: edge-triggered. 200,000 waveform data points were acquired for each sample. The relevant results are summarized in Table 2.

[0069] Table 2

[0070]

[0071] Example 6 (The impact of different data analysis methods on decay time test results)

[0072] The scintillation decay time test was repeated on a large number of LYSO sample crystals, and the acquired waveform data were processed using two different data analysis methods. The first method was the statistical average of a single pulse fit, and the second method was the superimposed average of all pulse intensities after normalization. The results are summarized in Table 3.

[0073] Table 3

[0074]

[0075]

[0076] Example 7 (Decay time test of BGO crystal)

[0077] The intrinsically light-emitting crystal (BGO) was coupled to the PMT via silicone oil, covered with a reflective layer, and a Na-22 standard source was placed. The photomultiplier R2059 was subjected to a negative high voltage of 2400V. The signal parameters of the Lecroy WaveRUNNER 8104 oscilloscope were set as follows: impedance matching 50 ohms, sampling rate 10GS / s, trigger condition: self-triggered, trigger mode: edge-triggered. The computer program processed the 100,000 waveform data collected and calculated the emission decay time and half-width at ten different pulse intensities.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing the decay time of a scintillator based on waveform sampling, characterized in that: include: The sample to be tested is irradiated by a radiation source, and the light emitted by the sample after being irradiated by the radiation source is converted into an electrical signal by a photoelectric conversion element. An oscilloscope is used to acquire electrical signals, obtain waveform data of voltage pulse signals, and transmit them to a computer for processing. The computer performs batch reading and processing of waveform data, takes the average value of the first 100 data points of the waveform as the base, subtracts the base value from the baseline, sets the peak position of the waveform as the coordinate zero point, and the data set from the coordinate zero point onwards is the decay time fitting dataset. The pulse voltage amplitudes at all time acquisition points are added together as the pulse intensity. The pulse intensity histogram is displayed to obtain the energy spectrum of the scintillator's emission, as well as the two-dimensional kernel density histogram of pulse intensity versus decay time; The normal distribution of the luminescence decay time of the scintillator is obtained from the two-dimensional kernel density histogram of pulse intensity-decay time, and the decay time of the peak position is regarded as the accurate value.

2. The method for testing the decay time of a scintillator based on waveform sampling according to claim 1, characterized in that: The photoelectric conversion element is a photomultiplier tube or a phototube.

3. The method for testing the decay time of a scintillator based on waveform sampling according to claim 1, characterized in that: When acquiring electrical signals using an oscilloscope, select the self-trigger mode. Electrical signals with amplitudes higher than the preset amplitude are used as the primary target electrical signals.

4. The method for testing the decay time of a scintillator based on waveform sampling according to claim 1, characterized in that: This also includes correcting the results: All pulse signals output by the computer are analyzed individually, and the obtained decay times are statistically distributed. The statistical values ​​are considered accurate values.

5. The method for testing the decay time of a scintillator based on waveform sampling according to claim 1, characterized in that: It also includes coupling the sample under test and the photoelectric conversion element with silicone grease, as well as wrapping a highly reflective layer.

6. The method for testing the decay time of a scintillator based on waveform sampling according to claim 1, characterized in that: The radioactive source is the Na-22 standard source.

7. The method for testing the decay time of a scintillator based on waveform sampling according to claim 1, characterized in that: This also includes shielding the test sample from strong afterglow before testing.

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