Liquid scintillation spectrometer energy spectrum detection signal processing device

Abstract

The utility model discloses a liquid scintillation spectrometer energy spectrum detection signal processing device, which comprises a photomultiplier, the photomultiplier is electrically connected with a circuit board 7 integrated with a voltage division circuit and a signal conversion circuit, the photomultiplier is a spherical photomultiplier, and the input voltage of the input end of the voltage division circuit is negative high voltage. According to the utility model, the voltage division circuit is used for dividing the input negative high voltage according to a certain proportion, so that the photomultiplier tube is ensured to convert the received optical signal into a current signal according to a fixed amplification factor, and the current signal passes through the signal conversion circuit to output a differential voltage signal which is easy to transmit and extract; the volume of the device is reduced by increasing the negative high voltage, the output signal-to-noise ratio is increased by forming differential output by using two paths of output signals which are equal in size and opposite in polarity, and the influence of a tube on a liquid flash background is reduced by using a photomultiplier tube made of quartz glass, so that the precision of a subsequent analysis result can be greatly improved.

Description

Technical Field

[0001] The utility model relates to the technical field of nuclear radiation measurement, in particular to a liquid scintillation spectrometer energy spectrum detection signal processing device. Background Art

[0002] Liquid scintillation spectrometers, as radionuclide analysis instruments, have a wide range of applications, such as determining the age of archaeological artifacts, detecting radioactivity in nuclear wastewater, detecting nuclear contamination in seafood, and performing medical examinations. To accurately analyze the dose of radioactive substances in our daily lives, the analytical capabilities of liquid scintillation spectrometers are gradually improving. The detector, as the signal capture device of the liquid scintillation spectrometer, plays a decisive role in its overall performance. To facilitate subsequent spectral analysis, the detector must ensure both high detection efficiency and low self-noise, while maintaining stable energy linearity throughout the entire signal conversion process. The detector's efficiency determines the upper limit of the liquid scintillation spectrometer's efficiency, and the detector's dark noise is often difficult to separate from the actual signal, resulting in an inability to reduce the background.

[0003] The core sensor of liquid scintillators is the detector. Its primary function is to convert the light signal emitted by the scintillation fluid during nuclear decay into an electrical signal. Only through this electrical signal can the liquid scintillation spectrometer analyze the nuclides in the sample. A liquid scintillator detector consists of three components: a photomultiplier tube (PMT), a voltage divider circuit, and a signal conversion circuit. Traditional liquid scintillator designs use a purchased PMT, a common voltage divider, and a current amplifier circuit for signal conversion and output. Because these conventional liquid scintillator detectors are simply pieced together, the output signal often suffers from significant linear distortion. Consequently, traditional liquid scintillators often suffer from low detection efficiency and uneven spectral distribution. These issues render liquid scintillator spectrum analysis highly uncertain, often limiting its use to general counter functions rather than precise analysis. Liquid scintillator detectors are primarily used for low-energy signals, often with a measurement range of only 0 to 18.6 keV. Liquid scintillators are required to be able to resolve signals less than 0.1 keV. The smaller the signal resolution, the better the performance. The amplitude of the signal output by the detector of a very low-energy signal will also be very small. Traditional liquid scintillators amplify the output signal of the detector and then extract it. However, since the signal is very small and cannot be well distinguished from the baseline noise, the noise is also amplified during amplification, making it difficult to extract the signal.

[0004] Therefore, how to design an energy spectrum detection signal processing method and device with stable energy linearity, large signal-to-noise ratio and high detection efficiency is a technical problem that needs to be solved urgently. Utility Model Content

[0005] In order to address the deficiencies of the prior art, the present invention provides a liquid scintillation spectrometer energy spectrum detection signal processing device, which utilizes a voltage divider circuit to divide the input negative high voltage according to a certain ratio, thereby providing suitable working conditions for the photomultiplier tube, ensuring that the photomultiplier tube converts the received light signal into a current signal according to a fixed amplification factor. The current signal is output through a signal conversion circuit as a differential voltage signal that is easy to transmit and extract. The present invention reduces the device volume by increasing the negative high voltage supply, utilizes two output signals of equal size and opposite polarity to form a differential output to improve the output signal-to-noise ratio, and uses a quartz glass photomultiplier tube to reduce the influence of the tube on the liquid scintillation background, thereby greatly improving the accuracy of subsequent analysis results.

[0006] The present invention provides the following solutions:

[0007] An embodiment of the utility model provides a liquid scintillation spectrometer energy spectrum detection signal processing device, including a photomultiplier tube, characterized in that: the photomultiplier tube is electrically connected to a circuit board integrated with a voltage divider circuit and a signal conversion circuit, the photomultiplier tube adopts a spherical photomultiplier tube, and the input voltage of the input end of the voltage divider circuit is a negative high voltage.

[0008] In an optional embodiment, the photomultiplier tube includes a shielding layer shell, the top of the shielding layer shell is provided with a quartz window for the entry of light signals, the inside of the shielding layer shell is provided with a spherical photocathode, a focusing electrode, a dynode and a P anode in sequence from the top to the tail end, and the tail end of the shielding layer shell is provided with pins for connecting each dynode and the P anode.

[0009] In an optional embodiment, in the voltage divider circuit, each level of the voltage divider terminal is connected one by one to each dynode pin of the photomultiplier tube.

[0010] In an optional embodiment, the negative high voltage range is -600V to -3000V.

[0011] In an optional embodiment, the signal conversion circuit includes a positive voltage output circuit connected to each level of the voltage divider circuit, and a negative voltage output circuit connected to the input end of the voltage divider circuit, and the positive voltage output circuit and the negative voltage output circuit respectively include a first resistor, a first capacitor and a second resistor connected in series.

[0012] In an optional embodiment, the photomultiplier tube uses 12 to 13 stages of dynodes.

[0013] In an optional embodiment, the voltage divider circuit adopts a 12-13 level voltage divider circuit.

[0014] The beneficial effects of the present invention based on its technical solution are:

[0015] (1) Spectral analysis refers to the use of the relationship between energy and counts to reflect the nuclear decay situation in the measured sample, such as radioactivity measurement, hazard, how long the nuclear decay has lasted, and how long it will decay. Under the same voltage conditions, the stronger the light received by the photomultiplier tube, the greater the energy, and the greater the amplitude of the output electrical signal. Under the same energy, the higher the voltage of the photomultiplier tube, the greater the output signal amplitude, which is more conducive to detection. It can be seen that the efficiency of the detection signal analysis determines the efficiency upper limit of the liquid scintillation spectrometer equipment, and the dark noise of the detector is often difficult to separate from the real signal, resulting in the inability to reduce the background. The utility model uses spherical photomultiplier tubes to increase the light collection efficiency. In order to avoid the influence of radioactive substances on the background, the photomultiplier tubes need to use quartz material. In order to obtain higher light sensitivity and higher gain, a high voltage of 2 to 3 times that of ordinary tubes is used. The higher high voltage improves the overall collection efficiency of the detector, but it also brings some problems. The voltage resistance requirements of the devices used are increased. By increasing the multiplication stages of the photomultiplier tube, the withstand voltage requirement of the voltage divider device can be reduced, while also avoiding the decoupling capacitor from causing leakage current due to excessively high applied voltage to affect the energy output linearity.

[0016] (2) The utility model adopts negative high voltage as the circuit design of the voltage divider, which greatly reduces the voltage rating of the components required by the circuit. This makes the voltage divider take up less space under high voltage conditions, making the integrated design of the detector easier to integrate and more reliable. The use of negative high voltage can also reduce the voltage requirements of the isolation capacitor used for output. When used for positive high voltage, the voltage resistance of the isolation capacitor must be greater than the power supply high voltage, which is generally between 600 and 3000V. The voltage at the last stage of the multiplier and the anode is close to the input voltage. Therefore, the capacitor used for output signal isolation can only be selected with a high voltage resistance. For example, if the input high voltage is 2.5KV, a capacitor with a voltage resistance of about 2.5KV is required. Such a capacitor must use at least a 7*22*14mm plug-in capacitor with an accuracy of ≥±5%. However, the utility model adopts negative high voltage input, and the voltage resistance of the isolation capacitor only needs to be greater than the maximum amplitude of the output signal, and the output signal amplitude is generally between 0 and 5V. According to capacitor manufacturing processes, the lower the capacitor's withstand voltage rating, the smaller the package that can be made, and the required electrical distance during integration is also reduced. The voltage difference between isolation capacitors will be reduced to below 100V. Common C0603 chip ceramic capacitors (1.6*0.8*0.2mm) can meet this requirement. The utility model has two outputs and requires two such capacitors, which significantly reduces space and allows the circuit board to be soldered to the photomultiplier tube without interference.

[0017] (3) The utility model adopts an isolated bipolar passive signal amplification output design. The isolation type refers to separating the pulse signal carried in the DC high voltage for detection and analysis, while the high voltage will be intercepted. The bipolar passive signal amplification output is a circuit design that only uses resistors and capacitors to convert the weak current signal output by the photomultiplier tube into a voltage signal, and transforms the amplitude and width of the signal to a specific easy-to-detect range. Compared with the liquid scintillation detector using active signal output, the input of the voltage source is reduced and the circuit is simpler. It can also allow the effective signal to output two signals of positive and negative polarity at the same time, forming a differential signal output.

[0018] (4) The present invention proposes a method for differential output of liquid scintillation signals to improve the signal-to-noise ratio and enhance the quality of signal capture. In the present invention, a differential signal output is used to identify the signal and noise. The real signal is that the positive and negative signals arrive at the same time, while the noise always rises or falls at the same time. Since the positive and negative signals arrive at the same time, the positive signal minus the negative signal during post-processing can increase the signal amplitude while suppressing the noise signal, which is beneficial to the amplitude extraction of the liquid scintillator detector at the post-stage. This method is to output a dual signal at the detector output, so the signal amplitude is twice that of the traditional liquid scintillator, and the noise is at least half of the original, and it also has better anti-interference ability in signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 The utility model is a structural diagram of a liquid scintillation spectrometer energy spectrum detection signal processing device.

[0021] Figure 2 The utility model provides a circuit connection diagram of a liquid scintillation spectrometer energy spectrum detection signal processing device.

[0022] In the figure: 1-shielding shell, 2-quartz window, 3-spherical photocathode, 4-focusing electrode, 5-dynode, 6-P anode, 7-circuit board, 8-photon signal, 9-photoelectron. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the embodiments of the present invention.

[0024] Reference Figure 1 and Figure 2 , the embodiment of the present utility model provides the following solutions:

[0025] This embodiment provides a liquid scintillation spectrometer energy spectrum detection signal processing device, including a photomultiplier tube, which is electrically connected to a circuit board 7 integrating a voltage divider circuit and a signal conversion circuit. The photomultiplier tube is a spherical photomultiplier tube, and the input voltage at the input end of the voltage divider circuit is a negative high voltage.

[0026] The photomultiplier tube adopts a spherical photomultiplier tube, including a shielding layer shell 1, a quartz window 2 for the entry of light signals is provided at the top of the shielding layer shell, a spherical photocathode 3, a focusing electrode 4, a dynode 5 and a P anode 6 are provided in sequence inside the shielding layer shell from the top to the tail end, and pins for connecting each dynode and the P anode are provided at the tail end of the shielding layer shell.

[0027] In the voltage divider circuit, each voltage divider terminal is connected to each dynode pin of the photomultiplier tube one by one;

[0028] The signal conversion circuit includes a positive voltage output circuit connected to each level of the voltage divider circuit, and a negative voltage output circuit connected to the input end of the voltage divider circuit. The positive voltage output circuit and the negative voltage output circuit respectively include a first resistor, a first capacitor and a second resistor connected in series.

[0029] In this embodiment, the photomultiplier tube adopts a 12-stage dynode, and the voltage divider circuit adopts a 12-stage voltage divider circuit.

[0030] The working process of this utility model is:

[0031] Step 1: The sample undergoes nuclear decay in a liquid scintillation spectrometer, stimulating the scintillation liquid to generate photon signals.

[0032] Step 2: Use a photomultiplier tube to capture photon signals 8, and generate photoelectrons 9 at the cathode of the photomultiplier tube. The photomultiplier tube is a spherical photomultiplier tube, including a shielding layer shell 1. The top of the shielding layer shell is provided with a quartz window 2 for light signal entry. The inside of the shielding layer shell is provided with a spherical photocathode 3, a focusing electrode 4, a dynode 5 and a P anode 6 in sequence from the top to the tail end. The tail end of the shielding layer shell is provided with pins for connecting each dynode and P anode, which are used to connect to a circuit board 7 for subsequent processing. The circuit board is integrated with a voltage divider circuit and a signal conversion circuit.

[0033] The present invention uses a spherical photomultiplier tube, which can increase the light collection efficiency. In order to avoid the influence of radioactive substances on the background, the photomultiplier tube needs to be made of quartz material. In order to obtain higher light sensitivity and higher gain, a high voltage that is 2 to 3 times higher than that of ordinary tubes is used. The higher high voltage improves the overall collection efficiency of the detector, but it also brings some problems. The voltage resistance requirements of the devices used become higher. By increasing the multiplication level of the photomultiplier tube, the voltage resistance requirements of the voltage divider device can be reduced. At the same time, it also avoids the leakage current of the decoupling capacitor due to the excessively high applied voltage affecting the linearity of the energy output. The present invention proposes a circuit design that uses negative high voltage as a voltage divider, which greatly reduces the voltage resistance level of the devices required by the circuit. This makes the voltage divider take up less space under high voltage conditions, making the integrated design of the detector easier to integrate and more reliable. The use of negative high voltage can also reduce the voltage resistance requirements of the isolation capacitor used for output. When used with positive high voltage, the isolation capacitor's withstand voltage must exceed the power supply high voltage, which is generally between 600 and 3000V. When used with negative high voltage, the isolation capacitor's withstand voltage only needs to exceed the maximum output signal amplitude, which is generally between 0 and 5V. Due to the capacitor's manufacturing process, the lower the capacitor's withstand voltage rating, the smaller the package that can be manufactured, and the lower the electrical distance required during integration.

[0034] Step 3: Using resistors of varying resistance connected in series in a voltage divider circuit, the negative high voltage at the input is distributed to each dynode in a predetermined ratio. The photoelectrons are amplified by each dynode, forming a current signal at the anode and the final dynode. The negative high voltage at the input ranges from -600V to -3000V, and the voltage divider circuit employs 10 to 12 dynodes.

[0035] Step 4. Using the signal conversion circuit, the current signal is converted into a voltage signal through the basic voltage formula U=I*R (voltage value equals current value multiplied by resistance value), and output in the form of a differential voltage signal. The differential voltage signal includes a positive signal and a negative signal. Differential output can improve the signal-to-noise ratio and enhance the signal capture quality. Because the real signal is the positive and negative signals arriving at the same time, and the noise always rises or falls at the same time. The utility model identifies the signal and noise through a differential signal output. The simultaneous arrival of positive and negative signals facilitates post-processing. The positive signal is subtracted from the negative signal to increase the signal amplitude while suppressing the noise signal, which is beneficial for the liquid scintillator detector to extract the amplitude. This method has dual signals at the detector output, so the signal amplitude is twice that of the traditional liquid scintillator signal output, and the noise is at least half of the original, and it also has a better anti-interference ability in signal transmission.

[0036] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0037] Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A liquid scintillation spectrometer energy spectrum detection signal processing device, comprising a photomultiplier tube, characterized in that: The photomultiplier tube is electrically connected to a circuit board integrated with a voltage divider circuit and a signal conversion circuit. The photomultiplier tube is a spherical photomultiplier tube, and the input voltage of the input end of the voltage divider circuit is a negative high voltage.

2. The liquid scintillation spectrometer energy spectrum detection signal processing device according to claim 1, characterized in that: The photomultiplier tube includes a shielding layer shell, the top of the shielding layer shell is provided with a quartz window for the entry of light signals, the inside of the shielding layer shell is provided with a spherical photocathode, a focusing electrode, a dynode and a P anode in sequence from the top to the tail end, and the tail end of the shielding layer shell is provided with pins for connecting each dynode and the P anode.

3. The liquid scintillation spectrometer energy spectrum detection signal processing device according to claim 1, characterized in that: In the voltage divider circuit, each level of the voltage divider terminal is connected one by one to each dynode pin of the photomultiplier tube.

4. The liquid scintillation spectrometer energy spectrum detection signal processing device according to claim 1, characterized in that: The negative high voltage range is negative 600V to negative 3000V.

5. The liquid scintillation spectrometer energy spectrum detection signal processing device according to claim 1, characterized in that: The signal conversion circuit includes a positive voltage output circuit connected to each level of the voltage divider circuit, and a negative voltage output circuit connected to the input end of the voltage divider circuit. The positive voltage output circuit and the negative voltage output circuit respectively include a first resistor, a first capacitor and a second resistor connected in series.

6. The liquid scintillation spectrometer energy spectrum detection signal processing device according to claim 1, characterized in that: The photomultiplier tube adopts 12 to 13 levels of dynodes.

7. The liquid scintillation spectrometer energy spectrum detection signal processing device according to claim 1, characterized in that: The voltage divider circuit adopts a 12-13 level voltage divider circuit.

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