Nuclide identification instrument

Abstract

The utility model discloses a nuclide identification instrument which comprises a detector and a gamma energy spectrum acquisition circuit. The gamma energy spectrum acquisition circuit comprises a voltage following circuit which is connected with a detector and can improve input impedance; the pole zero cancellation circuit is connected with the voltage follower circuit and can eliminate the tail overshoot of the signal; the in-phase proportional amplification circuit is connected with the pole-zero cancellation circuit and is used for amplifying the amplitude of the signal; the filtering shaping circuit is connected with the in-phase proportional amplification circuit and is used for converting the signals into Gaussian pulse signals; the baseline recovery circuit is connected with the filtering shaping circuit and used for keeping the baseline of the signal stable; the differentiating circuit is connected with the filtering shaping circuit and is used for differentiating the signal; the threshold comparison circuit is connected with the differentiating circuit and used for comparing the signals; and the MCU is respectively connected with the baseline recovery circuit and the threshold comparison circuit and can carry out AD conversion and storage on the signals. The acquired gamma energy spectrum is high in precision, low in power consumption and small in size, and can be applied to various working places.

Description

Technical Field

[0001] The utility model relates to an instrument for identifying nuclides, in particular to a nuclide identification instrument. Background Art

[0002] Nuclide identification equipment can perform radioactivity measurements and is widely used in nuclear power plants, food hygiene inspections, environmental radiation pollution, nuclear waste monitoring, earth sciences, radioactivity detection in nuclear medicine instruments, radioactive source theft prevention, and nuclear terrorism.

[0003] At present, the signal processing speed of radionuclide identifiers on the market is slow, resulting in a large system dead time; the noise interference is large, resulting in distortion of the low-energy part of the collected gamma spectrum data; the baseline is unstable, and the resolution is poor at high counting rates, so the accuracy of the collected gamma spectrum data is low; the use of independent AD chips has low integration and complex peripheral circuits, resulting in a large circuit board size and high power consumption, which makes the radionuclide identifier unable to be flexibly applied to various places. Utility Model Content

[0004] The utility model aims to provide a nuclide identification instrument to solve the problems of slow signal processing speed, large noise interference, unstable baseline, complex circuit and high power consumption of the nuclide identification instrument.

[0005] The technical solution of this utility model is as follows:

[0006] A nuclide identification instrument, comprising a detector and a gamma spectrum acquisition circuit;

[0007] The gamma spectrum acquisition circuit comprises:

[0008] The voltage follower circuit is connected to the detector and the pole-zero cancellation circuit respectively, and is used to increase the input impedance of the signal and output a stable pulse signal;

[0009] The pole-zero phase cancellation circuit is connected to the voltage follower circuit and the in-phase proportional amplifier circuit respectively, and is used to reduce the width of the pulse signal output by the voltage follower circuit and eliminate the tail overshoot of the pulse signal, and output a pulse signal with a reduced pulse width;

[0010] The in-phase proportional amplifier circuit is connected to the pole-zero cancellation circuit and the filter shaping circuit respectively, and is used to amplify the amplitude of the pulse signal output by the pole-zero cancellation circuit and output the amplified pulse signal;

[0011] The filter shaping circuit is connected to the in-phase proportional amplifier circuit, the baseline recovery circuit and the differential circuit respectively, and is used to shape the pulse signal output by the in-phase proportional amplifier circuit and output a Gaussian pulse signal;

[0012] The baseline recovery circuit is connected to the filter shaping circuit and the MCU respectively, and is used to keep the baseline of the pulse signal output by the filter shaping circuit stable and output a stable pulse signal;

[0013] A differential circuit is connected to the filter shaping circuit and the threshold comparison circuit respectively, and is used to differentiate the pulse signal output by the filter shaping circuit and output the differentiated pulse signal;

[0014] A threshold comparison circuit is connected to the differential circuit and the MCU respectively, and is used to compare the signal output by the differential circuit and output a signal to start AD conversion; and

[0015] The MCU is connected to the baseline recovery circuit and the threshold comparison circuit respectively, and is used to perform AD conversion on the pulse signal output by the baseline recovery circuit, and store the conversion result within a preset time period to obtain gamma energy spectrum data.

[0016] Furthermore, the structure of the voltage follower circuit is that two inputs are connected to the positive input terminal of the operational amplifier U3A, one is connected to the input signal of the voltage follower circuit through resistor R2, and the other is connected to a 2.5V power supply through resistor R4, the reverse input terminal of the operational amplifier U3A is connected to the output terminal of the operational amplifier U3A, the positive power input terminal of the operational amplifier U3A is connected to a 5V power supply through resistor R8; the negative power input terminal of the operational amplifier U3A is grounded.

[0017] Furthermore, the structure of the pole-zero cancellation circuit is that two ends of the variable resistor VR1 are connected in parallel with a voltage divider circuit composed of a resistor R19 and a resistor R35, one end of the parallel connection is connected to the output end of the operational amplifier U3A, the output end of the operational amplifier U3A is connected to the output end of the pole-zero cancellation circuit through a capacitor C24, and the other end of the parallel connection is grounded through a capacitor C21 on the one hand, and connected to a 2.5V power supply on the other hand; the middle pin of the variable resistor VR1 is respectively connected to the resistor R1 and the voltage divider node of the voltage divider circuit composed of the resistor R19 and the resistor R35, and the middle pin of the variable resistor VR1 is connected to the output end of the pole-zero cancellation circuit on the one hand after passing through the resistor R1, and is connected to the 2.5V power supply through a resistor R23 on the other hand.

[0018] Furthermore, the structure of the in-phase proportional amplifier circuit is that the positive input terminal of the operational amplifier U3B is connected to two inputs, one of which is connected to a 2.5V power supply through a resistor R5, and the other is connected to the input signal of the in-phase proportional amplifier circuit; the reverse input terminal of the operational amplifier U3B is connected to three inputs, one of which is connected to the output terminal of the operational amplifier U3B through a resistor R25, two of which are connected to the output terminal of the operational amplifier U3B through a capacitor C10, the output terminal of the operational amplifier U3B is connected to the output terminal of the in-phase proportional amplifier circuit, and three of which are connected to the 2.5V power supply through a resistor R6.

[0019] Furthermore, the structure of the filtering shaping circuit is that the positive input terminal of the operational amplifier U4A is connected to three inputs, one of which is connected to the input signal of the filtering shaping circuit through resistor R28 and resistor R9, two of which are connected to the output terminal of the operational amplifier U4A through resistor R9 and capacitor C37, the output terminal of the operational amplifier U4A is connected to the output terminal of the filtering shaping circuit, and three of which are grounded through capacitor C31; the reverse input terminal of the operational amplifier U4A is connected to three inputs, one of which is connected to the output terminal of the operational amplifier U4A through capacitor C34, two of which are connected to the output terminal of the operational amplifier U4A through resistor R31, and three of which are connected to a 2.5V power supply through resistor R30; the positive power input terminal of the operational amplifier U4A is connected to a 5V power supply, and the negative power input terminal of the operational amplifier U4A is grounded.

[0020] Furthermore, the structure of the baseline recovery circuit is that pin No. 2 of the dual diode D1 is connected to the input signal of the baseline recovery circuit through capacitor C16 on the one hand, is grounded through resistor R14 on the other hand, and is connected to the output end of the baseline recovery circuit on the other hand; pin No. 1 of the dual diode D1 is connected to three inputs, one is connected to a 2.5V power supply through resistor R13, two is grounded through resistor R32, and three is grounded through a power supply filter decoupling circuit, and both ends of capacitor C38 in the power supply filter decoupling circuit are connected in parallel with capacitor C39; pin No. 3 of the dual diode D1 is connected to a 3.3V power supply through resistor R17.

[0021] Furthermore, the structure of the differential circuit is that the inverting input terminal of the operational amplifier U4B is connected to two inputs, one is connected to the input signal of the differential circuit through the capacitor C32, and the other is connected to the output terminal of the operational amplifier U4B through the resistor R10, and the output terminal of the operational amplifier U4B is connected to the output terminal of the differential circuit.

[0022] Furthermore, the structure of the threshold comparison circuit is that the positive input pin of the comparator U6A is connected to three inputs, one is connected to a 2.5V power supply through a resistor R20, two is connected to a power supply through a resistor R16, and three is connected to an output pin of the comparator U6A through a resistor R21; the negative input pin of the comparator U6A is connected to the input signal of the threshold comparison circuit, the positive power supply pin of the comparator U6A is connected to a digital power supply, and the negative power supply pin and the analog negative pin of the comparator U6A are both grounded.

[0023] The models of operational amplifier U3A, operational amplifier U3B, operational amplifier U4A, and operational amplifier U4B are all OPA2830, and the voltage conversion speed of this type of operational amplifier reaches 500V / μs. The model of comparator U6A is CMP401, and the delay time of this comparator is short.

[0024] Furthermore, the structure of the AD conversion circuit is that the output end of the baseline recovery circuit is connected to the AIN0 pin of the MCU, and the output end of the threshold comparison circuit is connected to the CNVSTR0 pin of the MCU; when the signal output by the threshold comparison circuit is input to the CNVSTR0 pin, the MCU starts ADC0 when CNVSTR0 receives a rising edge trigger signal, and performs AD conversion on the input level input to the AIN0 pin. After the ADC0 conversion is completed, an ADC0 interrupt is generated, and the conversion result is read and saved in the interrupt.

[0025] The utility model utilizes the operational amplifier OPA2830 to form a voltage follower circuit, thereby improving the input impedance of the signal and ensuring the stability of the signal; utilizes the pole-zero phase cancellation circuit to eliminate the tail overshoot of the pulse signal, thereby making the baseline of the signal more stable and reducing the pulse width, thereby reducing the dead time of the system; and utilizes the operational amplifier OPA2830 in-phase proportional amplifier circuit to amplify the amplitude of the pulse signal, which is significantly different from the amplitude of the noise signal and reduces noise interference; utilizes the operational amplifier OPA2830 to form a filter shaping circuit (SK filter circuit), thereby reducing the interference of the low-frequency signal and converting it into a Gaussian pulse signal for subsequent signal processing; utilizes the dual-diode baseline restorer BAT54A to form a baseline recovery circuit, which has a fast discharge speed, thereby maintaining a stable baseline and further reducing the influence of pulse accumulation.

[0026] The utility model utilizes a detector, a voltage follower circuit, a pole-zero phase cancellation circuit, an in-phase proportional amplification circuit, a filter shaping circuit, a baseline recovery circuit, a differential circuit, a threshold comparison circuit and an AD conversion circuit to form a nuclide identification instrument with low power consumption and small size, and can be applied to various workplaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flowchart of the work flow of the utility model.

[0028] Figure 2 It is the circuit diagram of voltage follower circuit and pole-zero cancellation circuit.

[0029] Figure 3 This is a comparison chart of the pulse signal before and after entering the voltage follower circuit.

[0030] Figure 4 It is the overshoot of the pulse signal.

[0031] Figure 5 This is a comparison diagram of the pulse signal before and after entering the pole-zero cancellation circuit.

[0032] Figure 6 It is the circuit diagram of the in-phase proportional amplifier circuit.

[0033] Figure 7This is a comparison chart of the pulse signal before and after entering the in-phase proportional amplifier circuit.

[0034] Figure 8 It is the circuit diagram of the filter shaping circuit.

[0035] Fig. 9 This is a comparison chart of the pulse signal before and after entering the filter shaping circuit.

[0036] Fig.10 is the circuit diagram of the baseline restoration circuit.

[0037] Fig.11 It is the circuit diagram of a differential circuit.

[0038] Fig.12 This is a comparison chart of the pulse signal before and after entering the differential circuit.

[0039] Fig.13 is a circuit diagram of a threshold comparison circuit.

[0040] Fig.14 This is a comparison chart of the pulse signal before and after entering the threshold comparison circuit.

[0041] Fig.15 This is the circuit connection diagram of the MCU. DETAILED DESCRIPTION

[0042] The utility model is further described below.

[0043] like Figure 1 As shown, the nuclide identification instrument includes a detector and a gamma energy spectrum acquisition circuit.

[0044] The detector includes a sodium iodide crystal and a photomultiplier tube (PMT). After entering the sodium iodide crystal, the gamma rays interact with it and emit scintillation photons, which are multiplied by the photomultiplier tube to form an electron flow, thereby generating a pulse signal. The pulse signal enters the gamma spectrum acquisition circuit.

[0045] The gamma spectrum acquisition circuit comprises: a voltage following circuit respectively connected to the detector and the pole-zero cancellation circuit, a pole-zero cancellation circuit respectively connected to the voltage following circuit and the in-phase proportional amplifier circuit, an in-phase proportional amplifier circuit respectively connected to the pole-zero cancellation circuit and the filter shaping circuit, a filter shaping circuit respectively connected to the in-phase proportional amplifier circuit, the baseline recovery circuit and the differential circuit, a baseline recovery circuit respectively connected to the filter shaping circuit and the MCU, a differential circuit respectively connected to the filter shaping circuit and the threshold comparison circuit, a threshold comparison circuit connected to the MCU, the differential circuit and the MCU, and an MCU respectively connected to the baseline recovery circuit and the threshold comparison circuit.

[0046] The pulse signal is first processed in sequence by a voltage follower circuit, a pole-zero phase cancellation circuit, an in-phase proportional amplifier circuit, and a filter shaping circuit to form a quasi-Gaussian waveform pulse signal. The quasi-Gaussian waveform pulse signal is then divided into two paths. One path passes through a baseline recovery circuit and enters an AD conversion circuit to wait for conversion; the other path passes through a differential circuit and a threshold comparison circuit, is converted into a square wave, and enters the AD conversion circuit as a control signal. Finally, the MCU performs statistical analysis on the digital signal output by the AD conversion circuit and stores it.

[0047] like Figure 2 As shown, the structure of the voltage follower circuit is that two inputs are connected to the positive input terminal pin 3 of the operational amplifier U3A, one of which is connected to the input signal of the voltage follower circuit through resistor R2, and the other is connected to the 2.5V power supply through resistor R4; the reverse input terminal pin 2 of the operational amplifier U3A is connected to the output terminal pin 1 of the operational amplifier U3A; the 5V power supply is grounded through resistor R8 and capacitor C28, and capacitor C29 is connected in parallel at both ends of capacitor C28. Resistor R8, capacitor C28 and capacitor C29 form a filtering decoupling circuit, and the positive power input terminal pin 8 of the operational amplifier U3A is connected to the node between capacitor C28 and resistor R8 in the filtering decoupling circuit and then connected to the 5V power supply; the negative power input terminal pin 4 of the operational amplifier U3A is grounded; capacitor C28 and capacitor C29 are both grounded.

[0048] The output voltage of the voltage follower circuit is the same as the input voltage, that is, the voltage amplification factor of the voltage follower circuit is equal to 1. In the circuit, the voltage follower circuit is generally used as a buffer stage and an isolation stage, because the output impedance of the voltage amplifier is generally relatively high, usually in the thousands of ohms to tens of thousands of ohms. If the input impedance of the latter stage is relatively small, then a considerable part of the signal will be lost in the output resistance of the former stage. At this time, the voltage follower circuit acts as a buffer and plays a connecting role. Another effect of applying the voltage follower circuit is to increase the input impedance, so that the capacity of the input capacitor can be greatly reduced.

[0049] like Figure 3 As shown, the voltage follower circuit uses the OPA2830 operational amplifier. The signal is input from pin 3 of the operational amplifier U3A and output from pin 1. 137 The pulse signal output amplitude of the Cs source is 400mV, the pulse width is 5μs, the pulse signal amplitude does not change, and the pulse signal is stable. Signal 1 is the signal before entering the voltage follower circuit, and signal 2 is the signal after entering the voltage follower circuit. The amplitude of signal 1 and signal 2 is 200mV per square, so the amplitude of signal 1 and signal 2 is 400mV, and the pulse width of signal 1 and signal 2 is 1μs per square, so the pulse width of signal 1 and signal 2 is 5μs.

[0050] The signal output by the voltage follower circuit enters the pole-zero cancellation circuit. The structure of the pole-zero cancellation circuit is that the two ends of the variable resistor VR1 are connected in parallel with a voltage divider circuit composed of resistors R19 and R35. One end of the parallel connection is connected to the output end of the operational amplifier U3A. The output end of the operational amplifier U3A is connected to the output end OUT of the pole-zero cancellation circuit through capacitor C24. The other end of the parallel connection is grounded through capacitor C21 on the one hand, and connected to a 2.5V power supply on the other hand. Capacitor C21 is a power supply filter decoupling capacitor. The middle pin of the variable resistor VR1 is respectively connected to the resistor R1 and the voltage divider node of the voltage divider circuit composed of resistors R19 and R35. The middle pin of the variable resistor VR1 is connected to the output end OUT of the pole-zero cancellation circuit after passing through resistor R1 on the one hand, and is connected to the 2.5V power supply through resistor R23 on the other hand.

[0051] like Figure 4 and Figure 5 As shown in the figure, in the process of pole-zero cancellation, the pulse width is also reduced, reducing the pulse width from 5μs to 0.5μs, improving the counting rate response of the circuit and reducing the pulse superposition effect. Let R19 = 3.3kΩ, R35 = 6.8kΩ, R1 = 1kΩ, R23 = 470Ω, C24 = 270pF, adjust the potentiometer VR1, and the pulse signal will be reduced after the pole-zero cancellation. 137 The pulse signal output amplitude of the Cs source is 150mV and the pulse width is 0.5μs, which achieves the effect of reducing the pulse width and eliminating the overshoot at the tail of the pulse signal. Figure 4 The signal amplitude is 100mV per square and the pulse width is 0.5μs per square. Figure 4 The amplitude of the signal is 300mV, the pulse width is 2μs, Figure 4 A sharp pulse appears at the tail of the signal, that is, tail overshoot, which is not conducive to signal processing. Figure 5 Signal 1 is the signal before entering the pole-zero cancellation circuit, and signal 2 is the signal after entering the pole-zero cancellation circuit. One square of the amplitude of signal 1 is 200mV, so the amplitude of signal 1 is 400mV, and one square of the amplitude of signal 2 is 50mV, so the amplitude of signal 2 is 150mV; one square of the pulse width of signal 1 and signal 2 is 1μs, so the pulse width of signal 1 is 3μs, and the pulse width of signal 2 is 0.5μs.

[0052] like Figure 6As shown, the structure of the in-phase proportional amplifier circuit is that two inputs are connected to the positive input terminal pin 5 of the operational amplifier U3B, one of which is connected to the 2.5V power supply through the resistor R5, and the other is connected to the input signal of the in-phase proportional amplifier circuit; the reverse input terminal pin 6 of the operational amplifier U3B is connected to three inputs, one of which is connected to the output terminal of the operational amplifier U3B through the resistor R25, two of which are connected to the output terminal of the operational amplifier U3B through the capacitor C10, the output terminal pin 7 of the operational amplifier U3B is connected to the output terminal OUT of the in-phase proportional amplifier circuit, and three of which are connected to the 2.5V power supply through the resistor R6; one end of the capacitor C7 is connected to the 2.5V power supply, and the other end is grounded. The capacitor C7 is a filter decoupling capacitor of the 2.5V power supply.

[0053] like Figure 7 As shown in the figure, the amplitude of the pulse signal will be reduced after passing through the pole-zero cancellation circuit. The operational amplifier U3B is used to amplify the signal amplitude, and the resistance is adjusted to make R5=300Ω, R6=15kΩ, and R25=51kΩ. 137 The pulse signal amplitude of the Cs source is amplified from 150mV to 500mV, and the pulse width is 0.5μs. Figure 7 Signal 1 is the signal before entering the common-phase proportional amplifier circuit, and signal 2 is the signal after entering the common-phase proportional amplifier circuit. One square of the amplitude of signal 1 is 50mV, so the amplitude of signal 1 is 150mV, one square of the amplitude of signal 2 is 200mV, so the amplitude of signal 2 is 500mV, and one square of the pulse width of signal 1 and signal 2 is 0.5μs, so the pulse width of signal 1 is 0.5μs, and the pulse width of signal 2 is 0.5μs.

[0054] After magnification 137 The pulse signal amplitude of the Cs source is 500mV, and the energy of its gamma photon is 662keV. It can be calculated that the pulse amplitude corresponding to the gamma photon with an energy of 3MeV is 2.25V, which is less than the full amplitude of 2.5V, reducing the amplitude saturation of the operational amplifier and reducing interference.

[0055] like Figure 8As shown, the filter shaping circuit (SK filter circuit) shapes the pulse signal. The structure of the filter shaping circuit is that the positive input terminal pin 3 of the operational amplifier U4A is connected to three inputs, one of which is connected to the input signal of the filter shaping circuit through resistor R28 and resistor R29, and two of which are connected to the output terminal pin 1 of the operational amplifier U4A through resistor R9 and capacitor C37. The output terminal of the operational amplifier U4A is connected to the output terminal OUT of the filter shaping circuit, and three of which are grounded through capacitor C31; the reverse input terminal pin 2 of the operational amplifier U4A is connected to three inputs, one of which is connected to the output terminal of the operational amplifier U4A through capacitor C34, two of which are connected to the output terminal of the operational amplifier U4A through resistor R31, and three of which are connected to a 2.5V power supply through resistor R30; the positive power input terminal pin 8 of the operational amplifier U4A is connected to a 5V power supply, and resistors R30, R31 and C34 control the gain of the filter shaping circuit, and the negative power input terminal pin 4 of the operational amplifier U4A is grounded. Capacitor C30 and capacitor C9 are connected in parallel to form a filtering decoupling circuit of the 5V power supply, one end of the parallel connection is connected to the 5V power supply, and the other end is grounded.

[0056] like Fig. 9 As shown, the filter shaping circuit shapes the useful pulse signal and converts the input signal into a Gaussian pulse signal output. The amplitude of the pulse signal after passing through the SK filter circuit remains unchanged, still 500mV, and the pulse width is 0.5μs. Fig. 9 Signal 1 is the signal before entering the filter shaping circuit, and signal 2 is the signal after entering the filter shaping circuit. The amplitude of signal 1 and signal 2 is 200mV per square, so the amplitude of signal 1 and signal 2 is 500mV per square. The pulse width of signal 1 and signal 2 is 0.5μs per square, so the pulse width of signal 1 and signal 2 is 0.5μs per square.

[0057] like Fig.10 As shown, the structure of the baseline recovery circuit is that pin 2 of the dual diode D1 is connected to the input signal of the baseline recovery circuit through capacitor C16 on the one hand, is grounded through resistor R14 on the other hand, and is connected to the output end of the baseline recovery circuit on the other hand; pin 1 of the dual diode D1 is connected to three inputs, one is connected to a 2.5V power supply through resistor R13, two is grounded through resistor R32, and three is grounded through a power supply filter decoupling circuit; the structure of the power supply filter decoupling circuit is that both ends of capacitor C38 are connected in parallel with capacitor C39; pin 3 of the dual diode D1 is connected to a 3.3V power supply through resistor R17.

[0058] A high count rate will cause the baseline of the pulse signal to be unstable and offset, resulting in inaccurate measurement results. Since the capacitor fails to completely discharge its charge during the discharge time, when the next pulse signal arrives, the remaining charge on the capacitor will cause the baseline of the new pulse signal to offset, resulting in inaccurate measurement results. Use the baseline recovery circuit to keep the baseline stable, adjust the resistance values ​​of resistors R17, R13, R14, and R32, and make the voltage of pin 1 of the dual diode D1 equal to the voltage of pin 2. The baseline recovery circuit speeds up the discharge speed of capacitor C16, reduces the possibility of baseline offset, and keeps the baseline stable.

[0059] like Fig.11 As shown, the structure of the differential circuit is that the inverting input pin 6 of the operational amplifier U4B is connected to two inputs, one is connected to the input signal of the differential circuit through the capacitor C32, and the other is connected to the output of the operational amplifier U4B through the resistor R10, and the output pin 7 of the operational amplifier U4B is connected to the output terminal Out of the differential circuit.

[0060] like Fig.12 As shown, the output voltage of the differential circuit is proportional to the rate of change of the input voltage. When the input voltage reaches the minimum value, its rate of change is 0, that is, the output voltage is 0. Fig.12 Signal 1 is the signal before entering the differential circuit, and signal 2 is the signal after entering the differential circuit, which is convenient for the threshold comparison circuit to process the pulse signal. The amplitude of signal 1 and signal 2 is 200mV per square, so the amplitude of signal 1 is 400mV, the peak-to-peak value of signal 2 is 600mV, the maximum value is 400mV, and the minimum value is -200mV. The pulse width of signal 1 and signal 2 is 0.25μs per square, so the pulse width of signal 1 is 0.5μs, and the pulse width of signal 2 is 0.5μs.

[0061] The models of operational amplifier U3A, operational amplifier U3B, operational amplifier U4A, and operational amplifier U4B are all OPA2830. The utility model uses the high-speed operational amplifier OPA2830 with a voltage conversion speed of 500V / μs to perform analog signal processing, which meets the requirements of low noise, high linearity, and low drift, and has the basic characteristics of single 5V power supply and rail-to-rail operation.

[0062] like Fig.13As shown, the structure of the threshold comparison circuit is that the comparator pin structure is the same as that of the operational amplifier. The comparator U6A includes a positive input pin, a negative input pin, and an output pin. The positive input pin 6 of the comparator U6A is connected to three inputs, one of which is connected to a 2.5V power supply through a resistor R20, and the value of the resistor R20 is 130, the second is connected to the power supply through a resistor R16, and the third is connected to the output pin 2 of the comparator U6A through a resistor R21, and the value of the resistor R21 is 22K; the negative input pin 5 of the comparator U6A is connected to the input signal of the threshold comparison circuit, the positive power pin 3 of the comparator U6A is connected to the digital power supply (VDD), and VDD is the power supply of U6A. The negative power pin 14 of the comparator U6A and the analog negative pin 13 are both grounded, and the output pin of the comparator U6A is connected to the output end of the threshold comparison circuit, one end of the capacitor C40 is connected to the power supply, and the other end is grounded. The capacitor C40 is a filtering decoupling capacitor.

[0063] The threshold comparison circuit uses any input pin as a reference to fix the voltage, amplifies the voltage difference between the reference voltage and the other input pin, and outputs a High or Low level. The comparator can convert analog signals into digital signals. When the voltage of the positive input pin is greater than the voltage of the negative input pin, the output is a High level; when the voltage of the positive input pin is less than the voltage of the negative input pin, the output is a Low level.

[0064] The comparator U6A is of CMP401 type with short delay time. First, set a starting threshold for the comparator to filter out interference signals; when the differential signal amplitude is higher than the starting threshold, the comparator generates a falling edge, and when the differential signal is lower than the starting threshold, the comparator generates a rising edge.

[0065] Comparator U6A and resistors R16, R20 and R21 form a threshold comparison circuit. By adjusting resistors R16 and R20, the voltage at pin 6 of the comparator is adjusted to 2.53V. The Signal baseline voltage is set to 2.5V using a regulated power supply. Therefore, the input voltage difference of comparator U6A is 0.03V, reducing the interference of noise signals. R21 adjusts the hysteresis voltage of comparator U6A to return it to 2.5V, that is, when the differential signal is lower than 2.5V, the comparator generates a rising edge. VDD is the power supply for U6. Fig.14 As shown, signal 1 is the signal before entering the threshold comparison circuit, and signal 2 is the signal after entering the threshold comparison circuit. When the rising edge of the blue signal arrives, the AD conversion is started. The amplitude of signal 1 is 500mV per square, and the amplitude of signal 2 is 1V per square. Therefore, the peak-to-peak value of signal 1 is 1.7V, the maximum value is 1.2V, and the minimum value is -0.5V. The amplitude of signal 2 is 3.3V. The pulse width of signal 1 and signal 2 is 0.25μs per square. Therefore, the pulse width of signal 1 is 0.5μs, and the pulse width of signal 2 is 0.25μs.

[0066] like Fig.15 As shown, the output end of the baseline recovery circuit is connected to the AIN0 pin of the MCU, and the output end of the threshold comparison circuit is connected to CNVSTR0 of the MCU.

[0067] In the present invention, since the signals of different circuits captured by the oscilloscope are not necessarily the same signal, the width and amplitude of the pulse signals corresponding to different circuits are slightly different. For example, Figure 3 and Figure 5 .

[0068] When the signal output by the threshold comparison is input to the CNVSTR0 pin, the MCU starts ADC0 when receiving the rising edge trigger signal at CNVSTR0, and performs AD conversion on the input level input to the AIN0 pin, that is, converting the analog pulse signal into a digital signal. The rising edge of the square wave controls the timing of the AD conversion, and can accurately convert the peak value of the pulse signal into a digital signal. After the ADC0 conversion is completed, an ADC0 interrupt is generated, and the conversion result is read and saved in the interrupt.

[0069] MCU divides the pulse amplitude into two n An amplitude interval, every time a pulse signal arrives, the amplitude value of the pulse signal will correspond to an amplitude interval. Accordingly, just set a data buffer in the memory to correspond to the result of AD conversion, and then every time a pulse signal arrives, just add 1 to the corresponding data buffer array. After measuring for a period of time (i.e., the preset time period), the count of each address in the data buffer reflects the distribution of the pulse amplitude, which is the gamma spectrum data. The MCU saves the gamma spectrum data in the Flash memory.

[0070] The MCU sends the gamma spectrum data to the PDA terminal via the Bluetooth protocol.

[0071] The gamma spectrum acquisition circuit of the utility model can output 4096 channels of spectrum data, with energy linearity better than 0.5% and analog-to-digital conversion time of 0.9 μs; it has low power consumption and small size, and can be conveniently applied to various workplaces.

Claims

1. A nuclide identification instrument, characterized in that: It includes a detector and a gamma spectrum acquisition circuit; The gamma spectrum acquisition circuit comprises: The voltage follower circuit is connected to the detector and the pole-zero cancellation circuit respectively, and is used to increase the input impedance of the signal and output a stable pulse signal; The pole-zero phase cancellation circuit is connected to the voltage follower circuit and the in-phase proportional amplifier circuit respectively, and is used to reduce the width of the pulse signal output by the voltage follower circuit and eliminate the tail overshoot of the pulse signal, and output a pulse signal with a reduced pulse width; The in-phase proportional amplifier circuit is connected to the pole-zero cancellation circuit and the filter shaping circuit respectively, and is used to amplify the amplitude of the pulse signal output by the pole-zero cancellation circuit and output the amplified pulse signal; The filter shaping circuit is connected to the in-phase proportional amplifier circuit, the baseline recovery circuit and the differential circuit respectively, and is used to shape the pulse signal output by the in-phase proportional amplifier circuit and output a Gaussian pulse signal; The baseline recovery circuit is connected to the filter shaping circuit and the MCU respectively, and is used to keep the baseline of the pulse signal output by the filter shaping circuit stable and output a stable pulse signal; A differential circuit is connected to the filter shaping circuit and the threshold comparison circuit respectively, and is used to differentiate the pulse signal output by the filter shaping circuit and output the differentiated pulse signal; A threshold comparison circuit is connected to the differential circuit and the MCU respectively, and is used to compare the signal output by the differential circuit and output a signal to start AD conversion; and The MCU is connected to the baseline recovery circuit and the threshold comparison circuit respectively, and is used to perform AD conversion on the pulse signal output by the baseline recovery circuit, and store the conversion result within a preset time period to obtain gamma energy spectrum data.

2. The nuclide identification device according to claim 1, characterized in that: The structure of the voltage follower circuit is that two inputs are connected to the positive input terminal of the operational amplifier U3A, one is connected to the input signal of the voltage follower circuit through resistor R2, and the other is connected to a 2.5V power supply through resistor R4, the reverse input terminal of the operational amplifier U3A is connected to the output terminal of the operational amplifier U3A, the positive power input terminal of the operational amplifier U3A is connected to a 5V power supply through resistor R8; the negative power input terminal of the operational amplifier U3A is grounded.

3. The nuclide identification device according to claim 2, characterized in that: The structure of the pole-zero cancellation circuit is that two ends of the variable resistor VR1 are connected in parallel with a voltage divider circuit composed of a resistor R19 and a resistor R35, one end of the parallel connection is connected to the output end of the operational amplifier U3A, the output end of the operational amplifier U3A is connected to the output end of the pole-zero cancellation circuit through a capacitor C24, and the other end of the parallel connection is grounded through a capacitor C21 on the one hand, and connected to a 2.5V power supply on the other hand; the middle pin of the variable resistor VR1 is respectively connected to the resistor R1 and the voltage divider node of the voltage divider circuit composed of the resistor R19 and the resistor R35, and the middle pin of the variable resistor VR1 is connected to the output end of the pole-zero cancellation circuit on the one hand after passing through the resistor R1, and is connected to the 2.5V power supply on the other hand through the resistor R23.

4. The nuclide identification device according to claim 1, characterized in that: The structure of the in-phase proportional amplifier circuit is that the positive input terminal of the operational amplifier U3B is connected to two inputs, one of which is connected to the 2.5V power supply through the resistor R5, and the other is connected to the input signal of the in-phase proportional amplifier circuit; the reverse input terminal of the operational amplifier U3B is connected to three inputs, one of which is connected to the output terminal of the operational amplifier U3B through the resistor R25, two of which are connected to the output terminal of the operational amplifier U3B through the capacitor C10, the output terminal of the operational amplifier U3B is connected to the output terminal of the in-phase proportional amplifier circuit, and the third is connected to the 2.5V power supply through the resistor R6.

5. The nuclide identification device according to claim 1, characterized in that: The structure of the filtering shaping circuit is that the positive input terminal of the operational amplifier U4A is connected to three inputs, one of which is connected to the input signal of the filtering shaping circuit through resistor R28 and resistor R9, two of which are connected to the output terminal of the operational amplifier U4A through resistor R9 and capacitor C37, the output terminal of the operational amplifier U4A is connected to the output terminal of the filtering shaping circuit, and three of which are grounded through capacitor C31; the reverse input terminal of the operational amplifier U4A is connected to three inputs, one of which is connected to the output terminal of the operational amplifier U4A through capacitor C34, two of which are connected to the output terminal of the operational amplifier U4A through resistor R31, and three of which are connected to a 2.5V power supply through resistor R30; the positive power input terminal of the operational amplifier U4A is connected to a 5V power supply, and the negative power input terminal of the operational amplifier U4A is grounded.

6. The nuclide identification device according to claim 1, characterized in that: The structure of the baseline recovery circuit is that pin No. 2 of the dual diode D1 is connected to the input signal of the baseline recovery circuit through capacitor C16 on the one hand, is grounded through resistor R14 on the other hand, and is connected to the output end of the baseline recovery circuit on the other hand; pin No. 1 of the dual diode D1 is connected to three inputs, one is connected to a 2.5V power supply through resistor R13, two is grounded through resistor R32, and three is grounded through a power supply filter decoupling circuit, and both ends of capacitor C38 in the power supply filter decoupling circuit are connected in parallel with capacitor C39; pin No. 3 of the dual diode D1 is connected to a 3.3V power supply through resistor R17.

7. The nuclide identification device according to claim 1, characterized in that: The structure of the differential circuit is that the inverting input terminal of the operational amplifier U4B is connected to two inputs, one is connected to the input signal of the differential circuit through the capacitor C32, and the other is connected to the output terminal of the operational amplifier U4B through the resistor R10, and the output terminal of the operational amplifier U4B is connected to the output terminal of the differential circuit.

8. The nuclide identification device according to claim 1, characterized in that: The structure of the threshold comparison circuit is that the positive input pin of the comparator U6A is connected to three inputs, one is connected to a 2.5V power supply through a resistor R20, two is connected to a power supply through a resistor R16, and a third is connected to an output pin of the comparator U6A through a resistor R21; the negative input pin of the comparator U6A is connected to an input signal of the threshold comparison circuit, the positive power supply pin of the comparator U6A is connected to a digital power supply, and the negative power supply pin and the analog negative pin of the comparator U6A are both grounded.

9. The nuclide identification device according to claim 1, characterized in that: The output end of the baseline recovery circuit is connected to the AIN0 pin of the MCU, and the output end of the threshold comparison circuit is connected to the CNVSTR0 of the MCU; when the signal output by the threshold comparison circuit is input to the CNVSTR0 pin, the MCU starts ADC0 when CNVSTR0 receives a rising edge trigger signal, and performs AD conversion on the input level input to the AIN0 pin. After the ADC0 conversion is completed, an ADC0 interrupt is generated, and the conversion result is read and saved in the interrupt.

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