Low background alpha beta meter is the main instrument for measuring total radioactivity in environmental samples such as drinking water, soil, air, and food. It is widely used in emergency monitoring and radiation health, environmental protection, quality supervision and inspection. The four-channel low background αβ measuring instrument is composed of four independent working detection units, which can measure four samples at the same time. Compared with a single-channel measuring instrument, it is time-saving and efficient

In order to complete the measurement and analysis of radioactivity, the basic requirements of the four-channel low-background αβ meter circuit are as follows: the analog amplification circuit must have a large signal-to-noise ratio to achieve the amplification of weak signals output by the detector; it can simultaneously amplify multiple signals without Crosstalk with each other; anti-compliance and counting of multiple digital signals can be performed in real time, the counter width is not less than 16 bits; it has the function of communicating with the computer. The stability and reliability of this circuit directly affect the measurement accuracy and long-term stability of the measuring instrument. This paper uses a high-performance amplifier and comparator to design an amplification comparison matrix. Based on the programmable logic device CPLD and STM32 microcontroller, a four The circuit of the road low background αβ measuring instrument realizes high precision and reliable measurement.

Circuit design

The working principle of the four-channel low-background αβ measuring instrument circuit is: the weak analog analog signals output by the probe unit (including 4 main probes and 2 anti-compliance probes, a total of 6 signals) are amplified and screened, and then formed into digital pulses. After the anti-conformity filtering background signal is counted, the counting result is sent to the single-chip microcomputer for processing and display, etc. Finally, the measurement data is obtained through the computer, and the calculation, display, and printing of reports are completed. Its hardware composition is shown in Figure 1.It is mainly composed of 6 probe matrices (4 main probes and 2 anti-compliance probes), amplification matrix, comparator matrix, programmable logic device CPLD, MCU, RS232 interface, high voltage and high voltage control. Circuit and low voltage power supply.