Research On A Weak Signal Counting System For A Gas-flow Proportional Counter Tube

Flow proportional counter is a proportional counter that its working gas flows at a certain speed. This makes all the composition gas can be stay. the gas in a sealed proportional counter during gas multiplication is substantial decomposition,and it influence the counter performance and life. In addition, radioactive gas can be filled directly into the tube, so that it can increase the solid angle to improve the detection efficiency of proportional counter tube,and avoid to be absorbed by tube window.Due to the characteristics,flow proportional counter are often used to measure radioactive gas.Although gas proportional counter can multiplication, but its magnification is limited,so the signal is still weak signal.Because of the interference of environment and noise,the detected signal is very faint and the detection is very difficult.This paper will study the faint signal from the proportional counter,and to develop the related measurement system.The main work and achievements of this paper are as follows.First, according to the analysis of proportional counter structure and working principle,select the appropriate proportional counter to study the gas amplification and signal. For weak signal, analyze different factors influence weak signal measurement,and give suitable measurement program.Second, design the charge preamplifier and amplifier. Analyse the preamplifier circuit and the design key points.Through the simulation and experimental test, the charge conversion gain greater than magnitude to feedback capacitance choice at the same time a large number of repeated experiments, the smaller the feedback capacitance, gain cannot reach and reciprocal relations, because of the influence of other inevitable capacitance.The main amplifier is the use of precision instrument amplifier to achieve low power consumption1-10000 times magnification,to lead the output signal can be amplified.Third, design high-voltage power. High-voltage module is adjusted by microprocessor controlled digital-analog conversion of the output signal size to achieve continuous and stable0-2500 V adjustable, step 10 V, display settings voltage at the same time.Design theproportional counter master control module, using SCM to adjust the upper and lower thresholds, sampling time, real-time data display.and communicate with the host computer to transmit data and execute commands sent by the host computer.It also realized serial port communicating program. It can send the data to computer in time or receive the controlling command sent by the computer.Labview developing platform is used to develop system software in which data could be observed and further processing.In addition the PC can send commands to the lower position to receive orders to the lower computer.Fourth,test the counting system of gas proportional counter.On one hand,analyze the feasibility of the design.On the other hand,we measure activity of¹⁴CO₂ and analyze the of measurement influencing factors.In summary, this paper aim to design hardware and software development on the basis of weak signal measurement of a flow proportional counter. Such that the selected gas-flow proportional counter can reasonably measure radioactive and activity of ¹⁴CO₂.