A New Type Of Radon Measuring Instrument Based On High-voltage Electrostatic Collecting Method

With the development of science and technology and the continuous improvement of people’s living standards,people are more and more concerned about their environment.The harmfulness of radioactive radon due to internal exposure to the human body has attracted widespread attention.In this paper,the development of a new type of radon measuring instrument based on the high-voltage electrostatic collection method has important practical value.This paper was supported by the National Key Research and Development Program"High-resolution Aviation Gamma Spectrometry and Airborne Imaging Spectrometry"（Project Number:2017YFC0602100）.Under the research and development status at home and abroad,according to the characteristics of radon in the air and the conditions of field detection,this paper developed a new type of radon measuring instrument based on electrostatic collection method.The principle of the radon meter is to set a high-voltage electric field in the collection chamber.The air pump passes the air through the drying tube and the filter membrane into the collection chamber at a certain rate.After the pumping is completed,²²²Rn decays to produce the radon progeny ²¹⁸Po.Under the action of the electrostatic field in the collection cavity,the radon progeny will be adsorbed to the surface of the detector,and the adsorbed radon progeny ²¹⁸Po will further decay to produce alpha particles,and the collected alpha particles will be counted during the collection time.Finally,the radon concentration is determined according to the number of alpha particles collected.The new type radon measuring instrument is composed of gas collector,measuring room,electronic circuit unit and measuring software.This paper uses COMSOL to optimize the collecting cavity structure design of the traditional high-voltage electrostatic collection method radon instrument,and uses the particle tracking module to optimize the simulation of its internal electric field.This paper respectively simulated the shape of the collecting cavity and the size and voltage of the internal grid and proposed an optimized solution for the cylindrical dome measurement chamber and grid structure.When the collection cavity is a cylindrical dome and the grid voltage is 1800V,the radon daughter collection efficiency is increased from 73.3%to 86.6%,compared with not adding the grid,the collection efficiency is increased by 13.3%.In terms of hardware circuit design,the STM32F4 series of microcontrollers are used as the core,including GPS positioning module,WIFI module,temperature and humidity detection module,etc.The front circuit of the detector uses a charge sensitive amplifier,which is measured before the feedback capacitance is 0.6 p F.The discharged charge sensitivity is 1.73×10¹²V/C,which is higher than the theoretical charge sensitivity of 1.67×10¹²V/C;the power supply module（including 3.3V,5V,±6V,±12V,53V,2000V）has been designed and manufactured After the voltage is stable,the digital ground and analog ground are divided,which effectively reduces the power supply ripple.The measurement software of radon measuring instrument is written in C language,which realizes the simultaneous measurement of radon concentration and its daughters ²¹⁸Po and ²¹⁴Po,real-time display of time,position,temperature and humidity and other parameter values.Finally,the performance of the instrument was tested in a standard radon chamber and compared with the test data of the RAD7 type radon meter under the same environment.The error of the measured radon concentration between the new type radon meter and the RAD7 did not exceed 10%.The test results show that the newly developed radon meter based on the high-voltage electrostatic collection method has the characteristics of high stability and low power consumption,and the measurement data is accurate and it works stable and reliable.