The Development Of Radon Progenies Measuring System In Radon Chamber

High concentration of radon and its progenies is one of the main factors of lung cancer, radon and its progenies do more radiation doseto human than natural environment(1m Sv)50% of the mean dose of radiation by breathing. In our country,because of the radon progenies can not been traced back to the source, there are much difficulties in surveying about the radon progeny level, in dose assessment of radon progeny, in the implementation of the radon progeny control standards.In order to solve these problems,National Institute of Metrology(NIM) has launched some projects which is named of “the measurement method research of Radon daughter activity” to do research in the radon progeny nuclide alpha spectroscopy measurement technology and establish activity measurement method of radon progeny.The main work of this study is to design and build an activity measurement system of radon progeny by alpha spectrum method which is suitable for measuring radon indoor to lay the foundation for establishing a radon progeny activity measurement method.The system mainly includes two parts of hardware and software.The hardware is mainly composed of radon progeny sampling device, signal conditioning circuit and data acquisition card. The radon progeny sampling device including: sampling pump, a membrane, semiconductor detector and preamplifier, its main function is that it uses the membrane filter method to collect radon daughter, the semiconductor detector to measure radon daughter of a membrane filter, and output a pulse signal at the same time.The signal conditioning circuit includes a pole zero cancellation circuit, a linear amplification circuit, an integral filtering circuit and a buffer circuit,the main function of which is to amplify the output signal from the probe, to remove the noise, toplastic the Gaussian signal, at the same time putting out a synchronized trigger signal with the pulse signal to thedata acquisition card. The signal conditioning circuit are integrated working voltage, high pressure module circuit.The data acquisition cardcollects the Gaussian pulse signal, it receives the trigger signal and specifies the analog signal with a designatedsampling frequency and Do the A/D conversion, then it transfer the digital signal to the PC machine.It comes true the all peak sampling of the analog signal, and the digital conversion.It uses the Lab VIEW graphical language of the NI company to programthe software.Based on the driver of the data acquisition cardwe would like to do secondary development and invoke the function module of the Lab VIEW software. We can drive the acquisition card,set parameter to the acquisition card, receive data, analysis the amplitude of the signal, scale the energy,analysis alpha spectroscopy, draw the spectroscopy line,show the measured results and so on.The system has passed through the whole performance testing, it has met the design requirements. The energy resolution reached 3.6%(at 5.4 Me V all-around peak of Am-241). It has a good linear energy,a good stability, the stability of the peak position is better than ±2% when it continuously work 8 hours. The 6 Me V and 7.69 Me V radon progeny alpha particles can be accurately measured in the radon chamber.