The Study Of The Shield Of The Extremely Low Background Device And Radon And Its Daughter Influence In CJPL

Many international outstanding scientists show great interested in dark matter, and put forward many methods for measuring dark matter, mainly including: the indirect method and direct method of measuring dark matter.However, if take those methods to measure dark matter,which could only be possibility measured in the case of a very low background,so in order to providing good environment for measurement of dark matter,a lot of the experimental groups in the world have moved from the ground to the underground. And the main purpose of doing so among with those experimental groups is in order to avoid the interference of cosmic rays. In our country, China Jin Ping underground Laboratory already do this. This thesis mainly studies the influence of shield material and the radon concentration in laboratory hall to extremely low background device. This thesis studies the following steps:(1) This thesis studies the effect of radionuclide in lead and copper shield to extremely low background device, and I have been simulated respectively several times to confirm the influence of 238U、232Tu and 40 K to extremely low background device;(2) In this thesis, I will measure radon concentration in the experimental hall by using AlphaGuard ionization chamber instrument,for discussing the effect on radon concentration in the experimental hall to ventilation in the case of same conditions discussed. At the same time, high purity germanium detector will be used to measure gamma rays of radon and radon daughter in low background device, and we will discuss the influence of the radon concentration in experimental hall to extremely low background device;(3) According to the counting rate of radon daughter 214 Pb(351.9 keV) detected by the high purity germanium detector, and according to the long-term balance between radon and radon daughter, we can calculate the radon content in the sample. And finally, according to the results of calculation, we can discuss and conclude the influence of the radon concentration in experimental hall to extremely low background device.