Simulation Of Background Due To Radon Decay In Jinping Shan Underground Dark Matter Laboratory

Nowadays, Dark Matter research is one of the most challenge topics in theresearch of cosmography. Therefore, dark matter research becomes a hot subjectin the field of physics. As we all known, Dark Matter is an important componentof cosmic mass. Research of dark matter can help us understand how does ouruniverse form, and what the structure of our universe is. Among all the theoriesof dark matter particles, Weakly Interacting Massive Particle (WIMP) is one ofthe most important candidates.There are lots of underground laboratories sites worldwide searching forWIMP, such as Gran Sasso of Italy, Boulby of Britain, Soudan of America. Inorder to develop the domestic experimental research of dark matter, the first deepunderground laboratory of China (CJPL) have been built by Tsinghua Universityand the Ertan Hydropower companies at Jinping Mountain in Sichuan province.And it officially put into operating on12th, December in2010. It is the deepestunderground laboratory in the world. Tsinghua University, Sichuan University,China Institute of Atomic Energy, Taiwan Academia Sinica and NankaiUniversity formed the CDEX (China Dark matter EXperiment) Collaboration,which will carry out direct search for WIMP with Ultra-Low Energy ThresholdHigh Purity Germanium (HPGe) detector at CJPL.A complex shielding system, which consist of1m polythene,20cm lead,15cm steel support structure,20cm Boron-doped-polythene and10cmoxygen-free highly conductive copper, has been designed by collaboration tosuppressing backgrounds in the laboratory. In this thesis, Geant4Monte Carlosimulation program was used for simulating the transport process of radonbackground yield from CJPL laboratory environment. The fluxes of particlesfrom radon spontaneous decay on every layer of the shielding system arecalculated and their influences on the detector are estimated. The results provethat this shielding system can shield the radon background yield from external environment efficiently. But, the background from radon decay nearby thedetector area has not been shielded perfectly. Therefore, it is suggested thatnitrogen should be filled in to the inside of shield system to decrease the densityof radon. Our simulation results provide the valuable data for the backgroundanalysis of CDEX.