| At present, the detection of dark matter and the study of its properties are one of the hot topics in the astronomy and the particle physics.The indirect evidence of dark matter indicates that dark matter is a kind of unknown matter that has the gravitation interaction but no electromagnetic or strong interactions with other common particles, which is completely different from the known atomic and molecular in the physical world. There is likely to be weak interaction between dark matter and ordinary matter besides gravitation interaction, so dark matter is usually called as "Weakly Interacting Massive Particles (WIMPs) ". The best way to detect dark matter directly is to observe the nuclear recoil which is caused by the weak interaction between the WIMPs and the common atomic nucleus. We know the mean velocity and the approximate mass of dark matter and the kinetic energy of the nuclear recoil is from several eV to millions eV, which should be observed. There is very little probability of collisions between dark matter and the common nucleus in the process of dark matter through the earth. The signal is extremely exiguous and weak so that the detection must have high sensitive detectors and super low background. Therefore, it needs to shield a lot of neutrons, the cosmic background radiation and the radiation comes from the detector materials and the shielding materials.The main task of this paper is that for the neutron with strong penetrability, we use the Monte Carlo method to simulate the neutron detector that is made of 3He+ high-density polyethylene material and calculate which shape and thickness of the shields should be chosen to achieve the best detection efficiency in the neutron energy range of the background radiation. The result shows that use the high density polyethylene as slowing material and create a cylinder round the proportional counting tube that is placed in the focal plane have an ideal detection efficiency for both the fast and slow neutrons. |
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