【摘要】 在建的北京高能同步辐射光源是一个储存环电子能量6 GeV、流强200 mA的同步辐射光源。轫致辐射吸收器是光束线站中位于第一光学棚屋内的长方体铅或钨块,用来阻挡来自直线节的气体轫致辐射。基于工程材料线站的实际布局,使用蒙特卡罗软件FLUKA模拟计算了高能同步辐射正常运行工况下气体轫致辐射在第一光学棚屋内产生的散射光子和光核反应中子的能谱和角分布。结果表明:轫致辐射吸收器可以很好的阻止气体轫致辐射的传播,但产生的光核反应中子较难被棚屋铅墙屏蔽,根据光核反应中子的分布,设计了铅和含硼聚乙烯组合屏蔽的方式,有效地降低了第一光学棚屋内外的中子剂量当量率。更多还原

【Abstract】 [Background] The high energy photon source(HEPS) currently under construction in Beijing will be the brightest synchrotron radiation facilities in the world. The high energy electrons which generate the desired synchrotron radiation interact with matter(for example, residual gas molecules in the vacuum chamber), to produce a spectrum of bremsstrahlung photons with energies up to the electron energy – in HEPS 6 GeV. The bremsstrahlung is highly penetrating, and it can produce exotic reactions in any material that it strikes, leading to the production of other radiations, especially photoneutrons. The beam stops are made of either lead or tungsten of rectangular shape in order to prevent the gas bremsstrahlung when transmitting through beamline to an experimental enclosure. [Purpose]This study aims to design a new gas bremsstrahlung absorber to reduce the dose equivalent rate by simulation calculation based on the spectrum of scattered photons and photoneutrons for HEPS beamlines. [Methods] Based on the technical specification, layout and related parameters of HEPS and the first optical enclosure(FOE), Monte Carlo simulation software FLUKA was mainly utilized to investigate the gas bremsstrahlung production in HEPS straight sections. A complete treatment of electron, positron and photon interactions at energies above 100 eV were calculated for the gas bremsstrahlung generated in the HEPS storage ring straight section and the gas bremsstrahlung transmitted through the beamline and scatters from components and the radiation emanating through the hutch wall. [Results]The results show that the beam stop is effective in shielding photons, but the photoneutrons in HEPS beamlines is inevitable. The equivalent rate of neutrons outside the shield wall is still high. The maximum energy of neutrons in photonuclear reaction reaches upto 300 MeV. Giant resonance neutrons(0.1～5 MeV) account for 91% of the total flux of photoneutrons. Using polyethylene as local shield is a very effective method. [Conclusions] The combined shielding of lead and boron containing polyethylene can effectively reduce the neutron dose equivalent rate inside and outside FOE of HEPS beamlines.更多还原