（n,2n）反应实验研究中的中子准直器设计

用3He球形4中子探测器,通过直接反应法可以对核素的（n,2n）反应截面进行测量。在此类实验中,要求对中子束进行很好的准直。好的准直器设计要求能够提高样品处的中子注量率的均匀性,同时保证中子束流边缘处的下降幅度,能够降低低能中子所占份额。本工作采用FLUKA和MCNPX对圆柱形准直器、单锥形准直器及三种不同斜率的双锥形准直器对中子注量率的均匀性和低能中子所占份额进行了对比研究,结果表明,低斜率的双锥形准直器可以满足实验对这两方面的要求。同时,在有样品和无样品两种条件下,对探测系统经由这五种不同准直器准直后的中子束流的响应做了对比,结果显示,经过低斜率的双锥形准直器准直的中子束流,探测系统在有样品时表现为较高的计数率,在无样品时表现为较低的本底。除此之外,对准直器出口处的斜率对准直效果的影响也做了比较。最终中子准直器选用为这种低斜率的双锥形准直器,材料选用为紫铜、不锈钢、聚乙烯和铅。准直孔开口处直径为2.64 cm,长度为137 cm,经准直后样品处的中子束斑直径为3.2 cm。     

应用蒙特卡罗方法对比研究ADS颗粒靶和块状靶（英文）

应用蒙特卡罗软件FLUKA对比研究了颗粒靶和块状实体靶在中子、质子泄露,中子、质子流强,能量沉积,残余核活度及Gamma射线剂量率的差异。最终结果显示在靶的轴对称方向,相较块状靶,颗粒靶中的中子流强和能量沉积更加均匀,且侧壁泄露中子更多而反冲中子较少。除此之外,在散裂产物放射性方面,尽管有部分核素两种靶具有相似的活度,但是颗粒靶总的放射性活度要比块状靶低。因此以上特性使得颗粒靶相较块状实体靶更适合用于ADS的靶。Using the Fluka Monte Carlo code,the comparison study between granular target and monolith target in neutron and proton leakages,neutron and proton fluxes,energy deposition density and residual radioactivity as well as gamma dose rates were presented.Results shows that the neutron flux and energy deposition in tungsten spheres target are more homogeneous along the axial direction than monolith target.What's more,the granular target has a more lateral neutron yield and a relatively small amount of neutrons in the backward direction.In addition,the total radioactivity is found to be comparatively lower in granular target,although for some nuclei,the value of their activities are similar for both targets.So the above features make the granular target more suitable as a ADS target.