Research On The Method Of Pointing Probability Under The Condition Of Reflection Boundary

The neutron point flux is often required in the neutron physics researches,such as the problems of radiation shield and detector response simulations.Several methods have been proposed to calculate the point flux,while the next event estimation method is most widely applied in Monte Carlo simulation code such as MCNP and Geant.Besides,this method is also adopted to calculate the Flux Image by Pinhole(FIP).However,when reflecting,white,or periodic surfaces exist,the point flux calculated by the next event estimation method gives wrong answers because pseudoparticles travel only in straight lines.Therefore,the point detector tally will be lower than the correct answer and should not be used with reflecting,white,or periodic surfaces.The effect is even worse for problems with multiple reflecting,white,or periodic surfaces,which are often used in engineering applications.Fouces on the problem that the traditional next event estimation method conflict with reflecting surfaces,this paper describes a modified next event estimation method which could be used with reflecting surfaces.The new method has been implemented in the Monte Carlo transport code NPTS(Neutron Photon Transport System).Several numerical cases are adopted to verify this method.Numerical results show that the modified next event estimation method works well with reflecting surfaces.The point flux and the FIP calculated by the modified method is independent of reflecting surfaces.According to the researches,the modified next event estimation method works well with reflecting surfaces.The point flux and the FIP simulations with reflecting surfaces has important engineering application value,such as applications on off site monitoring and radiation shielding of nuclear power station.