From fc9ee0b67fc20019e95d61705a662abc143b98d0 Mon Sep 17 00:00:00 2001 From: Paul Romano Date: Fri, 27 Jul 2012 13:07:16 -0400 Subject: [PATCH] Added description of surface crossings. --- docs/source/methods/geometry.rst | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/docs/source/methods/geometry.rst b/docs/source/methods/geometry.rst index 4f9009c995..7dabd81be3 100644 --- a/docs/source/methods/geometry.rst +++ b/docs/source/methods/geometry.rst @@ -260,6 +260,8 @@ will then be either both positive or both negative. If they are both positive, the smaller (closer) one will be the solution with a negative sign on the square root of the discriminant. +.. _find-cell: + ---------------------------- Finding a Cell Given a Point ---------------------------- @@ -331,10 +333,32 @@ are satisfied, than the point is indeed inside the cell. Handling Surface Crossings -------------------------- +A particle will cross a surface if the distance to the nearest surface is closer +than the distance sampled to the next collision. A number of things happen when +a particle hits a surface. First, we need to check if a non-transmissive +boundary condition has been applied to the surface. If a vacuum boundary +condition has been applied, the particle is killed and any surface current +tallies are scored to as needed. If a reflective boundary condition has been +applied to the surface, surface current tallies are scored to and then the +particle's direction is changed according to the procedure in :ref:`reflection`. + +Next, we need to determine what cell is beyond the surface in the direction of +travel of the particle so that we can evaluate cross sections based on its +material properties. At initialization, a list of neighboring cells is created +for each surface in the problem as described in :ref:`neighbor-lists`. The +algorithm outlined in :ref:`find-cell` is used to find a cell containing the +particle except rather than searching all cells in the base universe, only the +list of neighboring cells is searched. If this search is unsuccessful, then a +search is done over every cell in the base universe. + +.. _neighbor-lists: + ----------------------- Building Neighbor Lists ----------------------- +.. _reflection: + ------------------- Reflective Surfaces -------------------