| Previous Topic | Next Topic | Contents | Features |
Sabrina uses a separate parser for MCNP input; the rules for general Sabrina input are not in effect. Comments in an MCNP input deck starting with a c (or C) in column 1 are accepted in Sabrina as valid comments. The use of $ as the inline comment character is recognized; it is not interpreted by Sabrina as a sentinel for a user symbol. Upper and lower case is accepted in the MCNP input. MCNP vertical input format cannot be read. Some later MCNP input features, such as new continuation syntax, are not yet recognized.
MCNP4A allows no more than 100 elements in a cell description
(elements include surfaces and operators). Sabrina allows more,
but issues a warning if it encounters cells that exceed the
MCNP4A limit. The warning lists the
command---DEBUG DWARN---that
will cause Sabrina to list each offending cell.
Even though Sabrina and later MCNP versions allow lengthy cell descriptions, their use is not a good idea. The complexity slows down tracking in MCNP and in Sabrina ray tracing significantly.
When geometry testing, cell descriptions exceeding 999 elements are not allowed.
Sabrina understands the MCNP repeated structure keywords, including TR (coordinate transformation), TRCL (cell transformation), the LIKE-BUT construct, U (universe), LAT (lattice), and FILL. The transformations and LIKE-BUT conditions are expanded as Sabrina encounters them; the expanded geometry is shown in the Sabrina LIST output, and is written when a geometry dump is requested. Geometry testing will indicate spurious errors when a lattice element is filled with itself (or nothing) and other such odd geometries. Sabrina will refuse to deal with a "real world lattice'' which is not contained within a cell. Properties, such as color and transparency, can not be set by lattice element, only by the cells or materials contained within the elements. Keywords on cell cards that make no sense for Sabrina, such as VOL and IMP, are ignored.
Sabrina recognizes reflecting surfaces, and treats them as such when ray tracing-the ray is reflected from the surface at the correct angle. Unfortunately, most models containing reflecting surfaces use them to surround the actual geometry. The usual Sabrina viewpoint is from the outside. Rays towards the model reflect off the surrounding surfaces and encounter the background; a rather dull picture (all background) results. For viewing with Sabrina, one or more of the reflecting surfaces must be made normal, or a cutter body used to expose the interior.