Material definitions

When and why do I need to input a MAT-PROP card?

The density which is provided by the user via the WHAT(3) of a MATERIAL card is used for transport, i.e. it is used to convert cross sections to mean free paths. Therefore, it must be the actual density in case of a gas at non-atmospheric pressure, or the average density in case of a non uniform material. However, it is not sufficient because:

• if the material is a gas, the Sternheimer-Peierls formula must be evaluated first at NTP and then corrected for actual TP. The density at NTP used in the evaluation of the formula is derived as MATERIAL-WHAT(3)/MAT-PROP-WHAT(1)
• the material density can be non-uniform (for instance a material with voids (like a sponge or a powder). Transport (mean free path) is evaluated based on the average density MATERIAL-WHAT(3), while dE/dx must be evaluated based on local density MATERIAL-WHAT(3)/MAT-PROP-WHAT(2).

When using names for region how are ranges of regions defined with ASSIGNMA?

The ranges refer to the order of appearance in the region definition section of your geometry and are not defined alphabetically.