# 
# material model file
#
#   format :
#   MediumType[string] number_of_materials[int]
#   material_pdg[int] weight[double]
#   .....
#
#    - no space before first column
#    - delimiter must be whitespaces
#    - MediumType must be consistent with the detector model files
#    - number_of_materials is the number of atm type in the medium
#    - weight must be normalized to 1 within a MediumType
#    - lines start from '#' or whitespace are treated
#      as comments
#
