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0001 # Detector material description
0002
0003 Two types of material description exist, one for a surface based material, one
0004 for a volume based material. They will be dealt with differently in the
0005 extrapolation.
0006
0007 The basic information for any material is:
0008
0009 * the radiation length X0 the nuclear interaction length L0 the atomic weight A
0010 * the atomic charge Z the density of the material
0011
0012 This information is confined together in the {class}`Acts::Material` class.
0013
0014 ```{note}
0015 In track reconstruction, only an effective material description is needed, i.e.
0016 non-physical values in regards of the atomic number, the elementary charge or
0017 even the density are allowed, as long as the effective relative radiation
0018 length and $A/Z \times \rho$ ratio can be retrieved. This enables the compactification
0019 of the material description, as the element composition record does not have to
0020 be kept.
0021 ```
0022
0023 Surface based material extends this material information by a representative
0024 thickness; the corresponding object is called {class}`Acts::MaterialSlab`. The
0025 thickness hereby can be arbitrarily chosen in order to regulate the material
0026 budget, it does not have to represent the actual thickness of a detector
0027 element. To attach it to a surface, a dedicated {class}`Acts::ISurfaceMaterial`
0028 class (or it's extensions) is used, which allows to also describe binned
0029 material.
0030
0031 Possible extensions are:
0032
0033 * {class}`Acts::HomogeneousSurfaceMaterial`, homogeneous material description on a surface
0034 * {class}`Acts::BinnedSurfaceMaterial`, an arbitrarily binned material description with a
0035 corresponding {class}`Acts::BinUtility` object
0036
0037 In addition, a dedicated extension exists to allow configuration of the material
0038 mapping process, that is in further described below.
0039
0040 * {class}`Acts::ProtoSurfaceMaterialT`, only binning description (without material) to be
0041 used in the material mapping process, which can be specified with a templated binning
0042 description.
