Materials and media definitions

In CMS(100) we follow this procedure for material definitions:

1. Use only external definitions via TZ title banks for all materials.
2. Refer to by name (character string) and not by number.
3. Use title banks GMAT and GMIX for material and mixture definitions.

Materials are defined by the GMAT titles as shown in the example for a few materials below:

*DO  GMAT   1    -A4CW -c1/80      #.          GMAT
  #.list of pure materials
  #.           A        Z       dens         X_0          abs_l
"Vacuum"       1.E-16   1.E-16   1.E-16      1.E16       1.E16
"Hydrogen"     1.00794  1.0     0.70800E-01  865.54      717.51
"Deuterium"    2.01     1.0     0.162        756.79      337.65

The full list of pure materials used (GMAT-bank) is given in Appendix A.2.

A material with density zero can be defined but may be used only in a mixture definition.

The mixtures are more varied and are defined as

``Name of mixture''     ``No. of components''  density
      ``component name''   fraction
        ...

via pure materials and other mixtures. A negative fraction indicates that the fraction is by volume, otherwise the fraction is by weight. Fraction by volume always works for compounds. To distinguish volume fractions from atomic percentages, one uses a negative sign for the number of components in pseudo mixtures where fraction by volume is required. In principle, the density of a mixture of solids can be calculated from the densities of the components and the composition. If one takes the calculated density, one can set the density to be negative. Otherwise, the specified density will be imposed. Some examples of mixture definitions are shown below:

*DO  GMIX   1    -A4CW -c1/50      #.          GMIX
  #.list of mixtures#                                                     
  #. list of mixtures
"Si O_2"                 2      2.64          #. Chemical compound
          "Silicon"            -1.0           #. Atomic proportions
          "Oxygen"             -2.0
"StainlessSteel"         5      8.02          #. Mixture with weight
          "Iron"               69.96          #. fraction
          "Carbon"              0.04
          "Manganese"           1.00
          "Chromium"           19.00
          "Nickel"             10.00
"FrontEnd Electronics"  -3     -1.0           #. Pseudo mixture with
          "Air"                -0.75          #. density computed
          "Silicon"            -0.20          #. from components
          "Lead"               -0.05
"MSGC_ele1"             -7      3.91
          "Carbon fibre str." -48.28          #. Pseudo mixture with
          "Hybrids"           -16.90          #. density imposed
          "Connector"         -17.46  
          "Alumina"            -1.98
          "Tin"                -0.40
          "Silicon"            -6.94
          "Peek"               -8.05

The first example, ``Si O_2'', is a compound or a mixture with components given in atomic proportions. The second case ``StainlessSteel'' is a mixture specified by weight fraction. The last two cases, ``FrontEnd Electronics'' and ``MSGC_ele1'' are so called pseudo mixtures and the density is imposed for ``MSGC_ele1'', whereas it is computed in the case of ``FrontEnd Electronics''. A more complete example is shown in Appendix A.3 and the full list of available mixtures can be found in module.

In general all media have the same name and number as the corresponding materials. Introduced are also a special medium for the same material due to difference in the tracking through them (precision, turning angle, special cutoff values, etc.). There are also special tracking media and materials which have the prefix which means that kinematical cuts for these media are increased (usually to 100 MeV for electrons and gamma and to 10 MeV for hadrons). The ``thick'' material and tracking media are generated automatically from standard one by any access to this media.

By default all the tracking medium parameters have the following parameters:

                ISVOL IFIELD FIELDM  TMAXFD  STEMAX  DEEMAX   EPSIL STMIN
                  0    -1      40.      90.    0.1     0.1     0.5   0.1

These default parameters can be changed for chosen media by using ``TMED'' title banks or keywords defined as in the example below:

*DO  TMED   1  -A4CW -c1/80      #. Media parameters
 "E_PbWO4"        1    -1      40.      10.     10.     0.1  0.001  0.005

A set of tracking medium parameters can be declared sensitive using the title block (or keyword) ``SENS''. There one specifies the names of the media chosen as explained in the example below:

*DO  SENS   1  -A4CW -c1/80      #. Sensitive media
 "V_Quartz"    #. Quartz fibres in VCAL
 "E_PbWO4"     #. PbWO4 crystals

Some special tracking medium parameters (various cuts and physics flags) can be changed through the title block ``TPAR''. There one supplies the name of the medium, the parameter to be changed and the value as in the example below:

*DO  TPAR   1  -A4CW -c1/80      #. Special tracking medium parameters
 "V_Quartz" "ILOSS" 2. #. Change ILOSS = 2 for V_Quartz

A material/medium number can be found in the Fortran code by the following call:

       CALL DCMATM (CMATE, ITM*)

where CMATE can be, for example, ``Cu/Sci spaghetti mix'' and ITM is the corresponding internal GEANT medium number.