\ARRAY MEDIA_LIST
!THE FORMAT OF THIS IS AS FOLLOWS
! Media name, media number, material number,ISVOL IFIELD FIELDM TMAXFD STEMAX
 DEEMAX EPSIL STMIN
! THE REMAINING PARAMETERS ARE THE ARGUMENTS TO THE CALL TO GSTMED
! ISVOL 1 !1= sensitive volume. 0=not sensitive
! IFIELD 3 !0=no field
 !1=tracking with Runge Kutta
! !2=inhomogeneous magnetic field. Field map from GUFLD
 !3=Uniform magnetic field along z axis of strength FIELDM
! FIELDM 20.0000 !Maximum field value in Kilo Gauss
! TMAXFD 1.0000 !Maximum angle due to field in degrees.
! STEMAX 0.1000 !Maximum displacement in one step for mult. scat
! DEEMAX 0.1000 !Maximum fractional energy loss per step
! EPSIL 2.0000E-03 !Tracking precision (cm)
! STMIN 2.0000E-03 !Minimum step due to energy loss or mult. scat.(cm)
! NU !NUMBER OF USER WORDS
! W(1:NU) !USER WORDS
!----------------------------------------------------------------------
! MEDIA DEFINITION. CALL TO GSTMED
!----------------------------------------------------------------------
 
! MEDNAME IMED IMAT ISVL IFLD FIELDM TMAXFD STEMAX DEEMAX EPSIL STMIN NU W
'AIR' 1 15 0 0 0.00 5.00 0.01 0.01 0.50E-03 0.50E-02 0
'TPC_P10_gas' 2 22 1 2 30.00 5.00 0.20 0.10 0.10E-01 0.50E-02 2 0.00 3.00
'TPC_vacuum' 3 16 0 2 30.00 5.00 0.20 0.00 0.10E-01 0.50E-02 2 0.00 0.00
'TPC_lead'  4 13 0 2 30.00 5.00 0.20 0.10 0.10E-01 0.50E-02 2 0.00 0.00
'TPC_rohacell' 5 39 0 2 30.00 5.00 0.20 0.00 0.10E-01 0.50E-02 2 0.00 4.00
'TPC_nitrogen' 6 21 0 2 30.00 5.00 0.20 0.10 0.10E-01 0.50E-02 2 0.00 3.00
'FC_copper_foil' 7 11 0 2 30.00 5.00 0.20 0.00 0.10E-02 0.50E-02 2 0.00 4.00
'FC_mylar_foil' 8 27 0 2 30.00 5.00 0.20 0.00 0.10E-02 0.50E-02 2 0.00 4.00
'Al_Honeycomb' 9 20 0 2 30.00 5.00 0.20 0.00 0.10E-01 0.50E-02 2 0.00 4.00
'NEMA_G10' 10 40 0 2 30.00 5.00 0.20 0.00 0.10E-02 0.50E-02 2 0.00 4.00
'FC_Al_window' 11 43 0 2 30.00 5.00 0.20 0.00 0.10E-02 0.50E-02 2 0.0 4.00
'Lucite' 12 44 0 2 30.00 5.00 0.20 0.00 0.10E-02 0.50E-02 2 0.00 4.00 
'FCW_P10_gas' 13 22 0 2 30.00 5.00 0.20 0.00 0.10E-02 0.50E-02 2 0.00 3.00
'Sens._Air1' 15 15 1 2 30.00 5.00 0.01 0.01 0.50E-03 0.50E-02 0
'Sens._Copper1' 16 11 0 1 30.00 5.00 0.01 0.01 0.50E-03 0.50E-02 0
'Sen._Steel1'  17 10 0 1 30.00 5.00 0.01 0.01 0.50E-03 0.50E-02 0
\END

This array defines the tracking media. A tracking medium is a material or mixture to which has been attached properties such as magnetic field, tracking precision etc as shown in the above example. Since these additional parameters are usually common to groups of materials or mixtures, the format of the above array is such that TRACKING MEDIA numbers from TLO to THI are defined consecutively on material (or mixture) numbers MLO to MHI. The parameter ISVOL =1(0) declares to GEANT that these media are sensitive (insensitive) to energy deposition. If media are sensitive, they can be digitized and read out. If they are insensitive, they act as dead material.
The IFIELD parameter declares to GEANT whether the medium possesses a magnetic field. IFLD=0 means no field, =1 means strongly inhomogeneous field specified GUFLD and tracked using RUNGE_KUTTA routines, =2 means GUFLD specified field tracked using helices and =3 means uniform magnetic field along the Z- axis specified by FIELDM.

For definitions of the remaining parameters see GSTMED