Purpose: Maximum duration of the simulation. 
Data Type: real number
Unit: h
Default: 8.76E+09 h  (~ 1 million years)
Comments: If a simulation includes a background dose rate greater than zero, TMAX (or TCUT) should be set to a positive number. Otherwise the simulation will automatically run for 1 million years.  Tmax does *not* control the amount of CPU time used to perform a simulation.