Geant4 User's Guide for Application Developers - Geant4 - CERN

Toolkit Fundamentals• G4UnitsTablePlaceholder for the system of units in Geant4.3.3. System of units3.3.1. Basic unitsGeant4 offers the user the possibility to choose and use the preferred units for any quantity. In fact, Geant4 takescare of the units. Internally a consistent set on units based on the HepSystemOfUnits is used:millimeter(mm)nanosecond(ns)Mega electron Volt (MeV)positron charge(eplus)degree Kelvin(kelvin)the amount of substance (mole)luminous intensity (candela)radian(radian)steradian(steradian)All other units are defined from the basic ones.For instance:millimeter = mm = 1;meter = m = 1000*mm;...m3 = m*m*m;...In the file $CLHEP_BASE_DIR/include/CLHEP/Units/SystemOfUnits.h from the CLHEP installation,one can find all untis definitions.One can also change the system of units to be used by the kernel.3.3.2. Input your data3.3.2.1. Avoid 'hard coded' dataThe user must give the units for the data to introduce:G4double Size = 15*km, KineticEnergy = 90.3*GeV, density = 11*mg/cm3;Geant4 assumes that these specifications for the units are respected, in order to assure indeipendence from theunits chosen in the client application.If units are not specified in the client application, data are implicitly treated in internal Geant4 system units; thispractice is however strongly discouraged.If the data set comes from an array or from an external file, it is strongly recommended to set the units as soonas the data are read, before any treatment. For instance:for (int j=0, j