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In Geant4 charged particles are tracked to the end of their range.
Range is used, rather than energy, as a more natural concept for designing
a coherent policy for different particles and materials. Definition of the cer-
tain value of the cut in range means the requirement for precision of spatial
radioactive dose deposition.
The value of cut is defined for electrons, positrons, gamma and protons.
At the beginning of initialization of Geant4 physics the conversion is per-
formed from unique cut in range to cuts (production thresholds) in kinetic
energy for each G4MaterialCutsCouple. At that moment no energy loss
or range table is created, so computation should be performed using original
formulas. For electrons and positrons ionization above 10keV a simplified
Berger-Seltzer energy loss formula is used. The contribution of the bremsstrahlung is added using empirical parametrized formula. For T < 10keV the linear dependence of ionization losses on electron velocity is assumed, bremsstrahlung contribution is neglected. A simple linear conversion formula is used to compute energy threshold from the value of cut in range, in particular, the cut in range 1 mm corresponds to the production threshold 100keV.
The conversion from range to energy can be studied using G4EmCalculator
class. This class allows access or recalculation of energy loss, ranges and other
For more information see Physics Ref. Manual Sec 7.4 (Page 116).