------------------------ The treatment of ionisation losses was completely re-written in 1991-1992 by Fasso` and Ferrari to eliminate many crude approximations, and delta-ray production was added. Ranging of stopping charged particle was also changed. Quenching according to the Birks law was introduced to calculate the response of scintillators. Application of FLUKA to proton therapy called for further refinements of stopping power routines in 1995, with the inclusion of tabulated data of effective ionisation potentials and density effect parameters. Shell corrections were added. The new treatment was fully compliant with ICRU recommended formulae and parameters and included all corrections, including low energy shell corrections as worked out by Ziegler et al. [Zie77] In 1996, a new formalism for energy loss fluctuations by Ferrari replaced the old treatment of Landau fluctuations. This formalism, based on the statistical properties of the cumulants of a distribution, was applied to both heavy charged particles and e+e-, and was fully compatible with any user-defined threshold for delta ray emission. Other improvements concerned the possibility to define materials with local density different from average (porous substances), and the ranging out of particles with energies lower than the transport cutoff. In 1999-2000, heavy ion dE/dx was improved by the inclusion of effective Z and straggling (Ferrari). High-energy energy loss mechanisms for heavy charged particles were implemented by Ferrari both as a continuous and as an explicit treatment: bremsstrahlung and pair production in 1992, nuclear interaction via virtual photons in 1993.
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