------------------------------------------------------------------------- After the SPS construction phase, a complete re-design of the code was started in 1978 on the initiative of Graham Stevenson (CERN), with the support of Klaus Goebel, then leader of the CERN Radiation Protection Group, and of Jorma Routti, Chairman of the Department of Technical Physics at the Helsinki University of Technology (HUT), in the form of a collaboration between CERN, HUT and Leipzig University [Moh81,Aar84,Aar84a,Ran85b]. The goal was to make FLUKA a more user friendly hadron cascade code with flexible geometry and with a modern formulation of the hadron interaction model. The new FLUKA code was started to be written by visitors from Leipzig University (H.-J. Moehring) and Helsinki Technical University (Jorma Sandberg). The project was finished by Pertti Aarnio, also visitor from Helsinki. Other contributions came from Jukka Lindgren (Helsinki) and by Stevenson himself, who was acting as a coordinator. The existing versions of Ranft's programs (at least 14) were unified into a single code under the name FLUKA. The new code was capable to perform multi-material calculations in different geometries and to score energy deposition, star density and differential "fluxes" (actually, angular yields around a target). This second generation resulted in the release of several versions. In FLUKA81 [Moh81] only one geometry was available (cylindrical). High-energy hadronic events were still sampled from inclusive distributions, but the low-energy generators HADRIN [Han79,Han86] and NUCRIN [Han80,Han86a] were introduced for the first time. In FLUKA82 [Aar84,Ran85b], Cartesian and spherical geometries were added, and in principle Combinatorial Geometry too (but the latter option was rarely used, since there was no scoring associated with it and it did not support charged particle multiple scattering and/or magnetic fields). After a first release with the old inclusive hadron generator, an update [Aar84a] was released soon in which a new quark-chain generator developed by Ranft and his collaborators was introduced in a tentative way [Ran83,Ran85,Ran85a]. At least four Ph.D. projects at Leipzig University did contribute to this new generator, based on the Dual Parton Model, known as EVENTQ. The model soon turned out to be superior by far to all those used before in hadron Monte Carlo, and various versions of it were later adopted also in other codes (HETC [Als89,Als90], HERMES [Clo88], CALOR [Gab89], and the simulation codes used for the H1 and ZEUS experiments). The link to the EGS4 program [Nel85] was introduced in the FLUKA86 version by G.R. Stevenson and A. Fasso`, as an alternative to the parameterised electromagnetic cascade used before. The link was working both ways, allowing to transport gammas issued from pi0 decay, and also photohadrons. Production of the latter was implemented only for energies larger than the Delta resonance, in the frame of the Vector Meson Dominance model [Bau78], by J. Ranft and W.R. Nelson [Ran87b]. The possibility to work with complex composite materials was introduced in the FLUKA81 version by Moehring and Sandberg. P. Aarnio restructured the code by encapsulating all COMMON blocks into INCLUDE files. In that version, and in FLUKA87 which soon followed [Aar87], several other new features were introduced. A first attempt at simulating ionisation fluctuations (with the Landau approach) was contributed by P. Aarnio, and a rudimentary transport of particles in magnetic fields was provided by J. Lindgren (for charged hadrons only). Some fluence estimators (boundary crossing, collision, tracklength) were added in a preliminary form by Alberto Fasso`, based on the same algorithms he had written for the MORSE code [Fas87]. J. Ranft and his group improved the EVENTQ hadron generator with the inclusion of diffractive events and Fermi momentum and provided a first model (later abandoned) of nucleus-nucleus collisions. Practically none of these features, however, is surviving today in same form: in all cases, with the exception of the hadron event generator, even the basic approach is now completely different.
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