18.2} Second generation (development of new hadron generators, 1978-1989)

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 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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