first results of the NA2 phase of the experiment showed that charm production was mediated by the photon-gluon fusion process. The collaboration then went on to show that the scattering rate in iron and deuterium were different. This showed that the quark sub-structure of nucleons bound in nuclei is different from that of free nucleons. The effect became known as the EMC effect and aroused great interest among theoretical physicists. It was planned to replace the iron, deuterium and hydrogen targets with a polarized target in 1981. However, it proved to be difficult to build the large volume target necessary and this experiment was postponed until 1984. In addition the Lund model of quark fragmentation (which later became known as PYTHIA) became available and much of the data on forward produced hadrons were used to tune this model. The NA9/NA28 phases of the experiment commenced taking data in 1981. The main results of these experiments were the confirmation of our understanding of the quark fragmentation process. Again the results were used to develop models of this process such as PYTHIA and the HERWIG model which had become available. The NA28 experiment discovered that the results of scattering in nuclei at small values of Bjorken x were much different from those at larger values. The process governing this behavior became known as shadowing in nuclei. The final phase of the experiment with the polarized target produced the most dramatic result from the experiment with the discovery only a small part of the proton spin is carried by quarks, and that the strange quark sea is probably polarized. This is sometimes referred to as the "proton spin crisis". See also Neutron detection Nucleon spin structure References External links EMC NA2 experiment record on INSPIRE-HEP Particle experiments CERN experiments