Neutron production and protection in medium-energy accelerators

In the medium incident-energy range (a few tens or hundreds of MeV) the variety of projectiles produced by accelerators has become much wider over the last decade. The production of neutrons by particles ranging from protons to heavy ions is main-protection problem to be solved at the preliminary draft stage of a machine and its knowledge is fundamental to the work of the radioprotection specialist. Medium-energy physical phenomena leading to neutrons of quite different relative abundances and energies according to the type of accelerated particle, especially for 'thick targets', are described. Developments in heavy ion physics and radioprotection experience at the Orsay IPN allow experimental results to be accounted for and new predictions made in the heavy ion field, as a function of energy per nucleon in particular. The neutron yield of the targets and the energy of the neutrons have a strong influence on the amount and choice of shielding around an accelerator