Neutron Scattering

In stage 1 the primary proton knocks on a nucleon, which in turn knocks on another nucleon
of thé saine nucleus (intea-nuclear cascade) or of a différent nucleus (inter-nuclear cascade)
. With increasing energy of thé primaiy particle thé nucléons kicked out of thé nuclei
will for kinematic reasons (transformation from center of mass to laboratoiy system) be
emitted into decreasing solid angles around forward direction . The energy distribution of thé
cascade particles extends up to thé primary proton energy . Alter emission of thé cascade particles
thé nuclei are in a highly excited state, whose energy is released in stage 2 mainly by
evaporation ofneutrons, protons, deuterons, a-particles and heavier fragments as well as y-radiation
. Depending on thé particular evaporation reaction course, différent radioactive nuclei
remain . These evaporation neutrons are isotropically emitted. They are thé primary source
neutrons, in which we are interested in thé prescrit context . The spectrum of thé evaporation
neutrons is very similar to that of nuclear fission and has a maximum at about 2 MeV . This is
thé veiy reason, why we cari utilize thé spallation neutrons as with a fission reactor .
The yield of evaporation neutrons increases with proton energy and depends on thé target
material . The following expression for thé yield has been found empirically
Y = f - (A + 20) - (E - b) neutrons / proton, (1 .2)
where A is thé mass number of thé target material (9