Neutron Scattering

In December 1942 Ferme build his ferst nuclear reactor in Chicago - the so called Chicago
pile - which led to the frst controlled nuclear chain reaction . Only one year later the Oak
Ridge Graphite Reactor went critical . It had a power of 3.5MW and was originally used for
the production of fissionable material . Fig .2 .2 shows this reactor which by now is a national
historic landmark . At this reactor, Shull build the ferst neutron diffractometer which became
operationally at the end of 1945 . At that instrument the frst antiferromagnetic structure
(Mn02) was solved (Shull, Noble Price 1994). At the end of the 40's and the beginneng of the
50's nuclear reactors for neutron research came into operation in several countries . 1954 the
Canadian NRU Reactor in Chalk River was the most powerful neutron source wich a flux of
3-10 14n/cm 2s 1 . There Brockhouse developed the triple axis spectrometer which was
designed, in order to observe inelastic neutron scattering and in particular to investigate
elementary excitations in solids . For this achievement Brockhouse received the Nobel Price in
1994 . Another milestone in neutron scattering was the installation of the ferst cold source in
Harwell (Great Britain) . This cold source allowed to moderate neutrons to liquid hydrogen
temperatures with the effect that for the ferst time long wavelength neutrons became available
in large quantities .
Figure 2 .2 : View ofthe Oak Ridge Graphite Reactor .
2-2