Page 18 - Neutrons for Sciences and Society

Neutrons for Science
Shull (Fig. 1.3) rejoined E. Wollan at Oak Ridge. In 1949 C.G. Shull and J.S. Smart demonstrated11 that at the temperature of liquid nitrogen the magnetic moments on the manganese atoms in MnO are arranged in two sub-lattices with the moments oriented opposed. Such an arrangement had been predicted a few years earlier by Louis Néel. Cliff Shull was awarded the Nobel Prize for Physics for this work in 1994. This new type of magnetic order was baptised with the name “antiferromagnetic” by F. Bitter, and the temperature below which it appeared was called the Néel temperature by C.J. Gorter.
This all demonstrated the utility of neutrons for studying solid-state physics, especially magnetic materials. There was
an absolute need for higher neutron fluxes than those produced by the reactor at Oak Ridge. The first steps in finding a solution to this problem were made at Brookhaven under the leadership
of Donald Hughes. This physicist was responsible for research
at Brookhaven involving neutrons. In 1953 he published his
book “Pile Neutron Research” which became a bible for young researchers who, like me, were entering the field. In 1954 he attracted the attention of the director of Brookhaven towards the need to give the Laboratory a reactor producing a higher flux than the graphite pile already available there. The steps that followed are very carefully described in Lawrence Passell contribution, “High Flux at Brookhaven”, in George Bacon’s book which was cited previously. The important feature of the reactor due to Jack Chernick was the concept of a core, under-moderated with heavy
11 C.G. Shull and J.S. Smart, Phys. Rev., (1949) 76, 1256-1257, DOI 10.1103/PhysRev.76.1256.2. 9