COLD NEUTRON INSTRUMENTS
Plan View of the NCNR Guide Hall
Seven neutron guides transport neutrons
emerging from the cold source through distances of tens of meters
to the stations in the guide hall. An eighth large neutron beam terminates
inside the confinement building, and will provide neutrons for an
advanced multi-axis crystal spectrometer
(MACS). The neutron guides work by a simple principle, i.e., total
external reflection of neutrons from the flat surfaces of a
rectangular tube formed by Ni-58-coated glass surfaces. Neutrons
which graze the surfaces within a small angle (theta less than theta-c =
1.18 deg. for 10 A neutrons incident on Ni-58) are totally reflected because
the index of refraction for neutrons is slightly less than one.
The use of Ni-58 is dictated by its relatively large values of
theta-c, an advantage for producing the highest possible neutron
flux at the experimental stations (listed below). The three newest
guides (NG-1,2,4) have multilayer coatings on top and bottom
surfaces which provide an additional factor of 1.7 in available
neutron intensity.
Operational instruments:
Under construction:
Last modified 19-January-2007