Research on slow-neutron cross-sections using the BR1 reactor

Research on slow-neutron eross-sections using the BR-1 reactor. Two pieces of
apparatus are now in regular use with the BR-1 reactor: a “chopper”-type spectrometer for slow neutrons and a single-crystal spectrometer. The main features of this equipment and the measurements made or in progress are described. The chopper is like the well-known Fermi model and has slits 0.1 cm high and 6cm wide. So far the maximum operating speed has been 12000 rev/min. The maximum length of the base is 2.80 m. A typical value for error in time determination is 1%, which makes possible an energy resolution of 3% or more. The programme involves measurement of partial and total cross-sections of and of boron. The crystal spectrometer uses the faces (111) of a Cu orystal (diam = 2083 A). The divergence of the beam is 3 x 10^-3 rad (10'). Resolution with a pile collimator and a rotating-arm collimator is estimated at 4% for an energy of 1 eV. The apparatus is used mainly for measurements of scattering cross-sections.