Performance of upgraded thermal neutron guides with supermirrors at JRR-3

Thermal neutron guides at the JRR-3 reactor have been upgraded from natural nickel mirror guides to Ni/Ti supermirror ones with two times critical angle as large as that of natural nickel mirror. We have performed the characteristics experiment of neutron beams transmitted through the supermirror neutron guides. The neutron spectra have been measured at the end of the thermal neutron guide by the time-of-flight method. It was observed that the characteristic wavelength for the neutron beam was shifted from 2 to 1.3 Å. Neutron flux at the end of the thermal neutron guide was measured by the gold foil activation method. It was measured 6.11×1011 n/m2 s and increases 4.32 times after upgrade. We have conducted Monte Carlo simulation in consideration of the reflectivity of fabricated supermirrors and their alignment errors for the purpose to examine the performance of supermirror neutron guides.