Development of an epithermal and fast neutron target station for the High Brilliance Neutron Source

Abstract

The conceptual design of an epithermal and fast neutron target–moderator–reflector (TMR) unit for the High BrillianceNeutron Source (HBS) project is presented. A total of 450 simulations with the Monte Carlo code PHITS were analyzed to exploredifferent combinations and thicknesses of pre-moderator and moderator materials. For each case, the highest epithermal outgoingneutron current at the end of an extraction channel was obtained. Analysis of the outgoing current density showed that the neutronspectra are independent of the proton pulse width, while the integral outgoing current is proportional to the pulse width, indicatinga trade-off between the time resolution obtained and the neutron flux per pulse expected at the sample position. The neutrontime distribution analysis showed that D2 O as pre-moderator, combined with D2 O, 7 LiF or graphite as moderators, will provide acompetitive epithermal neutron current. The averaged epithermal and fast values obtained for the 96 Hz station and 167 µs protonpulse width are 9 × 109 cm−2 s−1 and 2 × 1010 cm−2 s−1 for the epithermal and fast neutron extraction channels, respectively, withreductions expected for short proton pulses in burst-mode operation.