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 Brilliance Neutron Source (HBS) project is presented. A total of 450 simulations with the Monte Carlo code PHITS were analyzed to explore different combinations and thicknesses of pre-moderator and moderator materials. For each case, the highest epithermal outgoing neutron current at the end of an extraction channel was obtained. Analysis of the outgoing current density showed that the neutron spectra are independent of the proton pulse width, while the integral outgoing current is proportional to the pulse width, indicating a trade-off between the time resolution obtained and the neutron flux per pulse expected at the sample position. The neutron time distribution analysis showed that \(\hbox {D}_2\)O as pre-moderator, combined with \(\hbox {D}_2\)O, ⁷LiF or graphite as moderators, will provide a competitive epithermal neutron current. The averaged epithermal and fast values obtained for the 96 Hz station and 167 \(\upmu \)s proton pulse width are \(9 \times 10^{9}\,\hbox {cm}^{-2}\,\hbox {s}^{-1}\) and \(2 \times 10^{10}\,\hbox {cm}^{-2}\,\hbox {s}^{-1}\) for the epithermal and fast neutron extraction channels, respectively, with reductions expected for short proton pulses in burst-mode operation.