Neutron beamline shielding calculations at the SNS

A world-class accelerator driven short pulsed neutron source is in the final stages of construction at the Oak Ridge National Laboratory. A 1.4 MW proton beam at 1 GeV energy directed on a mercury target will free neutrons through spallation reactions that will be moderated to thermal and subthermal energies and serve neutron scattering instruments at up to 24 beamlines. At spallation neutron sources, the neutron beams are contaminated by a large fraction of fast neutrons with energies up to the energy of the proton beam incident on the mercury target. Results of design calculations for the Cold Neutron Chopper Spectrometer are presented as an example to demonstrate the neutronics design analyses that are being performed to optimize the lateral beamline shielding as well as the sample and detector area with regard to guaranteeing personal safety, minimizing neutron background and cost.