GEANT4 Simulations of the ISIS Muon Target at Rutherford Appleton Laboratory

MuSR science requires the availabilty of intense beams of polarised positive muons. At the ISIS pulsed muon facility at Rutherford Appleton Laboratory the muons are generated from a low Z thin slab graphite target inserted in the proton beam. We report on the use of the Monte Carlo simulation code Geant4 in simulations of the performance of the current muon target. The results are benchmarked against the experimental performance of the target. ISIS NEUTRON SPALLATION SOURCE The ISIS spallation neutron source is a pulsed neutron source for condensed matter research. Negatively charged hydride ions of 70 MeV are injected from the linear accelerator into the synchtrotron where they are stripped of their electrons and accelerated to 800 MeV. The nominal beam current is 200 μA and the proton beam is double-pulsed at 50 Hz. The two pulses are directed along the proton beam channel to the intermediate muon target and then to the spallation neutron target. The muon target is inserted into the proton beam line and pions are produced as a result of the proton interaction with the target nuclei. Low-Z materials are used in order to maximise the pion production while minimising multiple scattering of the proton beam itself. The pions decay to muons and neutrinos.