High energy spallation neutron sources may be used for radiation damage experiments on first-wall candidate materials of fusion reactors. In these experiments the neutron spectrum and the helium production rate must be measured at the location of material samples in the irradiation facility.
The planned spallation neutron source (SINQ) at the Swiss Institute for Nuclear Research (SIN) was simulated by using the 500 MeV proton beam of the TRIUMF accelerator in Canada and its molten lead beam stop as the source of spallation neutrons.
The neutron spectrum was measured by the multiple foil activation method. A set of foils (Al, Sc, Ti, Fe, Co, Ni, Cu, Zr, Nb, In, Tm and Au) was irradiated at several locations around the molten lead source. A total of 37 reactions were available with product nuclei suitable for Ge (Li) gamma spectroscopy. The neutron spectrum was obtained by unfolding procedure using the SANDA code. As neutron activation cross section libraries are not available in Europe, in the energy range above 20 MeV, it was necessary to develop and construct a new library.
The helium accumulation in Fe, Al, Cu, Zr, Ti and W was measured by means of a Rock-well International mass spectrometer.