Spectral fluence rates of the fast reactor neutron beam MedApp at FRM II

The MedApp facility at the research reactor FRM II supplies a beam of fast neutrons created by thermal fission of 235U. It can be used for medical applications like the irradiation of human cancer, for radiography and tomography in non-destructive material characterisation as well as for the irradiation of technical and biological objects. For such applications, a detailed knowledge of the neutron spectrum is required. To determine the spectrum, a MCNP simulation was performed and verified by multiple foil activation. An equalisation calculation confirmed the achieved spectral shape. The total flux was measured using a modified gold-water-bath technique. The geometrical shape of the beam was mapped using indium wires.