Response functions of a Bonner sphere spectrometer calculated with GEANT4

The response functions of a Bonner sphere spectrometer with gold activation foils as thermal neutron detectors were calculated with GEANT4. The spectrometer includes 15 polyethylene spheres with diameters between 1.3 and 15 in. and a bare gold foil. By comparison with results of MCNPX calculations, the neutron transport in GEANT4 was first extensively verified. In addition, the calculation method, which includes folding the neutron flux at the location of the gold foil with the neutron capture cross-section of gold, was tested in detail. The agreement between the GEANT4 and the MCNPX calculations was reasonable, and a complete set of Bonner sphere functions was calculated with GEANT4.