Description of irradiation facilities at Fraunhofer-INT and determination of an optimized polyethylene moderator for He-3 neutron detectors

Within the scope of the IAEA-Support-Project "Characterization of IAEA Radiation Detectors" the response of two He-3 neutron detectors with high neutron counting efficiency and low gamma sensitivity will be measured in neutron and gamma fields as well as in mixed neutron/gamma fields. Furthermore, measurements of the response of two silicon detectors will be performed in gamma fields of different intensity. The provided neutron and gamma radiation facilities are presented with their technical data in this report. They allow measurements in a wide range of intensity and dose rate. Neutrons are detected with He-3 filled proportional counters. These He-3 neutron detectors are moderated with polyethylene to enhance the neutron counting efficiency. Calculations have been performed to with MCNP obtain the optimized moderator thickness for maximum detection efficiency. Additionally we have compared the calculations with measurements performed with He-3 detectors.