Characterisation of the epithermal neutron irradiation facility at the Portuguese research reactor using MCNP

• An epithermal neutron irradiation facility modelled using MCNPX.
• Foils and TLDs used to measure dose in chamber and compared to simulations.
• Proposed modifications to the irradiation chamber outlined based upon results of simulations.

The radiation field at the epithermal beamline and irradiation chamber installed at the Portuguese Research Reactor (RPI) at the Campus Tecnológico e Nuclear of Instituto Superior Técnico was characterised in the context of Prompt Gamma Neutron Activation Analysis (PGNAA) applications. Radiographic films, activation foils and thermoluminescence dosimeters were used to measure the neutron fluence and photon dose rates in the irradiation chamber. A fixed-source MCNPX model of the beamline and chamber was developed and compared to measurements in the first step towards planning a new irradiation chamber. The high photon background from the reactor results in the saturation of the detector and the current facility configuration yields an intrinsic insensitivity to various elements of interest for PGNAA. These will be addressed in future developments.