Characterisation of neutron field in the polyethylene neutron irradiator.

The paper describes neutron field characterisation of low-flux multipurpose educational irradiator developed at Czech Technical University in Prague. The irradiator is aimed for demonstration experiments including neutron activation analysis, delayed neutron counting, or studies related to neutron and/or gamma detection and spectrometric devices. It may accommodate various neutron sources including Cf or AmBe radionuclide sources, D-D generator, or in-reactor irradiated nuclear material serving as delayed neutron source, or gamma sources including radionuclide ones or short-lived sources produced in the adjacent reactor. The characterisation was performed based on neutron activation technique using gold foils. It included two experimental parts. The first one verified the level of response symmetry in the four irradiation channels and characterisation of the axial distribution in the irradiation channels. Within the second one, the responses to thermal and epithermal neutrons and the cadmium ratio in the central irradiation position were determined. Whereas the former was determined solely with the Cf source, the latter was performed for all available sources: Cf, AmBe, and the D-D generator. The experimental results were further compared to calculations by the MCNP Monte Carlo code.