Thermal neutron detection with PMMA nanocomposites containing dysprosium fluoride nanocrystals

Naturally occurring dysprosium is attractive as a neutron detector because of its high thermal neutron capture cross section and high natural abundance. Neutron-induced transmutation of 164 Dy results in production of stable isotopes of holmium and erbium (the latter only at sufficiently high neutron fluxes), due to beta decays caused by nucleus instability. This mechanism, unaffected by gamma radiation, can be used to unambiguously detect neutrons, without having to discriminate against an accompanying gamma flux. Optically-enabled thermal neutron detection can be based on significant differences in optical properties of Dy and Ho or Er, which allows to determine the relative fractions of Dy, and Ho, and E in an irradiated sample. In our search for the most sensitive method of differentiating between Dy and Ho residing in the same host material, we produced various Dy- and Ho-containing nanocrystals and uniformly dispersed them in a PMMA polymer matrix. Optical properties of the nanocomposites were analyzed by means of absorption and PL spectroscopy. We also report on neutron irradiation experiments with Dy-containing nanocrystals and our attempts to optically detect neutron-induced conversion of Dy into Ho.