We propose a novel concept of optical detection of thermal neutrons in a passive device that exploits transmutation of Dy-164, a dominant, naturally occurring isotope of dysprosium, into a stable isotope of either holmium Ho-165 or erbium Er-166. Combination of the high thermal neutron capture cross section of ~2,650 barns and transmutation into two other lanthanides makes Dy-164 a very attractive alternative to traditional methods of neutron detection that will be completely insensitive to gamma irradiation, thus reducing greatly the likelihood of false alarms. The optically enabled neutron detection relies on significant differences in optical properties of Dy, Ho, and Er that are not sensitive to a particular isotope, but change considerably from one element to another. While the concept applies equally well to bulk materials and to nanocrystals, nanocrystalline approach is much more attractive due to its significantly lower cost, relative ease of colloidal synthesis of high quality nanocrystals (NCs), and superior optical and mechanical properties of NCs compared to their bulk counterparts. We report on colloidal synthesis of DyF3 NCs, both doped and undoped with Ho and co-doped with Ce and Eu to enhance their optical properties. We also report on DyF3:10%Ce and DyF3:10%Eu NCs irradiated with thermal neutrons from a Cf-252 source and their optical characterization.

Wide bandgap semiconductor films were obtained by spray pyrolysis, thermal evaporation and casting. These films were characterized under similar conditions in order to compare their structures, surface morphology and photocurrent properties. All films show either a crystalline or a polycrystalline structure. SEM pictures of sprayed films present holes and fissures and non-total covering of the substrate. The photoresponse was obtained for evaporated TlBr films, HgI2 casted with polystyrene (PS) scaffold, sprayed and evaporated PbI2 films. The photo to dark current ratio is discussed as well as the difference of photo to dark current at an electric field of 100 V/cm. The discussion also focuses on a future optimized material.

Eu2+– activated strontium iodide is a promising material for x-ray and gamma ray detector. A lot of difficulties are though encountered growing strontium iodide crystals due to the high oxygen-sensitivity, hygroscopic property and high impurity concentration. Single crystals of SrI2:Eu were grown from zone refined starting materials in silica ampoules. The crystals showed good optical qualities. The light yield of two samples cut from the same ingot was determined to be 53 000 photons/MeV and 119±22 photons/keV for a 0.4 cm3 sample and a 360 μm sample respectively, indicating some level of light trapping in the bulk sample.