Scintillators are usually consist of a transparent insulator and an impurity that functions as a luminescence center. They are often slow or how low efficiency. Colloidal nano-crystals in liquids, sol-gel and organic polymers will be developed. The nano-crystal surface will be modified to make them soluble. The optical response will be investigated and results compared across systems. The work will provide the first studies of the optical response of colloidal nano-crystals to irradiation. It is anticipated that this effort will lead to identification of high-efficiency, fast scintillators utilizing 3D confinement of electrons and holes in nano-crystals. It will provide a systematic database of gamma ray and neutron response and characterization of nano-crystals. The work will contribute to the investigation of basic radiation effects on nano-crystals and their utilization in handheld, efficient detectors of nuclear radiation. The work should have a major impact on the development of scintillating materials and expand the range to nano-crystals. The groups actively engages undergraduate students in the research through a specialized program focused on recruitment, mentoring, retention and graduation of members of underrepresented groups.
on NSF Grant IIS-0610201 Exploratory Studies of Optical Response to Gamma and Neutron Radiation of Doped and Undoped II-VI, III-V, and Novel Scintillating Core/Shell Nanocrystals PI: Marek Osinski, University of New Mexico Nuclear radiation detectors are becoming increasingly important for a wide range of applications, including the homeland security against catastrophic terrorist threats, nuclear forensic analysis, monitoring treaty compliance, counterproliferation, long term monitoring of nuclear waste storage sites, environmental safety, use of nuclear waste energy, high energy physics, biomedical imaging (PET, radiotherapy), industrial defectoscopy, and oil well logging. An ideal nuclear detector should combine a number of features presently distributed among many different types of detectors: high energy resolution, high sensitivity, high efficiency, room-temperature operation, scalability, robustness, etc. The tradeoffs between different detectors become even more apparent when other parameters are considered, such as high speed, low cost, good proportionality, high stopping power, portability, resistance to shock, and so on. Nanotechnology offers new prospects for meeting those competing requirements. In this project, we focused on exploratory investigations of a large number of different nanocrystals to determine their potential as gamma and neutron radiation detectors. Cerium-doped lanthanum halides are a class of scintillators that combine high levels of light output, relatively short scintillation decay time, high energy-resolution, and good linearity of response. In contrast to other lanthanide halide scintillators such as LaBr3 or LuI3 that are highly hygroscopic or even deliquescent, LaF3 is stable in presence of water. This makes it attractive for low-cost nanoscintillators, provided other parameters, such as energy resolution or energy conversion efficiency are proven to be satisfactory. In addition, undoped LaF3 is a very good candidate for a shell material protecting hygroscopic cores. Ce-doped LaF3 (LaF3:Ce) colloidal nanocrystals (NCs) and Eu-doped LaF3 (LaF3:Eu) Colloidal NCs have been synthesized in both aqueous solutions and anhydrously. An anhydrous synthesis has been developed for LaBr3:Ce and LaBr3:Ce/LaF3 core/shell colloidal NCs. Lead-based compound NCs are of interest as potential novel scintillation materials due to their high density and the high atomic weight of Pb. While the bulk materials may have poor efficiency of light emission at room temperature, the effects of quantum confinement are expected to greatly enhance the probability of radiative transitions, as well as reduce the radiative recombination lifetime. PbI2, PbIOH, and Pb3O2Cl2 NCs have been successfully synthesized, characterized and tested for gamma detection. Gadolinium has the highest thermal neutron absorption cross-section of any naturally occurring element. Even without any isotopic enrichment, naturally occurring Gd has an average value of sn = 49,000 barns. We have explored a novel concept of Gd-containing nanocrystalline materials for neutron detection. Gd2O3 NCs, Gd2O3 NCs doped with Ce, Gd2O3 NCs doped with Eu, Gd2O3 NCs co-doped with Ce and Eu, GdF3 NCs, GdF3 NCs doped with Ce, and LaF3 NCs doped with Gd for neutron detection applications have been obtained by means of colloidal synthesis. For applications that involve exposure of NCs to ionizing radiation, it is important to know the levels of irradiation that would degrade their optical properties. Optical degradation of the NCs has been evaluated based on the measured dependence of their photoluminescence intensity on the irradiation dose. The colloidal NCs under test showed a wide range of radiation hardness. The lanthanide halide and lead halide NCs displayed a remarkable stability whereas the reference CdSe/ZnSe NCs degraded rapidly under gamma irradiation. The lanthanide halide and lead-iodide-based NCs have produced a measurable signal when measuring their scintillation response and neutron detection has been confirmed in the neutron irradiation experiments with Gd-containing NCs. However, no energy spectra have been resolved in the experiments, which we ascribed to low NC material content in the solution. The future work on the development of the NC scintillating material will include fabrication of NC material into a composite with increased NC material loading to enable experimental determination of the light yield.
