Ultra-Radio-Pure Sodium Iodide Detectors for Dark Matter

The effort to understand dark matter is one of the major activities in modern particle physics and astrophysics.It is widely believed that dark matter is composed of a new type of subatomic particle that is not yet well understood.An important discovery in this area is the annual modulation signal measured by the DAMA group in Italy using NaI scintillation crystals.While the DAMA result runs contrary to the findings of some other experiments that utilized different techniques, there are also some recent results that seem to support DAMA.Therefore, there is a clear need for confirmation of the DAMA experiments.Several new NaI experiments are in planning or construction, requiring the availability of suitable crystals with lower radioactivity background levels, and thus higher sensitivity that could confirm or refute the DAMA result.The goal of the proposed Phase IIB project is to transition the demonstrated low-background NaI technology into production and to make commercially available detector crystals with the required radio-purity.This will be accomplished by scaling-up and improving the efficiencies of the processes for the NaI raw material purification, crystal growth, and detector fabrication.Radiation Monitoring Devices, Inc.(RMD), in collaboration with Princeton University, has produced large NaI scintillation crystals with unprecedented low background of radioactive impurities in the SBIR Phase II project.The proposed Phase IIB project will build upon that work.The essence of the proposed project is to further develop the processes that were demonstrated in Phase II in order to end up with effective crystal production.This will involve first of all developing a consistent supply of the raw materials and their subsequent purification.Crystal growth will be optimized to improve efficiency while maintaining the crystal purity and scintillation characteristics.Post-growth processing will also be optimized for best surface purity and scintillation characteristics.Dark matter detectors will be built with the necessary size, purity, and components to provide suitable performance for the DAMA experiments to be replicated with even better sensitivity.The impact of this work would be significant.The availability of a commercial supply of lowradioactivity NaI crystals would enable the development of major new dark matter experiments that could confirm or refute the controversial DAMA results.The scientific impact of this result would be significant in furthering the understanding of this fundamental mystery in modern physics and cosmology.The availability of radio-pure NaI crystals would potentially impact other application areas in which low-level radioactivity measurements are needed.These could include nuclear nonproliferation, environmental monitoring, well-logging, and nuclear medicine.