Optical Calibration Development for SNO+

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The overall target of this research is a facility that would make fundamental advances in our understanding of a diverse range of phenomena covering areas including how stars work, the geology of the earth and the nature of the most basic building blocks of matter. Such fundamental understandings provide the foundation that underpins the whole of technological and intellectual development that continues to advance society as a whole. Another "indirect" benefit lay in the instilling of scientific interest and training of students to think creatively and to develop and apply analytical skills to difficult problems. Such skills are highly prized as they are applicable to almost every corner of society, which has benefited greatly from the significant advances made by such trained individuals. In addition to this non-specific but very real benefit, potential direct technological spin-offs include: advances in the development of scintillators and radioactive sources, both of which are topics of interest having had important applications in medicine; novel use of fibre optics, a topic of importance in areas such as telecommunications; the development of techniques to measure extremely low levels of radioactivity, a topic of interest to both public health and safety as well as national defense; unique engineering challenges (including working in and maintaining an ultra-low radioactivity environment deep underground) that push the level of understanding of materials and the uses to which they can be put.

Liquid scintillator, let alone metal-loaded liquid scintillator, is a complex substance with intricate optical properties. The absorption and scattering lengths in the target volume for SNO+ will vary from ~20m for pure LAB in the solar phase to ~6m for 0.3% Nd loading in the double beta decay phase. Precise calibration and monitoring of these properties is therefore crucial to the event reconstruction and energy resolution and, thus, to the success of the experiment in all of its phases. This proposal specifically targets these issues though further develpment of the UK optical calibration system.

A pulse-monitored laser system along the lines proposed for development in this proposal would also have the potential for wider applicability outside of SNO+. Many other experiments have the need to make use of similar systems and, to some extent, this proposal represents the continued evolution of systems successfully employed on projects such as MINOS and Double Chooz. A number of large-scale liquid detectors proposed as future projects could also benefit from such a system, such as LENA, HanoHano, HyperK and LBNE. There are also potential applications outside of particle physics. In particular, applications involving precise monitoring in remote or hazardous environments might benefit from such a system. As one example, a group of nuclear scientists has proposed the use of a similar but much less sophisticated system to monitor real-time uranium leakage in cooling and condensation water during reprocessing (Lee, Shin and Kang, Journal of Korean Nuclear Society, Vol. 33, 2001). Similarly, the further development and characterisation of a new fast driver circuit for LEDs would provide a calibration system of significant interest both to SNO+ and to the next generation of scintillator or water Cherenkov systems as well as other applications where a reliable, fast-pulsed light source is required. Therefore, the R&D associated with this application has a natural link to critical problems in other areas of potential interest. We aim to publically disseminate the information derived from this reasearch via journal and electronic publications, international conference and workshop talks and proceedings, and open discussions with academics and representatives from industry.