Experiments and Monte Carlo Analysis for the Optical Properties of the Scintillator in SNO+

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Liu, Xu
Liquid Scintillator , Optical Properties , SNO+ , Nd-loaded , Radioactive Backgrounds
The SNO+ experiment will be the SNO detector filled with a neodymium-loaded liquid scintillator instead of heavy water. SNO+ will be used to detect neutrinos of much lower energy. Also, SNO+ will conduct a search for neutrinoless double beta decay with Nd-150. The Nd-loaded scintillator in SNO+ will be made from linear alkylbenzene (LAB). Both the LAB solvent and the Nd loading are new developments. The optical properties of this scintillator and information about radioactive backgrounds should be studied. A calibration source known as the scintillator bucket was deployed in the water-filled SNO detector in order to study some optical properties of Nd-loaded scintillator, raw LAB scintillator and distilled LAB scintillator. Using a neutron source attached to the bucket to produce events with known energy, with a model of the scintillator bucket simulated by an analysis tool called RAT, the light yield of the scintillator could be determined by comparing data measurements with simulations. This allowed the light yield, one of the main optical properties of the scintillator, to be measured and that value to be corrected in the Monte Carlo. The bucket was deployed both at the centre of the detector and at the bottom. After subtracting backgrounds from radon introduced in the scintillator during preparation and filling, constraints on the amount of Po-210 were obtained. Estimates on the K-40 content of the Nd-loaded scintillator were obtained by analyzing the radon-subtracted background spectra. By comparing the background spectra with the bucket deployed at the bottom of the acrylic vessel with spectra from the bucket at the centre, it was possible to estimate the K-40 content of the acrylic vessel.
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