3-D Wave Propagation in Cylindrical Single Crystal Solid-Liquid Bodies

The large difference in the ultrasonic velocity between the solid and the liquid phases of most semiconducting materials results in reflection/refraction of ultrasound at solid-liquid interfaces and an interest in using laser ultrasonics for sensing solid-liquid interfaces during single crystal growth. Using a ray tracing analysis, a set of measured ultrasonic time of flight (TOF) projection data can yield the ray paths connecting the source to the receiver, which can subsequently be used to reconstruct the solid-liquid interface. In previous work [1] 2-D wave propagation in cylindrical single crystal solid-liquid bodies was used to explore the feasibility of using ultrasound to characterize solid-liquid interfaces during vertical Bridgman growth of semiconductor materials. Detailed study of ray paths, wavefronts and TOF for ultrasound propagating in both transverse and diametral planes of liquid-solid single crystal (Ge) bodies was reported. Numerical simulations indicated that the magnitude and direction of the group velocity, the solid:liquid velocity ratio and the curvature of the interface together controlled the ray bending behavior and thus determined the ultrasonic data across the interface. Knowledge of ray paths at the interface enabled reconstruction of the interface using a small set of ultrasonic TOF’s

Search for Neutrinoless Double-Beta Decay in 136^{136}Xe with EXO-200

We report on a search for neutrinoless double-beta decay of $^{136}$Xe with EXO-200. No signal is observed for an exposure of 32.5 kg-yr, with a background of ~1.5 x 10^{-3} /(kg yr keV) in the $\pm 1\sigma$ region of interest. This sets a lower limit on the half-life of the neutrinoless double-beta decay $T_{1/2}^{0\nu\beta\beta}$($^{136}$Xe) > 1.6 x 10$^{25}$ yr (90% CL), corresponding to effective Majorana masses of less than 140-380 meV, depending on the matrix element calculation

Investigation of radioactivity-induced backgrounds in EXO-200

The search for neutrinoless double-beta decay (0{\nu}{\beta}{\beta}) requires extremely low background and a good understanding of their sources and their influence on the rate in the region of parameter space relevant to the 0{\nu}{\beta}{\beta} signal. We report on studies of various {\beta}- and {\gamma}-backgrounds in the liquid- xenon-based EXO-200 0{\nu}{\beta}{\beta} experiment. With this work we try to better understand the location and strength of specific background sources and compare the conclusions to radioassay results taken before and during detector construction. Finally, we discuss the implications of these studies for EXO-200 as well as for the next-generation, tonne-scale nEXO detector.Comment: 9 pages, 7 figures, 3 table