27The structure of liquid alumina at a temperature ≈2400 K near to its melting point was measured using 28 neutron and high-energy x-ray diffraction by employing containerless aerodynamic-levitation and laser-29 heating techniques. The measured diffraction patterns were compared to those calculated from molecular 30 dynamics simulations using a variety of pair potentials, and the model found to be in best agreement with 31 experiment was refined by using the reverse Monte Carlo (
The structure and thermal characteristics of aerodynamically levitated samples of yttria-alumina in the liquid, supercooled liquid and solid phases were explored in an extensive series of high energy x-ray diffraction, small angle neutron scattering, and pyrometric cooling measurements. Particular focus was placed on the compound (Y2O3)(x)(Al2O3)(1-x) with x = 0.2 for which a liquid-liquid phase transition at a temperature of 1788 K has recently been reported. No structural or thermal signature in support of this metastable phase transition could be found.
Barnes et al. Reply: Greaves et al. [1] raise issues regarding our Letter [2] which contested the validity of a reported [3] first-order liquid-liquid transition (LLT) in supercooled ðY 2 O 3 Þ x ðAl 2 O 3 Þ 100Àx (or AYx) with x ¼ 20. The principal concerns are (i) our use of uncorrected pyrometric temperature data, (ii) the accuracy of the composition of our samples, and (iii) surface scattering dominating our SANS signal.(i) An emissivity correction of ¼ 0:92 [4] implies an underestimate in temperature of 30 K at 2273 K which is small compared to the temperature gradient across a levitated sample (see the pyrometry traces in Fig. 1 of [1]). An emissivity correction does not materially affect the conclusions presented in [2]. The calculated cooling curves in [2] are correct with respect to the explicitly stated molar normalizations.(ii) Gravimetric and electron probe methods show that our sample compositions are reliably reproduced to AE1%[5], consistent with their visual appearance [5]. Also, our AY20 samples supercooled and crystallized at ' 1500 K, well below the AY15 crystallization temperature of ' 1925 K [3]. The assertion in [1] that our AY20 sample corresponds to AY15 is mainly from the peak positions and heights in the measured x-ray structure factor SðQÞ. Figure 1 shows these parameters (determined from the numerical data sets of [1,3,6] and from additional experiments) and also shows that our measured SðQÞ for AY20 compares favorably with the revised Advanced Photon Source (APS) data [1]. Differences in peak positions will arise from systematic errors in different diffractometer calibrations.(iii) A component of the SANS signal will come from the surface of our levitated sample and, for a spherical sample, will have a cutoff at Q ¼ 0:015 A À1 followed by a Q À4 falloff. In the absence of sample density fluctuations this would constitute the only SANS signal. However, calculations based on simple models show that this would not mask a change taking place in the SANS signal from the reported LLT [3]. In contrast, SAXS experiments of the type used in [3] need to stably maintain the sample and incident beam positions to better than 10 m.Greaves et al.[1] interpret the pyrometry data from our SANS experiment (trace B in their Fig. 1) as arising from a polyamorphic rotor, without reference to any other experimental observations. The temperature variations were, however, clearly observed to result from a small gas bubble in the sample which led to rotational instability. Given the evidence in (ii) that our sample is AY20, the assumption of a polyamorphic rotor would imply a second LLT in AY20 at 1927 K, an unlikely scenario.
Building a 0νββ experiment with the ability to probe neutrino mass in the inverted hierarchy region requires the combination of a large detector mass sensitive to 0νββ, on the order of 1-tonne, and unprecedented background levels, on the order of or less than 1 count per year in the 0νββ signal region. The Majorana Collaboration proposes a design based on using high-purity enriched 76 Ge crystals deployed in ultra-low background electroformed Cu cryostats and using modern analysis techniques that should be capable of reaching the required sensitivity while also being scalable to a 1-tonne size. To demonstrate feasibility, the collaboration plans to construct a prototype system, the Majorana Demonstrator, consisting of 30 kg of 86% enriched 76 Ge detectors and 30 kg of natural or isotope-76-depleted Ge detectors. We plan to deploy and evaluate two different Ge detector technologies, one based on a p-type configuration and the other on n-type.
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