Comparison of the thermal stability of β- and β″-alumina at high pressures

The high-pressure thermal stability of Na⁺ β-alumina and magnesium-stabilized Na⁺ β″-alumina was studied from 5 to 50 Kb and from room temperature to 1400°C. Above 5 Kb and 560°C, Na⁺ β-alumina decomposes into α-Al₂O₃ and NaAlO₂. Magnesium-stabilized Na⁺ β″-alumina decomposes at slightly higher temperatures to α-Al₂O₃, MgAl₂O₄, and probably NaAlO₂. Estimates of activation volume and enthalpy support a model for decomposition that depends on cation vacancies and proceeds by sodium diffusion in quasi-liquid conduction planes.     

Spectroscopic strengths for 6Li-induced alpha-particle transfers on 24Mg

²⁴Mg(⁶Li, d) angular distributions for transitions to low-lying states in ²⁸Si are well fitted by exact finite-range DWBA calculations and yield relative spectroscopic strengths in good agreement with theoretical predictions as well as with the corresponding results from other α-particle transfer reactions.     

The peel test in experimental adhesive-fracture mechanics

Several test specimens have been proposed for obtaining adhesive-fracture energy, γa, in bond systems. These tests include blister, cone, lap-shear and peel tests. Peel tests have been used for many years to compare relative strengths of different adhesives, different surface-preparation techniques, etc. This paper demonstrates the potential use of peel tests in obtaining γa values. There are several reasons for devloping the peel test for fracture-mechanics work. First, most laboratories have facilities for preparing peel specimens. In addition, the adhesivefracture energy has recently been shown to be a function of loading mode. In peel tests, various combinations of Mode I and Mode II loadings can be applied by varying the peel angle. Peel-test-analysis methods discussed include closed-form solutions for particular peel-specimen geometries loaded with a given force and numerical techniques for general peel-specimen analysis. This paper also points out the difference between debond load and maximum peel load. The debond-load to maximum-load ratio is shown to depend upon adhesive type but independent of load rate over three decades of time for two different adhesive systems tested.     

Experimental and computational simulation of beta-dose heterogeneity in sediment

Interpreting the spread in equivalent-dose estimates is an important aspect of optically stimulated luminescence (OSL) dating. Ideally, prior to age estimation, an assessment should be made of the likely spread in equivalent dose due to dose-rate heterogeneity in the sediment. Such a procedure would greatly increase the validity of OSL ages, particularly for sediments susceptible to partial bleaching, and for sediments with coarse or poorly sorted grain-size distributions. In this paper we take a step towards a general model of dose-rate heterogeneity by simulating the ⁴⁰K-derived beta dose to quartz. We present an experimental simulation of the ⁴⁰K beta dose, and compare the results with a Monte Carlo simulation of the same experiment. The experiment uses artificially produced ²⁴Na to simulate the ⁴⁰K beta dose to quartz, allowing a large, heterogeneous dose to be administered in a short period of time. The Monte Carlo simulation correctly predicts the shape of the equivalent-dose distribution, but underestimates the spread in dose received by different grains. The experimental set-up provides a new avenue of research into beta-dose heterogeneity.