Uniform solid deuterium--tritium fuel layers resulting from radioactively induced sublimation

Recently, it has been demonstrated that radioactive self-heating in a solid can induce preferential sublimation from thicker, warmer layers to thinner, cooler ones, thus tending to make the layers become uniform in thickness. Following experiments in pure T2 , we have investigated solid deuterium--tritium (DT) in optical cells with isothermal boundaries. Backlighting permits direct observations with a telescope and a video camera. As the temperature is lowered, we follow the stages of condensation, freezing, and subsequent layer equilibration or isotropization. Measured rate constants for freshly prepared DT samples agree well with the theoretically determined value of 26.6 min. Due to the impedance presented by 3 He in the vapor space, the rate constants for solid layers made from aged DT increase by nearly 12 min/day. Equilibrated shells of solid DT exhibit slow optical degradation, presumably due to 3He accumulation at grain boundaries. The optical effects can be reduced by annealing near the triple point