BETA-LAYERING OF SOLID DEUTERIUM-TRITIUM IN A SPHERICAL POLYCARBONATE SHELL

We have examined two of the variables that affect the beta-layering process in which nonuniform layers of solid deuterium-tritium (DT) are driven toward uniformity by beta-decay induced sublimation. For these experiments, a 9 mm diameter polycarbonate sphere was partially filled with a 50-50 mix of DT liquid, frozen, and then held at 17 K. We measured the equilibration time constant tau as functions of solid layer thickness, He-4 exchange gas pressure, and age. Solid layer thicknesses ranged from 200-mu-m to 650-mu-m, exchange gas pressures from 0 to 600 torr, and age from 0 to 104 days. Results show a significant final solid layer anisotropy with exchange gas pressures above 5 torr, and tau values that increased with age by 0.01 min/day for 200-mu-m-thick layers, and by 0.5 min/day for 650-mu-m-thick layers. The time constant is shown to be a weak function of exchange gas pressure.