Crystal properties and radiation effects in solid molecular hydrogens.

摘要

The crystal lattice structure, growth shapes and helium generated by beta-decay of solid deuterium-tritium (DT) mixtures have been studied. Understanding of these D-T properties is important for predicting and optimizing the target design of the National Ignition Facility (NIF).; Raman spectroscopy showed the D-T crystal structure is hexagonal close packed, common to the nontritiated isotopes. The isotopic mixtures of both tritiated and nontritiated species broadens the rotational transitions, especially of the lighter species in the mixture. The vibrational frequencies of each isotope is shifted to higher energy in the mixture than the pure components. The J = 1–0 population decreases exponentially with a 1/e time constant which rapidly increases above 10.5 K for both D₂ and T₂ in D-T. The conversion rate is nearly constant from 5 K to 10 K for both D ₂ and T₂ at 7.1 hours and 2.1 hours, respectively.; The smoothing of D-T layers by beta decay heating is limited by the crystal surface energy. Deuterium and hydrogen-deuteride crystals were grown at a number of temperatures below the triple point to determine the surface energy and roughening transition. Several distinct crystal shapes were observed on a number of different substrates. The a facet roughens between 0.9 T _TP and T_TP, while the c facet persists up to the melting temperature. This is very different from the behavior of the other rare gas crystals which grow completely rounded above 0.8 T_TP.; Helium bubbles formed as a product of the beta decay were observed using optical microscopy and the diffusion of smaller bubbles measured with dynamic light scattering. Bubble diffusion coefficients as high as 2.0 × 10 −16 m2/s were measured for 10–50 nm bubbles. The bubbles move in response to a thermal gradient, with speeds between 1 μm/s and 100 μm/s for thermal gradients and temperatures appropriate to NIF targets.