Deuterium atoms and molecules in nanoclusters of molecular deuterium

Abstract

Impurity-helium solids created by injecting deuterium atoms and molecules into superfluid ${}^{4}\mathrm{He}$ have been studied via x-ray-diffraction and electron-spin-resonance (ESR) techniques. X-ray-diffraction measurements show that these solids are highly porous gel-like structures consisting of ${\mathrm{D}}_{2}$ clusters with the characteristic cluster size of $90\ifmmode\pm\else\textpm\fi{}30\mathrm{\AA{}}.$ The densities of ${\mathrm{D}}_{2}$ molecules in the samples are $7\ifmmode\times\else\texttimes\fi{}{10}^{20}--3\ifmmode\times\else\texttimes\fi{}{10}^{21}{\mathrm{cm}}^{\ensuremath{-}3}.$ Each of the ${\mathrm{D}}_{2}$ clusters are either partially or totally surrounded by thin layers of adsorbed helium which may play an important role in preventing the coalescence of the clusters into larger crystallites of solid ${\mathrm{D}}_{2}.$ Using ESR, we find that average concentrations of D atoms of order $1\ifmmode\times\else\texttimes\fi{}{10}^{18}{\mathrm{cm}}^{\ensuremath{-}3}$ can be achieved in our samples. Measurements of the ground-state spectroscopic parameters and relaxation times of atomic deuterium show that the D atoms reside in the ${\mathrm{D}}_{2}$ clusters. The combined x-ray and ESR data show that local concentrations of D atoms as large as $2\ifmmode\times\else\texttimes\fi{}{10}^{19}{\mathrm{cm}}^{\ensuremath{-}3}$ are obtained in our experiments. The highly porous deuterium nanostructures studied in this work are promising for the production of high concentrations of ultracold neutrons and for significant nuclear polarization of ${\mathrm{D}}_{2}$ molecules by the ``brute force method'' at low temperatures.