Nuclear-Polarized Phases of H Atoms Embedded in Solid Molecular Hydrogen Films

We report on an electron-spin resonance study of nuclear-polarized phases of hydrogen atoms embedded in solid H2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{2}$$\end{document} films at temperatures 0.1–1.5 K and a high magnetic field of 4.6 T. The H atoms in solid H2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{2}$$\end{document} were generated by two different dissociation techniques: a cryogenic rf-discharge and bombardment by 5.7 keV electrons via tritium decay. In both studies, we observed a build-up of a spontaneous nuclear-polarized phase (SNPP, p=0.35) at temperatures below ∼\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim $$\end{document}0.8 K similar to that reported in our previous work. We were also able to create a highly nuclear-polarized phase (HNPP, p≃\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$p\simeq $$\end{document}0.75) using Dynamic Nuclear Polarization for samples exposed to a cryogenic rf discharge, whereas we failed to obtain this phase for the samples bombarded by 5.7 keV electrons. We suggest that failing to achieve the HNPP in the samples exposed to high-energy electrons released during tritium decay may be explained by an effect of faster nuclear relaxation stimulated by electrons bombarding the H2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{2}$$\end{document} matrix and rapidly relaxing centers in the film substrate created during accumulation of H atoms in solid H2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{2}$$\end{document}.