Measurements of the Nuclear Spin Relaxation Times for Small Grains of Solid Hydrogen Suspended in Liquid Helium

Abstract

Measurements of the nuclear spin-lattice relaxation times (T 1 ) and the nuclear spin-spin relaxation times (T 2 ) are reported for suspensions of small grains of solid hydrogen in liquid helium. The measurements have been carried out for temperatures 1.8 < T < 4.9 K and for a nuclear Larmor frequency of 4.0 MHz. The samples were prepared by rapid condensation of hydrogen'and helium gas in a precooled cell. The hydrogen pressure was maintained below the triple point to prepare a slush of hydrogen particles in liquid helium. The characteristic relaxation times are much shorter, typically by an order of magnitude for T 2 , than those observed and reported previously for bulk samples of solid hydrogen for the same ortho-hydrogen concentrations and applied magnetic fields. Possible origins for this difference between the relaxation in bulk and micro-geometries are discussed.