Title: Novel measurements of nuclear spin cross-relaxation in metal hydrides
Abstract: Recent NMR measurements of proton relaxation have shown an unexpected frequency dependence in several metal-hydrogen systems at low temperatures. An explanation proposed by the Ames group involves cross-relaxation of protons to quadrupolar metal nuclei. We test this hypothesis with relaxation experiments involving large amplitude field modulation. The field modulation sweeps the proton resonance through the distribution of metal frequencies. Thus the protons come into contact with more metal nuclei, increasing the proton relaxation rate. Relaxation measurements have been performed on several samples and the proton resonance frequency, the modulation frequency and the modulation amplitude have been varied. Also, proton relaxation rates T1−1 have been measured on slowly spinning samples where the rotation produces periodic variations of the metal quadrupolar frequencies.