Direct measurements have been made on the average singlehyphen;particle kinetic energies, lang;Ekrang;, of a series of solid and liquid specimens of heavy noble gases near melting. To do this, the distributions of energy losses of incident eV neutrons, scattered at angles ranging from 87 to 136 deg, were analyzed on the assumptions that atoms in these specimens have a Gaussian momentum distributionn(p) and that for these experimental conditions the atoms scatter independently of one another. It is known that the solids, Ar, Kr, and Xe show considerable differences in such characteristics as (a) their respective ratios of triple point to Debye temperatures, (b) the extent of multibody force contributions to cohesion, and (c) phonon anharmonicity. Regardless, it is found for all three solids near their respective triple points that lang;Ekrang; is equal to the equipartition value (3/2)kTwell within the various estimated experimental uncertainties of 3percnt; to 7percnt;. Moreover, liquid Kr near its triple point yields the same result, as does liquid Xe at temperature up to 1.8 times its triple point temperature. Because all these systems are expected to be classical at these temperatures, these results demonstrate applicability of this neutron recoil method to determine lang;Ekrang; even of heavy atoms in suitable cases where a value may not be known in advance.
展开▼
