Measurement of UCN scattering cross section of liquid and solid deuterium
In a recent UCN transmission experiment (3-14-311) on liquid and solid ortho-deuterium we could - for the first time - nearly perfectly interpret the measured scattering cross section in the liquid state (T = 20 K) with appropriate scattering laws. The same attempt in the solid state (T = 16 K) revealed an excess cross section of about 30 barn relative to theory. This cross section turned out to be velocity-independent, as opposed to the usual 1/v behaviour in the UCN region, and is hence of elastic origin. In a first approach we ascribed this excess cross section to defects in sD2 (cracks, voids), i. e. to a volume effect. A simple Guinier approximation - scaled properly to the UCN region- yields a cross section of about 30 barns in sD2. To scrutinize the bulk nature of the excess cross section, we plan a UCN transmission experiment performed with different sample thicknesses, strictly observing the necessary condition Sigma*D <1 to avoid uncorrectable multiple scattering. This proposal is part of a beginning PhD-thesis "UCN scattering cross sections of the cold hydrogens".
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GUTSMIEDL Erwin; Stefan Döge; GELTENBORT Peter; GUARINI Eleonora; LAUER Thorsten and MORKEL Christoph. (2015). Measurement of UCN scattering cross section of liquid and solid deuterium. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.3-14-351
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