Los Alamos Women in Science
Northern Chapter of the New Mexico Network for Women in Science and Engineering

sponsored by
the   Synergy Center  ,   the   Zocher Corporation
and the Bradbury Science Museum
Talk at 12:00, Tuesday, July 12, 2005
Bldg 1, Los Alamos Research Park
Synergy Center Conference Room, 3rd flr

Roberta N. Mulford, NMT-15, LANL
Radiation Damage and Aging in Plutonium Metal

The density of plutonium metal decreases as a function of time, over 30 years or more. Variations in the rate of change have been observed. A decrease in the density is expected with increasing age, as radiation damage resulting from the decay of the plutonium is complemented by the buildup of helium within the lattice, a product of that decay. Densities of a set of plutonium samples cut from retired pits exhibit decreases in density from the known manufactured density. Linear fits to the densities of the group of samples of various ages give two rates. Samples between about 20 and about 35 years of age exhibit a rate of about -0.005 %/annum, which is fairly consistent with independent measurements of the emergence of helium bubbles within the metal, and with theoretical predictions of the rate of helium bubble formation and growth. The rate of density decrease changes with age, and the density appears to decrease more rapidly for samples older than about 36 years. Older samples exhibit a rate of change in density of -0.06%/annnum. Each sample, measured repeatedly over two or more years shows a rate of change nearly commensurate with the rate determined by comparing different samples with various ages. Some samples are not consistent with the global rate, and some appear to increase in density. Possible systematic errors have been suggested to explain the observed decreases in density and the various rates of change observed among the individual samples. The possible magnitudes of these systematic errors are discussed, and shown to be too small to account for the observed changes.
(Work done with E. Ann Trujillo and Wendel Brown, LA-UR-04-3097.)

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