First positron annihilation lifetime measurement of Pu

Colmenares, C.A.; Howell, R.H.; Ancheta, D.; Cowan, T. E.; Hanafee, J.; Sterne, P.A.

doi:10.2172/491854

Cited by 4 publications

(4 citation statements)

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“…Experimental positron-annihilation lifetime measurements by Colmenares and Howell of 21-and 35-yr-old Pu-Ga alloys indicate the existence of He-vacancy complexes with a ratio of ϳ1 He/vacant site. 29,30 TEM characterization of aged Pu-Ga alloys is currently under way to verify the modeling predictions of Wolfer. The ability to image 1-nm microstructural features in the TEM is a challenging endeavor, made even more difficult by the highly oxidizing surface of a freshly prepared Pu specimen.…”

Section: Helium Accumulationmentioning

confidence: 96%

Fundamental Studies of Plutonium Aging

Wirth¹,

Schwartz²,

Fluss³

et al. 2001

MRS Bull.

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Plutonium metallurgy lies at the heart of science-based stockpile stewardship. One aspect is concerned with developing predictive capabilities to describe the properties of stockpile materials, including an assessment of microstructural changes with age. Yet, the complex behavior of plutonium, which results from the competition of its 5f electrons between a localized (atomic-like or bound) state and an itinerant (delocalized bonding) state, has been challenging materials scientists and physicists for the better part of five decades. Although far from quantitatively absolute, electronic-structure theory provides a description of plutonium that helps explain the unusual properties of plutonium, as recently reviewed by Hecker. (See also the article by Hecker in this issue.) The electronic structure of plutonium includes five 5f electrons with a very narrow energy width of the 5f conduction band, which results in a delicate balance between itinerant electrons (in the conduction band) or localized electrons and multiple lowenergy electronic configurations with nearly equivalent energies. These complex electronic characteristics give rise to unique macroscopic properties of plutonium that include six allotropes (at ambient pressure) with very close free energies but large (∼25%) density differences, a lowsymmetry monoclinic ground state rather than a high-symmetry close-packed cubic phase, compression upon melting (like water), low melting temperature, anomalous temperature-dependence of electrical resistance, and radioactive decay. Additionally, plutonium readily oxidizes and is toxic; therefore, the handling and fundamental research of this element is very challenging due to environmental, safety, and health concerns.

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Section: Helium Accumulationmentioning

confidence: 96%

Fundamental Studies of Plutonium Aging

Wirth¹,

Schwartz²,

Fluss³

et al. 2001

MRS Bull.

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“…Positron lifetime measurements on aged plutonium samples produced a single component lifetime of 184 picoseconds (ps) [31], indicating that all the positrons annihilate from the same type of state; either all the positrons remained in extended bulk-states, or they all trapped in similar defect states. Positron lifetime calculations were performed using our first principles approach [25] based on the linear muffin tin orbital method.…”

Section: Vacancies In Plutonium Studied By Positron Annihilationmentioning

confidence: 99%

Electronic structure calculations of vacancies and their influence on materials properties

Sterne

Howell

1998

Computational Materials Science

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August 1997This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. PREPRINTThis paper was prepared for submittal to the DISCLAIMER This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.

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“…The same measurements indicate that these vacancies are filled with helium generated through a decay rather than H-induced SAVs. [11][12][13] Beyond efforts to measure x V , H diffusivity measurements show a concentration dependence in the dilute regime (o1 at%) that has been posited to demonstrate SAV formation in d-Pu. The SAVs are assumed to trap dissolved H and therefore change the observed diffusivity.…”

Section: Introductionmentioning

confidence: 99%