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Positron Annihilation In Plutonium
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Book Synopsis Positron Annihilation in Plutonium by : Gary Thomas Barnes
Download or read book Positron Annihilation in Plutonium written by Gary Thomas Barnes and published by . This book was released on 1970 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Theory of Positron Annihilation in Helium-Filled Bubbles in Plutonium by : J. E. Pask
Download or read book Theory of Positron Annihilation in Helium-Filled Bubbles in Plutonium written by J. E. Pask and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Positron annihilation lifetime spectroscopy is a sensitive probe of vacancies and voids in materials. This non-destructive measurement technique can identify the presence of specific defects in materials at the part-per-million level. Recent experiments by Asoka-Kumar et al. have identified two lifetime components in aged plutonium samples--a dominant lifetime component of around 182 ps and a longer lifetime component of around 350-400ps. This second component appears to increase with the age of the sample, and accounts for only about 5 percent of the total intensity in 35 year-old plutonium samples. First-principles calculations of positron lifetimes are now used extensively to guide the interpretation of positron lifetime data. At Livermore, we have developed a first-principles finite-element-based method for calculating positron lifetimes for defects in metals. This method is capable of treating system cell sizes of several thousand atoms, allowing us to model defects in plutonium ranging in size from a mono-vacancy to helium-filled bubbles of over 1 nm in diameter. In order to identify the defects that account for the observed lifetime values, we have performed positron lifetime calculations for a set of vacancies, vacancy clusters, and helium-filled vacancy clusters in delta-plutonium. The calculations produced values of 143ps for defect-free delta-Pu and 255ps for a mono-vacancy in Pu, both of which are inconsistent with the dominant experimental lifetime component of 182ps. Larger vacancy clusters have even longer lifetimes. The observed positron lifetime is significantly shorter than the calculated lifetimes for mono-vacancies and larger vacancy clusters, indicating that open vacancy clusters are not the dominant defect in the aged plutonium samples. When helium atoms are introduced into the vacancy cluster, the positron lifetime is reduced due to the increased density of electrons available for annihilation. For a mono-vacancy in Pu containing one helium atom, the calculated lifetime is 190 ps, while a di-vacancy containing two helium atoms has a positron lifetime of 205 ps. In general, increasing the helium density in a vacancy cluster or He-filled bubble reduces the positron lifetime, so that the same lifetime value can arise fi-om a range of vacancy cluster sizes with different helium densities. In order to understand the variation of positron lifetime with vacancy cluster size and helium density in the defect, we have performed over 60 positron lifetime calculations with vacancy cluster sizes ranging from 1 to 55 vacancies and helium densities ranging fi-om zero to five helium atoms per vacancy. The results indicate that the experimental lifetime of 182 ps is consistent with the theoretical value of 190 ps for a mono-vacancy with a single helium atom, but that slightly better agreement is obtained for larger clusters of 6 or more vacancies containing 2-3 helium atoms per vacancy. For larger vacancy clusters with diameters of about 3-5 nm or more, the annihilation with helium electrons dominates the positron annihilation rate; the observed lifetime of 180ps is then consistent with a helium concentration in the range of 3 to 3.5 Hehacancy, setting an upper bound on the helium concentration in the vacancy clusters. In practice, the single lifetime component is most probably associated with a family of helium-filled bubbles rather than with a specific unique defect size. The longer 350-400ps lifetime component is consistent with a relatively narrow range of defect sizes and He concentration. At zero He concentration, the lifetime values are matched by small vacancy clusters containing 6-12 vacancies. With increasing vacancy cluster size, a small amount of He is required to keep the lifetime in the 350-400 ps range, until the value saturates for larger helium bubbles of more than 50 vacancies (bubble diameter> 1.3 nm) at a helium concentration close to 1 He/vacancy. These results, taken together with the experimental data, indicate that the features observed in TEM data by Schwartz et al are not voids, but are in fact helium-filled bubbles with a helium pressure of around 2-3 helium atoms per vacancy, depending on the bubble size. This is consistent with the conclusions of recently developed models of He-bubble growth in aged plutonium.
Author :G. M. Hood Publisher :Chalk River, Ont. : Reactor Materials Research Branch, Chalk River Laboratories ISBN 13 :9780660157979 Total Pages :5 pages Book Rating :4.1/5 (579 download)
Book Synopsis The Temperature Dependence of Position Annihilation in @-Hf by : G. M. Hood
Download or read book The Temperature Dependence of Position Annihilation in @-Hf written by G. M. Hood and published by Chalk River, Ont. : Reactor Materials Research Branch, Chalk River Laboratories. This book was released on 1994 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Positron Annihilation by : A.T. Steward
Download or read book Positron Annihilation written by A.T. Steward and published by Elsevier. This book was released on 2012-12-02 with total page 455 pages. Available in PDF, EPUB and Kindle. Book excerpt: Positron Annihilation focuses on the process of positron annihilation in different environments. Partitioned into two parts with 42 chapters, the book contains the contributions of authors who have done research on the annihilation of positrons, which brought about valuable information on the properties of matter. The first part of the book deals with lengthy review articles, including a survey of the physics of positron annihilation; positron annihilation in metals and the theory involved in the process; and positron annihilation in alkali halides and ionic crystals. Positronium formation and interaction in gases, molecular substances, and ionic crystals are also given attention. Gaseous positronics and positron annihilation in condensed gases and liquids are also discussed. The second part of the book focuses on developments on positron annihilation and the direction of research on this field. The studies concentrate on positron annihilation in various crystals, metals, mercury, liquefied gases, helium, and metal oxides. Numerical representations and analyses are presented to support the processes involved. The book can best serve the interest of those who want to explore further the annihilation of positrons.
Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1976-05 with total page 912 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Energy Research Abstracts written by and published by . This book was released on 1987 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Positron Annihilation by : Alec Thompson Stewart
Download or read book Positron Annihilation written by Alec Thompson Stewart and published by . This book was released on 1967 with total page 464 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Positron Annihilation - ICPA-17 by : Zhi Quan Chen
Download or read book Positron Annihilation - ICPA-17 written by Zhi Quan Chen and published by Trans Tech Publications Ltd. This book was released on 2017-03-24 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: Some theoretical aspects, practical results and experimental techniques of use of the positron annihilation phenomena in the research of the structure, defects of structure and other properties of different materials and mediums are covered in this journal volume. It comprises the papers presented at the 17th International Conference on Positron Annihilation (ICPA-17, Wuhan, China, 20-25 September, 2015).
Book Synopsis Plutonium Futures -- The Science by : Gordon D. Jarvinen
Download or read book Plutonium Futures -- The Science written by Gordon D. Jarvinen and published by American Institute of Physics. This book was released on 2003-07-09 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over 1,000 tons of plutonium exist throughout the world in the form of nuclear fuel, nuclear weapons, inventories of various types, and legacy materials. Regardless of ones views of how this condition came to be, or what actions are taken in the future, it is a certainty that large quantities of plutonium must be managed for many decades. Thus it is clear that the plutonium challenge is not only scientific, but political and socioeconomic as well. In view of the global nature of plutonium research efforts, the Plutonium Futures - The Science conference was established to increase awareness of the importance of the scientific underpinnings of plutonium research, and facilitate communication among its international practitioners. The 2003 conference is the third in this series; the two previous conferences were held in Santa Fe in 1997 and 2000. Extended abstracts of the presentations cover the latest results in plutonium condensed matter physics, materials science, compounds and complexes, environmental behavior, detection and analysis, separations and purification, nuclear fuel cycles, and waste isolation and disposal.
Book Synopsis Progress in Positron Annihilation by : Rados?aw Zaleski
Download or read book Progress in Positron Annihilation written by Rados?aw Zaleski and published by Trans Tech Publications Ltd. This book was released on 2010-12-30 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volume is indexed by Thomson Reuters CPCI-S (WoS). The aim of this special collection is to present recent progress made, and reflect current ideas, in research fields where positron and positronium are involved. The contents cover a wide range of positron-related research topics; including both fundamental (theoretical calculations, radiation chemistry, hyperfine interactions, positronium physics and chemistry) and applied (metal, polymer, thin film and other materials, development of experimental techniques) aspects.
Book Synopsis Principles And Applications Of Positron And Positronium Chemistry by : Jerry Y C Jean
Download or read book Principles And Applications Of Positron And Positronium Chemistry written by Jerry Y C Jean and published by World Scientific. This book was released on 2003-04-04 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive description of the principles and applications of positron and positronium chemistry. Pedagogical and tutorial in nature, it will be ideal for graduate students and researchers in the area of positron annihilation spectroscopy. The contributing authors are authoritative scientists prominent in the frontiers of research, actively pursuing positron annihilation research on chemical and applied systems.
Book Synopsis Government Reports Announcements & Index by :
Download or read book Government Reports Announcements & Index written by and published by . This book was released on 1988 with total page 1132 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis ERDA Energy Research Abstracts by : United States. Energy Research and Development Administration
Download or read book ERDA Energy Research Abstracts written by United States. Energy Research and Development Administration and published by . This book was released on 1976 with total page 772 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Scientific and Technical Aerospace Reports by :
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1971 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Positron Annihilation by : Wayne State University
Download or read book Positron Annihilation written by Wayne State University and published by . This book was released on 1967 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Nuclear Science Information of Japan by :
Download or read book Nuclear Science Information of Japan written by and published by . This book was released on 2002 with total page 234 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Annihilation of Positrons in Solids by : Ing-Jiunn Ma
Download or read book Annihilation of Positrons in Solids written by Ing-Jiunn Ma and published by . This book was released on 1960* with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: