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Languages : en
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The most intense sources of ultra cold neutrons (UCN) have bee built at reactors where the high average thermal neutron flux can overcome the low UCN production rate to achieve usable densities of UCN. At spallation neutron sources the average flux available is much lower than at a reactor, though the peak flux can be comparable or higher. The authors have built a UCN source that attempts to take advantage of the high peak flux available at the short pulse spallation neutron source at the Los Alamos Neutron Science Center (LANSCE) to generate a useful number of UCN. In the source UCN are produced by Doppler-shifted Bragg scattering of neutrons to convert 400-m/s neutrons down into the UCN regime. This source was initially tested in 1996 and various improvements were made based on the results of the 1996 running. These improvements were implemented and tested in 1997. In sections 2 and 3 they discuss the improvements that have been made and the resulting source performance. Recently an even more interesting concept was put forward by Serebrov et al. This involves combining a solid Deuterium UCN source, previously studied by Serebrov et al., with a pulsed spallation source to achieve world record UCN densities. They have initiated a program of calculations and measurements aimed at verifying the solid Deuterium UCN source concept. The approach has been to develop an analytical capability, combine with Monte Carlo calculations of neutron production, and perform benchmark experiments to verify the validity of the calculations. Based on the calculations and measurements they plan to test a modified version of the Serebrov UCN factory. They estimate that they could produce over 1,000 UCN/cc in a 15 liter volume, using 1 [micro]amp of 800 MeV protons for two seconds every 500 seconds. They will discuss the result UCN production measurements in section 4.
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Languages : en
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Book Description
The most intense sources of ultra cold neutrons (UCN) have bee built at reactors where the high average thermal neutron flux can overcome the low UCN production rate to achieve usable densities of UCN. At spallation neutron sources the average flux available is much lower than at a reactor, though the peak flux can be comparable or higher. The authors have built a UCN source that attempts to take advantage of the high peak flux available at the short pulse spallation neutron source at the Los Alamos Neutron Science Center (LANSCE) to generate a useful number of UCN. In the source UCN are produced by Doppler-shifted Bragg scattering of neutrons to convert 400-m/s neutrons down into the UCN regime. This source was initially tested in 1996 and various improvements were made based on the results of the 1996 running. These improvements were implemented and tested in 1997. In sections 2 and 3 they discuss the improvements that have been made and the resulting source performance. Recently an even more interesting concept was put forward by Serebrov et al. This involves combining a solid Deuterium UCN source, previously studied by Serebrov et al., with a pulsed spallation source to achieve world record UCN densities. They have initiated a program of calculations and measurements aimed at verifying the solid Deuterium UCN source concept. The approach has been to develop an analytical capability, combine with Monte Carlo calculations of neutron production, and perform benchmark experiments to verify the validity of the calculations. Based on the calculations and measurements they plan to test a modified version of the Serebrov UCN factory. They estimate that they could produce over 1,000 UCN/cc in a 15 liter volume, using 1 [micro]amp of 800 MeV protons for two seconds every 500 seconds. They will discuss the result UCN production measurements in section 4.
Author: France. Commissariat général du plan
Publisher:
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Category :
Languages : en
Pages : 402
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Author:
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Category : Laboratories
Languages : en
Pages : 466
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Author:
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Category : Chemistry
Languages : en
Pages : 232
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Author: Francisco J. Bermejo
Publisher: Elsevier Inc. Chapters
ISBN: 0128066482
Category : Science
Languages : en
Pages : 130
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Book Description
This chapter reviews the most significant developments that have taken place in the design, construction, and operation of new neutron sources as well as the refurbishment programs of others already serving the neutron-scattering community. Such advances in neutron production devices are to be considered in conjunction with impressive achievements in the optimization of neutron delivery systems as well as in neutron instrumentation which overall resulted in a truly remarkable improvement in neutron count rates. As a result, the capabilities of experimental neutron sources are nowadays larger than ever before, despite there being fewer sources available. It is also worth remarking the coming into line of compact, accelerator-driven neutron sources as well as work carried out at small research reactors which, as exemplified during the past decade, have played an important role in helping the large, user-based facilities to carry out development work geared toward the achievement of full performance.
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Category : Power resources
Languages : en
Pages : 806
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Semiannual, with semiannual and annual indexes. References to all scientific and technical literature coming from DOE, its laboratories, energy centers, and contractors. Includes all works deriving from DOE, other related government-sponsored information, and foreign nonnuclear information. Arranged under 39 categories, e.g., Biomedical sciences, basic studies; Biomedical sciences, applied studies; Health and safety; and Fusion energy. Entry gives bibliographical information and abstract. Corporate, author, subject, report number indexes.
Author: Susan J Seestrom
Publisher: World Scientific
ISBN: 9814571687
Category : Science
Languages : en
Pages : 193
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There is a great interest in improving the limits on neutron lifetime to the level of a precision of 0.1 s. The neutron lifetime is both an important fundamental quantity as well as a parameter influencing important processes such as nucleosynthesis (Helium production in the early universe) and the rate of energy production in the Sun.Aiming to create a roadmap of R&D for a next generation neutron lifetime experiment that can be endorsed by the North American neutron community, the focus of the workshop was on experiments using traps that utilize ultracold neutrons and confinement by a combination of magnetic and/or gravitational interaction in order to avoid systematic uncertainties introduced by neutron interactions with material walls. The papers in this volume summarize the limitations of present experiments, the discussion of new experiments in planning stage, and the discussion of systematic effects that must be addressed to achieve a lifetime measurement at an accuracy of 0.1 second.Cover image courtesy of Elena Fernández, Los Alamos National Laboratory.
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Publisher: Academic Press
ISBN: 0123983851
Category : Science
Languages : en
Pages : 570
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Book Description
This work covers in some detail the application of neutron scattering to different fields of physics, materials science, chemistry, biology, the earth sciences and engineering. Its goal is to enable researchers in a particular area to identify aspects of their work in which neutron scattering techniques might contribute, conceive the important experiments to be done, assess what is required to carry them out, write a successful proposal for one of the major user facilities, and perform the experiments under the guidance of the appropriate instrument scientist. The authors of the various chapters take account of the advances in experimental techniques over the past 25 years--for example, neutron reflectivity and spin-echo spectroscopy and techniques for probing the dynamics of complex materials and biological systems. Furthermore, with the third-generation spallation sources recently constructed in the United States and Japan and in the advanced planning stage in Europe, there is an increasing interest in time-of-flight techniques and short wavelengths. Correspondingly, the improved performance of cold moderators at both reactors and spallation sources has extended the long-wavelength capabilities. Chapter authors are pre-eminent in their field Seminal experiments are presented as examples Provides guidance on how to plan, execute and analyse experiments
Author: American Nuclear Society
Publisher:
ISBN:
Category : Nuclear engineering
Languages : en
Pages : 952
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Category :
Languages : en
Pages : 6
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Ultra Cold Neutrons (UCN) can be produced at spallation sources using a variety of techniques. To date the technique used has been to Bragg scatter and Doppler shift cold neutrons into UCN from a moving crystal. This is particularly applicable to short-pulse spallation sources. We are presently constructing a UCN source at LANSCE using this method. In addition, large gains in UCN density should be possible using cryogenic UCN sources. Research is under way at Gatchina to demonstrate technical feasibility of a frozen deuterium source. If successful, a source of this type could be implemented at future spallation sources, such as the long pulse source being planned at Los Alamos, with a UCN density that may be two orders of magnitude higher than that presently available at reactors.
