摘要:

Despite the end-of-year timing, 90 scientists attended the Neutrons and Numerical Methods Workshop held at ILL from December 9–12, 1998. While the majority of the participants came from Europe, both east and west, neutron centers in the United States (NIST and Los Alamos) were represented, and the most distant visitors were from Japan and Argentina. But the most striking aspect of the participants as a whole was the average age. Many of the senior scientists commented on how many young postgraduates came to the meeting.

ISSN:1044-8632    

DOI:10.1080/10448639908233665

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The VIII School on Neutron Physics was held from August 30 to September 5, 1998 i n Dubna, Rubbia and was hosted by the Joint Institute for Nuclear Research and Moscow State University. The 1998 school was oriented towards students and post-graduates with the aim ofacquainting young scientists with the possibilities offered by neutrons in different fields of research.

ISSN:1044-8632    

DOI:10.1080/10448639908233666

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The SNS Neutron Instrumentation Workshop and Oak Ridge Neutron Users Meeting were held in Knoxville, TN from November 9 to 11, 1998. Over 200 participants attended the meeting, which was jointly sponsored by the US Department of Energy (DOE) and the National Science Foundation (NSF). The purpose of the instrumentation workshop was primarily to discuss scientific community needs for instrumentation at the Spallation Neutron Source (SNS). Topics covered included: update on the current status and expected performance of the Spallation Neutron Source; priorities f o r the initial suite of ten instruments to be built at the high power target station as part of the SNS reference design; and the science case for a second targedinstrument suite optimized for long wavelength neutrons.

ISSN:1044-8632    

DOI:10.1080/10448639908233667

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The neutron scattering facilities at the High Flux Isotope Reactor (HFIR) make possible a full range of elastic and inelastic mcasurenients, from fundamental studies in solid state physics to applied measurements in materials science to engineering applications for industry. Several beam tube and instrument upgrades i n progress will make the instruments for triple-axis spectrometry, SANS, residual stress, reflectometry and powder diffraction among the brightest in the world.

ISSN:1044-8632    

DOI:10.1080/10448639908233668

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Above its critical point, carbon dioxide forms a supercritical (SC) solvent which promises to be an environmentally responsible replacement for the organic solvents currently used in polymer synthesis and processing. CO2–soluble molecules (e.g. tluoropolymers) have been charkterized using small angle neutron scattering (SANS). By analogy with light and small-angle X–ray scattering (SAXS) experiments on polymers in dilute solution, the radius of gyration (Rg), molecular weight (MW) and second osmotic virial coefficient (A,) are determined from SANS experiments in SC–CO2. However, many polymers do not dissolve in this medium and in order to promote the synthesis of such materials, a range of amphiphilic block copolymers has been developed. These molecules function as surfactants or emulsifying agents to solubilize the CO2–phobic polymers. In the case of diblock copolymers in SC–CO2, aggregation occurs when the solvent is preferential for one of the blocks, and SANS allows the size and shape of the aggregates (micelles) to be determined. Illustrative examples of these studies are given and neutron scattering promises to give the same level of insight into polymers and amphiphiles in supercritical media that it has provided in the condensed state and in aqueous systems.

ISSN:1044-8632    

DOI:10.1080/10448639908233669

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Small-angle neutron scattering (SANS) is a unique tool to study vortex lattices in superconductors in the mixed state. It can probe the crystallography of a flux line arrangement in the bulk sample and measure the effect of defects on lattice arrangement and orientation extremely accurately. One can also determine values of characteristic lengths in superconductors via this technique.

ISSN:1044-8632    

DOI:10.1080/10448639908233670

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Inelastic neutron scattering using the triple axis spectrometer is the technique of choice for studying collective magnetic excitations in condensed matter. Over the past several years, there has been a high level of interest in understanding the nature of magnetic excitations in high Tcsuperconductors, quantum magnets and other highly correlated electrons systems. This article provides a glimpse at a few of the exciting highlights of recent research on magnetic excitations conducted using the neutron scattering facilities at ORNL's High Flux Isotope Reactor.

ISSN:1044-8632    

DOI:10.1080/10448639908233671

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The neutron residual stress measurement is based on converting measured lattice strain to residual stress and has been well described in earlier articles in Nerrtron News [1,2]. Strain is obtained from a measurement of the shift in the Bragg diffraction peak position arising from the change in the lattice d-spacing due to residual stress in the scattering sample. The principal advantage in the neutron method derives from the large penetration depth of neutrons which permits a direct and nondestructive examination of engineering materials and structures. The method requires knowledge of the zerostress lattice d-spacing against which the lattice strain is determined. Because residual stress is a tensor, measurements of strain must be made in several directions to properly characterize the residual stress state at a given test point. The neutron scattering arrangement employs a penetrating beam defined by a small aperture and a neutron detector collecting the scattered beam at a scattering angle near 90” through a second small aperture. This arrangement defines a sampling volume, or gage volume, which is formed by the intersection of the incident and scattered beams. The success of the method is dependent on the size and orientation of the polycrystalline grains in the scattering sample as well as the number of phases, which constitute the test material. The international Versailles Project on Advanced Materials and Standards (VAMAS) is currently working on recommendations for procedures and standards for neutron residual stress methods, which are expected to render the method of greater interest to industrial users.

ISSN:1044-8632    

DOI:10.1080/10448639908233672

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639908233673

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor