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Showing papers in "Neutron News in 1992"


Journal ArticleDOI
TL;DR: The application of thermal neutron scattering to the study of the structure and dynamics of condensed matter requires a knowledge of the scattering lengths and the corresponding scattering and absorption cross sections of the elements as discussed by the authors.
Abstract: The application of thermal neutron scattering to the study of the structure and dynamics of condensed matter requires a knowledge of the scattering lengths and the corresponding scattering and absorption cross sections of the elements. Ln some cases, values for the individual isotopes are needed as well. This information is required to obtain an absolute normalization ofthe scatteredneutron distributions, tocalculate unit-cell structure factors in neutron crystallography, and to correct for effects such as absorption, self-shielding, extinction, multiple scattering, incoherent scattering, and detector efficiency.

3,077 citations


Journal ArticleDOI
TL;DR: The idea for an international conference in honour of Peter Egelstaff arose several years ago as the date for Peter's retirement as Professor at Guelph came closer as discussed by the authors, which was the first one.
Abstract: The idea for an international conference in honour of Peter Egelstaff arose several years ago as the date for Peter's retirement as Professor at Guelph came closer His achievements in the physics of fluids, which probably first came to worldwide attention with the publication of his book “An Introduction to the Liquid State,” and which have continued right on into the present with the new techniques of neutron Brillouin scattering and single pulse diffraction, have had a pivotal influence in the development of the study of liquids, both theoretical and experimental Throughout hiscareer, wheneverhevisitedplaces, Peter has spawned small local conferences of experts to discuss the latest developments Indeed even at Guelph there were frequent “round table discussions,” which were not so much discussions about “round tables,” but rather were short(ish) seminars by visiting speakers followed by informal discussion, which at times could last for an hour or more

74 citations


Journal ArticleDOI
TL;DR: In this article, a black box with a probe placed on the surface of a component is used to measure the internal residual stress fields within weldments and fabricated components. But this is not an absolute, nondestructive means of measurement.
Abstract: Welding or other non uniform heat treatments, and plastic deformation during fabrication, can leave strong residual stresses locked-up within components. These stresses can affect the component life in service as they may add to applied loads causing fatigue and failure. Consequently engineers have to allow for their presence, and they have sought for many years an absolute, nondestructive means of measurement of the internal residual stress fields within weldments and fabricated components. The engineer dreams of obtaining a simple small ‘black-box’ with a probe which could be placed on the surface of the component. On dialling the depth and direction of required stress, its value would be read off on a display! Unfortunately this ideal is still some way off full realisation, although a wide range of techniques exist to give limited information on the stress field (1). The engineer also has recourse to computer calculations of stress fields using finite element methods, or analytical models.

12 citations


Journal ArticleDOI
TL;DR: In this paper, the fracture behaviour of traditional engineering ceramics such as AI2O3 MgO and mullite, are discussed in terms of the fracture toughness (I), and several mechanisms for improving it have been discovered.
Abstract: Ceramic materials in general offer inany unique properties to the materials engineer, including low density, extreme hardness and wear resistance, and excellent resistance to corrosion and chemical attack. Often these properties are retained to much higher temperatures than in other materials. However, traditional engineering ceramics such as AI2O3 MgO and mullite, are more brittle than other engineering materials. This is of particular concern in applications in which they are subject to shock loading of either mechanical or thermal origin. The fracture behaviour of materials is commonly discussed in terms of the fracture toughness (I), and several mechanisms for improving it have been discovered. Pioneering work by Garvie, Hannink and Pascoe (2) identified ‘transformation toughening’ as a means to improve fracture toughness of ceramics, and their work has led to an entirely new class of engineering ceramic, based on zirconia, and termed ‘ceramic steel’.

8 citations


Journal ArticleDOI
TL;DR: The Orphee (I) as discussed by the authors is the third modern nuclear reactor built after those of Brookhaven (HFBR, 196.5) and Grenoble (HFR, 197 1), especially dedicated to providing neutron beams for fundamental research.
Abstract: The reactor Orphee (I) is the third modern reactor built after those of Brookhaven (HFBR, 196.5) and Grenoble (HFR, 197 1), especially dedicated to provide neutron beams for fundamental research. The reactor design is similar to the HFR of ILL. A core of very small size, which provides a high neutron density, surrounded by a heavy water tank to give a good thermal flux, is cooled by a downward circulation of light water. The biological shielding is achieved by a light water pool and a heavy concrete wall. Twenty neutron beams are issued from the reflector tank by nine horizontal beam ports in tangential position. The therma1 power is 14 MW and the maximum thermal neutron flux is 3 × 1014 n/cm2/s. The reactor operates for ∼250 days/year in 2½ cycles of ∼100 days each.

6 citations


Journal ArticleDOI
TL;DR: In the case of polycrystalline materials, the texture describes statistically the orientation distribution of the crystallographic axes of the grains (crystallites) with respect to a set macroscopic sample axes-i.e., the texture gives information about how large a volume fraction of the material having a specific crystallographic orientation but no information about where in the material thesedifferent grains are positioned as discussed by the authors.
Abstract: The great majority of technologically applied materials have a polycrystalline structure. In such materials the texture describes statistically the orientation distribution of the crystallographic axes of the grains (crystallites) with respect to a set macroscopic sample axes-i.e. the texturegives information about how large a volume fraction of the material having a specific crystallographic orientation but no information about where in the material thesedifferentgrains are positioned. When the texture is strong, most of the grains have almost identical orientations; whereas, when the texture is weak, the grain orientations are almost random.

6 citations


Journal ArticleDOI
TL;DR: The Advanced Neutron Source (ANS) as discussed by the authors is a new user experimental facility planned to be operational at Oak Ridge at the end of this decade, which will be the centerpiece of a new state-of-the-art research reactor of unprecedented thermal neutron flux, accompanied by extensive and comprehensive equipment and facilities for neutron-based research.
Abstract: The Advanced Neutron Source (ANS) is a new user experimental facility planned to be operational at Oak Ridge at the end of this decade. The centerpiece ofthe ANS will beasteady-stateresearch reactor of unprecedented thermal neutron flux (Φth∼9 × 10l9 m−2ss1) accompanied by extensive and comprehensive equipment and facilities for neutron-based research.

5 citations


Journal ArticleDOI
TL;DR: The High Flux Beam Reactor (HFBR) as mentioned in this paper was built at Brookhaven National Laboratory (BNL) to increase the thermal flux outside the core region where beam tubes can be placed.
Abstract: Brookhaven National Laboratory's High Flux Beam Reactor (HFBR) was built because the scientist always wants ‘more.’ In the mid-50's the Brookhaven Graphite reactor was churning away, producing anumber of new results, when the current generation of scientists, led by Donald Hughes, realized the need for a high flux reactor and started down the political, scientific and engineering path that led to the HFBR. The effort was joined by a number of engineers and scientists such as Chemick, Hastings, Kouts, and Hendrie that came up with the novel design of the HFBR. The two innovative features that have been incorporated in nearly all other research reactors built since are: (i) an undermoderated core arrangement which enables the thermal flux to peak outside the core region where beam tubes can be placed, and (ii) beam tubes that are tangential to the core which decrease the fast neutron background without affecting the thermal beam intensity. Construction began in the fall of 1961 and four years later...

5 citations


Journal ArticleDOI
TL;DR: The technique of neutron high-angle fiber diffraction has been used to undertake isotopic replacement studies on the location of water around the deoxyribonucleic acid (DNA) double helix.
Abstract: The technique of neutron high-angle fiber diffraction has been developed and used to undertake isotopic replacement studies on the location of water around the deoxyribonucleic acid (DNA) double helix. The ability to isotopically replace H2O by D2O in fibers of DNA provides a very powerful probe of water structure around this important macromolecule. The results of these experiments are being complemented by X-ray fiber diffraction work on the location of cations around DNA and on the stereochemical pathways followed during conformational changes between the five principal forms that DNA can adopt.

5 citations


Journal ArticleDOI
TL;DR: The European Spallation Source (ESS) as mentioned in this paper is a 3rd generation spallation source with a 5 MW beam of protons with a short pulse length of ∼1 μ delivered onto two (or more) stationary targets surrounded by a variety of moderators.
Abstract: A meeting of about 70 experts in condensed-matter science took place in late February at Abingdon, UK, to discuss the scientific opportunities and technological challenges of a new 3rd generation spallation source-the so-called European Spallation Source (ESS). This Workshop was, in fact, the third in a series: the first, in September last year at Simonskall near Jiilich, considered the accelerator options; the second in February, in PSI, Villigen, Switzerland, considered the problems of providing targets and monochromators. The meeting openedwithtalksfromS. Martin(Jiilich), G. Bauer (PSI) and J. Carpenter (Argonne) on the accelerator, target, and moderator options, respectively. Although the problems are formidable in all areas, there donot seemtobe any insuperableobstacles for building a system with a 5 MW beam of protons with a short pulse length of ∼1 μ delivered onto two (or more) stationary targets surrounded by a variety of moderators. The heat load on the target could approach 4 MWAitre, ...

2 citations


Journal ArticleDOI
TL;DR: The Paul Scherrer Institute (PSI) as discussed by the authors is a national research institute in Switzerland, which was founded in 1988 as a joint institute of the former Federal Institute for Reactor Research (EIR) and the Swiss Institute for NuclearResearch (SIN).
Abstract: The Paul Scherrer Institute (PSI) is a national research institute in Switzerland. It was founded in 1988 as a joint institute of the former Federal Institute for Reactor Research (EIR) and the Swiss Institute for NuclearResearch (SIN). ThePSIis active in a variety of fields such as nuclear and particle physics, life sciences, condensed mattedmaterials sciences, and nuclear and general energy research. As a ‘heritage’ from the two predecessor institutes, PSI operates a swimming pool type reactor (Saphir) and is constructing a continuous spallation neutron source (SINQ). SINQ is expected to be operational in 1995, and around that time the ‘switch over’ from the ‘present’ tothe ‘future’ will takeplace.

Journal ArticleDOI
TL;DR: In this article, it was shown that the four constituents, i.e., DNA helices, counterions, water hull, and excess salt, form a highly correlated system with a subtle balance of interactions.
Abstract: X-ray diffraction by deoxyribonucleic acid (DNA) fibers has provided the basis for the famous unravelling of the double helical structure by Watson and Crick (1). Since the observation of Franklin and Gosling (2), “the most highly ordered structure was that obtained when operating at about 75 percent r.h. (structure A),” it has become progressively evident (3–5) that the four constituents, i.e., DNA helices, counterions, water hull, and excess salt, form a highly correlated system with a subtle balance of interactions. This is reflected in the various conformations of DNA helices as well as in the range and dimensionality of their correlation.

Journal ArticleDOI
TL;DR: The pulsed spallation neutron facility (KENS) at the National Laboratory for High Energy Physics (KEK) is located in Tsukuba, near Tokyo, Japan as mentioned in this paper.
Abstract: The pulsed spallation neutron facility (KENS) at the National Laboratory for High Energy Physics (KEK) is located in Tsukuba, near Tokyo, Japan. It began operation in June 1980. It is open to all scientists from the universities and national laboratories in Japan; During fiscal year (FY) 1990, 76 experiments, including 12 large proposals by the groups responsible for the instruments, were carried out at the facility. Scientists who visited the KENS facility spent about 4000 man days.


Journal ArticleDOI
TL;DR: In this article, the authors indicate how recent neutron measurements are leading to a new understanding of the elementary excitations of liquid 4He and their connection to the superfluid state, and there is alsocontinuing interest intheinteractions between excitations and here (isotropic)4He, with its single well-defined (phonon-roton) mode-which is significantly affected by modest pressure and temperature changes-may be considered as a “model” substance forthe study of condensed matter.
Abstract: Despite almost thirty years of investigation (I), neutron scattering studies of the excitations of liquid 4He are still providing surprise and excitement. Why there should be this continuing interest is not difficult to understand. First of all there is the innate attraction of this fascinating and unique substance. The hope that neutron scattering would help provide a microscopic understanding of the phenomenon of superfluidity had, until recently, been largely unfulfilled; in this article I shall indicate how recent neutron measurements are leading to a new understanding of the elementary excitations of liquid 4He and their connection to the superfluid state. But thereis alsocontinuing interest intheinteractions between excitations and here (isotropic)4He, with its single well-defined (phonon-roton) mode-which is significantly affected by modest pressure and temperature changes-may be considered as a “model” substance forthe study of the excitations of condensed matter.

Journal ArticleDOI
TL;DR: In the early nineties, Dubna hosted the first meeting for experts on pulsed neutron sources (PNS) and the primary question was which type of intense neutron source should be built at the Laboratory of Neutron Physics (LNP) ofthe Joint Institute ForNuclearResearch (JINR) as discussed by the authors.
Abstract: Twenty-five years ago Dubna hosted the first meeting for experts on pulsed neutron sources (PNS). At that time the primary question was which type of intense neutron source should be built at the Laboratory of Neutron Physics (LNP) ofthe Joint Institute ForNuclearResearch (JINR). Preference was given to a repetitively pulsed reactor, IBR-2, which was constructed and put into operation in the early eighties. In the last 10 years effective spallation neutron sources (SNS) have been constructed throughout the world. Both typesof PNS (pulsed reactors and SNS) are complimentary to each other as instruments for physics research, but rnodern physics and technology need more effective neutron sources.

Journal ArticleDOI
TL;DR: In this paper, some geometrical aspects peculiar to measurements with PSD's are discussed and a brief review is given of applications of PSD' s to single-crystal diffractometry.
Abstract: One of the most significant recent advances in singlecrystal neutron diffractometry has been the introduction of one- and two-dimensional (2-D) position-sensitive detectors (PSD's). The first PSD's on monochromatic beams were relatively large being intended primarily for measurement of a large number of Bragg reflections simultaneously, especially in macromolecular crystallography (1). It soon became obvious though that such detectors could also offer several advantages for measurement of single reflections, and smaller PSD's of higher resolution are being introduced for crystallographic studies of smaller unit cells (2). At pulsed neutron sources PSD's have virtually become mandatory for efficient data collection using time-of-flight techniques (3). Hardware aspects are covered extensively in recent reviews (43). In this article some geometrical aspects peculiar to measurements with PSD's are discussed and a brief review is given of applications of PSD' s to single-crystal diffractometry.