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A design for a high resolution very-low-Q time-of flight diffractometer.

Description: The design of a high resolution view low-Q time of flight diffractometer was motivated by the anticipated need to perform small-angle neutron scattering measurements at far lower momentum transfer and higher precision than currently available at either pulsed or steady state sources. In addition, it was recognized that flexibility in the configuration of the instrument and ease in which data is acquired are important. The design offers two configurations, a high intensity/very low Q geometry employing a focusing mirror and a medium to high Q-precision/low Q configuration using standard pinhole collimation geometry. The quality of the mirror optics is very important to the performance of the high intensity/very low Q configuration. We believe that the necessary technology exists to fabricate the high quality mirror optics required for the instrument.
Date: September 29, 1998
Creator: Hjelm, R. P.
Partner: UNT Libraries Government Documents Department

Time-of-flight small-angle neutron scattering data reduction and analysis at LANSCE with program SMR

Description: A user-friendly integrated system, SMR, for the display, reduction and analysis of data from time-of-flight small-angle neutron diffractometers is described. Its purpose is to provide facilities for data display and assessment, and to provide these facilities in near real time. This allows the results of each scattering measurement to be available almost immediately, and enables the user to use the results of a measurement as a basis for other measurements in the same time allocation of the instrument. 8 refs., 10 figs.
Date: January 1, 1988
Creator: Hjelm, R.P. Jr. & Seeger, P.A.
Partner: UNT Libraries Government Documents Department

The structure of fillers, polymers and their interfaces in polymer composites using neutron scattering methods

Description: The neutron scattering methods, small-angle neutron scattering and neutron reflectometry, provide information on the structure of polymer composite materials that is not available from other structural probes. The unique capabilities of these methods derive from three factors. First, the length scales probed correspond to polymer conformation, molecular and domain scales and to the characteristic sizes of many fillers. Second, neutrons are able to penetrate relatively thick samples, allowing bulk samples to be measured, and enabling buried interfaces to be studied. This characteristic also allows for the construction of special sample containment needed for studying materials under stress, extremes in pressure and temperature, etc. Third, neutrons readily distinguish between different light elements, and between different isotopes of the same element. The ability to distinguish between hydrogen and deuterium is particularly important in this regard. New ways of exploiting the capabilities of neutrons are opening up with the development of improved sources and instruments in the US and elsewhere. In this talk the author will discuss the basic concepts that give rise to the unique capabilities of neutron scattering, giving several examples of the uses of neutron scattering techniques in the study of polymer composites. The examples will include the morphology of fillers, polymer binders and matrices, interfaces and defect structures.
Date: December 1, 1998
Creator: Hjelm, R.P.
Partner: UNT Libraries Government Documents Department

Proceedings of a workshop on methods for neutron scattering instrumentation design

Description: The future of neutron and x-ray scattering instrument development and international cooperation was the focus of the workshop. The international gathering of about 50 participants representing 15 national facilities, universities and corporations featured oral presentations, posters, discussions and demonstrations. Participants looked at a number of issues concerning neutron scattering instruments and the tools used in instrument design. Objectives included: (1) determining the needs of the neutron scattering community in instrument design computer code and information sharing to aid future instrument development, (2) providing for a means of training scientists in neutron scattering and neutron instrument techniques, and (3) facilitating the involvement of other scientists in determining the characteristics of new instruments that meet future scientific objectives, and (4) fostering international cooperation in meeting these needs. The scope of the meeting included: (1) a review of x-ray scattering instrument design tools, (2) a look at the present status of neutron scattering instrument design tools and models of neutron optical elements, and (3) discussions of the present and future needs of the neutron scattering community. Selected papers were abstracted separately for inclusion to the Energy Science and Technology Database.
Date: September 1, 1997
Creator: Hjelm, R.P.
Partner: UNT Libraries Government Documents Department

A very-low-Q diffractometer for an advanced spallation source

Description: Proposals to build new, more powerful spallation sources and the introduction of advanced moderator concepts will result in neutron sources that are 20 times more luminous than the brightest available today. These developments provide opportunity and challenge to expand the capabilities of present low-Q instruments using new designs. A particularly interesting case is the design of an instrument capable of measurements to very low'' momentum transfer, say Q [approx] 0.0007 [Angstrom][sup [minus]1]. We consider an instrument to be built on a 20 Hz, 330 kW target and viewing a coupled liquid-hydrogen moderator. The instrument would use a frame-definition chopper to select a wavelength band suitable for the required Q-domain. Monte Carlo optimization of the geometry was performed by choosing the minimum observable Q always to be 0.0007 [Angstrom][sup [minus]1] and then maximizing intensity/variance at Q = 0.0020 [Angstrom][sup [minus]1] while maintaining reasonable constraints. The resulting design is 48 m long, with a maximum wavelength band 16.9 [Angstrom] [le] [lambda] [le] 20.5 [Angstrom]. The Monte Carlo simulations of instrument performance include wavelength-dependent effects from aluminum and fused silica windows, air, chopper opening and closing times and phase jitter, measured spectrum and detector efficiencies, sample transmission and multiple scattering, and gravity. The results were normalized by the measured flux from the present LANSCE moderator, and scaled by the expected performance of a coupled hydrogen moderator. The results compare well with the 76-m configuration of the D11 instrument at ILL in both count rate and Q-precision, due in part to the ability to correct for gravitation effects using the time of flight of the detected neutrons. The validity of these comparisons was demonstrated by comparison of measurements and Monte Carlo simulations made on the present LANSCE Low-Q instrument (LQD) and on D11.
Date: January 1, 1993
Creator: Seeger, P.A. & Hjelm, R.P.
Partner: UNT Libraries Government Documents Department

Small-angle neutron scattering at pulsed spallation sources

Description: The importance of small-angle neutron scattering (SANS) in biological, chemical, physical, and engineering research mandates that all intense neutron sources be equipped with SANS instruments. Four existing instruments are described, and the general differences between pulsed-source and reactor-based instrument designs are discussed. The basic geometries are identical, but dynamic range is achieved by using a broad band of wavelengths (with time-of-flight analysis) rather than by moving the detector. This allows a more optimized collimation system. Data acquisition requirements at a pulsed source are more severe, requiring large, fast histogramming memories. Data reduction is also more complex, as all wave length-dependent and angle-dependent backgrounds and non-linearities must be accounted for before data can be transformed to intensity vs Q. A comparison is shown between the Los Alamos pulsed instrument and D-11 (Institute Laue-Langevin), and examples from the four major topics of the conference are shown. The general conclusion is that reactor-based instruments remain superior at very low Q or if only a narrow range of Q is required, but that the current generation of pulsed-source instruments is competitive at moderate Q and may be faster when a wide range of Q is required. In principle, a user should choose which facility to use on the basis of optimizing the experiment; in practice the tradeoffs are not severe and the choice is usually made on the basis of availability.
Date: January 1, 1990
Creator: Seeger, P.A. & Hjelm, R.P. Jr.
Partner: UNT Libraries Government Documents Department

Design and implementation of low-Q diffractometers at spallation sources

Description: Low-Q diffractometers at spallation sources that use time of flight methods have been successfully implemented at several facilities, including the Los Alamos Neutron Scattering Center. The proposal to build new, more powerful, advanced spallation sources using advanced moderator concepts will provide luminosity greater than 20 times the brightest spallation source available today. These developments provide opportunity and challenge to expand the capabilities of present instruments with new designs. The authors review the use of time of flight for low-Q measurements and introduce new designs to extend the capabilities of present-day instruments. They introduce Monte Carlo methods to optimize design and simulate the performance of these instruments. The expected performance of the new instruments are compared to present day pulsed source- and reactor-based small-angle neutron scattering instruments. They review some of the new developments that will be needed to use the power of brighter sources effectively.
Date: January 1, 1993
Creator: Seeger, P.A. & Hjelm, R.P.
Partner: UNT Libraries Government Documents Department

The structure of carbon black and its composites with elastomers: A study using neutron scattering

Description: The authors have been exploring the use of small-angle neutron scattering and the method of contrast variation to give a new look at a very old problem--reinforcement of elastomers by carbon black in durable rubber products. The method has yielded some interesting information on the structure of an experimental carbon black, HSA, and on the associations of HSA in polyisoprene composites. Carbon black has a hierarchy of structures consisting of particles covalently bound into aggregates, which in turn associate by weak interactions into agglomerates. The authors found that in HSA the aggregates are rodlike, containing an average of 4--6 particles. The aggregates have an outer graphitic shell and an inner core of lower density carbon. The core is continuous throughout the carbon black aggregate. Contrast variation of swollen HSA-polyisoprene gels show that the HSA is completely embedded in polyisoprene and that the agglomerates are formed predominantly by end on associations of the rodlike aggregates. The surface structure of the carbon black appears smooth over length scales above about 10 {angstrom}. Further studies on production carbon blacks suggest that the shell-like aggregate structure is present in commercial carbon blacks.
Date: July 1, 1996
Creator: Hjelm, R.P.; Wampler, W. & Gerspacher, M.
Partner: UNT Libraries Government Documents Department

The structure of carbon black-elastomer composites by small-angle neutron scattering and the method of contrast variation

Description: We have been exploring the use of small-angle neutron scattering and the method of contrast variation to give a new look at a very old problem: reinforcement of elastomers by carbon black in durable rubber products. Carbon black has a hierarchy of structures consisting of particles covalently bound into aggregates, which in turn associate by weak interactions into agglomerates. We found that in one carbon black, HSA, the aggregates are rodlike, containing an average of 4-6 particles. The aggregates have an outer graphitic shell and an inner core of lower density carbon. The core is continuous throughout the carbon black aggregate. Contrast variation of swollen HSA-polyisoprene gels shows that the HSA is completely embedded in polyisoprene and that the agglomerates are formed predominantly by end on associations of the rodlike aggregates. The surface structure of the carbon black appears smooth over length scales above about 10 {angstrom}. Further studies using production carbon blacks suggest that these structural characteristics are generally present in commercial rubber composites.
Date: July 1, 1996
Creator: Hjelm, R.P.; Wampler, W. & Gerspacher, M.
Partner: UNT Libraries Government Documents Department

Parameterization of structures in HE composites using surrogate materials: A small angle neutron scattering investigation

Description: High explosive materials used in the nuclear stockpile are composites of crystalline high explosives (HE) with binder materials, such as Estane. In such materials, there are naturally occurring density fluctuations (defects) due to cracks, internal (in the HE) and external (in the binder) voids and other artifacts of preparation. Changes in such defects due to material aging can affect the response of explosives due to shock, impact and thermal loading. Modeling efforts are attempting to provide quantitative descriptions of explosive response from the lowest ignition thresholds to the development of full blown detonations and explosions, however, adequate descriptions of these processes require accurate measurements of a number of structural parameters of the HE composite. Since different defects are believed to affect explosive sensitivity in different ways it is necessary to quantitatively differentiate between defect types. The authors report here preliminary results of SANS measurements on surrogates for HE materials. The objective of these measurements was to develop methodologies using SANS techniques to parameterize internal void size distributions in a surrogate material, sugar, to simulate an HE used in the stockpile, HMX. Sugar is a natural choice as a surrogate material, as it has the same crystal structure, has similar intragranular voids and has similar mechanical properties as HMX. It is used extensively as a mock material for explosives. Samples were used with two void size distributions: one with a sufficiently small mean particle size that only small occluded voids are present in significant concentrations, and one where the void sizes could be larger. By using methods in small-angle neutron scattering, they were able to isolate the scattering arising from particle-liquid interfaces and internal voids.
Date: July 1, 1996
Creator: Mang, J.T.; Hjelm, R.P.; Skidmore, C.B. & Howe, P.M.
Partner: UNT Libraries Government Documents Department

Small angle neutron scattering studies of vesicle stability

Description: Small angle neutron scattering (SANS) was used to investigate the structure of mixed colloids of egg yolk phosphatidylcholine (EYPC) with the bile salt, cholylglycine (CG), in D{sub 2}O as a function of pressure (P) and temperature (T). At atmospheric pressure, the system forms an isotropic phase of mixed, single bilayer vesicles (SLV`s). Increasing the external hydrostatic pressure brought about significant changes in particle morphology. At T = 25 C, application of a pressure of 3.5 MPa resulted in the collapse of the SLV`s. Further increase of P, up to 51.8 MPa, resulted in a transition from a phase of ordered (stacked), collapsed vesicles to one of stacked, ribbon-like particles. A similar collapse of the vesicles was observed at higher temperature (T = 37 C) with increasing P, but at this temperature, no ribbon phase was found at the highest pressure explored.
Date: October 1, 1997
Creator: Mang, J.T. & Hjelm, R.P.
Partner: UNT Libraries Government Documents Department

Quantification of microstructural features in HMX using small angle neutron scattering techniques

Description: Microstructural features in raw powders of High Explosives have been qualitatively observed by many researchers, using polarized light and scanning electron microscopy. Here, the authors present a method for non-destructive quantification of volume fraction and structure of intragranular cracks and crystallization voids in a bulk sample (100--300 mg). By employing Small Angle Neutron Scattering (SANS) in conjunction with the method of contrast variation, they can effectively highlight different structural features of a complex system. The technique of contrast variation relies on immersing the sample in a uniform fluid of known neutron scattering length density. By selectively varying the scattering length density of the immersion fluid, scattering contributions from internal and external structures can be separated. This approach is analogous to varying the index of refraction for immersion oil relative to a sample in polarized light microscopy. SANS experiments on HMX were conducted using loose powders (261 and 10 micron mean particle diameters) and pellets made by uniaxial consolidation (without binder) to 7 and 10 volume percent porosity respectively. Detailed modeling of the SANS data indicate significant alteration of the intragranular void/crack/pore structure, with pressing, of the HMX powders.
Date: December 1, 1998
Creator: Mang, J.T.; Skidmore, C.B.; Hjelm, R.P. & Howe, P.M.
Partner: UNT Libraries Government Documents Department

A user-friendly, graphical interface for the Monte Carlo neutron optics code MCLIB

Description: The authors describe a prototype of a new user interface for the Monte Carlo neutron optics simulation program MCLIB. At this point in its development the interface allows the user to define an instrument as a set of predefined instrument elements. The user can specify the intrinsic parameters of each element, its position and orientation. The interface then writes output to the MCLIB package and starts the simulation. The present prototype is an early development stage of a comprehensive Monte Carlo simulations package that will serve as a tool for the design, optimization and assessment of performance of new neutron scattering instruments. It will be an important tool for understanding the efficacy of new source designs in meeting the needs of these instruments.
Date: December 1, 1995
Creator: Thelliez, T.; Daemen, L.; Hjelm, R.P. & Seeger, P.A.
Partner: UNT Libraries Government Documents Department

Neutron scattering as a probe of liquid crystal polymer-reinforced composite materials

Description: This is the final report of a three-year Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This research project sought to obtain nanoscale and molecular level information on the mechanism of reinforcement in liquid crystal polymer (LCP)-reinforced composites, to realize molecular-reinforced LCP composites, and to test the validity of the concept of molecular reinforcement. Small-angle neutron scattering was used to study the structures in the ternary phase diagram of LCP with liquid crystal thermosets and solvent on length scales ranging from 1-100 nm. The goal of the scattering measurements is to understand the phase morphology and degree of segregation of the reinforcing and matrix components. This information helps elucidate the physics of self assembly in these systems. This work provides an experimental basis for a microengineering approach to composites of vastly improved properties.
Date: December 31, 1995
Creator: Hjelm, R.P.; Douglas, E.P.; Benicewicz, B.C. & Langlois, D.A.
Partner: UNT Libraries Government Documents Department

Small-angle scattering instruments on a 1 MW long pulse spallation source

Description: Two small-angle neutron scattering instruments have been designed and optimized for installation at a 1 MW long pulse spallation source. The first of these instruments allows access to length scales in materials from 10 to 400 {angstrom}, and the second instrument from 40 to 1200 {angstrom}. Design characteristics were determined and optimization was done using the MCLIB Monte Carlo instrument simulation package. The code has been {open_quote}benchmarked{close_quote} by simulating the {open_quote}as-built{close_quote} D11 spectrometer at ILL and a performance comparison of the three instruments was made. Comparisons were made by evaluating the scattered intensity for {delta} scatterers at different Q values for various instrument configurations needed to span a Q-range of 0.0007 - 0.44 {angstrom}{sup {minus}1}.
Date: December 1, 1995
Creator: Olah, G.A.; Hjelm, R.P. & Seeger, P.A.
Partner: UNT Libraries Government Documents Department

Solutions for implementing time-of-flight techniques in low-angle neutron scattering, as realized on the Low-Q Diffractometer at Los Alamos

Description: The implementation of small-angle (Low-momentum transfer) neutron scattering at pulsed spallation sources, using time of flight methods, has meant the introduction of some new ideas in instrument design, data acquisition, data reduction and computer management of the experiment and the data. Here we recount some of the salient aspects of solutions for implementing time of fight small-angle neutron scattering instruments at pulsed sources, as realized on the Low-Q Diffractometer, LQD, at Los Alamos. We consider, fortlier, some of the problems that are yet to be solved, and take a short excursion into the future of SANS instrumentation at pulsed sources.
Date: January 1, 1992
Creator: Hjelm, R.P. Jr. & Seeger, P.A.
Partner: UNT Libraries Government Documents Department

Solutions for implementing time-of-flight techniques in low-angle neutron scattering, as realized on the Low-Q Diffractometer at Los Alamos

Description: The implementation of small-angle (Low-momentum transfer) neutron scattering at pulsed spallation sources, using time of flight methods, has meant the introduction of some new ideas in instrument design, data acquisition, data reduction and computer management of the experiment and the data. Here we recount some of the salient aspects of solutions for implementing time of fight small-angle neutron scattering instruments at pulsed sources, as realized on the Low-Q Diffractometer, LQD, at Los Alamos. We consider, fortlier, some of the problems that are yet to be solved, and take a short excursion into the future of SANS instrumentation at pulsed sources.
Date: December 1, 1992
Creator: Hjelm, R. P. Jr. & Seeger, P. A.
Partner: UNT Libraries Government Documents Department

The microstructure and morphology of carbon black: A study using small angle neutron scattering and contrast variation

Description: This is a study of the microstructure of particles of an experimental high surface area carbon black (HSA) and of the morphology of the particle aggregates using small-angle neutron scattering and the method of contrast variation. Contrast variation was effected by studying suspensions of the carbon black in cyclohexane containing different fractions of deuterocyclohexane. We find that the approximately 29 nm diameter HSA particles are arranged as small, linear aggregates with average aggregation number between 4 and 6. The structure averaged over the particle population is best represented by a prolate ellipsoid of revolution with semi axes 14.5 and 76.4 nm. The surface of the aggregates appears smooth over length scales longer than 1 nm, which places an upper limit on the surface roughness observed by other methods. The intemal structure of the aggregates is described by a shell-core model, with the shell density being consistent with a graphitic structure and the core being of lower density, more like amorphous carbon. Some fraction of the core volume (0.1 to 0.2) is taken up by voids that are not accessible to the solvent. An estimate of the shell thickness gives 1 to 2 nm along the ellipsoid minor axis and 6 to 10 nm along the major axis. The particles of the aggregate appear to be fused so that the less dense amorphous core is continuous through the inner parts of the aggregate. The information that can be obtained on the internal structure using contrast variation is limited by nonheterogeneity in the chemical composition of carbon black aggregates.
Date: April 1, 1994
Creator: Hjelm, R. P. Jr.; Seeger, P. A.; Wampler, W. A. & Gerspacher, M.
Partner: UNT Libraries Government Documents Department

Variation of solvent scattering-length density small-angle neutron scattering as a means of determining structure of composite materials

Description: As part of our work on the, structure of composite materials we have been exploring the use of small-angle neutron scattering using the method of contrast variation to dissect the component form, structure and distribution. This approach has resulted in a new look at very old problem reinforcement of elastomers by carbon black. Using this approach we studied an experimental high surface area (HSA) carbon black and a gel of ``HSA-bound`` rubber in cyclohexane/deuterocyclohexane mixtures. HSA in cyclohexane is found to be short rodlike particle aggregates. The aggregates have a shell-core structure with a high density graphitic outer shell and an inner core of lower density amorphous carbon. The core is continuous throughout the carbon black aggregate, making the aggregate a stiff, integral unit. Contrast variation of swollen composite gels shows that there are two length scales in the gel structure. Above 10 {Angstrom}, scattering from carbon black predominates, and below 10 {Angstrom} the scattering is from both carbon black and the elastomer. The HSA in the composite is completely embedded in polyisoprene. An estimate of the carbon black structure factor shows strong exclusion of neighboring aggregates, probably from excluded volume effects. The surface structure of the carbon black is unaltered by the interactions with elastomer and appears smooth over length scales above about 10 {Angstrom}. These results show that contrast variation can provide information on composite structure that is not available by other means. This information relates to the reinforcement mechanism of elastomers by carbon blacks.
Date: December 31, 1994
Creator: Hjelm, R. P.; Wampler, W. & Gerspacher, M.
Partner: UNT Libraries Government Documents Department

Analysis and simulation of a small-angle neutron scattering instrument on a 1 MW long pulse spallation source

Description: We studied the design and performance of a small-angle neutron scattering (SANS) instrument for a proposed 1 MW, 60 Hz long pulsed spallation source at the Los Alamos Neutron Science Center (LANSCE). An analysis of the effects of source characteristics and chopper performance combined with instrument simulations using the LANSCE Monte Carlo instrument simulations package shows that the T{sub 0} chopper should be no more than 5 m from the source with the frame overlap and frame definition choppers at 5.6 and greater than 7 m, respectively. The study showed that an optimal pulse structure has an exponential decaying tail with {tau} {approx} 750 {mu}s. The Monte Carlo simulations were used to optimize the LPSS SANS, showing that an optimal length is 18 m. The simulations show that an instrument with variable length is best to match the needs of a given measurement. The performance of the optimized LPSS instrument was found to be comparable with present world standard instruments.
Date: December 31, 1996
Creator: Olah, G.A.; Hjelm, R.P. & Lujan, M. Jr.
Partner: UNT Libraries Government Documents Department

Monte Carlo simulation of neutron scattering instruments

Description: A code package consisting of the Monte Carlo Library MCLIB, the executing code MC{_}RUN, the web application MC{_}Web, and various ancillary codes is proposed as an open standard for simulation of neutron scattering instruments. The architecture of the package includes structures to define surfaces, regions, and optical elements contained in regions. A particle is defined by its vector position and velocity, its time of flight, its mass and charge, and a polarization vector. The MC{_}RUN code handles neutron transport and bookkeeping, while the action on the neutron within any region is computed using algorithms that may be deterministic, probabilistic, or a combination. Complete versatility is possible because the existing library may be supplemented by any procedures a user is able to code. Some examples are shown.
Date: December 1998
Creator: Seeger, P. A.; Daemen, L. L. & Hjelm, R. P., Jr.
Partner: UNT Libraries Government Documents Department

The neutron instrument Monte Carlo library MCLIB: Recent developments

Description: A brief review is given of the developments since the ICANS-XIII meeting made in the neutron instrument design codes using the Monte Carlo library MCLIB. Much of the effort has been to assure that the library and the executing code MC{_}RUN connect efficiently with the World Wide Web application MC-WEB as part of the Los Alamos Neutron Instrument Simulation Package (NISP). Since one of the most important features of MCLIB is its open structure and capability to incorporate any possible neutron transport or scattering algorithm, this document describes the current procedure that would be used by an outside user to add a feature to MCLIB. Details of the calling sequence of the core subroutine OPERATE are discussed, and questions of style are considered and additional guidelines given. Suggestions for standardization are solicited, as well as code for new algorithms.
Date: June 1998
Creator: Seeger, P. A.; Daemen, L. L.; Hjelm, R. P., Jr. & Thelliez, T. G.
Partner: UNT Libraries Government Documents Department