Intense Pulsed Neutron Source Research Articles

Polarized [formula omitted]He analyzers for neutron reflectometry

At the National Institute of Standards and Technology (NIST) and Indiana University, we are developing polarized 3 He analyzers for neutron reflectometry. We have employed 3 He analyzers at two polarized neutron reflectometers, NG1 at the NIST Center for Neutron Research (NCNR) and POSY I at the Intense Pulsed Neutron Source (IPNS), Argonne National Laboratory. The long-term goal for both efforts is to perform efficient studies of magnetic diffuse scattering. At the NCNR, we tested a 3 He analyzer by comparing measurements of specular scattering obtained with a supermirror analyzer to those obtained with a 3 He analyzer. For this test, we measured the spin-flip and nonspin-flip scattering from a Mn 0.52Pd 0.48/Fe thin film. The results with the 3 He analyzer show very good agreement with those obtained with the supermirror analyzer. We have also carried out tests of the 3 He analyzer for application to magnetic diffuse scattering experiments. We discuss the development of a 3 He analyzer for IPNS that will be employed for studies of patterned magnetic arrays.

A neutron detector to monitor the intensity of transmitted neutrons for small-angle neutron scattering instruments

A semiconductor-based neutron detector was developed at Argonne National Laboratory (ANL) for use as a neutron beam monitor for small-angle neutron scattering instruments. The detector is constructed using a coating of 10B on a gallium–arsenide semiconductor detector and is mounted directly within a cylindrical (2.2cm dia. and 4.4cm long) enriched 10B4C beam stop in the time-of-flight Small Angle Neutron Diffractometer (SAND) instrument at the Intense Pulsed Neutron Source (IPNS) facility at ANL. The neutron beam viewed by the SAND is from a pulsed spallation source moderated by a solid methane moderator that produces useful neutrons in the wavelength range of 0.5–14Å. The SAND instrument uses all detected neutrons in the above wavelength range sorted by time-of-flight into 68 constant ΔT/T=0.05 channels. This new detector continuously monitors the transmitted neutron beam through the sample during scattering measurements and takes data concurrently with the other detectors in the instrument. The 10B coating on the GaAs detector allows the detection of the cold neutron spectrum with reasonable efficiency. This paper describes the details of the detector fabrication, the beam stop monitor design, and includes a discussion of results from preliminary tests using the detector during several run cycles at the IPNS.

Neutron facilities managers meet

Managers of the six North American neutron experimental facilities (Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory, Center for Neutron Research at National Institute of Standards and Technology (NIST), Neutron Program for Materials Research of the National Research Council Canada (NRC-CNRC), High Flux Isotope Reactor (HFIR) and the Spallation Neutron Source (SNS) of Oak Ridge National Laboratory, and Los Alamos Neutron Science Center (LANSCE) at Los Alamos National Laboratory) attended the inaugural meeting of the Neutron Facilities Roundtable at Los Alamos National Laboratory in January 2003. The Snteragency Working Group of the White House's Office of Science and Technology Policy recommended periodic meetings of the neutron facilities in their June 2002 report on the Status and Needs of Major Neutron Scattering Facilities in the United States (the report is available at http://www.ostp.gov/html/neutron.pdf).

Status of Pelletised Moderator Neutronics Research for the Spallation Neutron Source Long Wavelength Target Station

We explore methods for making detailed calculations on the neutronic performance of a pelletised moderator, wherein a significant fraction of the moderating medium is heterogeneously distributed. This pellet approach appears to be necessary to provide cooling capabilities to a solid moderator material under heavy heat loads, and furthermore appears to offer the only realistic mechanism for permitting solid moderators in situations where the moderator material stores energy from radiation damage at a significant rate. Current use of solid moderators (e.g. methane at the Intense Pulsed Neutron Source facility) is significantly limited by the need to avoid catastrophic release of this stored energy.

Simultaneous polarization analysis of Zeeman splitting in polarized neutron reflectometry using a polarized 3 He neutron-spin filter

A polarized 3He neutron-spin filter was used to analyze polarized neutrons reflected from a 1000-A-thick Fe film immersed in a magnetic field. The spin filter analyzed both the specularly reflected component and the off-specular component caused by the phenomenon of Zeeman splitting of surface-scattered neutrons observed by Felcher et al. and investigated in more detail in subsequent experiments. The sample of polarized 3He was polarized by metastability-exchange optical pumping and compressed into a glass cell at the Indiana University Cyclotron Facility. The polarized gas was transported by car in a battery-powered solenoid holding field to the neutron reflectometry instrument POSY I at the Intense Pulsed Neutron Source at Argonne National Laboratory. Using the large solid angle of the polarized 3He spin filter, we were able to simultaneously analyze both components to the scattering and verify (as expected) that the polarization of the specular component was unchanged upon reflection and that the polarization of the off-specular component was reversed. To our knowledge this work represents the second experiment to employ a polarized 3He neutron-spin filter in polarized neutron reflectometry.

Oliver Cecil Simpson

Oliver Cecil Simpson

Proposal for a chopper spectrometer with very high energy resolution

Resolution functions of general-purpose chopper spectrometers at an intense pulsed-neutron source estimated by a Monte Carlo simulation technique are reported. The results indicate that a chopper spectrometer installed at a decoupled liquid-H2 moderator gives an energy resolution, Δe/Ei, of 1% when a very thin detection system is developed. We have also estimated resolution functions for a double Fermi chopper spectrometer for very high resolution measurements.

The upgrade of intense pulsed neutron source (IPNS) through the change of coolant and reflector

The current intense pulsed neutron source (IPNS) depleted uranium target is cooled by light water. The inner reflector material is graphite and the outer reflector material is beryllium. The presence of H 2O in the target moderates neutrons and leads to a higher absorption loss in the target than is necessary. D 2O coolant in the small quantities required minimizes this effect. We have studied the possible improvement in IPNS beam fluxes that would result from changing the coolant from H 2O to D 2O and the inner reflector from graphite to beryllium. Neutron intensities were calculated for directions normal to the viewed surface of each moderator for four different cases of combinations of target coolant and reflector materials. The simulations reported here were performed using the MCNPX (version 2.1.5) computer program. Our results show that substantial gains in neutron beam intensities can be achieved by appropriate combination of target coolant and reflector materials. The combination of D 2O coolant and beryllium inner and outer reflectors improves facility performance about 1.3 times. The purpose of this summary is to report our simulation and to recommend to change target coolant and inner reflector materials based on our simulation results.

A neutron diffraction study of Cp 2Ti{(μ-H) 2BC 8H 14}

The structure of Cp 2Ti{(μ-H) 2BC 8H 14} has been determined by single-crystal neutron diffraction methods. The geometrical parameters of the central four-atom core, Ti(μ-H) 2B, are: TiH=1.904(15), 1.933(17) Å; BH=1.298(15), 1.333(13) Å; TiHB=94.1(8)°, 96.7(9)°; HTiH=65.3(6)°, HBH=103.8(9)°; Ti⋯B=2.426(12) Å; H⋯H=2.071(19) Å. The final weighted agreement factor is R w=8.7% for 2635 unique reflections collected at 20 K from a crystal of volume 0.8 mm 3 at the Argonne Intense Pulsed Neutron Source (IPNS). This structure determination represents the first neutron diffraction analysis of a TiH bonding distance in a molecule, as well as the first neutron analysis of a TiHB bridge bond.

The Hydration Structure of Ni 2+ in Aqueous Solution by Neutron Diffraction Isotope Substitution: a Case Study on the Effects of Systematic Error

The technique of neutron diffraction with isotope substitution has been used to probe the hydration structure around the Ni2þ ion in a concentrated aqueous solution of 3.87 m NiCl2. The scattering from two heavy water solutions containing, respectively, nickel in natural abundance and enriched in the Ni isotope, were measured under ambient conditions on the GLAD instrument at the Intense Pulsed Neutron Source, Argonne, using time-of-flight neutron diffraction. Because there have been several earlier neutron measurements, aqueous NiCl2 is widely regarded as a reference system for studies of hydration in aqueous solution. An unexpectedly large difference in deuterium enrichment between our heavy water solutions was detected, initially from analysis of the scattering data. This imbalance, although on the face of it undesirable, has yielded a useful opportunity to gain insights into the effects of such a systematic error on the present results by comparing them to those from earlier measurements.

Nanomaterials experts convene at the IPNS

An iternational workshop on “Nanocomposites: Materials, Neutrons and Data Interpretation,” was held from March 28–30, 2002, at the Intense Pulsed Neutron Source Division, Argonne National Laboratory, USA. Neutron user facilities serve as an important infrastructure component to nanoscience and nanotechnology research under the U.S. National Nanotechnology Initiative (NNI, http://nano.gov). This workshop was organized by IPNS to bring together experts in the fields of nanomaterials synthesis and characterization, using a variety of techniques. The objective of this workshop was to identify the key nanocomposite systems and their properties and data-interpretation schemes for neutron-scattering studies. The sample systems discussed included biological systems, ceramics, polymers, complex fluids, magnetic materials, porous materials, and thin films. The methodologies used to s6dy these systems included advanced neutron scattering techniques and computational methods for nanomaterials research. Over eighty scientists from the U.S., Europe, and Japan participated in the workshop. The progtam of the workshop consisted of a plenary session, a poster session, and a panel discussion.

Present status and perspectives on neutron scattering instrumentation development at IPNS

Since its beginnings in ZING-P in the early 1970s, the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory has played an important role in the development of neutron scattering instrumentation, particularly in the utilization of time-of-flight techniques such as time-focusing for diffractometers. IPNS operates a user program for 11 instruments 25 weeks per year with a call for proposals every 6 months. As a medium-flux user facility, it serves the needs of the broader scientific community while providing training in the design and use of neutron scattering instruments for the next generation of scientists. The instruments at IPNS are continually being upgraded and evaluated; a significantly improved quasielastic neutron spectrometer was commissioned in 2000, and a similar enhancement on the high-resolution, medium-energy-range chopper spectrometer is currently underway. An enhancement plan, which includes improvements to most of the instruments and would approximately double the scientific throughput of IPNS, was recently reviewed and highly recommended. IPNS has lead responsibility for neutron scattering instruments for the Spallation Neutron Source being built at Oak Ridge National Laboratory and has played a leading role in developing a proposal for target station and instruments for a long wavelength target station submitted in January 2001 to the National Science Foundation. Through these and other projects, IPNS will continue to be a source and testbed for novel neutron scattering instrumentation concepts. Thus, IPNS will play a vital role in the global neutron scattering community for the foreseeable future.

Polarized [formula omitted]He neutron spin filter development and application at Indiana University and NIST

Neutron spin filters based on polarized 3 He promise to significantly expand the range of applications of polarized neutron scattering, particularly for experiments with divergent beams. At NIST and at Indiana University, we are pursuing both methods of polarizing 3 He by optical pumping: the metastability exchange method, and spin exchange with optically pumped Rb. The status of the respective apparatus and application to small angle neutron scattering (SANS) at the National Institute of Standards and Technology (NIST) and neutron reflectometry at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory are discussed.

Rietveld texture analysis of Dabie Shan eclogite from TOF neutron diffraction spectra

Orientation distributions of garnet and omphacite in eclogite from the ultra-high pressure Dabie Shan belt in east-central China were determined from neutron diffraction data by the Rietveld method. Diffraction spectra were recorded in 16 sample orientations with seven detectors, with a kappa-geometry texture goniometer at the time-of-flight (TOF) neutron facility at the Intense Pulsed Neutron Source (IPNS). The textures of the two minerals were extracted simultaneously from 16 × 7 = 112 diffraction spectra, covering a large portion of the pole figure. The texture analysis was performed both with the Williams–Imhof–Matthies–Vinel (WIMV) method and the harmonic method, implemented in the program packageMAUD. The incomplete pole-figure coverage introduced artificial oscillations in the case of the harmonic method. The discrete WIMV method produced better results, which illustrate a more or less random orientation distribution for cubic garnet. Apparently elongated grains turned out to be layers of randomly oriented crystals. Monoclinic omphacite displays a sharp texture, with [001] parallel to the lineation direction. The texture data obtained by neutron diffraction were verified with EBSP (electron backscatter pattern) measurements.

The effects of the electronic structure of micropores on the small angle scattering of X-rays and neutrons

The effects of the electronic structure of micropores on the small angle scattering of X-rays and neutrons

Argonne hosts ICANS XIV

ICANS XIV, the fourteenth meeting of the International Collaboration on Advanced Neutron Sources, took place at Starved Rock Lodge, Utica. Illinois, from June 14–19. 1998. Argonne's Intense Pulsed Neutron Source division served as host. The US Department of Energy, The University of Chicago Board of Governors, Argonne National Laboratory. Los Alamos National Laboratory, Oak Ridge National Laboratory and the Neutron Scattering Society of America sponsored the meeting. Jack Carpenter was conference chair and organizer, with Erik Iverson assisting, while Laura Miller, IPNS executive secretary, served as conference secretary. Beverly Marzec. Cathy Riblon, Carolyn Tobin, Ira Bresof and Merle Fuber, all of IPNS, ably and goodnaturedly saw to all the needs of the attendees. One hundred twenty-seven participants registered for the meeting, representing 27 institutionsand tencountries.

The low-temperature structure and phase transition of hemimorphite, Zn4Si2O7(OH)2 · H2O

Abstract The low-temperature structure of hemimorphite, Zn4Si2O7(OH)2 · H2O, was investigated by neutron diffraction at 20 K using the “Time-Of-Flight” (TOF) method with a four-circle single-crystal diffractometer and a position-sensitive detector at the Intense Pulsed Neutron Source (IPNS) at the Argonne National Laboratory, IL. The reversible second-order phase transition, which had previously been determined at 98(2) K by optical measurements, was confirmed by two TOF neutron histograms acquired at 20 K and 120 K. Whereas the 20 K histogram showed superlattice reflections hkl with k, l = n/2 and intensities up to 30 σ(I), these reflections were absent in the 120 K data set. In contrast to the room-temperature structure of hemimorphite (Imm2, a ∼ 8.37 Å, b ∼ 10.73 Å, c ∼ 5.12 Å), the additional reflections of the low-temperature structure lead to a supercell with a = 8.354(1) Å, b = 21.519(4) Å, c = 10.240(1) Å. According to the general reflection conditions, the low-temperature superstructure of hemimorphite was refined in space group Abm2 (= Acm2 = Aem2) with Rw(F 2) = 0.058. Whereas the room-temperature structure shows dynamically disordered hydroxyl and H2O groups, the low-temperature structure is characterized by an ordered arrangement of non-equivalent hydroxyl groups and rotated H2O molecules linked by an enhanced H bond system along the channels of the structure, thus leading to a doubled c lattice parameter. A partially ordered arrangement of the channels across the structure (using the [1/2, 1/4, 1/4] or [1/2, 1/4, −1/4] translation vectors) results in doubling of the b lattice parameter. According to space group symmetry and additional non-space group reflection conditions 0kl with k + l = 4n and h00 with h = 2n, an order/dis-order (OD) structure model with microdomains and twinning is proposed.

Simulation of the response of the IPNS neutron time-of-flight chopper spectrometers to samples in the Compton limit

We describe the comprehensive biased Monte Carlo code SPEC_SIM used to obtain accurate estimates of instrument response functions for neutron Compton scattering studies of the atomic momentum distribution of noble gas solids and liquids. The code is tailored to simulate epithermal neutron transport in the Intense Pulsed Neutron Source (IPNS) chopper spectrometers. The simulation begins with the neutrons emitted from the face of the moderator. The neutron trajectories are traced through a curved slit Fermi rotor (chopper) and are allowed to scatter multiple times from the sample region which may contain a sample, sample cell, and set of thermal radiation shields in any of a complex set of geometries. The scattered neutrons are tracked to the detector bank where they are again allowed to scatter before being “absorbed” and converted into a time-of-flight (TOF) signal which is histogrammed. A similar simulation code calculates the TOF response of two beam monitors to the incident neutron pulse, including the effects of scattering in the walls of the monitors. All of the scattering in the simulation is treated within a generalization of the impulse approximation. The results of the Monte Carlo simulations compare very favorably with experiments on solid and liquid He, Ar, and Ne.

Hydrothermal Synthesis of a Dense Metal−Organic Layered Framework That Contains Cu(I)−Olefinic Bonds, Cu2(O2CCHCHCO2)

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTHydrothermal Synthesis of a Dense Metal−Organic Layered Framework That Contains Cu(I)−Olefinic Bonds, Cu2(O2CCHCHCO2)Dianna M. Young, Urs Geiser, Arthur J. Schultz, and H. Hau WangView Author Information Intense Pulsed Neutron Source Chemistry and Materials Science Divisions Argonne National Laboratory, Argonne, Illinois 60439 Cite this: J. Am. Chem. Soc. 1998, 120, 6, 1331–1332Publication Date (Web):January 30, 1998Publication History Received6 October 1997Published online30 January 1998Published inissue 1 February 1998https://doi.org/10.1021/ja973483oCopyright © 1998 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views550Altmetric-Citations46LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (46 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information SUBJECTS:Chemical synthesis,Copper,Crystal structure,Hydrocarbons,Layers Get e-Alerts

Structural Analysis of a Completely Amorphous 238Pu-Doped Zircon by Neutron Diffraction

AbstractThe structure of a completely amorphous zircon was determined by time-of-flight neutron diffraction at Argonne's Intense Pulsed Neutron Source (IPNS). The sample of metamict zircon (ZrSiO4), initially doped to 8.85 weight percent 238pu, had been completely amorphized by alpha-recoil damage since its synthesis in 1981 at the Pacific Northwest National Laboratory (PNNL). The measured diffraction structure factor, S(Q), indicated a completely amorphous sample, with no signs of residual zircon microcrystallinity. The pair distribution function obtained indicated that the structure was that of an oxide glass, retaining the Si–O, Zr–O, and O–O bond lengths of crystalline zircon.