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LA—11933-PR DE91 000513 The Manuel Lujan, Jr. Neutron Scattering Center LANSCE Experiment Reports 1989 Run Cycle Compiled by Dianne K. Hyer Maria A. DiStravolo LosAlam0NATIONAL LABORATORSY Los Alamos, Ntw M«*<co 87545 MASTER Contents High Density Powder Diffraction (HIPD) 1 Experiment reports 4 Neutron Powder Diffractometer (NPD) 65 Experiment reports 68 Single Crystal Diffractometer (SCD) 111 Experiment reports 114 Lozv-Q Diffractometer (LQD) 135 Experiment reports 138 Surface Profile Analysis Reflectometer (SPEAR) 201 Experiment reports 204 Filter Difference Spectrometer (FDS) 211 Experiment reports 214 Constant-Q Spectrometer (CQS) 235 New Instruments 239 PHAROS meV Spectrometer LANSCE User Group 245 Science Seminar Abstracts November 1989 Index 263 The Manuel Lujan, Jr. Neutron Scattering Center LANSCE Experiment Reports 1989 Run Cycle Compiled by Dianne K. Hyer and Maria A. DiStravolo ABSTRACT This year was the second in which LANSCE ran a formal user program. A call for proposals was issued before the scheduled run cycles, and experiment proposals were submitted by scientists from universities, industry, and other research facilities around the world. An external program advisory committee, which LANSCE shares with the Intense Pulsed Neutron Source (IPNS), Argonne National Laboratory, examined the proposals and made recommendations. At LANSCE, neutrons are produced by spallation when a pulsed, 800-MeV proton beam impinges on a tungsten target. The proton pulses are provided by the Los Alamos Meson Physics Facility (LAMPF) accelerator and an associated Proton Storage Ring (PSR), which can alter the intensity, time structure, and repetition rate of the pulses. The LAMPF protons of line D are shared between the LANSCE target and the Weapons Neutron Research facility, which results in LANSCE spectrometers being available to external users for unclassified research about 60% of each six-month LAMPF run cycle. Measurements of interest to the Los Alamos National Laboratory may also be performed and may occupy up to an additional 20% of the available beam time. These experiments are reviewed by an internal program advisory committee. Ninety-five proposals were submitted for unclassified research and eight proposals for research of a programmatic nature to the Laboratory. Oversubscription for instrument beam time by a factor of two was evident with 439 total days requested and only 246 available for allocation. Our definition of beam availability is when the proton current from the PSR exceeds 50% of the planned value. The PSR ran at 50 jiA current (average) at 20 Hz for most of 1989. The overall beam availability averaged as follows: • 80% during cycle 53 (May 15 to June 15) • 71 % during cycle 54 Qune 28 to August 9) • 74% during cycle 55 (August 18 to September 26) All of the scheduled experiments were performed (excluding those few withdrawn because of problems with samples), and experiments in support of the LANSCE research program were accomplished during the discretionary periods. High Density Powder Diffractometer (HIPD) High Intensity Powder Diffractometer (HIPD) pattern yields exact information on the atomic arrangement in the sample. The HIPD offers The High Intensity Powder Diffractometer (HIPD) exceptionally high data rates with nearly three is designed to study the atomic structures of decades of range in momentum transfer or materials that are available only in polycrystalline d-spacing. An ambient-temperature, high-inten- or noncrystalline form. In the HIPD the pulsed sity water moderator provides a usable neutron neutron beam is directed through a collimator onto flux at wavelengths out to 4 A. Low backgrounds a cylindrical or flat plate sample supported in a permit the routine use of wavelengths down vacuum chamber. Neutrons are detected by banks to 0.1 A. The HIPD is intended primarily of detectors located at various angles to the inci- for studies of liquids and amorphous solids, for dent beam. The data from each detector are magnetic diffraction studies, and for crystallogra- collected as a function of time of flight (TOF) and phic studies of samples that are either very small stored in a FASTBUS memory module, which is or are in extreme environments of temperature, controlled by a micro-VAX II computer. Because pressure, or magnetic fields. This instrument is the neutron TOF is directly proportional to the also appropriate for experiments that require neutron wavelength, the measured diffraction time-resolved diffraction measurements. Detectors Final collimator 10B-AI Collimator pipe Incident neutron beam Beam incident beam monitor 3" long 1/4* diameter 153° 12" long 1/2" diameter g Ad/d-0.3% 1/2" ctametor Ad/d-3% 40° 6" long 1/2" diameter Ad/d-1% 90° 12" long Moderator to sample distance * 9 meters 1/2" diameter AdfcUO.5% Instrument Details Wavelength range, X 0.05 - 4.0 A Beam width 1.23 cm Beam height 2.54 - 5.08 cm, variable Q range 0.1 - 200 A1 Range of scattering angle 5° -153° Moderator Chilled water at 10° C Sample environment 13 - 300 K, closed cycle refrigerator; furnace is planned for 1500° C Sample size 0.01 - 20 cm3 Experiment duration 5 minutes -1 day, depending on sample size Robert Von Dreele, instrument scientist John Thomas, instrument technician Instrument used: (please type) Local contact: Proposal number: (for LANSCE use only) HIPD A. C. Lawson & R. B. Von Dreele D-'O.o Title: Report received: (for LANSCE use only) Magnetic Structure of UPdSn Authors and affiliations: R. A. Robinson, LANSCE, LANL A. C. Lawson, MST Division, LANL K. H. J. Buschow, Philips Research Labs., Eindhoven Experiment report: A few years ago, a systematic study of the magnetic properties of a number of ternary uranium compounds was made by Palstra et al.[l]. Many of these compounds showed evidence of gaps in their band structures and a few were thought to be antiferromagnetic. One of us [2] had already studied UNiSn on a reactor powder diffractometer at NBS and this summer, we studied some of the other antiferromagnets on HIPD at LANSCE. The most dramatic results were on the hexagonal compound UPdSn, which has a Neel temperature of 29K. We took data both above and below TN, at 45K and 10K. The high temperature data fit well to the CaLi2 structure [1], with space group P63/mmc, except for three impurity lines which we have so far been unable to identify. The data Tom one of the two 40° banks are shown in the Figure. In the low temperature pattern, there are clearly 7 extra peaks, which are indexed in the lower figure. We interpret these as being magnetic, with cell doubling in the hexagonal plane. These are some of the best magnetic neutron diffraction data taken on an accelerator-based neutron source [3-6], with observable reflections out to a d- spacing of 8A. The analysis of these data is incomplete, but we have established that our data are nconsistent with all of the collinear structures catalogued for this space group by Prandl[7]. We have found a simple non-collinear structure that appears to fit our data, but have not completed the analysis yet. However, we have every confidence that these data are good enough to determine the magnetic structure and the uranium moment. Experiment report (continued): UPDSN AT 45K (SET AT 40K) BANK NO. = 6 TWO-THETA = -39.81 OBSERVED PROFILE 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0-SPACING, A X10E 1 (a) Portion of the 45K diffraction pattern in one of the 40° banks on HIPD, on UPdSn. UPDSN AT 10K (1.9 ON SENSORB) BANK NO. = S TWO-THETA = -39.81 OBSERVED PROFILE 0.0 0.2 0.4 0.6 0.8 1.0 1.2 D-SPACING. A X10E 1 (b) Portion of the 10K diffraction pattern in one of the 40° banks on HIPD, on References: UPdSn. The extra peaks are shaded in black and indexed in the hexagonal cell. ] T. T. M. Palstra, G. J. Niewenhuys, R. F. M. Vlastuin, J. van den Berg, J. A. Mydosh and K. H. J. Buschow, J. Magn. Magn. Mater. 67, 331 (1987). :] M. Yethiraj, R. A. Robinson, J. J. Rhyne, J. A. Gotaas and K. H. J. Buschow, J. Magn. Magn. Mater. 79, 355 (1989). G. P. Felcher, J. D. Jorgensen and R. P. Wappling, J. Phys. C: Solid State Phys. 16,6281 (1983). A. C. Lawson, A. Williams, J. L. Smith, P. A. Seeger, J. A. Goldstone, J. A. CRourke and Z. Fisk, J. Magn. Magn. Mater. 50,83 (1985). >] A. C. Lawson, A. Williams, J. G. Huber and R. B. Roof, J. Less-Common Metals 120,113 (1986). 6] A. L. Giorgi, A. C. Lawson, J. A. Goldstone, K. J. Violin and J. D. Jorgensen, J. Appl. Phys. 63, 3604 (1988). 7] W. Prandl, in "Neutron Diffraction", ed. H. Dachs, Springer-Veriag, Berlin 1978, p.l 13. Instrument used: (please type) Local contact: Proposal number: (for LANSCE use only) HIPD Robert Von Dreele D-3J • 0 Titie: Report received: (for LANSCE use only) Neutron Powder Diffraction Study of [Na(ND3)4]+I" 2/7/90 Authors and affiliations: Dr. Victor G. Young, Jr. Department of Chemistry Arizona State University Dr. William S. Glaunsinger Department of Chemistry Arizona State University Mr. Gary L. Burr Department of Chemistry Arizona State University Dr. Robert B. Von Dreele P-LANSCE Los Alamos National Laboratory Experiment report: It is known that alkali metal halides form stable complexes with water and alcohols. However, little is known concerning similar complexes containing ammonia or simple amines, even though there are several literature reports on their physical properties. One reason for this is that all of these complexes have a high partial pressure of ammonia (or amine) at room temperature which makes handling difficult and hazardous.