Ames Laboratory / Iowa State University

Neutron Scattering

at

Oak Ridge National Laboratory

The Group

The Ames Laboratory Neutron Scattering group (ALNS) is part of the Ames Laboratory Condensed Matter Physics group (CMP). The ALNS group works in collaboration with the Oak Ridge National Laboratory's (ORNL) High Flux Isotope Reactor (HFIR), Center for Neutron Scattering (CNS).

Members of the ALNS group are:
Robert McQueeney
David Vaknin
Alan Goldman
Andreas Kreyssig
Jerel Zarestky (based at Oak Ridge)
Wei Tian (postdoc based at Oak Ridge)

group photo
HFIR story in the Oak Ridger

History

power point document of the ALNS group (Mar-2006)

Neutron scattering began at Ames Laboratory and Iowa State University in the late 1940s with Robert Rundle collaborating with Cliff Schull and Ernie Wollan at ORNL. The hay days of neutron scattering at the Ames Laboratory began with the Ames Laboratory Research Reactor (ALRR) coming on line in 1965. Allan Mackintosh lead the Ames group based at the ALRR which was later lead by Sunil Sinha and then Costa Stassis. When the ALRR was shut down in 1977, the group relocated to the Oak Ridge Research Reactor (ORR) at ORNL, moving three instruments, a triple axis spectrometer, TRIAX, and two diffractometers (one a polarized instrument and one fixed Ei machine), to that facility in 1978. Around 1986-7 the group became involved in plans to renovate the HB1A spectrometer at the HFIR. The instrument was built as a collaboration of the Ames Laboratory and ORNL neutron scattering groups with respect to funding and design effort. It was on line in 1990 when the HFIR came back up after an extended outage. The ORR had been shut down permanently by this time and the HFIR became the group's base of operations at ORNL. The TRIAX spectrometer was moved and installed at the Missouri University Research Reactor (MURR) in 1993-1995 and continues to be a productive neutron instrument.

The Ames Laboratory Neutron Scattering Group (ALNS) uses neutron scattering techniques to study the physical properties of condensed matter, with emphasis on materials of considerable scientific and/or technological importance. To conduct our research we use steady state (research reactors) and spallation neutron sources in the US and in Europe with the majority of our neutron scattering investigations being conducted using the neutron scattering facilities at the Oak Ridge National Laboratory. Often, we perform research at other facilities such as the Los Alamos Neutron Science Center (LANSCE) at Los Alamos National Laboratory, the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory, the Center for Neutron Research (NCNR) at the National Institute of Science and Technology (NIST), and less frequently, at European reactors and spallation sources (ILL at Grenoble and Orph at Saclay, France; PSI, Switzerland; ISIS, England).

Our group is actively involved in the development of instrumentation for the SNS and HFIR neutron scattering facilities. The HB1A Ames Laboratory triple-axis spectrometer is installed at the HFIR and is operated as a users facility of the Center for Neutron Scattering (CNS). One of us (Dr. Zarestky) is permanently residing at Oak Ridge and is the instrument scientist of this facility; Dr. Garlea who is also permanently at Oak Ridge, is assisting with this task. Also, Dr. Zarestky, in collaboration with Dr. S. Nagler (ORNL neutron scattering group) is working on the conceptual design of the Subthermal Triple Axis Research instrument (STAR) proposed for the CG1 beam line in the HFIR cold guide hall. The group is also actively involved in the development of instrumentation and a research program at the SNS. Of particular importance is our participation in the construction of the HYSPEC, SEQUOIA and ARCS spectrometers as well as the development of SNS reflectometers.

For investigations of thin organic films, soft and magnetic materials, combined neutron and X-ray scattering studies are conducted. These complementary X-ray scattering studies of magnetic materials and soft matter are conducted at the APS, and at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory.


The Research

Research interests of the ALNS group;


The Instrument

HB1A is a fixed-initial-energy triple-axis spectrometer operating with Ei = 14.6 meV. The monochromator is a double crystal system with a vertically focusing pyrolitic graphite monochromator (M1) in the main beam of the HB1 beam tube. At the second monochromator position (M2), two PG monochromator options are available: a vertically focusing unit and a double focusing unit, the choice depending on experiment. The double crystal monochromator configuration provides one of the most intense beams of this energy at the HFIR and the cleanest beam in terms of higher order contamination by l/2 (Il/2 10-4 x Il and very low gamma and fast neutron background. The analyzer can be selected from various analyzer crystals available: pyrolitic graphite, beryllium, silicon and germanium..

click here for larger picture

HB1A Spectrometer Parameters
 Monochromator  PG(002) double crystal
Monochromator angle
Analyzers  PG(002), Be(101), Be(002), Si(111), Ge(111)
Sample Angle
Scattering Angle
Analyzer Angle
Collimations (FWHM)  C1:  open (40' effective, premonochromator)
   C2:  open (40' effective), 30', 20', 10' (mono-sample)
   C3:  40', 30', 20', 10' (sample-analyzer)
    C4:  105', 70', 35' (analyzer-detector)
Beam Size  50 (high) X 37 (wide) mm maximum
Filters  Sapphire (pre-Monochromator-1)
   HOPG located between M-1 and M-2
Flux at Sample


HB1A instrument control software; SPICE


Ames Laboratory auxiliary equipment


Continued Improvements

The recent upgrade of the HFIR at ORNL provided larger beam tubes for extracting much taller beams. This together with a larger monochromator at the M1 position as well as an evacuated flight path for 2 meters of the beam line, combined to improve the flux on sample by a factor of 2-3. The M2 shield was also replaced with a much larger and more effective version. The evacuated flight path, taller opening beam plug and M2 shield were designed and fabricated at Ames Laboratory. One of the major changes was eliminating the airpad module and tanzboden for support and motion of the analyzer/detector system and replacing it with a precision circular rail system. This has been very successful.

The electronics and computer system controlling the spectrometer were also completely replaced. The SPICE triple-axis control software was implemented on HB1A by the HFIR neutron scattering staff. This is a state-of-the-art instrument operation and data acquisition application using PC's and LabView software. The transition to this system was very smooth, one of the design goals of the SPICE software design, and the spectrometer was brought into a functioning condition the same day the software was installed. This change required the complete replacement of almost all of the electronics on the machine. The beam intensity at the sample is comparable to ILL spectrometers, and the upgrade which is planned will result in about a factor of two more intensity.


Some photos of the instrument

The spectrometer became operational in April of 2003 and is now actively in use in the HFIR Center for Neutron Scattering (CNS) user program. Since Apr-2003, sixty one experiments involving twenty seven different investigators have been performed on the instrument. The HB1A spectrometer has proven to be an outstanding spectrometer for inelastic studies below room temperature of excitations up to ~9 meV and high temperature studies of excitations well above 30 meV. It is also an excellent instrument for elastic studies of structural and magnetic transitions because of very low higher-order contaminations.

Continued upgrades of the instrument are planned for the instrument; analyzer detector shield replacement and shielded/collimated/evacuated flight path between M2 and sample.





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