A workshop on "Materials Research Using Cold Neutrons at Pulsed
Sources" was held at Argonne National Laboratory on August 25 and
26, 1997. It was organized by the Intense Pulsed Neutron Source (IPNS)
as a satellite meeting associated with the International Conference on
Neutron Scattering in Toronto. Some 80 participants from eight countries
attended the two-day meeting which featured about two dozen invited talks
and a poster session.
The apparent lack of awareness of the availability of cold neutrons
in the US, particularly at pulsed sources, by the materials research community
was the motivation for this workshop. Accordingly, the meeting was intended
to provide information regarding the present status and future trends in
research opportunities using cold neutrons. Four overview talks provided
a perspective of cold-neutron sciences and instrumentation. Colin Carlile
(Rutherford) used the IRIS beamline, a high resolution quasielastic and
inelastic spectrometer at ISIS, to illustrate the emergence and outlook
of utilization of cold neutrons at pulsed sources; Charlie Glinka (NIST)
presented a spectrum of small-angle neutron scattering (SANS) studies of
materials at the Cold Neutron Research Facility at the NIST reactor; Kent
Crawford (Argonne) described the tricks, pitfalls and challenges of designing
cold-neutron instruments at pulsed sources; and John White (Australian
National Univ.) demonstrated the applications of SANS and reflectivity
measurements of model molecular systems towards the understanding of the
formation of novel materials.
The remaining topical talks focused on the areas of SANS, reflectivity
and spectroscopic studies of a rich variety of materials, from adsorbed
molecules to thin films to coal to metallic glasses. There were a number
of converging themes which were brought up by various speakers from different
areas.
1. The current high degree of sophistication and maturity of SANS and
reflectometry was demonstrated by the many studies of kinetics of materials
behavior. Rather than taking sporadic snapshots of a multi-component system,
researchers concentrated on quantitative monitoring of a series of evolving
events driven by controlled external or intrinsic conditions. Investigations
included homogeneous nucleation of TPA-Br/SiO2 solution
(J. White), morphology of very complex porous structures at thermodynamic
equilibrium (Sow-Hsin Chen, MIT), radiation-induced precipitates in metals
(C. Glinka), corrosion of Ti film in solutions (Chuck Majkrzak, NIST),
crystallization/phase separation in bulk metallic glasses (P. Thiyagarajan,
Argonne), cure rates of adhesive films (Mike Kent, Sandia), and micellar
alignment under shear (Lee Magid, Univ. Tennessee).
2. The powerful technique of contrast variation unique to neutron scattering
was applied creatively to derive new insights into the problems, such as
H/D contrast matching in template molecular systems (J. White) and polymers
(Sanjeeva Murthy, Allied Signal), H/D isotopic effects in inelastic scattering
to probe the adsorption sites in zeolites (Juergen Eckert, LANSCE), contrast
between magnetic and nuclear scattering in the study of embrittlement of
metals (C. Glinka), Q-dependent contrast behavior in carbon black reinforced
composites (Rex Hjelm, LANSCE) and in coal extract/solvent systems (George
Cody, Carnegie Inst. Washington), and contrast among simultaneous low-to-high
Q measurements using pulsed-source SANS instruments (S.-H. Chen and P.
Thiyagarajan).
3. The recognition of the complementarity and the combined strength
of one aspect of neutron scattering in conjunction with other aspects of
neutron scattering or other experimental techniques or theories was touched
upon by almost every speaker. Without going into specific details, it is
perhaps sufficient to just mention the combined elements: quasielastic
and elastic scattering (C. Carlile), quasielastic and inelastic scattering
(Frans Trouw, Argonne), reflectivity (out-of-plane structure) and in-plane
SANS (C. Glinka and Huey Huang, Rice Univ.), spectroscopy and MD simulations
(F. Trouw and M. Kent), SANS and a theoretical treatment using the concept
of interfacial curvatures (S.-H. Chen), reflectivity and inversion techniques
(C. Majkrzak), and lastly but not the least, neutrons and photons - visible
light and x-rays (everyone!).
The poster session included about 20 papers and several displays from
industrial companies who contributed financial support to the workshop.
It was pleasing to see the presentations of industrial applications of
cold neutrons on catalytic, petroleum and natural gas storage systems,
as well as the contributions from UK, Hungary, Austria, Czech Republic,
Germany and Japan. Lively discussions prevailed throughout the question-and-answer
period following each talk and during the poster session (and then became
even more relaxed and delightful during the cocktail hours before and after
the conference dinner).
Although pulsed-source based cold-neutron technology was not an explicit
topic of the workshop, there were reminders of developments in the design
and operation of target-(cold) moderator systems from which a high-flux
of useful cold neutrons is realized (C. Carlile and K. Crawford). The pivotal
contributions from Jack Carpenter (Argonne) to the advancement of this
important field quickly came to the minds of the neutron scientists. Following
the conference dinner, Jack's many achievements, introduced by John
White, were joyfully celebrated, and a plaque was presented to Jack as
a tribute to his successful and (ongoing) tireless endeavors.
In less than two decades cold neutron instrumentation at pulsed sources
sprang up from nonexistent to becoming a part of the mainstream neutron-scattering
enterprise with multi-disciplinary applications. This tantalizing phenomenon
is not unlike a fairy tale. No wonder C. Carlile compared pulsed-source
cold neutrons to Cinderella. He even asserted the princess' prevalence
in the next-generation facilities. Hence we expect an evolving story with
plenty of offspring of cold neutrons to come. Proceedings of the Argonne
workshop will be published by World Scientific in the next 6 months.
Chun Loong
ckloong@anl.gov
An engaging discussion between Keith Ross (Univ. Salford) and Sow-Hsin
Chen (MIT). It is safe, perhaps, to assume that the topic is neutron
scattering from water.
John White presenting Jack Carpenter a plaque in thanking him for his
pioneering contributions to target and cold moderator technology at pulsed
sources.
