Pressure and Temperature:

1
Pressure and Temperature Pushing the Limits of
Neutron Scattering Sample Environment Kenneth J.
Volin Argonne National Laboratory, Argonne, IL
Abstract Neutron diffraction is a powerful tool
for structural studies of samples in special
sample environments because of the high
penetrating power of neutrons compared to x-rays.
The Intense Pulsed Neutron Source (IPNS) at
Argonne National Laboratory (ANL) offers its
users a variety of sample environments for pulsed
neutron scattering and diffraction experiments.
Included in these are numerous pressure cells
that span a wide range of temperatures and
pressures. Each has been designed to achieve the
temperatures and pressures that the current
science being investigated requires while
operating within the constraints of the
particular neutron scattering instrument. High
pressures along with variable temperatures are
parameters set by the range of the experiment.
Stability, reproducibility, and a reasonably low
background are among the constraints imposed by
the neutron scattering instruments and their data
acquisition systems. Safe operation by the user,
documented design, maintenance and repair, and
reasonable costs are also primary design
requirements imposed by the operation of the
neutron scattering facility. Different
scattering geometries for powder diffraction,
single crystal diffraction, and small angle
diffraction have lead to a variety of innovative
designs. Some experiments require the use of a
pressure transmitting fluid, which may be a
liquid or a gas, or require that the sample
itself is the pressure transmitting fluid. The
effects of temperature and pressure on the cell
materials utilized, along with the contribution
of the particular cell material to the cell
background must be considered from the start.
The use of these pressure cells for neutron
scattering experiments must be tailored to the
particular experiment. Requirements of chemical
compatibility of the sample under investigation
with the cell materials and the pressure
transmitting fluid must be considered and
documented.
Pressure vs. Background Materials Balancing
negative and positive coherent scattering
lengths, Titanium66Zirconium34 "null scattering
alloy" will not contaminate your data with
unwanted Bragg reflections. It also has good
mechanical strength and is most often used to
make high pressure cells.
VCU
Acknowledgements The work featured here is, for
the most part, not our own. In addition to the
various institutional credits posted throughout,
we should credit several individuals
including Ian Bailey (ISIS/RAL) John Dreyer
(ISIS/RAL) Rob Done (ISIS/RAL) Jim Jorgenson
(MSD/ANL) Bob Kleb (IPNS/ANL) Lou Santodonato
(SNS/ORNL) Mark McHugh (VCU)
Pressure vs. Background Size This pressure cell,
machined from a single billet of aluminum, is
capable of allowing the neutron scientist to
measure the structure of single crystals of
only1-2mm size up to 2kbar in pressure and, when
mounted on a helium closed cycle refrigerator, at
temperatures from room temperature down to 10K.
The work reported in this paper is supported by
the U.S. Department of Energy, BES Materials
Sciences, under contract W-31-109-ENG-38