Page 9 - PR 2014 2016 07 Nuclear Science and Technology

Nuclear Science and Technology | Progress Report 151

Study of the crystalline
and magnetic structures

of materials by neutron

and X-ray diffraction

The high-resolution neutron powder diffrac-
tometer Aurora, installed on the IEA-R1 re-
search reactor at IPEN-CNEN/SP, has a position
sensitive detector (PSD) which allows a quite
fast measurement of powder patterns with
good resolution. The PSD measures 20° of a
pattern at once. An extensive pattern can be
obtained by collecting data in contiguous 20°
segments, in an angular interval ranging from
5 to 130°. A double-bent silicon monochroma-
tor permits measurements with four different
wavelengths namely 1.111, 1.399, 1.667 and
2.191 Å (nominal values). The research staff at
the IPEN Neutron Diffraction Laboratory, which
is in charge of the operation of Aurora, has
Fig 5. Experimental NMD pattern (small circles), obtained
participated in several studies carried out in with magnetite in the paramagnetic phase (976 K), compared
cooperation with other laboratories or by itself. with simulated patterns (continuous lines) simulated by
MULTI for the three different cases mentioned in the text.
In the following sections, papers published in
the past three years are presented.
results of application to structural studies like,
Neutron multiple diffraction used for instance, the refinement of the ferri- and
as a tool for structural studies paramagnetic phases of magnetite (Fe O ). At
3 4
room temperature, magnetite (Fe O ) is a fer-
3 4
During numerous years, neutron multiple rimagnet; above the Curie temperature (853 K),
diffraction (NMD) has being developed as it becomes a paramagnet. NMD patterns of a
a tool for structural studies in the Neutron natural sample of magnetite were measured
Diffraction Laboratory at IPEN. Several papers at room temperature and 976 K. With the
have resulted from the application of NMD in patterns, lattice, positional and thermal pa-
structural crystallography. Recently, the Neu- rameters were refined in three different cases:
tron News magazine dedicated a special issue assuming an overall isotropic thermal param-
to the development of neutron scattering in eter, assuming different isotropic parameters
South America. A Scientific Review, condens- and assuming anisotropic parameters. In this
ing the results found in the papers published application and in the others reviewed in the
by the Neutron Diffraction Laboratory was work, the program MULTI, of simulation of
published in this issue together with others NMD patterns, revealed to be an essential tool
from Brazil and Argentina. It presents a brief for the analyses. This program was developed
history of the development of neutron diffrac- by the staff of the Neutron Diffraction Labo-
tion as a tool for structural studies and some ratory in the nineties.