Page 156 - 00. Complete Version - Progress Report IPEN 2014-2016

156 Nuclear Science and Technology | Progress Report

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 posi-
tion 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 mono-
chromator permits measurements with four
different wavelengths namely 1.111, 1.399,
1.667 and 2.191 Å (nominal values). The re-
search staff at the IPEN Neutron Diffraction
Laboratory, which is in charge of the oper-
Fig 5. Experimental NMD pattern (small circles), obtained
ation of Aurora, has participated in several with magnetite in the paramagnetic phase (976 K), com-
studies carried out in cooperation with other pared with simulated patterns (continuous lines) simulated by
MULTI for the three different cases mentioned in the text.
laboratories or by itself. In the following sec-
tions, papers published in the past three years as a tool for structural studies and some re-
are presented. sults of application to structural studies like,
for instance, the refinement of the ferri- and
Neutron multiple diffraction used paramagnetic phases of magnetite (Fe3O4). At
as a tool for structural studies room temperature, magnetite (Fe3O4) is a fer-
rimagnet; above the Curie temperature (853
During numerous years, neutron multiple dif- K), it becomes a paramagnet. NMD patterns
fraction (NMD) has being developed as a tool of a natural sample of magnetite were mea-
for structural studies in the Neutron Diffrac- sured at room temperature and 976 K. With
tion Laboratory at IPEN. Several papers have the patterns, lattice, positional and thermal pa-
resulted from the application of NMD in struc- rameters were refined in three different cases:
tural crystallography. Recently, the Neutron assuming an overall isotropic thermal param-
News magazine dedicated a special issue to the eter, assuming different isotropic parameters
development of neutron scattering in South and assuming anisotropic parameters. In this
America. A Scientific Review, condensing the application and in the others reviewed in the
results found in the papers published by the work, the program MULTI, of simulation of
Neutron Diffraction Laboratory was published NMD patterns, revealed to be an essential tool
in this issue together with others from Bra- for the analyses. This program was developed
zil and Argentina. It presents a brief histo- by the staff of the Neutron Diffraction Labo-
ry of the development of neutron diffraction ratory in the nineties.

Instituto de Pesquisas Energéticas e Nucleares