DSpace Coleção:https://ri.ufs.br/jspui/handle/riufs/24672026-09-07T09:46:35Z2026-09-07T09:46:35ZComportamento dos fônons e magnetismo gerado por vacâncias em nanocristais de CeO2− dopado com MnAssis, Maria Suêd Macêdohttps://ri.ufs.br/jspui/handle/riufs/260462026-09-04T17:33:16Z2026-02-02T00:00:00ZTítulo: Comportamento dos fônons e magnetismo gerado por vacâncias em nanocristais de CeO2− dopado com Mn
Autor(es): Assis, Maria Suêd Macêdo
Abstract: We investigated the influence of doping CeO2 nanocrystals with Mn through structural, spectroscopic, and magnetic analyses. The materials were synthesized by the sol-gel method and
characterized by X-ray diffraction, X-ray absorption spectroscopy (XANES), Raman spectroscopy, and magnetic measurements. The results of Rietveld refinement together with the
Raman spectrum confirm the formation of a single phase of CeO2 with a fluorite-type cubic
structure. These results show that Mn insertion modifies the lattice parameters, crystallite size,
and microdeformation in a non-monotonic manner, revealing a balance between local disorder
and lattice relaxation induced by phonons and vacancy formation. The XANES results reveal
mixed valence of Mn ions as Mn3+
/Mn2+
, resulting in charge compensation through partial
reduction of Ce4+
to Ce3+
. The ZFC/FC curves suggest an anisotropic distribution originating
from Mn–vacancy and show blocked superparamagnetic behavior at low temperatures. The study
identified an antiferromagnetic regime derived from Dzyaloshinskii-Moriya (DM) influenced
by oxygen vacancies. These results present a framework that quantifies the defect chemistry
and magnetic behavior in (Ce1−xMnxO2−, 0 ≤ x ≤ 0.09) nanocrystals, highlighting the role of
oxygen vacancies and doping-induced structural disorder.2026-02-02T00:00:00ZAvaliação de risco radiológico e radioepidemiológico em centros urbanos: simulação de um incidente nuclear hipotético em uma cidade litorâneaSilva, Karla Pereira Carneiro dahttps://ri.ufs.br/jspui/handle/riufs/260202026-09-03T20:03:05Z2026-07-29T00:00:00ZTítulo: Avaliação de risco radiológico e radioepidemiológico em centros urbanos: simulação de um incidente nuclear hipotético em uma cidade litorânea
Autor(es): Silva, Karla Pereira Carneiro da
Abstract: uclear accidents release large quantities of radioactive materials into the atmosphere, exposing the population to radiation doses and contamination. Given the threat of accidental
and/or intentional radiological events, it is essential to employ tools that aid in decisionmaking for risk analysis and the protection of the occupationally exposed population. This
study presents an in-depth assessment of the effects of a hypothetical nuclear incident
involving an LWR reactor in the city of Aracaju, accounting for the population and affected
area. The analysis of the event is based on the Pasquill-Gifford classification of atmospheric
stability (PG Classes) at the time, the prevailing wind direction, and census data on the
individuals. Simulations were performed using the HotSpot Health Physics Code v3.1.2
software to determine the Total Equivalent Effective Dose (TEDE) and the Excess Relative
Risk (ERR) associated with radiation-induced cancers, such as leukemia. The estimates
considered low-dose radioepidemiological models, Biological Effects of Ionizing Radiation
(BEIR) V and VII, and vulnerability criteria such as age and sex, analyzing groups of
males, females, children, and the elderly in the affected areas. To collect population data,
Geographic Information Systems (GIS) were used to delineate impacted zones and groups,
and information from the National Institute of Meteorology (INMET) was used to assess
wind patterns. The results indicated variations between exposure and risk, attributed to
local atmospheric conditions and wind direction, predominantly from the East-Southeast
(ESE) and Southeast (SE). The expansion of isodoses is explained by the capital’s flat
and rugged terrain, combined with PG classes and wind direction. The study highlights
the importance of geospatial models for demographic analysis, census data, and informed
decisions about the exposed population.2026-07-29T00:00:00ZAnálise teórica das propriedades térmicas das matrizes de Y2O3, YF3 e Y7O6F9, dopadas com Nd3+ via modelagem computacionalOliveira, Renato Willy Vieira dehttps://ri.ufs.br/jspui/handle/riufs/254342026-07-09T17:49:23Z2026-02-04T00:00:00ZTítulo: Análise teórica das propriedades térmicas das matrizes de Y2O3, YF3 e Y7O6F9, dopadas com Nd3+ via modelagem computacional
Autor(es): Oliveira, Renato Willy Vieira de
Abstract: In this work, classical atomistic computational modeling techniques and crystal field theory
studies were applied to the case of yttrium oxide (Y2O3), yttrium fluoride (YF3), and yttrium Voxyfluoride (Y7O6F9) matrices doped with neodymium lanthanide ions (Nd3+) from the
perspective of thermometric variations within the temperature range of 273 K to 373 K, whose
applications are based on thermometry in the biological window. The study was initially based
on the interatomic potential model and the lattice energy minimization method. For the set of
potentials used to simulate the crystal structures studied, an agreement above 97.9% was
obtained for Y7O6F9, 98.7% for Y2O3, and 98% for YF3 within the proposed thermal scales.
From this, the incorporation of the Nd3+ ion was carried out following the Mott-Littleton
method, through isovalent substitution, in which the neodymium ion directly replaces the Y3+
ion in the matrices. For the Y2O3 and Y7O6F9 lattices, the Y3+ sites with the highest probabilities
of neodymium incorporation into the matrix were evaluated. From these results, it was possible
to note that the first Y3+ site (Y1) will have the lowest solution energy in the Y2O3 matrix, while
for the Y7O6F9 matrix, the Y1 and Y2 sites have similar probabilities of neodymium
incorporation. YF3 has only one available Y3+. From the atomistic modeling study, it was
possible to perform crystal field theory calculations for the crystalline matrices studied. The
calculation performed consists of applying two models found in the literature to obtain the
results of the crystal field parameters, the PCEM and SOM models. In these calculations, it was
possible to observe the electrostatic interaction in each matrix, and, after that, calculations of
crystal field forces were performed. Crystal field forces were calculated from the rotational
invariants. From these calculations, it was possible to define the limits of the spectroscopically
active coordination spheres of neodymium at each site in the three crystalline matrices. Starting
from the crystal field parameters, the energy levels of the ground state of Nd3+
,
4
I9/2, and the
excited state, 4F3/2, were calculated. From the results obtained for the energy levels, it was
possible to evaluate the thermal sensitivity from the variation between the energy levels of the
excited state, correlating them to Boltzmann statistics.2026-02-04T00:00:00ZSíntese e caracterização estrutural, morfológica, elementar e dosimétrica de CaSO4:Tm,Li preparado por evaporação lenta, coprecipitação e difusão em estado sólidoSantos, Marcelo Franklin da Silvahttps://ri.ufs.br/jspui/handle/riufs/254332026-07-09T17:48:55Z2026-02-04T00:00:00ZTítulo: Síntese e caracterização estrutural, morfológica, elementar e dosimétrica de CaSO4:Tm,Li preparado por evaporação lenta, coprecipitação e difusão em estado sólido
Autor(es): Santos, Marcelo Franklin da Silva
Abstract: Calcium sulfate (CaSO₄) based thermoluminescent dosimeters are widely used in ionizing
radiation dosimetry, with CaSO₄:Dy being particularly noteworthy. In this study, the structural,
thermal, morphological, elemental, and dosimetric properties of CaSO₄ phosphors doped with
thulium (in metallic and oxide forms) and co-doped with lithium, produced by slow evaporation
synthesis (SEL), solid-state diffusion (SES), and coprecipitation (PRE) syntheses, were
investigated. The work involved the preparation and characterization of the phosphor. For
structural characterization, X-ray diffractometry (XRD), thermogravimetric analysis (TGA),
scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used.
For dosimetric characterizations, thermoluminescence (TL) and optically stimulated
luminescence (OSL) techniques were used. The samples in the form of pellets were irradiated
with a ⁹⁰Sr+⁹⁰Y source in the dose range of 0.142 Gy to 500 Gy. XRD analyses confirmed the
formation of the CaSO₄ crystalline phase for all production routes, SEM analyses revealed
significant morphological differences between the materials obtained by the different routes,
and EDS analyses confirmed the incorporation of thulium into the compounds. The CaSO₄
samples produced by SEL showed significantly higher TL and OSL intensities than those
obtained by SES and PRE. The TL emission curves exhibited multiple peaks, with predominant
emissions in the blue region (455 nm), characteristic of Tm³⁺. Co-doping with lithium
contributed to intensifying the luminescent signal of the samples. The OSL curves exhibited
typical exponential decay for all samples, with the samples obtained via SEL exhibiting slow
decay emission, indicating low photoionization cross section and charge transfer in the blue
LED stimulation process. All CaSO₄:Tm,Li phosphors exhibited homogeneous TL and OSL
responses to the dose (with a coefficient of variation less than 10%), adequate response linearity
for the dose range studied, and TL signal stability for traps associated with peaks above 200 °C
(fading). The results indicate that the CaSO₄:Tm,Li compound, especially when synthesized by
slow evaporation, has high potential for applications in ionizing radiation dosimetry.
Complementary studies, such as assessments of energy dependence, lower dose detection limit,
and longer fading periods, will contribute to a comprehensive evaluation of its dosimetric
performance, will contribute to a comprehensive evaluation of its dosimetric performance.2026-02-04T00:00:00Z