44 research outputs found
A mathematical model to describe the alpha dose rate from a UO2 surface
A model to determine the dose rate of a planar alpha-emitting surface, has
been developed. The approach presented is a computationally efficient
mathematical model using stopping range data from the Stopping Ranges of Ions
in Matter (SRIM) software. The alpha dose rates as a function of distance from
irradiated UO2 spent fuel surfaces were produced for bench-marking with
previous modelling attempts. This method is able to replicate a Monte Carlo
(MCNPX) study of an irradiated UO2 fuel surface within 0.6 % of the resulting
total dose rate and displays a similar dose profile
Structure and Phase Transitions of Metastable Hexagonal Uranium Thin Films
We report a simple technique for the synthesis of uniaxially textured,
metastable hexagonal close-packed-like uranium thin films with thicknesses
between 175-2800 \r{A}. The initial structure and texture of the layers have
been studied via X-ray diffraction and reflectivity and the time-dependent
transitions of the samples into various orientations of orthorhombic
-U have been mapped by similar techniques. The final crystallographic
orientations of each system and the timescales on which the transitions occur
are found to depend on the lattice parameters of the original layer. The
absence of the -U (001) orientation in the transition products
suggests that the transitions in these layers are mediated by mechanisms other
than the [110] transverse acoustic phonon mode previously suggested for the
cubic -U(110) to hcp-U(00.1) to -U(001) displacive phase
transition. Alternative transition pathways are discussed
Synchrotron x-ray scattering of magnetic and electronic structure of UN and U2N3 epitaxial films
We examine the magnetic ordering of UN and of a closely related nitride,
U2N3, by preparing thin epitaxial films and using synchrotron x-ray techniques.
The magnetic configuration and subsequent coupling to the lattice are key
features of the electronic structure. The well-known antiferromagnetic (AF)
ordering of UN is confirmed, but the expected accompanying distortion at Tn is
not observed. Instead, we propose that the strong magneto-elastic interaction
at low temperature involves changes in the strain of the material. These
strains vary as a function of the sample form. As a consequence, the accepted
AF configuration of UN may be incorrect. In the case of cubic a-U2N3, no single
crystals have been previously prepared, and we have determined the AF ordering
wave-vector. The AF Tn is close to that previously reported. In addition,
resonant diffraction methods have identified an aspherical quadrupolar charge
contribution in U2N3 involving the 5f electrons; the first time this has been
observed in an actinide compound
XPS Study of Ion Irradiated and Unirradiated UO2 Thin Films
XPS determination of the oxygen coefficient k O =2+x and ionic (U 4+ , U 5+ and U 6+ )
composition of oxides UO 2+x formed on the surfaces of differently oriented (hkl) planes of thin
UO 2 films on LSAT (Al 10 La 3 O 51 Sr 14 Ta 7 ) and YSZ (yttria-stabilized zirconia) substrates was
performed. The U 4f and O 1s core-electron peak intensities as well as the U 5f relative intensity
before and after the 129 Xe 23+ and 238 U 31+ irradiations were employed. It was found that the
presence of uranium dioxide film in air results in formation of oxide UO 2+x on the surface with
mean oxygen coefficients k O in the range 2.07-2.11 on LSAT and 2.17-2.23 on YSZ substrates.
These oxygen coefficients depend on the substrate and weakly on the crystallographic
orientation.
On the basis of the spectral parameters it was established that uranium dioxide films
AP2,3 on the LSAT substrates have the smallest k O values, and from the XRD and EBSD results
it follows that these samples have a regular monocrystalline structure. The XRD and EBSD
results indicate that samples AP5-7 on the YSZ substrates have monocrystalline structure,
however, they have the highest k O values. The observed difference in the k O values, probably,
caused by the different nature of the substrates: the YSZ substrates provide 6.4% compressive
strain, whereas (001) LSAT substrates result only in 0.03% tensile strain in the UO 2 films.
129 Xe 23+ irradiation (92 MeV, 4.8 × 10 15 ions/cm 2 ) of uranium dioxide films on the LSAT
substrates was shown to destroy both long range ordering and uranium close environment, which
results in increase of uranium oxidation state and regrouping of oxygen ions in uranium close
environment. 238 U 31+ (110 MeV, 5 × 10 10 , 5 × 10 11 , 5 × 10 12 ions/cm 2 ) irradiations of uranium
dioxide films on the YSZ substrates were shown to form the lattice damage only with partial
destruction of the long range ordering
Preocupações de carreira e adaptabilidade : estudo exploratório com uma amostra de candidatos a sargentos e oficiais do Exército Português
Tese de mestrado, Psicologia (Psicologia dos Recursos Humanos, do Trabalho e das Organizações), Universidade de Lisboa, Faculdade de Psicologia, 2010O presente trabalho consiste num estudo exploratório sobre as preocupações de
carreira e as dimensões da adaptabilidade, baseando-se na Perspectiva de
Desenvolvimento da Carreira de Donald Super e na Perspectiva Construtivista de
Mark Savickas. Pretende-se, ainda, contribuir para a investigação acerca do Inventário
sobre Adaptabilidade, que se encontra ainda em estudo no âmbito de um Projecto
Internacional.
Foram aplicados o Inventário das Preocupações de Carreira e o Inventário sobre
Adaptabilidade a uma amostra de 75 adultos candidatos a Sargentos e Oficiais do
Exército Português. Os resultados obtidos tendem a confirmar as hipóteses de
investigação formuladas, apontando para a relação entre a variável idade e as tarefas
de desenvolvimento das fases da carreira Exploração e Estabelecimento, para a
predominância das dimensões Confiança e Cooperação, e para a relação entre
preocupações de carreira e dimensões da adaptabilidade. Apresentam-se as
conclusões do presente estudo, algumas limitações deste e futuras linhas de
investigação. Tecem-se também algumas considerações sobre as implicações do
estudo para as práticas de gestão de carreira.This work is an exploratory study about the career concerns and the dimensions of
adaptability, based on the Perspective of the Career Development of Donald Super
and the Constructivist Perspective of Mark Savickas. It is also intended to contribute
to the research on the Career Adapt-Abilities Inventory, which is still under
investigation as part of an International Project.
The Career Concerns Inventory and the Career Adapt-Abilities Inventory were
applied to a sample of 75 adult candidates to Sergeants and Officers of the Portuguese
Army. The results seem to confirm the research hypotheses, pointing to the relation
between the variable age and the developmental tasks of the Exploration and
Establishment career phases, to the predominance of the dimensions Cooperation, and
Confidence and also to the relation between career concerns and adaptability
dimensions. The findings of this study, some of its limitations and future research
paths are presented. Some reflections are also discussed in what concerns the study's
implications for the career management practices