104 research outputs found
Second T = 3/2 state in B and the isobaric multiplet mass equation
Recent high-precision mass measurements and shell model calculations~[Phys.
Rev. Lett. {\bf 108}, 212501 (2012)] have challenged a longstanding explanation
for the requirement of a cubic isobaric multiplet mass equation for the lowest
isospin quartet. The conclusions relied upon the choice of the
excitation energy for the second state in B, which had two
conflicting measurements prior to this work. We remeasured the energy of the
state using the reaction and significantly disagree
with the most recent measurement. Our result supports the contention that
continuum coupling in the most proton-rich member of the quartet is not the
predominant reason for the large cubic term required for nuclei
Levantamento da produção de hortaliças no município de Parintins na feira da Paraíba.
O trabalho teve como objetivo realizar um levantamento sobre a olericultura na cidade de Parintins-Am especialmente na Feira da Paraíba na rua do mesmo nome
Percepção ambiental de docentes e discentes da rede de ensino público superior do município de Parintins - CESP/ UEA.
As questões ambientais são pautas das arenas de discussão locais e globais. Todos reconhecem que o nosso ambiente está sendo devastado, pois são constantes as notícias vinculadas na mídia falada e escrita sobre mudanças climáticas, poluição de rios e do ar, destruição da floresta, extinção de espécies, esgotamento dos recursos minerais. A importância da pesquisa em percepção ambiental para o planejamento ambiental é uma ação coordenada para minimizar estes impactos antrópicos negativos gerados por nossas ações ao ambiente. "Uma das dificuldades para a proteção dos ecossistemas naturais está na existência de diferenças nas percepções dos valores e da importância dos mesmos entre indivíduos de culturas diferentes ou de grupos sócio-econômicos que desempenham funções, no plano social. Neste cenário, caracterizar o conhecimento e a percepção ambiental dos atores envolvidos, docentes e discentes da rede de ensino público (superior) do município de Parintins, instigando-os através de abordagem participativa na construção de estratégias e ações transformadoras, pode ajudar a clarear os passos a serem trilhados na expectativa de implantação de um programa de educação ambiental com começo, meio e fim
Study of proton-unbound states in relevant for the reaction in novae
Background: The nucleosynthesis of several proton-rich nuclei is determined
by radiative proton-capture reactions on unstable nuclei in nova explosions.
One such reaction is , which links the
NeNa and MgAl cycles in oxygen-neon (ONe) novae.
Purpose: To extract resonance
strengths from a study of proton-unbound states in , produced
via the Mg(He,) reaction.
Methods: A beam of ions at 50.7 MeV was used to produce
the states of interest in Al. Proton-triton angular correlations were
measured with a QDD magnetic spectrometer and a silicon detector array,
located at iThemba LABS, South Africa.
Results: We measured the excitation energies of the four lowest
proton-unbound states in Al and place lower-limits on
values for these four states. Together with USD-C shell-model calculations of
partial gamma widths, the experimental data are also used to determine
resonance strengths for the three lowest
resonances.
Conclusions: The energy of the dominant first
resonance is determined to be keV, with a resonance
strength meV
Isoscalar giant monopole strength in Ni, Zr, Sn and Pb
Inelastic -particle scattering at energies of a few hundred MeV and
very-forward scattering angles including has been established as a
tool for the study of the isoscalar giant monopole (IS0) strength distributions
in nuclei. An independent investigation of the IS0 strength in nuclei across a
wide mass range was performed using the facility at iThemba
Laboratory for Accelerator Based Sciences (iThemba LABS), South Africa, to
understand differences observed between IS0 strength distributions in previous
experiments performed at the Texas A\&M University (TAMU) Cyclotron Institute,
USA and the Research Center for Nuclear Physics (RCNP), Japan. The isoscalar
giant monopole resonance (ISGMR) was excited in Ni, Zr,
Sn and Pb using -particle inelastic scattering with
MeV beam and scattering angles
and . The K magnetic spectrometer at iThemba LABS was used to
detect and momentum analyze the inelastically scattered particles. The
IS0 strength distributions in the nuclei studied were deduced with the
difference-of-spectra (DoS) technique including a correction factor for the
data based on the decomposition of cross sections in previous
experiments. IS0 strength distributions for Ni, Zr, Sn
and Pb are extracted in the excitation-energy region MeV.Using correction factors extracted from the RCNP experiments, there is
a fair agreement with their published IS0 results. Good agreement for IS0
strength in Ni is also obtained with correction factors deduced from the
TAMU results, while marked differences are found for Zr and Pb.Comment: 12 pages, 10 figures, regular article submitted to PR
Fine structure of the isoscalar giant monopole resonance in Ni, Zr, Sn and Pb
Over the past two decades high energy-resolution inelastic proton scattering
studies were used to gain an understanding of the origin of fine structure
observed in the isoscalar giant quadrupole resonance (ISGQR) and the isovector
giant dipole resonance (IVGDR). Recently, the isoscalar giant monopole
resonance (ISGMR) in Ni, Zr, Sn and Pb was
studied at the iThemba Laboratory for Accelerator Based Sciences (iThemba LABS)
by means of inelastic -particle scattering at very forward scattering
angles (including ). The good energy resolution of the measurement
revealed significant fine structure of the ISGMR.~To extract scales by means of
wavelet analysis characterizing the observed fine structure of the ISGMR in
order to investigate the role of different mechanisms contributing to its decay
width. Characteristic energy scales are extracted from the fine structure using
continuous wavelet transforms. The experimental energy scales are compared to
different theoretical approaches performed in the framework of quasiparticle
random phase approximation (QRPA) and beyond-QRPA including complex
configurations using both non-relativistic and relativistic density functional
theory. All models highlight the role of Landau fragmentation for the damping
of the ISGMR especially in the medium-mass region. Models which include the
coupling between one particle-one hole (1p-1h) and two particle-two hole
(2p-2h) configurations modify the strength distributions and wavelet scales
indicating the importance of the spreading width. The effect becomes more
pronounced with increasing mass number. Wavelet scales remain a sensitive
measure of the interplay between Landau fragmentation and the spreading width
in the description of the fine structure of giant resonances.Comment: 13 pages,7 figures, regular articl
Isospin mixing and the cubic isobaric multiplet mass equation in the lowest <i>T</i>=2, <i>A</i>=32 quintet
The isobaric multiplet mass equation (IMME) is known to break down in the
first T = 2, A = 32 isospin quintet. In this work we combine high-resolution
experimental data with state-of-the-art shell-model calculations to investigate
isospin mixing as a possible cause for this violation. The experimental data
are used to validate isospin-mixing matrix elements calculated with newly
developed shell-model Hamiltonians. Our analysis shows that isospin mixing with
nonanalog T = 1 states contributes to the IMME breakdown, making the
requirement of an anomalous cubic term inevitable for the multiplet
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