254 research outputs found
Beta-decay of nuclei around Se-90. Search for signatures of a N=56 sub-shell closure relevant the r-process
Nuclear structure plays a significant role on the rapid neutron capture
process (r-process) since shapes evolve with the emergence of shells and
sub-shells. There was some indication in neighboring nuclei that we might find
examples of a new N=56 sub-shell, which may give rise to a doubly magic Se-90
nucleus. Beta-decay half lives of nuclei around Se-90 have been measured to
determine if this nucleus has in fact a doubly-magic character. The
fragmentation of Xe-136 beam at the National Superconducting Cyclotron
Laboratory at Michigan State University was used to create a cocktail of nuclei
in the A=90 region. We have measured the half lives of twenty-two nuclei near
the r-process path in the A=90 region. The half lives of As-88 and Se-90 have
been measured for the first time. The values were compared with theoretical
predictions in the search for nuclear-deformation signatures of a N=56
sub-shell, and its possible role in the emergence of a potential doubly-magic
Se-90. The impact of such hypothesis on the synthesis of heavy nuclei,
particularly in the production of Sr, Y and Zr elements was investigated with a
weak r-process network. The new half lives agree with results obtained from a
standard global QRPA model used in r-process calculations, indicating that
Se-90 has a quadrupole shape incompatible with a closed N=56 sub-shell in this
region. The impact of the measured Se-90 half-life in comparison with a former
theoretical predication associated with a spherical half-life on the
weak-r-process is shown to be strong
Beta-decay half-lives and beta-delayed neutron emission probabilities of nuclei in the region below A=110, relevant for the r-process
Measurements of the beta-decay properties of r-process nuclei below A=110
have been completed at the National Superconducting Cyclotron Laboratory, at
Michigan State University. Beta-decay half-lives for Y-105, Zr-106,107 and
Mo-111, along with beta-delayed neutron emission probabilities of Y-104,
Mo-109,110 and upper limits for Y-105, Zr-103,104,105,106,107 and Mo-108,111
have been measured for the first time. Studies on the basis of the quasi-random
phase approximation are used to analyze the ground-state deformation of these
nuclei.Comment: 21 pages, 10 figures, article accepted for publication in Physical
Review
r-process experimental campaign at the National Superconducting Cyclotron Laboratory (NSCL/MSU)
Atomic-scale confinement of optical fields
In the presence of matter there is no fundamental limit preventing
confinement of visible light even down to atomic scales. Achieving such
confinement and the corresponding intensity enhancement inevitably requires
simultaneous control over atomic-scale details of material structures and over
the optical modes that such structures support. By means of self-assembly we
have obtained side-by-side aligned gold nanorod dimers with robust
atomically-defined gaps reaching below 0.5 nm. The existence of
atomically-confined light fields in these gaps is demonstrated by observing
extreme Coulomb splitting of corresponding symmetric and anti-symmetric dimer
eigenmodes of more than 800 meV in white-light scattering experiments. Our
results open new perspectives for atomically-resolved spectroscopic imaging,
deeply nonlinear optics, ultra-sensing, cavity optomechanics as well as for the
realization of novel quantum-optical devices
Measurement of the J/ photoproduction cross section over the full near-threshold kinematic region
We report the total and differential cross sections for
photoproduction with the large acceptance GlueX spectrometer for photon beam
energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full
kinematic range of momentum transfer squared, . Such coverage facilitates
the extrapolation of the differential cross sections to the forward ()
point beyond the physical region. The forward cross section is used by many
theoretical models and plays an important role in understanding
photoproduction and its relation to the proton interaction. These
measurements of photoproduction near threshold are also crucial inputs
to theoretical models that are used to study important aspects of the gluon
structure of the proton, such as the gluon Generalized Parton Distribution
(GPD) of the proton, the mass radius of the proton, and the trace anomaly
contribution to the proton mass. We observe possible structures in the total
cross section energy dependence and find evidence for contributions beyond
gluon exchange in the differential cross section close to threshold, both of
which are consistent with contributions from open-charm intermediate states.Comment: 15 pages 18 figure
β-decay measurements of A ≃ 70 − 110 r-process nuclei at the National Superconducting Cyclotron Laboratory
The present paper reports on several r-process motivated β-decay experiments undertaken at the National Superconducting Cyclotron Laboratory. β-decay half-lives and β-delayed neutron-emission probabilities were measured for nuclei around the r-process A = 70–80 and A = 90 – 110 mass regions. The data are discussed on the basis of quasi-random phase approximation calculations. The emphasis is made on the impact of these data upon calculations of r-process abundances
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