1,674 research outputs found
First decay study of the very neutron-rich isotope Br-93
The decay of the mass-separated, very neutron-rich isotope Br-93 has been
studied by gamma-spectroscopy. A level scheme of its daughter Kr-93 has been
constructed. Level energies, gamma-ray branching ratios and multipolarities
suggest spins and parities which are in accord with a smooth systematics of the
N=57 isotones for Z less-equal 40, suggesting the N=56 shell closure still to
be effective in Kr isotopes. So far, there is no indication of a progressive
onset of deformation in neutron-rich Kr isotopes.Comment: 17 pages, 3 figures, Phys. Rev. C, in prin
A K=3 two-quasiparticle isomer in Sr
The decay of on-line mass-separated
98
Rb
to
98
Sr
is studied by
Îł
spectroscopy. The revised decay scheme adds further evidence of the coexistence of very different shapes in
98
Sr
.
A set of levels is proposed to originate from particle-hole pair excitations across the
Z
=
40
spherical gap in analogy with
96
Sr
.
A deformed
K
=
3
band with probable even parity is built on a 7.1-ns isomer at 1838 keV. It is interpreted as a two-quasineutron excitation in accordance with a quantum Monte Carlo pairing calculation based on a deformed shell model. Configurations of the calculated lowest-lying two-quasiparticle levels confirm the importance of the [404]9/2 neutron orbital at the largest deformations in the neutron-rich
A
â
100
region
Dependence of direct neutron capture on nuclear-structure models
The prediction of cross sections for nuclei far off stability is crucial in
the field of nuclear astrophysics. We calculate direct neutron capture on the
even-even isotopes Sn and Pb with energy levels,
masses, and nuclear density distributions taken from different
nuclear-structure models. The utilized structure models are a
Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a
macroscopic-microscopic model based on the finite-range droplet model and a
folded-Yukawa single-particle potential. Due to the differences in the
resulting neutron separation and level energies, the investigated models yield
capture cross sections sometimes differing by orders of magnitude. This may
also lead to differences in the predicted astrophysical r-process paths.
Astrophysical implications are discussed.Comment: 25 pages including 12 figures, RevTeX, to appear in Phys. Rev.
Improving Ebola infection prevention and control in primary healthcare facilities in Sierra Leone: a single-group pretest post-test, mixed-methods study
Background Accomplishing infection prevention and control (IPC) in health facilities in Sub-Saharan Africa is challenging. Owing to poor IPC, healthcare workers (HCWs) were frequently infected during Sierra Leone's Ebola epidemic. In late 2014, IPC was rapidly and nationally scaled up. We carried out workshops in sampled facilities to further improve adherence to IPC. We investigated HCW experiences and observed practice gaps, before and after the workshops. Methods We conducted an uncontrolled, before and after, mixed-methods study in eight health facilities in Bo and Kenema Districts during December 2014 and January 2015. Quantitative methods administered to HCWs at baseline and follow-up included a survey on attitudes and self-efficacy towards IPC, and structured observations of behaviours. The intervention involved a workshop for HCWs to develop improvement plans for their facility. We analysed the changes between rounds in survey responses and behaviours. We used interviews to explore attitudes and self-efficacy throughout the study period. Results HCWs described IPC as âlife-savingâ and personal protective equipment (PPE) as uncomfortable for providers and frightening for patients. At baseline, self-efficacy was high (median=4/strongly agree). Responses reflecting unfavourable attitudes were low for glove use (median=1/strongly disagree, IQR, 1â2) and PPE use with ill family members (median=1, IQR, 1â2), and mixed for PPE use with ill HCWs (median=2/disagree, IQR, 1â4). Observations demonstrated consistent glove reuse and poor HCW handwashing. The maintenance of distance (RR 1.09, 95% CI 1.02 to 1.16) and patient handwashing (RR 1.19, 95% CI 1.3 to 1.25) improved to >90%. Conclusions We found favourable attitudes towards IPC and gaps in practice. Risk perceptions of HCWs and tendencies to ration PPE where chronic supply chain issues normally lead to PPE stock-outs may affect practice. As Sierra Leone's Ebola Recovery Strategy aims to make all facilities IPC compliant, socio-behavioural improvements and a secure supply chain are essential
Direct Neutron Capture for Magic-Shell Nuclei
In neutron capture for magic--shell nuclei the direct reaction mechanism can
be important and may even dominate. As an example we investigated the reaction
Ca(n,Ca for projectile energies below 250\,keV in a direct
capture model using the folding procedure for optical and bound state
potentials. The obtained theoretical cross sections are in agreement with the
experimental data showing the dominance of the direct reaction mechanism in
this case. The above method was also used to calculate the cross section for
Ca(n,Ca.Comment: REVTeX, 7 pages plus 3 uuencoded figures, the complete uuencoded
postscript file is available at ftp://is1.kph.tuwien.ac.at/pub/ohu/calcium.u
Nucleosynthesis in the Early Galaxy
Recent observations of r-process-enriched metal-poor star abundances reveal a
non-uniform abundance pattern for elements . Based on non-correlation
trends between elemental abundances as a function of Eu-richness in a large
sample of metal-poor stars, it is shown that the mixing of a consistent and
robust light element primary process (LEPP) and the r-process pattern found in
r-II metal-poor stars explains such apparent non-uniformity. Furthermore, we
derive the abundance pattern of the LEPP from observation and show that it is
consistent with a missing component in the solar abundances when using a recent
s-process model. As the astrophysical site of the LEPP is not known, we explore
the possibility of a neutron capture process within a site-independent
approach. It is suggested that scenarios with neutron densities
or in the range best
explain the observations.Comment: 28 pages, 7 Postscript figures. To be published in The Astrophysical
Journa
Sorption Behaviour of W, Hf, Lu, U, and Th on Ion Exchangers from HCI/H2O2 Solutions. Model Experiments for Chemical Studies of Seaborgium (Sg)
Half Life of the Doubly-magic r-Process Nucleus 78Ni
Nuclei with magic numbers serve as important benchmarks in nuclear theory. In
addition, neutron-rich nuclei play an important role in the astrophysical rapid
neutron-capture process (r-process). 78Ni is the only doubly-magic nucleus that
is also an important waiting point in the r-process, and serves as a major
bottleneck in the synthesis of heavier elements. The half-life of 78Ni has been
experimentally deduced for the first time at the Coupled Cyclotron Facility of
the National Superconducting Cyclotron Laboratory at Michigan State University,
and was found to be 110 (+100 -60) ms. In the same experiment, a first
half-life was deduced for 77Ni of 128 (+27 -33) ms, and more precise half-lives
were deduced for 75Ni and 76Ni of 344 (+20 -24) ms and 238 (+15 -18) ms
respectively.Comment: 4 pages, 3 figure
Reaction rate for two--neutron capture by He
Recent investigations suggest that the neutrino--heated hot bubble between
the nascent neutron star and the overlying stellar mantle of a type--II
supernova may be the site of the r--process. In the preceding --process
building up the elements to , the He(2n,)He--
and He(,n)Be--reactions bridging the instability gap at
and could be of relevance. We suggest a mechanism for
He(2n,)He and calculate the reaction rate within the
+n+n approach. The value obtained is about a factor 1.6 smaller than
the one obtained recently in the simpler direct--capture model, but is at least
three order of magnitude enhanced compared to the previously adopted value. Our
calculation confirms the result of the direct--capture calculation that under
representative conditions in the --process the reaction path proceeding
through He is negligible compared to He(n,)Be.Comment: 13 pages, 4 postscript figures, to appear in "Zeitschrift f. Physik
A", changed internet address and filename, the uuencoded postscript file
including the figures is available at
ftp://is1.kph.tuwien.ac.at/pub/ohu/twoneutron.u
- âŠ