140 research outputs found
Time-of-flight mass measurements of neutron-rich chromium isotopes up to N = 40 and implications for the accreted neutron star crust
We present the mass excesses of 59-64Cr, obtained from recent time-of-flight
nuclear mass measurements at the National Superconducting Cyclotron Laboratory
at Michigan State University. The mass of 64Cr is determined for the first
time, with an atomic mass excess of -33.48(44) MeV. We find a significantly
different two-neutron separation energy S2n trend for neutron-rich isotopes of
chromium, removing the previously observed enhancement in binding at N=38.
Additionally, we extend the S2n trend for chromium to N=40, revealing behavior
consistent with the previously identified island of inversion in this region.
We compare our results to state-of-the-art shell-model calculations performed
with a modified Lenzi-Nowacki-Poves-Sieja interaction in the fp shell,
including the g9/2 and d5/2 orbits for the neutron valence space. We employ our
result for the mass of 64Cr in accreted neutron star crust network calculations
and find a reduction in the strength and depth of electron-capture heating from
the A=64 isobaric chain, resulting in a cooler than expected accreted neutron
star crust. This reduced heating is found to be due to the >1-MeV reduction in
binding for 64Cr with respect to values from commonly used global mass models.Comment: Accepted to Physical Review
Ideal magnetohydrodynamic simulations of unmagnetized dense plasma jet injection into a hot strongly magnetized plasma
We present results from three-dimensional ideal magnetohydrodynamic
simulations of unmagnetized dense plasma jet injection into a uniform hot
strongly magnetized plasma, with the aim of providing insight into core fueling
of a tokamak with parameters relevant for ITER and NSTX (National Spherical
Torus Experiment). Unmagnetized dense plasma jet injection is similar to
compact toroid injection but with much higher plasma density and total mass,
and consequently lower required injection velocity. Mass deposition of the jet
into the background appears to be facilitated via magnetic reconnection along
the jet's trailing edge. The penetration depth of the plasma jet into the
background plasma is mostly dependent on the jet's initial kinetic energy, and
a key requirement for spatially localized mass deposition is for the jet's
slowing-down time to be less than the time for the perturbed background
magnetic flux to relax due to magnetic reconnection. This work suggests that
more accurate treatment of reconnection is needed to fully model this problem.
Parameters for unmagnetized dense plasma jet injection are identified for
localized core deposition as well as edge localized mode (ELM) pacing
applications in ITER and NSTX-relevant regimes.Comment: 16 pages, 8 figures and 2 tables; accepted by Nuclear Fusion (May 11,
2011
Identifying and addressing barriers to implementing core electronic health record use metrics for ambulatory care: Virtual consensus conference proceedings
Precise, reliable, valid metrics that are cost-effective and require reasonable implementation time and effort are needed to drive electronic health record (EHR) improvements and decrease EHR burden. Differences exist between research and vendor definitions of metrics. PROCESS: We convened three stakeholder groups (health system informatics leaders, EHR vendor representatives, and researchers) in a virtual workshop series to achieve consensus on barriers, solutions, and next steps to implementing the core EHR use metrics in ambulatory care. CONCLUSION: Actionable solutions identified to address core categories of EHR metric implementation challenges include: (1) maintaining broad stakeholder engagement, (2) reaching agreement on standardized measure definitions across vendors, (3) integrating clinician perspectives, and (4) addressing cognitive and EHR burden. Building upon the momentum of this workshop\u27s outputs offers promise for overcoming barriers to implementing EHR use metrics
Isomeric excitation energy for In from mass spectrometry reveals constant trend next to doubly magic Sn
The excitation energy of the 1/2 isomer in In at is
measured to be 671(37) keV and the mass uncertainty of the 9/2 ground state
is significantly reduced using the ISOLTRAP mass spectrometer at ISOLDE/CERN.
The measurements exploit a major improvement in the resolution of the
multi-reflection time-of-flight mass spectrometer. The results reveal an
intriguing constancy of the isomer excitation energies in
neutron-deficient indium that persists down to the shell closure, even
when all neutrons are removed from the valence shell. This trend is used to
test large-scale shell model, \textit{ab initio}, and density functional theory
calculations. The models have difficulties describing both the isomer
excitation energies and ground-state electromagnetic moments along the indium
chain.Comment: 13 pages, 4 figure
Nuclear Structure Towards N=40 60Ca: In-beam gamma-ray Spectroscopy of 58,60Ti
Excited states in the neutron-rich N=38,36 nuclei \nuc{60}{Ti} and
\nuc{58}{Ti} were populated in nucleon-removal reactions from \nuc{61}{V}
projectiles at 90~MeV/nucleon. The \gamma-ray transitions from such states in
these Ti isotopes were detected with the advanced \gamma-ray tracking array
GRETINA and were corrected event-by-event for large Doppler shifts (v/c \sim
0.4) using the \gamma-ray interaction points deduced from online signal
decomposition. The new data indicate that a steep decrease in quadrupole
collectivity occurs when moving from neutron-rich N=36,38 Fe and Cr toward the
Ti and Ca isotones. In fact, \nuc{58,60}{Ti} provide some of the most
neutron-rich benchmarks accessible today for calculations attempting to
determine the structure of the potentially doubly-magic nucleus \nuc{60}{Ca}.Comment: Accepted for publication in Physical Review letter
First g(2+) measurement on neutron-rich 72 Zn, and the high-velocity transient field technique for radioactive heavy-ion beams
The high-velocity transient-field (HVTF) technique was used to measure the g factor of the 2+ state of 72Zn produced as a radioactive beam. The transient-field strength was probed at high velocity in ferromagnetic iron and gadolinium hosts using 76Ge beams. The potential of the HVTF method is demonstrated and the difficulties that need to be overcome for a reliable use of the TF technique with high-Z, high-velocity radioactive beams are revealed. The polarization of K-shell vacancies at high velocity, which shows more than an order of magnitude difference between Z = 20 and Z = 30 is discussed. The g-factor measurement hints at the theoretically predicted transition in the structure of the Zn isotopes near N = 40
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