72 research outputs found
Upgrade of the ultracold neutron source at the pulsed reactor TRIGA Mainz
The performance of the upgraded solid deuterium ultracold neutron source at
the pulsed reactor TRIGA Mainz is described. The current configuration stage
comprises the installation of a He liquefier to run UCN experiments over
long-term periods, the use of stainless steel neutron guides with improved
transmission as well as sputter-coated non-magnetic NiMo alloy at the
inside walls of the thermal bridge and the converter cup. The UCN yield was
measured in a `standard' UCN storage bottle (stainless steel) with a volume of
32 litres outside the biological shield at the experimental area yielding UCN
densities of 8.5 /cm; an increase by a factor of 3.5 compared to the former
setup. The measured UCN storage curve is in good agreement with the predictions
from a Monte Carlo simulation developed to model the source. The growth and
formation of the solid deuterium converter during freeze-out are affected by
the ortho/para ratio of the H premoderator.Comment: 12 pages, 7 figure
Nuclear Charge Radius of Be
The nuclear charge radius of Be was precisely determined using the
technique of collinear laser spectroscopy on the transition in the Be ion. The mean square charge radius increases
from Be to Be by \delta ^{10,12} = 0.69(5) \fm^{2}
compared to \delta ^{10,11} = 0.49(5) \fm^{2} for the
one-neutron halo isotope Be. Calculations in the fermionic molecular
dynamics approach show a strong sensitivity of the charge radius to the
structure of Be. The experimental charge radius is consistent with a
breakdown of the N=8 shell closure.Comment: 5 pages, 3 figure
Test of Time Dilation Using Stored Li+ Ions as Clocks at Relativistic Speed
We present the concluding result from an Ives-Stilwell-type time dilation
experiment using 7Li+ ions confined at a velocity of beta = v/c = 0.338 in the
storage ring ESR at Darmstadt. A Lambda-type three-level system within the
hyperfine structure of the 7Li+ triplet S1-P2 line is driven by two laser beams
aligned parallel and antiparallel relative to the ion beam. The lasers' Doppler
shifted frequencies required for resonance are measured with an accuracy of < 4
ppb using optical-optical double resonance spectroscopy. This allows us to
verify the Special Relativity relation between the time dilation factor gamma
and the velocity beta to within 2.3 ppb at this velocity. The result, which is
singled out by a high boost velocity beta, is also interpreted within Lorentz
Invariance violating test theories
Collinear laser spectroscopy of atomic cadmium
Hyperfine structure and factors of the atomic 5s\,5p\,\; ^3\rm{P}_2
\rightarrow 5s\,6s\,\; ^3\rm{S}_1 transition are determined from collinear
laser spectroscopy data of Cd and Cd. Nuclear
magnetic moments and electric quadrupole moments are extracted using reference
dipole moments and calculated electric field gradients, respectively. The
hyperfine structure anomaly for isotopes with and nuclear
ground states and isomeric states is evaluated and a linear
relationship is observed for all nuclear states except . This
corresponds to the Moskowitz-Lombardi rule that was established in the mercury
region of the nuclear chart but in the case of cadmium the slope is
distinctively smaller than for mercury. In total four atomic and ionic levels
were analyzed and all of them exhibit a similar behaviour. The electric field
gradient for the atomic 5s\,5p\,\; ^3\mathrm{P}_2 level is derived from
multi-configuration Dirac-Hartree-Fock calculations in order to evaluate the
spectroscopic nuclear quadrupole moments. The results are consistent with those
obtained in an ionic transition and based on a similar calculation.Comment: 12 pages, 5 figure
Observation of the hyperfine transition in lithium-like Bismuth : Towards a test of QED in strong magnetic fields
We performed a laser spectroscopic determination of the hyperfine
splitting (HFS) of Li-like and repeated the measurement
of the HFS of H-like . Both ion species were
subsequently stored in the Experimental Storage Ring at the GSI
Helmholtzzentrum f\"ur Schwerionenforschung Darmstadt and cooled with an
electron cooler at a velocity of . Pulsed laser excitation of
the hyperfine-transition was performed in anticollinear and collinear
geometry for and , respectively, and
observed by fluorescence detection. We obtain for , different from the literature
value, and for .
These values provide experimental evidence that a specific difference between
the two splitting energies can be used to test QED calculations in the
strongest static magnetic fields available in the laboratory independent of
nuclear structure effects. The experimental result is in excellent agreement
with the theoretical prediction and confirms the sum of the Dirac term and the
relativistic interelectronic-interaction correction at a level of 0.5%
confirming the importance of accounting for the Breit interaction.Comment: 5 pages, 2 figure
Transport of Magnetic Fields in Convective, Accreting Supernova Cores
We consider the amplification and transport of a magnetic field in the
collapsed core of a massive star, including both the region between the
neutrinosphere and the shock, and the central, opaque core. An analytical
argument explains why rapid convective overturns persist within a newly formed
neutron star for roughly 10 seconds ( overturns), consistent with
recent numerical models. A dynamical balance between turbulent and magnetic
stresses within this convective layer corresponds to flux densities in excess
of G. Material accreting onto the core is heated by neutrinos and also
becomes strongly convective. We compare the expected magnetic stresses in this
convective `gain layer' with those deep inside the neutron core.
Buoyant motions of magnetized fluid are greatly aided by the intense neutrino
flux. We calculate the transport rate through a medium containing free neutrons
protons, and electrons, in the limiting cases of degenerate or non-degenerate
nucleons. Fields stronger than G are able to rise through the
outer degenerate layers of the neutron core during the last stages of
Kelvin-Helmholtz cooling (up to 10 seconds post-collapse), even though these
layers have become stable to convection. We also find the equilibrium shape of
a thin magnetic flux rope in the dense hydrostatic atmosphere of the neutron
star, along with the critical separation of the footpoints above which the rope
undergoes unlimited expansion against gravity. The implications of these
results for pulsar magnetism are summarized, and applied to the case of late
fallback over the first 1,000-10,000 s of the life of a neutron starComment: 45 pages, 3 figures, Astrophysical Journal, in pres
Precision Test of Many-Body QED in the Be Fine Structure Doublet Using Short-Lived Isotopes
Absolute transition frequencies of the 2s\; ^2{\rm S}_{1/2} \rightarrow
2p\;^2\mathrm{P}_{1/2,3/2} transitions in Be were measured for the
isotopes Be. The fine structure splitting of the state and its
isotope dependence are extracted and compared to results of \textit{ab initio}
calculations using explicitly correlated basis functions, including
relativistic and quantum electrodynamics effects at the order of
and . Accuracy has been improved in both the theory and
experiment by 2 orders of magnitude, and good agreement is observed. This
represents one of the most accurate tests of quantum electrodynamics for
many-electron systems, being insensitive to nuclear uncertainties.Comment: 5 pages, 2 figure
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