77 research outputs found
Reduced transition probabilities for the gamma decay of the 7.8 eV isomer in Th
The reduced magnetic dipole and electric quadrupole transition probabilities
for the radiative decay of the Th 7.8 eV isomer to the ground state are
predicted within a detailed nuclear-structure model approach. We show that the
presence and decay of this isomer can only be accounted for by the Coriolis
mixing emerging from a remarkably fine interplay between the coherent
quadrupole-octupole motion of the nuclear core and the single-nucleon motion
within a reflection-asymmetric deformed potential. We find that the magnetic
dipole transition probability which determines the radiative lifetime of the
isomer is considerably smaller than presently estimated. The so-far disregarded
electric quadrupole component may have non-negligible contributions to the
internal conversion channel. These findings support new directions in the
experimental search of the Th transition frequency for the development
of a future nuclear frequency standard.Comment: 5 pages, 1 figure, supplementary material is available as pdf with
the source files, v3 includes small corrections to match the published
version, results unchange
Stopping narrow-band x-ray pulses in nuclear media
A control mechanism for stopping x-ray pulses in resonant nuclear media is
investigated theoretically. We show that narrow-band x-ray pulses can be mapped
and stored as nuclear coherence in a thin-film planar x-ray cavity with an
embedded nuclear layer. The pulse is nearly resonant to the
14.4 keV M\"ossbauer transition in the nuclei. The role of
the control field is played here by a hyperfine magnetic field which induces
interference effects reminding of electromagnetically induced transparency. We
show that by switching off the control magnetic field, a narrow-band x-ray
pulse can be completely stored in the cavity for approximately 100 ns.
Additional manipulation of the external magnetic field can lead to both group
velocity and phase control of the pulse in the x-ray cavity sample.Comment: 5 pages, 3 figures; v2 slight modifications in title, abstract,
marketing, to match the final published version; added a supplementary
material; results unchange
Determination of plasma screening effects for thermonuclear reactions in laser-generated plasmas
Due to screening effects, nuclear reactions in astrophysical plasmas may
behave differently than in the laboratory. The possibility to determine the
magnitude of these screening effects in colliding laser-generated plasmas is
investigated theoretically, having as a starting point a proposed experimental
setup with two laser beams at the Extreme Light Infrastructure facility. A
laser pulse interacting with a solid target produces a plasma through the
Target Normal Sheath Acceleration scheme, and this rapidly streaming plasma
(ion flow) impacts on a secondary plasma created by the interaction of a second
laser pulse on a gas jet target. We model this scenario here and calculate the
reaction events for the astrophysically relevant reaction C(He,
)O. We find that it should be experimentally possible to determine
the plasma screening enhancement factor for fusion reactions by detecting the
difference in reaction events between two scenarios of ion flow interacting
with the plasma target and a simple gas target. This provides a way to evaluate
nuclear reaction cross-sections in stellar environments and can significantly
advance the field of nuclear astrophysics.Comment: 9 pages, 4 figures, 4 tables; minor changes made, accepted by The
Astrophysical Journa
Coherent control of nuclear forward scattering
The possibility to control the coherent decay of resonant excitations in
nuclear forward scattering is investigated. By changing abruptly the direction
of the nuclear hyperfine magnetic field, the coherent scattering of photons can
be manipulated and even completely suppressed via quantum interference effects
between the nuclear transition currents. The efficiency of the coherent decay
suppression and the dependence of the scattered light polarization on the
specific switching parameters is analyzed in detail. Using a sophisticated
magnetic switching sequence involving four rotations of the hyperfine magnetic
field, two correlated coherent decay pulses with different polarizations can be
generated out of one excitation, providing single-photon entanglement in the
keV regime. The verification of the generated entanglement by testing a
single-particle version of Bell's inequality in an x-ray optics experimental
setup is put forward.Comment: 22 pages, 6 figures; revised to match the published version: added
one figure, small modifications in tex
Optomechanically induced transparency of x-rays via optical control
The search for new control methods over light-matter interactions is one of
the engines that advances fundamental physics and applied science alike. A
specific class of light-matter interaction interfaces are setups coupling
photons of distinct frequencies via matter. Such devices, nontrivial in design,
could be endowed with multifunctional tasking. Here we envisage for the first
time an optomechanical system that bridges optical and robust, high-frequency
x-ray photons, which are otherwise notoriously difficult to control. The
x-ray-optical system comprises of an optomechanical cavity and a movable
microlever interacting with an optical laser and with x-rays via resonant
nuclear scattering. We show that optomechanically induced transparency of a
broad range of photons (10 eV-100 keV) is achievable in this setup, allowing to
tune nuclear x-ray absorption spectra via optomechanical control. This paves
ways for metrology applications, e.g., the detection of the Thorium
clock transition, and an unprecedentedly precise control of x-rays using
optical photons.Comment: 2 figures, supplementary material available with the file
Quantum interference between nuclear excitation by electron capture and radiative recombination
We investigate the quantum interference between the resonant process of
nuclear excitation by electron capture (NEEC) followed by the radiative decay
of the excited nucleus, and radiative recombination (RR). In order to derive
the interference cross section, a Feshbach projection operator formalism is
used. The electromagnetic field is considered by means of multipole fields. The
nucleus is described by a phenomenological collective model and by making use
of experimental data. The Fano profile parameters as well as the interference
cross section for electric and magnetic multipole transitions in various heavy
ions are presented. We discuss the experimental possibility of discerning NEEC
from the RR background
Coupling highly excited nuclei to the atomic shell in dense astrophysical plasmas
In dense astrophysical plasmas, neutron capture populates highly excited
nuclear states close to the neutron threshold. The impact of additional
low-energy nuclear excitations via coupling to the atomic shell on the ability
of the so-formed compound nucleus to retain the captured neutron is
investigated. We focus on the mechanism of nuclear excitation by electron
capture in plasmas characterized by electron fluxes typical for the slow
neutron capture process of stellar nucleosynthesis. The small effect of this
further excitation on the neutron capture and gamma decay sequence relevant for
nucleosynthesis is quantified and compared to the corresponding effect of an
additional low-energy photoexcitation step.Comment: 11 pages, 10 figures; v2 minor modifications to match the published
version, results unchange
Quantum interference effects in an ensemble of Th nuclei interacting with coherent light
As a unique feature, the Th nucleus has an isomeric transition in the
vacuum ultraviolet that can be accessed by optical lasers. The interference
effects occurring in the interaction between coherent optical light and an
ensemble of Th nuclei are investigated theoretically. We consider the
scenario of nuclei doped in vacuum ultraviolet-vacuum ultraviolet transparent
crystals and take into account the effect of different doping sites and
therefore different lattice fields that broaden the nuclear transition width.
This effect is shown to come in interplay with interference effects due to the
hyperfine splitting of the ground and isomeric nuclear states. We investigate
possible experimentally available situations involving two-, three- and
four-level schemes of quadrupole sublevels of the ground and isomeric nuclear
states coupling to one or two coherent fields. Specific configurations which
offer clear signatures of the isomer excitation advantageous for the more
precise experimental determination of the transition energy are identified.
Furthermore, it is shown that population trapping into the isomeric state can
be achieved. This paves the way for further nuclear quantum optics applications
with Th such as nuclear coherent control.Comment: 14 papes, 13 figure
The electric quadrupole channel of the 7.8 eV transition
The unique isomeric transition at 7.8 eV in has a
magnetic dipole () and an electric quadrupole () multipole mixing. So
far, the component has been widely disregarded. Here, we investigate the
nuclear physics nature and the impact of the decay channel for the nuclear
coupling to the atomic shell based on the newest theoretical predictions for
the corresponding reduced nuclear transition probabilities. Our results show
that the contribution of the channel is dominant or at least of the same
order of magnitude for internal conversion or electronic bridge transitions
involving the atomic orbitals , and . Notable exceptions are the
internal conversion of the electron and the electronic bridge between the
electronic states and , for which the component dominates by two
to three orders of magnitude. Caution is therefore advised when considering
isomeric excitation or decay via nuclear coupling to the atomic shell, as the
involved orbitals determine which multipole transition component dominates
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