121 research outputs found
Towards a direct transition energy measurement of the lowest nuclear excitation in 229Th
The isomeric first excited state of the isotope 229Th exhibits the lowest
nuclear excitation energy in the whole landscape of known atomic nuclei. For a
long time this energy was reported in the literature as 3.5(5) eV, however, a
new experiment corrected this energy to 7.6(5) eV, corresponding to a UV
transition wavelength of 163(11) nm. The expected isomeric lifetime is
3-5 hours, leading to an extremely sharp relative linewidth of Delta E/E ~
10^-20, 5-6 orders of magnitude smaller than typical atomic relative
linewidths. For an adequately chosen electronic state the frequency of the
nuclear ground-state transition will be independent from influences of external
fields in the framework of the linear Zeeman and quadratic Stark effect,
rendering 229mTh a candidate for a reference of an optical clock with very high
accuracy. Moreover, in the literature speculations about a potentially enhanced
sensitivity of the ground-state transition of Th for eventual
time-dependent variations of fundamental constants (e.g. fine structure
constant alpha) can be found. We report on our experimental activities that aim
at a direct identification of the UV fluorescence of the ground-state
transition energy of 229mTh. A further goal is to improve the accuracy of the
ground-state transition energy as a prerequisite for a laser-based optical
control of this nuclear excited state, allowing to build a bridge between
atomic and nuclear physics and open new perspectives for metrological as well
as fundamental studies
Towards High Performance Relativistic Electronic Structure Modelling: The EXP-T Program Package
Modern challenges arising in the fields of theoretical and experimental
physics require new powerful tools for high-precision electronic structure
modelling; one of the most perspective tools is the relativistic Fock space
coupled cluster method (FS-RCC). Here we present a new extensible
implementation of the FS-RCC method designed for modern parallel computers. The
underlying theoretical model, algorithms and data structures are discussed. The
performance and scaling features of the implementation are analyzed. The
software developed allows to achieve a completely new level of accuracy for
prediction of properties of atoms and molecules containing heavy and superheavy
nuclei
Discovery of Very High Energy -Rays from Markarian~180 Triggered by an Optical Outburst
The high-frequency-peaked BL Lacertae object Markarian~180 (Mrk~180) was
observed to have an optical outburst in 2006 March, triggering a Target of
Opportunity observation with the MAGIC telescope. The source was observed for
12.4 hr and very high energy -ray emission was detected with a
significance of 5.5 . An integral flux above 200 GeV of
was measured, corresponding to
11% of the Crab Nebula flux. A rather soft spectrum with a photon index of
has been determined. No significant flux variation was found.Comment: Accepted by ApJ Letters, minor revision
Precision Measurement of the First Ionization Potential of Nobelium
One of the most important atomic properties governing an element’s chemical behavior is the energy required to remove its least-bound electron, referred to as the first ionization potential. For the heaviest elements, this fundamental quantity is strongly influenced by relativistic effects which lead to unique chemical properties. Laser spectroscopy on an atom-at-a-time scale was developed and applied to probe the optical spectrum of neutral nobelium near the ionization threshold. The first ionization potential of nobelium is determined here with a very high precision from the convergence of measured Rydberg series to be 6.626 21 ± 0.000 05 eV . This work provides a stringent benchmark for state-of-the-art many-body atomic modeling that considers relativistic and quantum electrodynamic effects and paves the way for high-precision measurements of atomic properties of elements only available from heavy-ion accelerator facilities
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