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.
Laser spectroscopic methods are reviewed which are of potential interest for the investigation of atomic and ionic level structures of superheavy elements. The latter are defined here as the ...trans-fermium elements with Z>100 for which no experimental atomic or ionic level structure information is known so far, and which cannot be bred in high flux nuclear power reactors via successive neutron capture. The principles of suitable laser spectroscopic methods are described, and illustrated by examples of real experiments. The addressed methods include single-ion spectroscopy in Paul traps, laser-induced fluorescence spectroscopy (LIF), radiation-detected optical pumping (RADOP), radioactive decay-detected resonance ionization spectroscopy (RADRIS), and ion-guide-detected resonance ionization spectroscopy (IGRIS). With the exception of the first all take advantage of a storage of the ions or atoms in so-called buffer-gas traps.
The developed experimental methods can, in principle, also be employed for studying ion-chemical reactions with gas admixtures like O2 as well as for performing ion mobility measurements. Both provide complementary information on the electronic structure of superheavy ions. First attempts on this road of research are reviewed as well.
Until recently, ground-state nuclear moments of the heaviest nuclei could only be inferred from nuclear spectroscopy, where model assumptions are required. Laser spectroscopy in combination with ...modern atomic structure calculations is now able to probe these moments directly, in a comprehensive and nuclear-model-independent way. Here we report on unique access to the differential mean-square charge radii of ^{252,253,254}No, and therefore to changes in nuclear size and shape. State-of-the-art nuclear density functional calculations describe well the changes in nuclear charge radii in the region of the heavy actinides, indicating an appreciable central depression in the deformed proton density distribution in ^{252,254}No isotopes. Finally, the hyperfine splitting of ^{253}No was evaluated, enabling a complementary measure of its (quadrupole) deformation, as well as an insight into the neutron single-particle wave function via the nuclear spin and magnetic moment.
The method of laser spectroscopy in supersonic gas jets was proposed for high-resolution and high-efficiency in-gas laser ionization and spectroscopy studies of short-lived nuclei. The flow ...properties of such supersonic gas jets have been characterized under off-line conditions. Planar laser-induced fluorescence spectroscopy of seeded copper atoms has been applied to nonintrusively measure velocity, temperature, and relative density profiles of gas jets formed by different de Laval nozzles. For validation, planar laser-induced fluorescence spectroscopy was applied on supersonic free jets with well-known flow parameters. The performance of the in-gas-jet laser spectroscopy method is determined by the achievable spectral resolution, which requires an optimization and a precise manufacturing of the nozzle inner contour as well as a pressure matching of the background medium at the nozzle exit. Our studies now enable a thorough understanding and quantification of these requirements and a determination of the final performance of the in-gas-jet method. Additionally, a comparison between the experimental results and the numerical calculations was performed for the temperature, velocity, and Mach number profiles of underexpanded and quasiuniform jets formed by a de Laval nozzle.
Direct high-precision mass spectrometry of the heaviest elements with SHIPTRAP, at GSI in Darmstadt, Germany, requires high efficiency to deal with the low production rates of such exotic nuclides. A ...second-generation gas stopping cell, operating at cryogenic temperatures, was developed and recently integrated into the relocated system to boost the overall efficiency. Offline measurements using 223Ra and 225Ac recoil-ion sources placed inside the gas volume were performed to characterize the gas stopping cell with respect to purity and extraction efficiency. In addition, a first online test using the fusion-evaporation residue 254No was performed, resulting in a combined stopping and extraction efficiency of 33(5)%. An extraction time of 55(44)ms was achieved. The overall efficiency of SHIPTRAP for fusion-evaporation reaction products was increased by an order of magnitude to 6(1)%. This will pave the way for direct mass spectrometry of heavier and more exotic nuclei, eventually in the region of superheavy elements with proton numbers Z⩾104.
The extraction of 229Th3+ from a buffer-gas stopping cell Wense, L.v.d.; Seiferle, B.; Laatiaoui, M. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
06/2016, Letnik:
376
Journal Article
Recenzirano
Odprti dostop
In the whole landscape of atomic nuclei, 229Th is currently the only known nucleus which could allow for the development of a nuclear-based frequency standard, as it possesses an isomeric state of ...just 7.6eV energy above the ground state. The 3+ charge state is of special importance in this context, as Th3+ allows for a simple laser-cooling scheme. Here we emphasize the direct extraction of triply-charged 229Th from a buffer-gas stopping cell. This finding will not only simplify any future approach of 229Th ion cooling, but is also used for thorium-beam purification and in this way provides a powerful tool for the direct identification of the 229Th isomer to ground state nuclear transition.
The cryogenic gas stopping cell of SHIPTRAP Droese, C.; Eliseev, S.; Blaum, K. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
11/2014, Letnik:
338
Journal Article
Recenzirano
The overall efficiency of the Penning-trap mass spectrometer SHIPTRAP at GSI Darmstadt, employed for high-precision mass measurements of exotic nuclei in the mass region above fermium, is presently ...mostly limited by the stopping and extraction of fusion-evaporation products in the SHIPTRAP gas cell. To overcome this limitation a second-generation gas cell with increased stopping volume was designed. In addition, its operation at cryogenic temperatures leads to a higher gas density at a given pressure and an improved cleanliness of the helium buffer gas. Here, the results of experiments with a 219Rn recoil ion source are presented. An extraction efficiency of 74(3)% was obtained, a significant increase compared to the extraction efficiency of 30% of the present gas stopping cell operated at room temperature. The optimization of electric fields and other operating parameters at room as well as cryogenic temperatures is described in detail. Furthermore, the extraction time of 219Rn ions was determined for several operating parameters.
.
The superheavy isotope
258
Db was produced in the
209
Bi(
50
Ti, 1n)
258
Db reaction at GSI, Germany. A detailed
α
-spectroscopy study of this isotope and its
α
-decay daughter products was ...performed. Two long-lived
α
-decaying states in
258
Db are observed. A spin-parity of
0
-
is tentatively assigned to the ground state for which a half-life of
2
.
17
±
0
.
36
s is determined. Spins and parities of either
5
+
or
10
-
are proposed for the isomeric state found at an excitation energy of 51 keV with a half-life of
4
.
41
±
0
.
21
s. The
α
-decay daughter isotope
254
Lr displays a similar behavior. A half-life of
11
.
9
±
0
.
9
s is determined for the
254
Lr ground state which is tentatively assigned a spin-parity of
4
+
. The isomeric level of this isotope placed at 108 keV with a half-life of
20
.
3
±
4
.
2
s is tentatively assigned a spin-parity of
1
-
. Two long-lived
α
-decaying states are observed in the granddaughter isotope
250
Md . The ground state has a half-life of
59
.
5
±
9
.
1
s. A half-life of
42
.
4
±
4
.
5
s is measured for the isomeric state positioned at an excitation energy of 123 keV. Partial, tentative level schemes for
254
Lr,
250
Md and
246
Es are proposed based on the
α
-
γ
coincidences.
To study exotic nuclides at the borders of stability with laser ionization and spectroscopy techniques, highest efficiencies in combination with a high spectral resolution are required. These usually ...opposing requirements are reconciled by applying the in-gas-laser ionization and spectroscopy (IGLIS) technique in the supersonic gas jet produced by a de Laval nozzle installed at the exit of the stopping gas cell. Carrying out laser ionization in the low-temperature and low density supersonic gas jet eliminates pressure broadening, which will significantly improve the spectral resolution. This article presents the required modifications at the Leuven Isotope Separator On-Line (LISOL) facility that are needed for the first on-line studies of in-gas-jet laser spectroscopy. Different geometries for the gas outlet and extraction ion guides have been tested for their performance regarding the acceptance of laser ionized species as well as for their differential pumping capacities. The specifications and performance of the temporarily installed high repetition rate laser system, including a narrow bandwidth injection-locked Ti:sapphire laser, are discussed and first preliminary results on neutron-deficient actinium isotopes are presented indicating the high capability of this novel technique.
PDF
