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Direct mass measurements in the region of the heaviest elements were performed with the Penning-trap mass spectrometer SHIPTRAP at GSI Darmstadt. Utilizing the phase-imaging ion-cyclotron-resonance massspectrometry technique, the atomic masses of 251No (Z = 102), 254Lr (Z = 103), and 257Rf (Z = 104) available at rates down to one detected ion per day were determined directly for the first time. The ground-state masses of 254No and 255,256Lr were improved by more than one order of magnitude. Relative statistical uncertainties as low as δm/m ≈ 10−9 were achieved. Mass resolving powers of 11 000 000 allowed resolving long-lived low-lying isomeric states from their respective ground states in 251,254No and 254,255Lr. This provided an unambiguous determination of the binding energies for odd-A and odd-odd nuclides previously determined only indirectly from decay spectroscopy., Federal Ministry of Education & Research (BMBF) 05P15HGFNA 05P19HGFNA 05P21HGFN1 05P15UMFNA 05P21UMFN1, Max Planck Society, Foundation CELLEX, Netherlands Organization for Scientific Research (NWO) 680-91-103, European Commission under Marie Sklodowska-Curie Action FP7 MSC COFUND scheme European Research Council (ERC) 819957, Ministry of Science and Innovation, Spain (MICINN) Spanish Government FPA2015-67694-P PID2019-104093GB-I00/AEI

© 2019 Fusion-evaporation reactions with the doubly magic projectile 48 Ca were used to access neutron-deficient nuclei around neptunium at the velocity filter SHIP, and investigated using the COMPASS decay spectroscopy station. With the use of digital electronics, several isotopes produced via neutron, proton, and α evaporation channels were identified by establishing correlated α-decay chains with short-lived sub-μs members. Data are given on decay chains stemming from 225,226 Np, 225 U, and 222,223 Pa. New information on the isotopes 225,226 Np and 222 Pa was obtained. Production cross sections of nuclei in the region using a variety of projectiles are discussed. The measured production cross-sections indicate that the usual advantages of using 48 Ca as a beam projectile to produce nuclei Z>100 are absent in the production of these slightly lighter nuclei. ispartof: NUCLEAR PHYSICS A vol:987 pages:337-349 status: published

A compact silicon detector array with high spatial granularity and fast, fully digital data recording has been developed and commissioned for the investigation of heavy and superheavy nuclear species. The detector array can be combined in close geometry with large volume germanium detectors. It offers comprehensive particle and photon coincidence and correlation spectroscopy by highly efficient evaporation residue, α , γ , conversion electron and X-ray detection supported by the high granularity of the implantation chip. Access to fast decay events in the sub-microsecond region is made possible by the fast timing properties of the digital signal processing. A novel Si-chip support design allows direct cooling of the Si-chips and short signal transport. The compact and modular mechanical design equipped with a standard flange facilitates its transport and connection to different separators at different ion beam facilities. After initial tests, first α - γ coincidence spectroscopy experiments have been performed at the LISE separator of GANIL in Caen, France, in FULIS (velocity filter) mode and at the velocity filter SHIP of GSI in Darmstadt, Germany.

International audience; The superheavy isotope$^{258}$Db was produced in the$^{209}$Bi($^{50}$Ti, 1n)$^{258}$Db reaction at GSI, Germany. A detailed $ \alpha$ -spectroscopy study of this isotope and its $ \alpha$ -decay daughter products was performed. Two long-lived $ \alpha$ -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 \pm 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 \pm 0.21$ s. The $ \alpha$ -decay daughter isotope$^{254}$Lr displays a similar behavior. A half-life of $ 11.9 \pm 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 \pm 4.2$ s is tentatively assigned a spin-parity of $ 1^{-}$ . Two long-lived $ \alpha$ -decaying states are observed in the granddaughter isotope$^{250}$Md . The ground state has a half-life of $ 59.5 \pm 9.1$ s. A half-life of $ 42.4 \pm 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 $ \alpha$ - $ \gamma$ coincidences.

The experimental determination of atomic levels and the first ionization potential of the heaviest elements ( Z ⩾ 100 ) is key to challenge theoretical predictions and to reveal changes in the atomic shell structure. These elements are only artificially produced in complete-fusion evaporation reactions at on-line facilities such as the GSI in Darmstadt at a rate of, at most, a few atoms per second. Hence, highly sensitive spectroscopic methods are required. Laser spectroscopy is one of the most powerful and valuable tools to investigate atomic properties. In combination with a buffer-gas filled stopping cell, the Radiation Detected Resonance Ionization Spectroscopy (RADRIS) technique provides the highest sensitivity for laser spectroscopy on the heaviest elements. The RADRIS setup, as well as the measurement procedure, have been optimized and characterized using the α -emitter 155 Yb in on-line conditions, resulting in an overall efficiency well above 1%. This paves the way for a successful search of excited atomic levels in nobelium and heavier elements.

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 .

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. ispartof: PHYSICAL REVIEW LETTERS vol:120 issue:26 pages:263003-263003 ispartof: location:United States status: published

An experimental scheme combining the mass resolving power of a Penning trap with contemporary decay spectroscopy has been established at GSI Darmstadt. The Universal Linear Accelerator (UNILAC) at GSI Darmstadt provided a $^{48}\mathrm{Ca}$ beam impinging on a thin $^{170}\mathrm{Er}$ target foil. Subsequent to velocity filtering of reaction products in the Separator for Heavy Ion reaction Products (SHIP), the nuclear ground state of the $5n$ evaporation channel $^{213}\mathrm{Ra}$ was mass-selected in SHIPTRAP, and the $^{213}\mathrm{Ra}$ ions were finally transferred into an array of silicon strip detectors surrounded by large composite germanium detectors. Based on comprehensive geant4 simulations and supported by theoretical calculations, the spectroscopic results call for a revision of the decay path of $^{213}\mathrm{Ra}$, thereby exemplifying the potential of a combination of a mass-selective Penning trap device with a dedicated nuclear decay station and contemporary geant4 simulations.

International audience; The new COMPASS detection system designed and developed at GSI, Darmstadt was employed in the focal plane of the SHIP velocity filter on-line during a period of commissioning. The isotope 254No was initially measured for control purposes, following which the nuclei, 227,228,230U, 229Np, and 229,230Pu were synthesized. The obtained data from α-decay spectroscopy is evaluated and compared with previous measurements.

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.

Atomic nuclei far from stability continue to challenge our understanding. For example, theoretical models have predicted an “island of stability” in the region of the superheavy elements due to the closure of spherical proton and neutron shells. Depending on the model, these are expected at Z = 114, 120 or even 126 and N = 172 or 184. Valuable information on the road to the island of stability is derived from high-precision mass measurements, which give direct access to binding energies of short-lived trans-uranium nuclei. Recently, direct mass measurements at SHIPTRAP have been extended to nobelium and lawrencium isotopes around the deformed shell gap N = 152. In order to further extend mass measurements to the region of superheavy elements, new technical developments are required to increase the performance of our setup. The sensitivity will increase through the implementation of a new detection method, where observation of one single ion is sufficient. Together with the use of a more efficient gas stopping cell, this will us allow to significantly enhance the overall efficiency of SHIPTRAP.

With the Penning-trap mass spectrometer SHIPTRAP at GSI, Darmstadt, it is possible to investigate exotic nuclei in the region of the heaviest elements. Few years ago, challenging experiments led to the direct measurements of the masses of neutron-deficient isotopes with Z = 102,103 around N = 152. Thanks to recent advances in cooling and ion-manipulation techniques, a major technical upgrade of the setup has been recently accomplished to boost its efficiency. At present, the gap to reach more rare and shorter-lived species at the limits of the nuclear landscape has been narrowed. ispartof: pages:423-429 ispartof: Acta Physica Polonica B vol:48 issue:3 pages:423-429 ispartof: location:Zakopane: POLAND status: published

Quantum-mechanical shell effects are expected to strongly enhance nuclear binding on an "island of stability" of superheavy elements. The predicted center at proton number $Z=114,120$, or $126$ and neutron number $N=184$ has been substantiated by the recent synthesis of new elements up to $Z=118$. However the location of the center and the extension of the island of stability remain vague. High-precision mass spectrometry allows the direct measurement of nuclear binding energies and thus the determination of the strength of shell effects. Here, we present such measurements for nobelium and lawrencium isotopes, which also pin down the deformed shell gap at $N=152$., Comment: 9 pages, 3 figures

The mass difference of the nuclides 180 W and 180 Hf has been measured with the Penning-trap mass spectrometer SHIPTRAP to investigate 180 W as a possible candidate for the search for neutrinoless double-electron capture. The Q ϵ ϵ -value was measured to 143.20(27) keV. This value in combination with the calculations of the atomic electron wave functions and other parameters results in a half-life of the 0 + → 0 + ground-state to ground-state double-electron capture transition of approximately 5 × 10 27 years / 〈 m ϵ ϵ [ eV ] 〉 2 .

Penning traps have proven to be powerful tools for the determination of nuclear masses with high accuracy. A crucial parameter for precision mass measurements in Penning traps is the accurate determination of the magnetic-field strength. However, the magnetic field of a superconducting magnet is not constant in time, but changes due to intrinsic effects of the solenoid and external perturbations. These effects have been investigated for SHIPTRAP. Furthermore, a stabilization of the temperature in the magnet bore as well as of the pressure in the liquid-helium cryostat has been implemented. Thus, the magnetic-field related uncertainties have been reduced to 7(6)×10−11/h.

Penning traps are widely used for high-precision mass measurements of radionuclides related to nuclear astrophysics studies and the evolution of nuclear structure far away from stability. With the stopping of secondary beams in gas cells together with advanced ion-beam manipulation techniques their reach has been extended to rare isotopes of essentially all elements. The Penning trap mass spectrometer SHIPTRAP at GSI Darmstadt has recently demonstrated that even high-precision mass measurements of transfermium elements can be performed despite low production rates of only about one particle per second. This important milestone opens new perspectives for the study of superheavy elements with ion traps.

For the first time a direct determination of the atomic mass difference of 187Re and 187Os has been performed with the Penning-trap mass spectrometer SHIPTRAP applying the novel phase-imaging ion-cyclotron-resonance technique. The obtained value of 2492(30stat)(15sys) eV is in excellent agreement with the Q values determined indirectly with microcalorimetry and thus resolves a long-standing discrepancy with older proportional counter measurements. This is essential for the determination of the neutrino mass from the beta-decay of 187Re as planned in future microcalorimetric measurements. In addition, an accurate mass difference of 187Re and 187Os is also important for the assessment of 187Re for cosmochronology.

A novel approach to mass measurements at the 10−9 level for short-lived nuclides with half-lives well below one second is presented. It is based on the projection of the radial ion motion in a Penning trap onto a position-sensitive detector. Compared with the presently employed time-of-flight ion-cyclotron-resonance technique, the novel approach is 25-times faster and provides a 40-fold gain in resolving power. Moreover, it offers a substantially higher sensitivity since just two ions are sufficient to determine the ion’s cyclotron frequency. Systematic effects specific to the technique that can change the measured cyclotron frequency are considered in detail. It is shown that the main factors that limit the maximal accuracy and resolving power of the technique are collisions of the stored ions with residual gas in the trap, the temporal instability of the trapping voltage, the anharmonicities of the trapping potential and the uncertainty introduced by the conversion of the cyclotron to magnetron motion.

A novel approach based on the projection of the Penning-trap ion motion onto a position-sensitive detector opens the door to very accurate mass measurements on the ppb level even for short-lived nuclides with half-lives well below a second. In addition to the accuracy boost, the new method provides a superior resolving power by which low-lying isomeric states with excitation energy on the 10-keV level can be easily separated from the ground state. A measurement of the mass difference of ^{130}Xe and ^{129}Xe has demonstrated the great potential of the new approach.

Penning-trap mass spectrometry of radionuclides provides accurate mass values and absolute binding energies. Such mass measurements are sensitive indicators of the nuclear structure evolution far away from stability. Recently, direct mass measurements have been extended to the heavy elements nobelium (Z=102) and lawrencium (Z=103) with the Penning-trap mass spectrometer SHIPTRAP. The results probe nuclear shell effects at N=152. New developments will pave the way to access even heavier nuclides.

The masses of the nuclides 203-207Rn and 213Ra were measured directly for the first time with the Penning-trap mass spectrometer SHIPTRAP at GSI Darmstadt. The results confirm the previously determined mass values. The mass uncertainties for 205Rn and 213Ra were significantly reduced. The results are relevant for the investigation of the nuclear shell structure between N = 82 and N = 126 . As an indicator of structural changes the two-neutron separation energies $ S_{2n}(Z,N)$ have been studied.

The Q values of double-electron capture in ${}^{124}$Xe, ${}^{130}$Ba, and ${}^{136}$Ce and double-beta decay of ${}^{124}$Sn and ${}^{130}$Te have been determined with the Penning-trap mass spectrometer SHIPTRAP with a few hundred eV uncertainty. These nuclides are members of three isobaric triplets with common daughter nuclides. The main goal of this work was to investigate the existence of the resonant enhancement of the neutrinoless double-electron-capture rates in ${}^{124}$Xe and ${}^{130}$Ba in order to assess their suitability for the search for neutrinoless double-electron capture. Based on our results, in neither of these cases is the resonance condition fulfilled.

The theory of octupolar-excitation ion-cyclotron-resonance mass spectrometry is presented which predicts an increase of up to several orders of magnitude in resolving power under certain conditions. The new method has been applied for a direct Penning-trap mass-ratio determination of the $^{164}\mathrm{Er}\mathrm{\text{\ensuremath{-}}}^{164}\mathrm{Dy}$ mass doublet. $^{164}\mathrm{Er}$ is a candidate for the search for neutrinoless double-electron capture. However, the measured ${Q}_{ϵϵ}$ value of 25.07(12) keV results in a half-life of ${10}^{30}$ years for a 1 eV Majorana-neutrino mass.

The Q values for double-electron capture in {sup 102}Pd, {sup 106}Cd, and {sup 144}Sm have been measured by Penning-trap mass spectrometry. The results exclude at present all three nuclides from the list of suitable candidates for a search for resonant neutrinoless double-electron capture.

A superposition of multiple resonance states in neutrinoless double-electron capture in ${}^{156}\text{Dy}$ has been discovered. Penning-trap mass spectrometry has been used for atomic-mass-difference measurements and careful calculations of electron wave functions and double-hole binding energies have been performed to determine the resonance-enhancement factors. Transitions to four nuclear excited states in the daughter nuclide ${}^{156}\text{Gd}$ have been identified as resonantly enhanced, including one with a full resonant enhancement, within the uncertainty of 100 eV. This phenomenon is unique in that it can be used to probe the mechanisms of neutrinoless processes.

The $Q$ values of the neutrinoless double-electron capture transitions in ${}^{96}\text{Ru}$, ${}^{162}\text{Er}$, and ${}^{168}\text{Yb}$ have been determined by Penning-trap mass-ratio measurements. Based on our new high-precision results for the $Q$ values, neither of these transitions shows a resonant enhancement of the capture rate. At present, this excludes these nuclides from the list of suitable candidates in the search for neutrinoless double-electron capture.

The theory of octupolar-excitation ion-cyclotron-resonance mass spectrometry is presented which predicts an increase of up to several orders of magnitude in resolving power under certain conditions. The new method has been applied for a direct Penning-trap mass-ratio determination of the (164)Er-(164)Dy mass doublet. (164)Er is a candidate for the search for neutrinoless double-electron capture. However, the measured Q(ϵϵ) value of 25.07(12) keV results in a half-life of 10(30) years for a 1 eV Majorana-neutrino mass.

The masses of 15 stable nuclides in the rare-earth region have been measured with the Penning-trap mass spectrometer TRIGA-TRAP. This is the first series of absolute mass measurements linking these nuclides to the atomic-mass standard $^{12}\mathrm{C}$. Previously, nuclear reaction studies almost exclusively determined the literature values of these masses in the Atomic-Mass Evaluation. The TRIGA-TRAP results show deviations on the order of 3--4 standard deviations from the latest published values of the Atomic-Mass Evaluation 2003 for some cases. However, the binding-energy differences that are important for nuclear structure studies have been confirmed and improved. The new masses are discussed in the context of valence proton-neutron interactions using double differences of binding energies, $\ensuremath{\delta}{V}_{\mathit{pn}}(Z,N)$.

In the search for the nuclide with the largest probability for neutrinoless double-electron capture, we have determined the ${Q}_{ϵϵ}$ value between the ground states of $^{152}\mathrm{Gd}$ and $^{152}\mathrm{Sm}$ by Penning-trap mass-ratio measurements. The new ${Q}_{ϵϵ}$ value of 55.70(18) keV results in a half-life of ${10}^{26}\text{ }\text{ }\mathrm{yr}$ for a 1 eV neutrino mass. With this smallest half-life among known $0\ensuremath{\nu}ϵϵ$ transitions, $^{152}\mathrm{Gd}$ is a promising candidate for the search for neutrinoless double-electron capture.

The mass of an atom incorporates all its constituents and their interactions. The difference between the mass of an atom and the sum of its building blocks (the binding energy) is a manifestation of Einstein's famous relation E = mc(2). The binding energy determines the energy available for nuclear reactions and decays (and thus the creation of elements by stellar nucleosynthesis), and holds the key to the fundamental question of how heavy the elements can be. Superheavy elements have been observed in challenging production experiments, but our present knowledge of the binding energy of these nuclides is based only on the detection of their decay products. The reconstruction from extended decay chains introduces uncertainties that render the interpretation difficult. Here we report direct mass measurements of trans-uranium nuclides. Located at the farthest tip of the actinide species on the proton number-neutron number diagram, these nuclides represent the gateway to the predicted island of stability. In particular, we have determined the mass values of (252-254)No (atomic number 102) with the Penning trap mass spectrometer SHIPTRAP. The uncertainties are of the order of 10 keV/c(2) (representing a relative precision of 0.05 p.p.m.), despite minute production rates of less than one atom per second. Our experiments advance direct mass measurements by ten atomic numbers with no loss in accuracy, and provide reliable anchor points en route to the island of stability.