In recent years, significant efforts have been made to investigate the atomic structure of lawrencium (Lr, Z=103 )—the heaviest actinide element—using laser spectroscopy. This article presents the current status of the experimental search for atomic transitions in lawrencium at GSI, Darmstadt, Germany, along with the necessary developments toward achieving laser spectroscopy of this element. We have advanced the method of radiation-detected resonance ionization spectroscopy (RADRIS), which has previously enabled the first laser spectroscopic studies of nobelium. We have conducted essential preparatory studies, demonstrating that lawrencium can be efficiently evaporated from hafnium filaments. Using two-step laser resonance ionization, we scanned a spectral range of approximately 800 cm ^-1 around each of two different, theoretically predicted strong atomic transitions. Based on the measured background and the determined system efficiency, we demonstrate that our experimental setup is sensitive enough to detect these atomic transitions, albeit no atomic transitions have been observed to date.

In this article we report laser Resonance Ionization Spectroscopy (RIS) experiments on natSm with the assistance of a ToF-gated ion detection. This detection scheme enabled measurements of a given atomic transition for each isotope simultaneously without the need for isotopically enriched samples. Using this approach, multiple different excitation schemes were developed and specific mass and field shifts and the hyperfine parameter A of the transitions were determined. Furthermore this setup was used to commission a MR-ToF MS, which shall be integrated in the in-gas-Jet Resonance Ionization Spectroscopy (JetRIS) setup at GSI to enhance its capabilities for on-line measurements. This upgrade will enable on-line laser spectroscopy experiments on neutron-deficient samarium isotopes and heavy nuclides independent of their decay mode with a suitable half-life time, that are inaccessible with present techniques, such as 254Md.

In this paper, we present ion-optical simulation for the design studies of a new solenoid separator as part of the NEXT experiment. Our aim is to separate Neutron-rich, EXotic, heavy nuclei produced in multinucleon Transfer reactions (NEXT) from the primary beam and un-wanted by-products within the magnetic field. The goal of the simulation is to find the optimum arrangement of the components within the NEXT solenoid separator to achieve the highest transmission efficiencies of transfer products and a good suppression of background. In our simulations, we focused on two complementary reactions to produce transfermium isotopes and to produce neutron-rich nuclei around the neutron number N = 126. Transmission yields above 50% for the transfermium isotopes of interest were reached in the simulations. The simulated yields for N = 126 lie between 5% and 20%.

The heaviest actinide elements are only accessible in accelerator-based experiments on a one-atom-at-a-time level. Usually, fusion–evaporation reactions are applied to reach these elements. However, access to the neutron-rich isotopes is limited. An alternative reaction mechanism to fusion–evaporation is multinucleon transfer, which features higher cross-sections. The main drawback of this technique is the wide angular distribution of the transfer products, which makes it challenging to catch and prepare them for precision measurements. To overcome this obstacle, we are building the NEXT experiment: a solenoid magnet is used to separate the different transfer products and to focus those of interest into a gas-catcher, where they are slowed down. From the gas-catcher, the ions are transferred and bunched by a stacked-ring ion guide into a multi-reflection time-of-flight mass spectrometer (MR-ToF MS). The MR-ToF MS provides isobaric separation and allows for precision mass measurements. In this article, we will give an overview of the NEXT experiment and its perspectives for future actinide research.

In modern rare isotope facilities, ion cooling and bunching lies at the heart of the ion transfer along a low-energy beam line that consists of several differential pumping stages. We present a conceptual design of an ion guide as an alternative to the conventional linear Radio-Frequency Quadrupole (RFQ) for cooling and bunching rare isotopes. The ion guide is composed of stacked ring electrodes of varying apertures, to which a confining RF potential following a rectangular waveform is applied. The thicknesses of the rings and the gaps in between are varied accordingly to maximize the confining volume and to reduce ion losses. Ion transport within the ion guide is facilitated by a lower-frequency wave traveling on top of the higher-frequency confining field. The former is induced by locally adjusting the duty cycle of the rectangular waveform of the confining potential. Design parameters are first calculated by analytical studies and then optimized by ion trajectory simulations with SIMION®. The results show that the ion guide enables high ion transmission and produces well focused ion bunches. It will be used in the NEXT project—an experimental study of atomic masses of Neutron-rich EXotic nuclei produced in multi-nucleon Transfer reactions.

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 delta m/m approximate to 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.

A gas-filled miniature Radio-Frequency Quadrupole (mini-RFQ) was recently implemented into the SHIPTRAP laser ablation ion source to thermalize the laser-ablated ions and thus improve production efficiency as well as sample preparation. This source provides reference ions of various elements for online experiments with the SHIPTRAP mass spectrometer. In addition, it can be used to provide long-lived rare and radioactive isotopes available only in small sample sizes for high-precision mass measurements or to study systematic uncertainties. The performance of the laser ablation ion source was simulated using the COMSOL Multiphysics modeling software package. These studies indicate that a revised mechanical geometry and an optimized RF field improve the performance significantly.

A search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the Ti-50 + Bk-249 and Ti-50 + Cf-249 fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the Bk-249 target partially decayed into Cf-249, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the Ti-50 + Bk-249 and Ti-50 + Cf-249 reactions, respectively, at a midtarget beam energy of E-lab = 281.5 MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical predictions on the fission-barrier heights of superheavy nuclei in the region of the island of stability.

The ISAC facility (Isotope Separation and Acceleration) at TRIUMF has recently started to provide isotopes for pre-clinical nuclear medicine studies. By irradiating ISOL (Isotope Separation OnLine) targets with a 480 MeV proton beam from the TRIUMF H- cyclotron, the facility can deliver a large variety of radioactive isotope beams (RIB) for research in the fields of nuclear astrophysics, nuclear structure and material science with half-lives down to a few milliseconds via an electrostatic beamline network. For the collection of medical isotopes, typically with half-lives in the range of hours or days, we have developed a compact apparatus for the implantation of mass-separated RIB on a target disc at energies between 20-55 keV. In this paper, we also discuss two different retrieval methods of the implanted activity from the implantation target: by chemical etching of the target surface and by recoil collection of implanted alpha emitters.

The neutron-deficient isotopes 254,255Rf were produced in the fusion-evaporation reaction 50Ti+206Pb at the gas-filled recoil separator TASCA. Decay properties of these nuclei were investigated by applying fast digital electronics. A search for isomeric states in both isotopes was performed by using the accompanying conversion electron emissions. Isomeric states with half-lives of 4(1) μs and >30 μs were measured for 254Rf and 255Rf, respectively, which confirm the findings at different separators. The present experimental results demonstrate the great potential of fast digital electronics for measurements of isomeric states in the heaviest nuclei, which are only producible in small quantities.

J. Khuyagbaatar,1,2,* A. Yakushev,2 Ch. E. Düllmann,1,2,3 D. Ackermann,2,† L.-L. Andersson,1 M. Asai,4 M. Block,2 R. A. Boll,5 H. Brand,2 D. M. Cox,6,‡ M. Dasgupta,7 X. Derkx,1,3 A. Di Nitto,3 K. Eberhardt,1,3 J. Even,1,§ M. Evers,7 C. Fahlander,8 U. Forsberg,8 J. M. Gates,9 N. Gharibyan,10 P. Golubev,8 K. E. Gregorich,9 J. H. Hamilton,11 W. Hartmann,2 R.-D. Herzberg,6 F. P. Heßberger,1,2 D. J. Hinde,7 J. Hoffmann,2 R. Hollinger,2 A. Hübner,2 E. Jäger,2 B. Kindler,2 J. V. Kratz,3 J. Krier,2 N. Kurz,2 M. Laatiaoui,2 S. Lahiri,12 R. Lang,2 B. Lommel,2 M. Maiti,12,‖ K. Miernik,5 S. Minami,2 A. Mistry,6,¶ C. Mokry,1,3 H. Nitsche,9,** J. P. Omtvedt,13 G. K. Pang,9 P. Papadakis,6,14 D. Renisch,3 J. Roberto,5 D. Rudolph,8 J. Runke,2 K. P. Rykaczewski,5 L. G. Sarmiento,8 M. Schädel,2,4 B. Schausten,2 A. Semchenkov,13 D. A. Shaughnessy,10 P. Steinegger,15,16 J. Steiner,2 E. E. Tereshatov,10,†† P. Thörle-Pospiech,1,3 K. Tinschert,2 T. Torres De Heidenreich,2 N. Trautmann,3 A. Türler,15,16 J. Uusitalo,14 D. E. Ward,8 M. Wegrzecki,17 N. Wiehl,1,3 S. M. Van Cleve,5 and V. Yakusheva1 1Helmholtz Institute Mainz, 55099 Mainz, Germany 2GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany 3Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany 4Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan 5Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 6University of Liverpool, Liverpool L69 7ZE, United Kingdom 7The Australian National University, Canberra, ACT 0200, Australia 8Lund University, 22100 Lund, Sweden 9Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 10Lawrence Livermore National Laboratory, Livermore, California 94551, USA 11Vanderbilt University, Nashville, Tennessee 37235, USA 12Saha Institute of Nuclear Physics, Kolkata 700064, India 13University of Oslo, 0315 Oslo, Norway 14University of Jyväskylä, 40351 Jyväskylä, Finland 15Paul Scherrer Institute, 5232 Villigen, Switzerland 16University of Bern, 3012 Bern, Switzerland 17The Institute of Electron Technology, 02-668 Warsaw, Poland

The superheavy isotope 258Db was produced in the 209Bi(50Ti, 1n)258Db 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 258Db 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 254Lr displays a similar behavior. A half-life of $ 11.9 \pm 0.9$ s is determined for the 254Lr 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 250Md . 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 254Lr, 250Md and 246Es are proposed based on the $ \alpha$-$ \gamma$ coincidences.

Gas catchers are widely used to thermalize nuclear reaction products and subsequently extract them for precision measurements. However, impurities in the inert stopping gas can chemically react with the ions and thus influence the extraction efficiency. So far, chemical reactions in the gas-catcher have not been investigated in detail. Therefore, we are currently building a new setup to develop Chemical Isobaric SEparation (CISE) with the aim to understand the chemistry inside the gas-catcher and to explore its potential as a new technique for separation of isobars. In this paper, we give a short description of the setup together with the ion transportation studies performed via ion-optics simulations.

The exotic Borromean nucleus Mg-20 with N = 8, located at the proton drip line provides a unique testing ground for nuclear forces and the evolution of shell structure in the neutron-deficient region. We report on the first observation of proton unbound resonances together with bound states in Mg-20 from the Mg-20(d, d') reaction performed at TRIUMF. Phenomenological shell-model calculations offer a reasonable description. However, our experimental results present a challenge for current first-principles nuclear structure approaches and point to the need for improved chiral forces and ab initio calculations. Furthermore, the differential cross section of the first excited state is compared with distorted-wave Born approximation calculations to deduce a neutron quadrupole deformation parameter of beta(n) = 0.46 +/- 0.21. This provides the first indication of a possible weakening of the N = 8 shell closure at the proton drip line.

Khuyagbaatar, J.; Yakushev, A.; Düllmann, Ch E.; Ackermann, D.; Andersson, L. L.; Asai, M.; Block, M.; Boll, R. A.; Brand, H.; Cox, D. M.; Dasgupta, M.; Derkx, X.; Di Nitto, A.; Eberhardt, K.; Even, J.; Evers, M.; Fahlander, C.; Forsberg, U.; Gates, J. M.; Gharibyan, N.; Golubev, P.; Gregorich, K. E.; Hamilton, J. H.; Hartmann, W.; Herzberg, R. D.; Heßberger, F. P.; Hinde, D. J.; Hoffmann, J.; Hollinger, R.; Hübner, A.; Jäger, E.; Kindler, B.; Kratz, J. V.; Krier, J.; Kurz, N.; Laatiaoui, M.; Lahiri, S.; Lang, R.; Lommel, B.; Maiti, M.; Miernik, K.; Minami, S.; Mistry, A.; Mokry, C.; Nitsche, H.; Omtvedt, J. P.; Pang, G. K.; Papadakis, P.; Renisch, D.; Roberto, J.

The heaviest currently known nuclei, which have up to 118 protons, have been produced in Ca-48 induced reactions with actinide targets. Among them, the element tennessine (Ts), which has 117 protons, has been synthesized by fusing Ca-48 with the radioactive target Bk-249, which has a half-life of 327 d. The experiment was performed at the gas-filled recoil separator TASCA. Two long and two short a decay chains were observed. The long chains were attributed to the decay of Ts-294. The possible origin of the short-decay chains is discussed in comparison with the known experimental data. They are found to fit with the decay chain patterns attributed to Ts-293. The present experimental results confirm the previous findings at the Dubna Gas-Filled Recoil Separator on the decay chains originating from the nuclei assigned to Ts.

The isotopic distribution of nuclei produced in the 50Ti + 249Cf reaction has been studied at the gas-filled recoil separator TASCA at GSI Darmstadt, which separates ions according to differences in magnetic rigidity. The bombardment was performed at an energy around the Bass barrier and with the TASCA magnetic fields set for collecting fusion-evaporation reaction products. Fifty-three isotopes located “north-east” of 208Pb were identified as recoiling products formed in non-fusion channels of the reaction. These recoils were implanted with energies in two distinct ranges; besides one with higher energy, a significant low-energy contribution was identified. The latter observation was not expected to occur according to kinematics of the known types of reactions, namely quasi-elastic, multi-nucleon transfer, deep-inelastic collisions or quasifission. The present observations are discussed within the framework of two-body kinematics passing through the formation of a composite system.

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 isotopic distribution of nuclei produced in the 50 Ti + 249 Cf reaction has been studied at the gas- filled recoil separator TASCA at GSI Darmstadt, which separates ions according to differences in magnetic rigidity. The bombardment was performed at an energy around the Bass barrier and with the TASCA magnetic fields set for collecting fusion-evaporation reaction products. Fifty-three isotopes located “north-east” of 208 Pb were identified as recoiling products formed in non-fusion channels of the reaction. These recoils were implanted with energies in two distinct ranges; besides one with higher energy, a significant low-energy contribution was identified. The latter observation was not expected to occur according to kinematics collisions or quasifission. The present observations are discussed within the framework of two-body kinematics passing through the formation of a composite system.