The radioactive decay properties of 242Es were studied at the gas -filled recoil separator TASCA. This isotope was produced in the 3n evaporation channel of the fusion reaction of 48Ca + 197Au. A half-life of 16.9(8) s was deduced from 662 alpha decays of 242Es, resulting in an alpha-decay branching of 41(3)%. Twenty-six fission events with a half-life of 18.2+4.5 -3.0 s were assigned to originate from the electron -capture delayed fission of 242Es. The probability for the electron -capture delayed fission was measured to be 0.015(4), which improves and resolves ambiguities in available experimental data. We discuss all known cases for electron -capture delayed fission in Es, Bk, and Am isotopes and compare experimental data with predictions from a recent semiempirical model. A cross section of 27(3) nb was measured for the production of 242Es.

Chemical reactivity of the superheavy elements nihonium (Nh, element 113) and moscovium (Mc, element 115) has been studied by the gas-solid chromatography method using a new combined chromatography and detection setup. The Mc isotope, 288Mc, was produced in the nuclear fusion reaction of 48Ca ions with 243Am targets at the GSI Helmholtzzentrum Darmstadt, Germany. After isolating 288Mc ions in the gas-filled separator TASCA, adsorption of 288Mc and its decay product 284Nh on silicon oxide and gold surfaces was investigated. As a result of this work, the values of the adsorption enthalpy of Nh and Mc on the silicon oxide surface were determined for the first time, −∆HadsSiO2Mc=54−5+11 kJ/mol and −∆HadsSiO2Nh=58−3+8 kJ/mol (68% c.i.). The obtained −ΔHads values are in good agreement with results of advanced relativistic calculations. Both elements, Nh and Mc, were shown to interact more weakly with the silicon oxide surface than their lighter homologues Tl and Bi, respectively. However, Nh and Mc turned out to be more reactive than the neighbouring closed-shell and quasi-closed-shell elements copernicium (Cn, element 112) and flerovium (Fl, element 114), respectively. The established trend is explained by the influence of strong relativistic effects on the valence atomic orbitals of these elements.

Flerovium isotopes (element Z = 114) were produced in the fusion-evaporation reactions 48Ca + 242,244Pu and studied with an upgraded TASISpec decay station placed in the focal plane of the gas-filled separator TASCA at the GSI Helmholtzzentrum fur Schwerionenforschung in Darmstadt, Germany. Twenty-nine flerovium decay chains were identified by means of correlated implantation, alpha decay, and spontaneous fission events. Data analysis aspects and statistical assessments, primarily based on measured rates of various events, which laid the foundation for the comprehensive spectroscopic information on the flerovium decay chains, are presented in detail. Various decay scenarios of an excited state observed in 282Cn are examined in depth with the help of GEANT4 simulations and assessed by predictions of beyond mean-field calculations including triaxial shape degrees of freedom. Previous, revised, and newly derived fission probabilities of even-even superheavy nuclei are compared with various theoretical predictions.

Fifteen correlated alpha-decay chains starting from the odd-A superheavy nucleus 289Fl were observed following the fusion-evaporation reaction Ca-48 + Pu-244. The results call for at least two parallel alpha-decay sequences starting from at least two different states of (289)Fl. This implies that close-lying levels in nuclei along these chains have quite different spin-parity assignments. Further, observed alpha-electron and alpha-photon coincidences, as well as the alpha decay fine structure along the decay chains, suggest a change in the ground-state spin assignment between (285)Cn and (281)Ds. Our experimental results, on the excited level structure of the heaviest odd-N nuclei to date, provide a direct testing ground for theory. This is illustrated by comparison with new nuclear structure calculations based on the symmetry-conserving configuration mixing theory.

A Low Energy Branch for the MARA separator, MARA-LEB, is under construction at the University of Jyvaskyla, Finland. It will be used to purify and study exotic beams initially via nuclear decay and laser spec-troscopy. Two experiments have been performed using the MARA separa-tor to determine the acceptance of the gas cell and to assess the feasibility of future experiments at the new facility. Products of different reaction mech-anisms have been produced and their transmission from the focal plane of MARA into the LEB gas cell has been estimated. In one experiment, medium-mass nuclei have been produced in fusion-evaporation reactions. In a second experiment, with the primary goal of studying the non-fusion reaction dynamics, heavy target-like fragments from multi-nucleon transfer reactions have been produced. Production cross sections have been mea-sured and are presented in this work.

In the present work, a K isomeric state in No-250, which is more stable against fission than the ground state, was experimentally studied. The aim was to measure the fission branch of this isomeric state. In total, 780 fission events attributed to the decay of No-250 were detected. Among them 133 cases were attributed to the ground-state decay with a half-life of 4.0(4) mu s, which was populated by the deexcitation of the isomeric state via electromagnetic transitions with a half-life of 23(4) mu s. In addition, in two more cases, this long-lived isomeric state was populated in the deexcitation of a hitherto unknown, yet higher-lying and short-lived isomeric state with a half-life of 0.7(-0.3)(+1.4) mu s. No direct fission from the long-lived isomeric state, i.e., with a lifetime of longer than 40 mu s, was identified. This results in an upper limit of 0.035 for the branching ratio for fission. This is a significantly more strict limit than the previously known value of 0.5. Nonobservation of fission branching of the long-lived isomer is discussed relative to theoretical predictions and within various semiempirical ways, which resulted in an attribution of a lower limit of 10(4) for the fission-hindrance factor, caused by the K quantum number. The presences of multiple high-K isomeric states seemingly is a widespread phenomenon in deformed heavy nuclei.

Flerovium (Fl, element 114) is the heaviest element chemically studied so far. To date, its interaction with gold was investigated in two gas-solid chromatography experiments, which reported two different types of interaction, however, each based on the level of a few registered atoms only. Whereas noble-gas-like properties were suggested from the first experiment, the second one pointed at a volatile-metal-like character. Here, we present further experimental data on adsorption studies of Fl on silicon oxide and gold surfaces, accounting for the inhomogeneous nature of the surface, as it was used in the experiment and analyzed as part of the reported studies. We confirm that Fl is highly volatile and the least reactive member of group 14. Our experimental observations suggest that Fl exhibits lower reactivity towards Au than the volatile metal Hg, but higher reactivity than the noble gas Rn.

Nihonium (Nh, element 113) and flerovium (Fl, element 114) are the first superheavy elements in which the 7p shell is occupied. High volatility and inertness were predicted for Fl due to the strong relativistic stabilization of the closed 7p 1/2 sub-shell, which originates from a large spin-orbit splitting between the 7p 1/2 and 7p 3/2 orbitals. One unpaired electron in the outermost 7p 1/2 sub-shell in Nh is expected to give rise to a higher chemical reactivity. Theoretical predictions of Nh reactivity are discussed, along with results of the first experimental attempts to study Nh chemistry in the gas phase. The experimental observations verify a higher chemical reactivity of Nh atoms compared to its neighbor Fl and call for the development of advanced setups. First tests of a newly developed detection device miniCOMPACT with highly reactive Fr isotopes assure that effective chemical studies of Nh are within reach.

In the heaviest elements, the instability of atomic nuclei against spontaneous fission leads to ever shorter nuclear half-lives. Upon falling below a timescale of 10(-14) s, the border of existence of isotopes is crossed because this is the timescale on which the formation of atomic shells occurs. Analysis of the experimental data on the spontaneous fission half-lives of Rf isotopes in relation with their expected single-particle orbitals hint at a potentially abrupt decrease in half-lives of unknown neutron-deficient Rf isotopes with neutron numbers <149, which suggests that the isotopic border is already almost reached. However, this conjecture, which cannot be explained within the current knowledge, was directly related to uncertainty in the experimental data on (253)Rf. We revisited the decay of (253)Rf and identified two fission activities, which are attributed to decays of the two different states with half-lives of 12.8(-3.4)(+7.0) ms and 44(-10)(+17) mu s. In addition, hitherto unknown alpha decay in (253)Rf, which is followed by alpha decay of the new isotope No-249 with a half-life of 15(7)(+74) ms, was observed. Based on our new data, no abrupt decreases in half-lives of the neutron-deficient No and Rf isotopes are expected, which is in line with theoretical predictions. Fission half-lives of the two different states in (253)Rf are benchmark cases for the theoretical description of the single-particle orbital influence on the fission process.

A nuclear spectroscopy experiment was conducted to study α-decay chains stemming from isotopes of flerovium (element Z=114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ^{48}Ca+^{242}Pu and ^{48}Ca+^{244}Pu provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to ^{286}Fl and ^{288}Fl, respectively. A prompt coincidence between a 9.60(1)-MeV α particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made elements, namely ^{282}Cn. Spectroscopy of ^{288}Fl decay chains fixed Q_{α}=10.06(1)  MeV. In one case, a Q_{α}=9.46(1)-MeV decay from ^{284}Cn into ^{280}Ds was observed, with ^{280}Ds fissioning after only 518  μs. The impact of these findings, aggregated with existing data on decay chains of ^{286,288}Fl, on the size of an anticipated shell gap at proton number Z=114 is discussed in light of predictions from two beyond-mean-field calculations, which take into account triaxial deformation.

To study the chemical properties of the heaviest elements, a fast and efficient stopping and extraction of the highly energetic residues from heavy ion fusion reactions into the chemistry setup is essential. Currently used techniques like Recoil Transfer Chambers (RTC) relying on gas flow extraction provide high efficiencies for chemically non-reactive volatile species, but operate at extraction times t(extr) of about 0.5 s or more. Buffer Gas Cells (BGC) with electric and Radio-Frequency (RF) fields offer much faster extraction times. Here, we demonstrate the successful coupling of a BGC to a gas chromatography setup as is used for studies of chemical properties of superheavy elements. Using Ra-223 and Ac-225 recoil ion sources providing Rn-219 and Fr-221 ions for off-line tests, an extraction time t(extr) = 55(4) ms and an extraction efficiency of 35(3)% were achieved for the non-reactive Rn-219, while Fr-221 was retained. The results show a BGC-based setup to be suitable for gas-phase experiments with short-lived volatile transactinide elements like Cn and Fl with half-lives substantially below 1 s.

The question of the number and origin of isomeric states in (256)Rf arose from two independent experiments but remained unanswered for a decade. To shed light on this puzzle, we studied isomeric decay in (256)Rf by measuring conversion electrons with fast fully digital electronics. (256)Rf was produced in the fusion-evaporation reactions of Ti-50 + Pb-207 and Ti-50 + Pb-208 at the gas-filled recoil separator TransActinide Separator and Chemistry Apparatus. Among a total of 120 decays of (256)Rf, we detected 22 and 12 decays proceeding through one and two isomeric states. Half-lives of the low- and higher-lying states were assigned to be T-1/2 = 14(-4)(+6) and 10(-3)(+5) mu s, respectively. Population rates of these isomeric states were estimated to be approximate to 18% and >10%, which are similar to those for two-quasiparticle K isomeric states in this region of nuclei. The results, thus, confirm an earlier claim on the existence of multiple K isomeric states in (256)Rf and show their population rates are as high as in No isotopes. Suggestively, K remains a good quantum number in isotopes of heavier elements like Sg and Hs, where yet unknown high-K isomeric states still could exist. The present experimental results demonstrate that the "triggerless" measurement guarantees an efficient detection of delayed conversion electron signals. Thus, it is a very efficient method for the identification of isomeric states in experiments with one nucleus-at-a-time production rates.

A novel combination of advanced gas-chromatography and detection systems coupled to a buffer-gas cell was characterized on-line to allow gas-phase chemical studies of accelerator-produced short-lived α-decaying mercury, francium, and astatine isotopes. These were produced in 40Ar- and 48Ca-induced nuclear fusion–evaporation reactions, subsequently isolated in the recoil separators MARS at Texas A&M University, USA, and TASCA at GSI Darmstadt, Germany, before being thermalized in a buffer-gas-stopping cell. From the latter, the nuclear reaction products were extracted into gas-phase chromatographic systems, suitable for registering α-decaying short-lived radionuclides, such as isotopes of superheavy elements. Efficiencies of 21(3)% for 204-209Fr were reached for the extraction into the optimized miniCOMPACT gas-chromatography setup, indicating that this technique enables the identification of isotopes of volatile as well as non-volatile elements. These studies guide the path towards chemical investigations of superheavy elements beyond flerovium, which are out of reach with currently used setups.

The electron-capture decay followed by a prompt fission process was searched for in the hitherto unknown most neutron-deficient Md isotope with mass number 244. Alpha decay with α-particle energies of 8.73-8.86 MeV and with a half-life of 0.30_{-0.09}^{+0.19}  s was assigned to ^{244}Md. No fission event with a similar half-life potentially originating from spontaneous fissioning of the short-lived electron-capture decay daughter ^{244}Fm was observed, which results in an upper limit of 0.14 for the electron-capture branching of ^{244}Md. Two groups of fission events with half-lives of 0.9_{-0.3}^{+0.6}  ms and 5_{-2}^{+3}  ms were observed. The 0.9_{-0.3}^{+0.6}  ms activity was assigned to originate from the decay of ^{245}Md. The origin of eight fission events resulting in a half-life of 5_{-2}^{+3}  ms could not be unambiguously identified within the present data while the possible explanation has to invoke previously unseen physics cases.

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.

An upgraded TASISpec setup, with the addition of a veto DSSD and the new Compex detector-germanium array, has been employed with the gas-filled recoil separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung Darmstadt, to study flerovium (element 114) decay chains. The detector upgrades along with development of new analytical techniques have improved the sensitivity of the TASISpec setup for measuring α-photon coincidences. These improvements have been assessed with test reactions. The reaction 48Ca+206,207Pb was used for verification of experimental parameters such as transmission to implantation DSSD and target-segment to α-decay correlations. The reaction 48Ca+ nat Hf was used to produce several short-lived nuclei with multiple-α decay chains to investigate pile-up event deconvolution.

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