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Journal Articles

Towards saturation of the electron-capture delayed fission probability; The New isotopes $$^{240}$$Es and $$^{236}$$Bk

Konki, J.*; Khuyagbaatar, J.*; Uusitalo, J.*; Greenlees, P. T.*; Auranen, K.*; Badran, H.*; Block, M.*; Briselet, R.*; Cox, D. M.*; Dasgupta, M.*; et al.

Physics Letters B, 764, p.265 - 270, 2017/01

 Times Cited Count:6 Percentile:18.72(Astronomy & Astrophysics)

Journal Articles

Stability and synthesis of superheavy elements; Fighting the battle against fission - Example of $$^{254}$$No

Lopez-Martens, A.*; Henning, G.*; Khoo, T. L.*; Seweryniak, D.*; Alcorta, M.*; Asai, Masato; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.

EPJ Web of Conferences (Internet), 131, p.03001_1 - 03001_6, 2016/12

 Times Cited Count:1 Percentile:39.82

Fission barrier height and its angular-momentum dependence have been measured for the first time in the nucleus with the atomic number greater than 100. The entry distribution method, which can determine the excitation energy at which fission starts to dominate the decay process, was applied to $$^{254}$$No. The fission barrier of $$^{254}$$No was found to be 6.6 MeV at zero spin, indicating that the $$^{254}$$No is strongly stabilized by the nuclear shell effects.

Journal Articles

Fission barrier of superheavy nuclei and persistence of shell effects at high spin; Cases of $$^{254}$$No and $$^{220}$$Th

Henning, G.*; Khoo, T. L.*; Lopez-Martens, A.*; Seweryniak, D.*; Alcorta, M.*; Asai, Masato; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.

Physical Review Letters, 113(26), p.262505_1 - 262505_6, 2014/12

 Times Cited Count:22 Percentile:14.95(Physics, Multidisciplinary)

Fission barrier heights of a shell-stabilized superheavy nucleus $$^{254}$$No have been determined as a function of spin up to 19$$hbar$$ through the measured distribution of entry points of $$gamma$$ deexcitations in the excitation energy vs. spin plane. The fission barrier height of $$^{254}$$No was determined to be 6.0 MeV at spin 15$$hbar$$, and 6.6 MeV at spin 0$$hbar$$ by extrapolation. This demonstrates that the shell effect actually enlarges the fission barrier in such heavy nuclei and keeps the barrier high even at high spin.

Journal Articles

Exploring the stability of super heavy elements; First measurement of the fission barrier of $$^{254}$$No

Henning, G.*; Lopez-Martens, A.*; Khoo, T. L.*; Seweryniak, D.*; Alcorta, M.*; Asai, Masato; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.

EPJ Web of Conferences (Internet), 66, p.02046_1 - 02046_8, 2014/03

 Times Cited Count:3 Percentile:19.3

Fission barrier heights of $$^{254}$$No have been determined through the entry distribution method. The entry distribution is the initial distribution of excitation energy and spin from which the $$gamma$$ deexcitation starts in the fusion-evaporation reaction. The initial distribution is extracted from measured $$gamma$$-ray multiplicity and total $$gamma$$-ray energy. This paper describes the details of the entry distribution method, and reports the first determination of the fission barrier heights of $$^{254}$$No, which is the heaviest nucleus whose fission barrier has been measured.

Journal Articles

Superheavy element flerovium (element 114) is a volatile metal

Yakushev, A.*; Gates, J. M.*; T$"u$rler, A.*; Sch$"a$del, M.; D$"u$llmann, Ch. E.*; Ackermann, D.*; Andersson, L.-L.*; Block, M.*; Br$"u$chle, W.*; Dvorak, J.*; et al.

Inorganic Chemistry, 53(3), p.1624 - 1629, 2014/02

 Times Cited Count:51 Percentile:1.81(Chemistry, Inorganic & Nuclear)

We report on a gas-solid chromatography study of the adsorption of element 114 (flerovium, Fl) on a Au surface. Fl was produced in the nuclear fusion reaction $$^{244}$$Pu($$^{48}$$Ca, 3-4n)$$^{288,289}$$Fl and was isolated in-flight from the primary $$^{48}$$ beam in a physical recoil separator. The adsorption behavior of Fl, its nuclear $$alpha$$-decay product Cn, their lighter homologues in groups 14 and 12, i.e., Pb and Hg, and the noble gas Rn were studied simultaneously by isothermal gas chromatography and thermochromatography. Two Fl atoms were detected. They adsorbed on a Au surface at room temperature, but not as readily as Pb and Hg. The observed adsorption behavior of Fl points to a higher inertness compared to its nearest homologue in the group, Pb. However, the measured lower limit for the adsorption enthalpy of Fl on a Au surface points to the formation of a metal-metal bond of Fl with Au. Fl is the least reactive element in the group, but still a metal.

Journal Articles

First prompt in-beam $$gamma$$-ray spectroscopy of a superheavy element; The $$^{256}$$Rf

Rubert, J.*; Dorvaux, O.*; Gall, B. J. P.*; Greenlees, P. T.*; Asfari, Z.*; Piot, J.*; Andersson, L. L.*; Asai, Masato; Cox, D. M.*; Dechery, F.*; et al.

Journal of Physics; Conference Series, 420, p.012010_1 - 012010_10, 2013/03

 Percentile:100

The first prompt in-beam $$gamma$$-ray spectroscopy of a superheavy element, $$^{256}$$Rf, has been performed successfully. A development of an intense isotopically enriched $$^{50}$$Ti beam using the MIVOC method enabled us to perform this experiment. A rotational band up to a spin of 20 $$hbar$$ has been discovered in $$^{256}$$Rf, and its moment of inertia has been extracted. These data suggest that there is no evidence of a significant deformed shell gap at $$Z$$ = 104.

Journal Articles

Shell-structure and pairing interaction in superheavy nuclei; Rotational properties of the $$Z$$=104 nucleus $$^{256}$$Rf

Greenlees, P. T.*; Rubert, J.*; Piot, J.*; Gall, B. J. P.*; Andersson, L. L.*; Asai, Masato; Asfari, Z.*; Cox, D. M.*; Dechery, F.*; Dorvaux, O.*; et al.

Physical Review Letters, 109(1), p.012501_1 - 012501_5, 2012/07

 Times Cited Count:37 Percentile:11.7(Physics, Multidisciplinary)

Rotational band structure of the $$Z$$=104 nucleus $$^{256}$$Rf has been observed for the first time using an in-beam $$gamma$$-ray spectroscopic technique. This nucleus is the heaviest among the nuclei whose rotational band structure has ever been observed. Thus, the present result provides valuable information on the single-particle shell structure and pairing interaction in the heaviest extreme of nuclei. The deduced moment of inertia indicates that there is no deformed shell gap at $$Z$$=104, which is predicted in a number of current self-consistent mean-field models.

Journal Articles

Rapid synthesis of radioactive transition-metal carbonyl complexes at ambient conditions

Even, J.*; Yakushev, A.*; D$"u$llmann, C. E.*; Dvorak, J.*; Eichler, R.*; Gothe, O.*; Hild, D.*; J$"a$ger, E.*; Khuyagbaatar, J.*; Kratz, J. V.*; et al.

Inorganic Chemistry, 51(12), p.6431 - 6433, 2012/06

 Times Cited Count:22 Percentile:20.56(Chemistry, Inorganic & Nuclear)

Carbonyl complexes of radioactive transition metals can be easily synthesized with high yields by stopping nuclear fission or fusion products in a gas volume containing CO. Here, we focus on Mo, W, and Os complexes. The reaction takes place at pressures of around 1 bar at room temperature, i.e., at conditions that are easy to accommodate. The formed complexes are highly volatile. They can thus be transported within a gas stream without major losses to setups for their further investigation or direct use. The rapid synthesis holds promise for radiochemical purposes and will be useful for studying, e.g., chemical properties of superheavy elements.

Journal Articles

Search for a 2-quasiparticle high-$$K$$ isomer in $$^{256}$$Rf

Robinson, A. P.*; Khoo, T. L.*; Seweryniak, D.*; Ahmad, I.*; Asai, Masato; Back, B. B.*; Carpenter, M. P.*; Chowdhury, P.*; Davids, C. N.*; Greene, J.*; et al.

Physical Review C, 83(6), p.064311_1 - 064311_7, 2011/06

 Times Cited Count:22 Percentile:16.44(Physics, Nuclear)

We have identified an isomer with a half-life of 17 $$mu$$s in $$^{256}$$Rf through a calorimetric conversion electron measurement tagged with implanted $$^{256}$$Rf nuclei using the fragment mass analyzer at Argonne National Laboratory. The low population yield for this isomer suggests that this isomer should not be a 2-quasiparticle high-$$K$$ isomer which is typically observed in the N = 152 isotones, but should be a 4-quasiparticle one. Possible reasons of the non-observation of a 2-quasiparticle isomer are this isomer decays by fission with a half-life similar to that of the ground state of $$^{256}$$Rf. Another possibility, that there is no 2-quasiparticle isomer at all, would imply an abrupt termination of axially symmetric deformed shape at Z=104.

Journal Articles

The Recoil transfer chamber; An Interface to connect the physical preseparator TASCA with chemistry and counting setups

Even, J.*; Ballof, J.*; Br$"u$chle, W.*; Buda, R. A.*; D$"u$llmann, Ch. E.*; Eberhardt, K.*; Gorshkov, A.*; Gromm, E.*; Hild, D.*; J$"a$ger, E.*; et al.

Nuclear Instruments and Methods in Physics Research A, 638(1), p.157 - 164, 2011/03

 Times Cited Count:18 Percentile:12.26(Instruments & Instrumentation)

Journal Articles

Experimental study of the $$^{238}$$U($$^{36}$$S, 3-5$$n$$)$$^{269-271}$$Hs reaction leading to the observation of $$^{270}$$Hs

Graeger, R.*; Ackermann, D.*; Chelnokov, M.*; Chepigin, V.*; D$"u$llmann, C. E.*; Dvorak, J.*; Even, J.*; Gorshkov, A.*; He${ss}$berger, F. P.*; Hild, D.*; et al.

Physical Review C, 81(6), p.061601_1 - 061601_5, 2010/06

 Times Cited Count:33 Percentile:10.02(Physics, Nuclear)

Journal Articles

Bridging the nuclear structure gap between stable and super heavy nuclei

Seweryniak, D.*; Khoo, T. L.*; Ahmad, I.*; Kondev, F. G.*; Robinson, A.*; Tandel, S. K.*; Asai, Masato; Back, B. B.*; Carpenter, M. P.*; Chowdhury, P.*; et al.

Nuclear Physics A, 834(1-4), p.357c - 361c, 2010/03

 Times Cited Count:7 Percentile:45.82(Physics, Nuclear)

Experimental data on single-particle energies in nuclei around Z=100 and N=152 play an important role to test validity of theoretical predictions for shell structure of superheavy nuclei. We found high-K two-quasiparticle isomers in $$^{252}$$No and $$^{254}$$No, and evaluated energies of proton single-particle orbitals around Z=100. We also found a new high-K three quasiparticle isomer in $$^{257}$$Rf. Energies of neutron single-particle orbitals were also evaluated from experimental data of the $$alpha$$ decay of $$^{257}$$Rf. Comparisons between the present experimental data and various theoretical calculations for the proton single-particle orbitals indicate that the calculation by using the Woods-Saxon potential gives the best agreement with the data.

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