Papers by Dieter Ackermann
Relativistic effects influence the valence electron configuration of the heaviest elements having... more Relativistic effects influence the valence electron configuration of the heaviest elements having a big impact on their physical and chemical properties. These effects can be described using the modern multi configuration Dirac-Fock (MCDF) and Relativistic Coupled-Cluster [1, 2, 3] calculations. To have a benchmark for theoretical calculations, a comparison between the measured and predicted atomic properties is needed. At present, no spectroscopic data is available for the atomic properties of transfermium elements (Z>100). Thus the study of the atomic structure of these elements is of great interest. In our experiments we aim to search for the atomic levels of the element nobelium based on the Radiation Detected Resonance Ionization Spectroscopy (RADRIS) [3] technique. 254 No can be produced at the UNILAC at GSI with rates of approximately 17/s via the reaction 208 Pb(48 Ca,2n) 254 No. The separated fusion-product beam from SHIP is stopped in a buffer gas cell in 90 mbar argon gas of 99.9999% purity and collected on a tantalum filament. After an appropriate collection time, the accumulated ions are then re-evaporated as neutral atoms by a short heating pulse into the buffer gas, during the beam-off period. We then employ a two-step photoionization process to ionize the atoms. In case of resonant ionization, the photoions are transported by suitable electric fields to a particle detector (PIPS detector) where they are identified by their characteristic α-decay. Laser light for the first excitation-step, from four tunable dye lasers (Lambda Physik, FL series) and an optical parametric oscillator (OPO) (GWU, SFM housing) system, is transported to the experimental setup using UVfibers. The dye lasers-operated in the UV-range, were pumped by two excimer lasers (Lambda Physik, LPX 210i and EMG104MSC) at 248 nm. The OPO pumped by a frequency-tripled Nd:YAG (Continuum, Precision II) laser, was operated in a frequency mixing mode, delivering light in the range below 400 nm. The 351 nm-light for the second non-resonant step was provided by a high power excimer laser (Lambda Physik, LPX220) and was transported to the experimental setup by high reflectivity UVmirrors. The wavelengths of the dye lasers and the OPOsystem were monitored by wavemeter capable of measuring wavenumbers with a precision of 0.01 cm −1. LabView based software was designed, for experiment control and data acquisition. Preceding the measurements in nobelium, the cell efficiency was determined using ytterbium, which is the chemical homologue of nobelium. The radionuclide of interest 155 Yb was produced by the fusion reaction
Approaching SN-100 with Gasp Plus Si-Ball Plus Recoil Mass-Spectrometer - Collective States of SN-105 and IN-103,IN-105
Physica Scripta, 1995
Very proton rich nuclei in the A approximate to 100 region have been investigated using the GASP ... more Very proton rich nuclei in the A approximate to 100 region have been investigated using the GASP array coupled with the Recoil Mass Spectrometer (RMS) and the GASP Si-ball. High-spin slates of Sn-105 rind In-103.105 nuclei formed with the reaction Ni-58 +
Proceedings of XLVIII International Winter Meeting on Nuclear Physics in Memoriam of Ileana Iori — PoS(BORMIO2010), 2010
Acta Physica Polonica B, 2018
The new COMPASS detection system designed and developed at GSI, Darmstadt was employed in the foc... more The new COMPASS detection system designed and developed at GSI, Darmstadt was employed in the focal plane of the SHIP velocity filter online during a period of commissioning. The isotope 254 No was initially measured for control purposes, following which the nuclei, 227,228,230 U, 229 Np, and 229,230 Pu were synthesized. The obtained data from α-decay spectroscopy is evaluated and compared with previous measurements.
Reflets de la physique, 2017
Version complète du tableau périodique des éléments chimiques, validée par l'IUPAC en 2016. Les d... more Version complète du tableau périodique des éléments chimiques, validée par l'IUPAC en 2016. Les derniers éléments découverts (Z = 113 à 118) sont colorés en jaune..
Journal of Physics: Conference Series, 2016
The unexplored area of heavy neutron rich nuclei is extremely important for nuclear astrophysics ... more The unexplored area of heavy neutron rich nuclei is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleogenesis. For the production of heavy neutron rich nuclei located along the neutron closed shell N=126 (probably the last "waiting point" in the r-process of nucleosynthesis) the low-energy multi-nucleon transfer reaction 136 Xe+ 208 Pb at E lab =870MeV was explored. Due to the stabilizing effect of the closed neutron shells in both nuclei, N=82 and N=126, and the rather favorable proton transfer from lead to xenon, the light fragments formed in this process are well bound and the Q-value of the reaction is nearly zero. Measurements were performed with the PRISMA spectrometer in coincidence with an additional time-of-flight (ToF) arm on the +20 beam line of the PIAVE-ALPI accelerator in Legnaro, Italy. The PRISMA spectrometer allows identification of the A, Z and velocity of the projectile-like fragments (PLF), while the second arm gives access to the target-like fragments (TLF). Details on the experimental setup and preliminary results are reported.
Nuclear structure studies in the seaborgium region at SHIP
AIP Conference Proceedings, 2015
New decay data for the isotopes 259Sg and 255Rf were obtained at the velocity filter SHIP using a... more New decay data for the isotopes 259Sg and 255Rf were obtained at the velocity filter SHIP using an α-decay spectroscopy measurement. Both isotopes were produced and studied via a one neutron evaporation channel in the compound fusion reaction 54Cr+208Pb. New isomeric states were observed and the single-particle level systematics for isotones with 151 and 153 neutrons were extended. A change of the ground-state configuration for the heaviest N = 151 isotones was observed. Detailed Monte-Carlo simulation for the α decay of 259Sg applying the Geant4 toolkit was performed and compared with experimental data.
Viewpoint: A 21st century Rutherford experiment
Physics, Nov 30, 2009
Collisions of neutron-rich helium nuclei with gold targets show how the internal arrangement of n... more Collisions of neutron-rich helium nuclei with gold targets show how the internal arrangement of nucleons influences nuclear fusion reaction mechanisms.
Achievements and Perspectives in the Search for Super Heavy Elements
Springer Proceedings in Physics, 2004
The elements with the atomic numbers 107-112 have been synthesized and unambiguously identified a... more The elements with the atomic numbers 107-112 have been synthesized and unambiguously identified at the velocity filter SHIP at GSI. The technique allowing for this successful experimental program is the combination of the detection of correlations between evaporation residues and subsequent a-decays with a powerful separator. The sensitivity limit of the set-up at GSI has reached the lpb level. For systematic investigation in this region of extremely low cross section and to synthesize nuclei of higher Z this limit has to be pushed to even lower values. An extensive development program is pursued at SHIP in order to reach at least an order of magnitude lower cross sections. Apart from target cooling and separator development a super conducting CW linear accelerator is studied to reach this goal. To design a successful experimental program for the possible discovery of new elements the nuclear structure of the heaviest nuclei has to be understood as well as the reaction mechanism which leads to their production in heavy ion reactions. We have initiated series of systematic studies for both subjects.
Studies of SHE at SHIP
An overview of present experimental investigation of superheavy elements is given. The data are c... more An overview of present experimental investigation of superheavy elements is given. The data are compared with theoretical descriptions. Results are reported from an experiment to confirm production of element 112 isotopes in irradiation of 238UF4 with 48Ca. One spontaneous fission event was measured, which agrees with three events of previously measured data which had been assigned to the decay of 283112. However, more experimental work is needed in order to obtain an independent and unambiguous confirmation of previous results.
Physical Review C, 2014
The isotope 176 Au has been studied in the complete fusion reaction 40 Ca + 141 Pr → 176 Au + 5n ... more The isotope 176 Au has been studied in the complete fusion reaction 40 Ca + 141 Pr → 176 Au + 5n at the velocity filter SHIP (GSI, Darmstadt). The complex fine-structure α decay of two isomeric states in 176 Au feeding several previously unknown excited states in the daughter nucleus 172 Ir is presented. An α-decay branching ratio of b α = 9.5(11)% was deduced for the high-spin isomer in 172 Ir.
A case study of collectivity, transfer and fusion enhancement
Nuclear Physics A, 1998
Precise fusion and quasi-elastic scattering excitation functions have been measured for the syste... more Precise fusion and quasi-elastic scattering excitation functions have been measured for the systems 40Ca + 90,96Zr at energies spanning the Coulomb barrier. From both the fusion and the quasi-elastic scattering data representations of the barrier distributions have been extracted. The barrier distributions of the two reactions are qualitatively very different. While the lighter system is well described by coupled-channels calculations
Journal of Radioanalytical and Nuclear Chemistry, 2014
Rapid in situ formation of metal carbonyl complexes with short-lived nuclides has been demonstrat... more Rapid in situ formation of metal carbonyl complexes with short-lived nuclides has been demonstrated to be feasible with recoiling ions formed in nuclear fusion and fission reactions. These carbonyl complexes are highly volatile and can be transported rapidly in a gas-stream to counting or chemistry devices. This method was already successfully applied in the chemical investigation of the superheavy element seaborgium (Z = 106) and appears promising for various fields of nuclear research. In this article, we give an overview on the current status of metal carbonyl complex studies with short-lived d-element isotopes.
Extending Penning trap mass measurements with SHIPTRAP to the heaviest elements
AIP Conference Proceedings, 2013
ABSTRACT Penning-trap mass spectrometry of radionuclides provides accurate mass values and absolu... more ABSTRACT 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.
Physical Review C, 2009
A new isomer with a half-life of 0.48(2) ms was identified in the nuclide 181 Hg, which was produ... more A new isomer with a half-life of 0.48(2) ms was identified in the nuclide 181 Hg, which was produced in the complete fusion reaction 40 Ca + 144 Sm → 184 Pb * at the velocity filter SHIP (GSI, Darmstadt). The isomeric state was tentatively assigned a spin-parity of 13/2 +. We propose that this isomer de-excites by a yet unobserved low-energy, strongly converted γ-ray transition, followed by a newly identified cascade composed of a 90.3 keV M1 and a 71.4 keV E2 γ-ray transition.
Physical Review C, 2003
Near-barrier excitation functions have been measured for evaporation-residue production and fissi... more Near-barrier excitation functions have been measured for evaporation-residue production and fission in the 12 Cϩ 204,206,208 Pb and 48 Caϩ 168,170 Er systems that lead to the compound nuclei 216,218,220 Ra*. A pronounced suppression of evaporation-residue production is observed for the more symmetric combinations, 48 Ca ϩ 168,170 Er. We relate this to the significant quasifission components already observed for these systems.
Physical Review C, 2013
Detailed α-decay studies of 179 Tl g and its daughter products 175 Au g and 171 Ir g were carried... more Detailed α-decay studies of 179 Tl g and its daughter products 175 Au g and 171 Ir g were carried out in two complementary experiments at the mass separator ISOLDE (CERN) and velocity filter SHIP (GSI). First unambiguous determination of the α-decay properties of 175 Au g was performed as follows: E α = 6433(4) keV, T 1/2 = 207(7) ms, and α-decay branching ratio 90(7)%. First determination of the α-decay branching ratios for 179 Tl g and 171 Ir g was also made: b α (179 Tl g) = 60(2)% and b α (171 Ir g) = 15(2)%. The spins of the ground states in 175 Au and 171 Ir are established as 1/2 + .
Physical Review C, 2014
Decay properties of the neutron-deficient nuclides 201-203 Ra and 200-202 Fr were investigated us... more Decay properties of the neutron-deficient nuclides 201-203 Ra and 200-202 Fr were investigated using αand γ-decay spectroscopy. The nuclei were produced in fusion-evaporation reactions of 56 Fe projectiles with enriched 147 Sm and 149 Sm targets at the velocity filter SHIP at GSI in Darmstadt (Germany). The α decay from the (3/2 −) state in 201 Ra was identified with an energy E α = 7842(12) keV and half-life T 1/2 = 8 +40 −4 ms. Ambiguous decay properties for 202 Ra from previous measurements were clarified by remeasuring with significantly improved precision, resulting in values of E α = 7722(7) keV and T 1/2 = 3.8 +1.3 −0.8 ms. New short-lived isomeric states were identified in 200 Fr and 201 Fr with half-lives of 0.6 +0.5 −0.2 μs and 0.7 +0.5 −0.2 μs, respectively. A tentative spin and parity of 13/2 + were assigned to the latter. One event attributed to β-delayed fission of 200 Fr was observed.
Physical Review C, 1997
Four new superdeformed bands have been observed with the Gammasphere array and have been assigned... more Four new superdeformed bands have been observed with the Gammasphere array and have been assigned to the 195 Hg nucleus. Two of the bands are interpreted as signature partners most likely based on N osc ϭ6 neutron quasiparticles coupled to a superdeformed core, while the other two appear to be based on a j 15/2 intruder orbital. These four bands do not exhibit a simple, ''identical bands'' relationship to other superdeformed bands in this mass region. ͓S0556-2813͑97͒06001-9͔
Physical Review C, 2010
The deformed doubly magic nucleus 270 Hs has so far only been observed as the four-neutron (4n) e... more The deformed doubly magic nucleus 270 Hs has so far only been observed as the four-neutron (4n) evaporation residue of the reaction 26 Mg + 248 Cm, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of 270 Hs in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions 48 Ca + 226 Ra and 36 S + 238 U result in higher cross sections due to lower reaction Q values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using HIVAP predict cross sections for the reaction 36 S + 238 U that are similar to those of the 26 Mg + 248 Cm reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction 36 S + 238 U and the observation of 270 Hs, which is produced in the 4n evaporation channel, with a measured cross section of 0.8 +2.6 −0.7 pb at 51-MeV excitation energy. The one-event cross-section limits (68% confidence level) for the 3n, 4n, and 5n evaporation channels at 39-MeV excitation energy are 2.9 pb, while the cross-section limits of the 3n and 5n channel at 51 MeV are 1.5 pb. This is significantly lower than the 5n cross section of the 26 Mg + 248 Cm reaction at similar excitation energy.
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Papers by Dieter Ackermann