N. Trautmann

Chemical properties of element 106 (seaborgium)

The synthesis, via nuclear fusion reactions, of elements heavier than the actinides, allows one to probe the limits of the periodic table as a means of classifying the elements. In particular, deviations in the periodicity of chemical properties for the heaviest elements are predicted as a consequence of increasingly strong relativistic effects on the electronic shell structure. The transactinide elements have now been extended up to element 112 (ref. 8), but the chemical properties have been investigated only for the first two of the transactinide elements, 104 and 105 (refs 9,10,11,12,13,14,15,16,17,18,19). Those studies showed that relativistic effect render these two elements chemically different from their lighter homologues in the same columns of the periodic table (Fig. 1). Here we report the chemical separation of element 106 (seaborgium, Sg) and investigations of its chemical behaviour in the gas phase and in aqueous solution. The methods that we use are able to probe the reactivity of individual atoms, and based on the detection of just seven atoms of seaborgium we find that it exhibits properties characteristic of the group 6 homologues molybdenum and tungsten. Thus seaborgium appears to restore the trends of the periodic table disrupted by relativistic effects in elements 104 and 105.

Realization of a broad band neutron spin filter with compressed, polarized 3He gas☆

The strongly spin dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize beams of thermal and epithermal neutrons. An effective 3He neutron spin filter (NSF) requires high 3He nuclear polarization as well as a filter thickness corresponding to a gas amount of the order of 1 barl. We realized such a filter using direct optical pumping of metastable 3He∗ atoms in a 3He plasma at 1 mbar. Metastable exchange scattering transfers the angular momentum to the whole ensemble of 3He atoms. At present 3 × 1018 3He-atoms/s are polarized up to 64%. Subsequent polarization preserving compression by a two stage compressor system enables to prepare NSF cells of about 300 cm3 volume with 3 bar of polarized 3He within 2 h. 3He polarizations up to 53% were measured in a cell with a filter length of about 15 cm. By this cell a thermal neutron beam from the Mainz TRIGA reactor was polarized. A wavelength selective polarization analysis by means of Bragg scattering revealed a neutron polarization of 84% at a total transmission of 12% for a neutron wavelength of 1 A.

TRIGA-SPEC: A setup for mass spectrometry and laser spectroscopy at the research reactor TRIGA Mainz

Abstract The research reactor TRIGA Mainz is an ideal facility to provide neutron-rich nuclides with production rates sufficiently large for mass spectrometric and laser spectroscopic studies. Within the TRIGA-SPEC project, a Penning trap as well as a beamline for collinear laser spectroscopy are being installed. Several new developments will ensure high sensitivity of the trap setup enabling mass measurements even on a single ion. Besides neutron-rich fission products produced in the reactor, also heavy nuclides such as 235 U or 252 Cf can be investigated for the first time with an off-line ion source. The data provided by the mass measurements will be of interest for astrophysical calculations on the rapid neutron-capture process as well as for tests of mass models in the heavy-mass region. The laser spectroscopic measurements will yield model-independent information on nuclear ground-state properties such as nuclear moments and charge radii of neutron-rich nuclei of refractory elements far from stability. TRIGA-SPEC also serves as a test facility for mass and laser spectroscopic experiments at SHIPTRAP and the low-energy branch of the future GSI facility FAIR. This publication describes the experimental setup as well as its present status.

Identification of Short-lived Isotopes of Zirconium, Niobium, Molybdenum, and Technetium in Fission by Rapid Solvent Extraction Techniques

Einige mehr orientierende Versuche mit anderen Nukliden sollten schließlich noch zeigen, daß das hier eingehend untersuchte System kein Sonderfall ist. Dazu wurden wägbare Mengen an radioaktiv markiertem Kobalt, Zink, Thallium oder Blei gemeinsam mit Wismut aus komplexalkalischem, borsäurehaltigem Medium abgeschieden; die Wismutschicht war 1,0 mg/cm, die der Fremdkomponente 0,2 mg/cm dick. Nach der Abscheidung wurde die Schicht bei einem Potential von 0 , 0 5 bis 0 , 1 5 V in 0,5 η Salzsäure (Zn, Tl) oder 0,5 η Salpetersäure (Co, Pb) von 70 °C gebracht. Innerhalb von 2-3 min waren 97 + 4% des Zinks, 98 + 2 % des Thalliums und 90% des Bleis abgelöst, während die Ablösung des Kobalts langsam verlief und nach 20 min erst 75% umfaßte.

Production of monodisperse uranium oxide particles and their characterization by scanning electron microscopy and secondary ion mass spectrometry

Abstract Secondary ion mass spectrometry (SIMS) can be confidently used to measure uranium isotopic ratios in single particles. Dense particles of known isotopic composition and size allow the precision and the accuracy of the applied procedure to be estimated. These particles can be obtained by dissolving standard reference uranium materials, nebulizing the solution in droplets of proper diameter and collecting the particles after the desolvation and calcination of the droplets. A new instrumental set up, based on a commercial vibrating orifice aerosol generator to generate monodisperse droplets of the solutions from four uranium oxide reference materials, is described. The droplets were dried and calcined in a sequence of three furnaces. The morphology of the monodisperse uranium oxide particles was studied by scanning electron microscopy. It was observed that the particles were nearly spherical and consisted of dense material. Their diameter distribution evidenced the presence of two populations mainly, the first showing a narrow distribution with a maximum centered at approximately 1 μm. The first statistical moment ratios between the two populations remained practically constant at 1.24±0.01. This demonstrated that the second population was due to the formation of one particle from two droplets of solution (theoretical double mass≡diameter ratio of 2 3 =1.26). Secondary ion mass spectrometry was used to verify the isotopic composition of the produced particles. Typical accuracies of better than 0.4% for 235U/238U and a few percent for the minor isotopes have been achieved. For the determination of the 236U content, the signal at mass M=239 (due to 238UH+) was used to correct the 235UH+ contribution to 236U at mass M=236, greatly improving the accuracy of the 236/238 ratio with increasing enrichment of the 235U isotope.

A resonance ionization mass spectrometer as an analytical instrument for trace analysis

Abstract An instrument for trace analysis based on resonance ionization mass spectroscopy has been developed. It consists of three tunable pulsed dye lasers pumped by one or two copper vapour lasers and a time-of-flight mass spectrometer. The properties of the laser system, the quartz fibres that are used for the transport of the laser beams, the time-of-flight spectrometer, the atomic beam sources and the data acquisition and laser control electronics are described in detail. A mass resolution of 2700 was obtained with gadolinium evaporated from an oven. The detection efficiency after evaporation from a filament was measured to be a few times 10 −6 for plutonium as well as for technetium at a very low background. Measurements of the isotopic ratios of plutonium samples yielded a satisfactory agreement with mass spectrometric data. Examples are given for some spectroscopic applications of the instrument such as the investigation of autoionizing states.

Humic colloid-borne Np migration: influence of the oxidation state

The migration behavior of Np(IV/V) is investigated by column experiments using a sandy sediment with groundwater rich in humic substances. NIR spectroscopy, redox speciation by TTA extraction and ultrafiltration are used for the Np speciation in the groundwater prior to its introduction into the column and after elution. Np is found to be transported as humic colloid-bound species which are eluted slightly faster than the water flow velocity. The fraction of humic colloid-borne Np increases with the reduction progress of Np(V) to Np(IV), because the interaction of Np(IV) with humic substances is much stronger than Np(V). The results demonstrate the importance of the speciation of redox sensitive actinides in natural aquifers for the assessment of the humic colloid facilitated migration.

Determination of the first ionization potential of nine actinide elements by resonance ionization mass spectroscopy (RIMS)

The high sensitivity of RIMS enables the precise determination of the first ionization potential of actinide elements with a sample size of ≤1012 atoms. By multiple resonant laser excitation, the actinide atoms under investigation are ionized in the presence of an electric field, and the ions are mass-selectively detected in a time-of-flight spectrometer. The first ionization potential is obtained by scanning the wavelength of the laser used for the last excitation step across the ionization threshold Wth—indicated by a sudden increase of the ion count rate—at various electric field strengths. Extrapolation of Wth to electric field strength zero leads directly to the first ionization potential. The first ionization potentials (IP) of Am, Cm, Bk, Cf and Es were determined for the first time as IPAm=5.9736(3) eV, IPCm=5.9914(2) eV, IPBk=6.1979(2) eV, IPCf=6.2817(2) eV, IPEs=6.3676(5) eV with samples of 1012 atoms. Furthermore, the ionization potentials of Th, U, Np and Pu were remeasured.

Measurement of the first ionization potential of lawrencium, element 103

The chemical properties of an element are primarily governed by the configuration of electrons in the valence shell. Relativistic effects influence the electronic structure of heavy elements in the sixth row of the periodic table, and these effects increase dramatically in the seventh row—including the actinides—even affecting ground-state configurations. Atomic s and p1/2 orbitals are stabilized by relativistic effects, whereas p3/2, d and f orbitals are destabilized, so that ground-state configurations of heavy elements may differ from those of lighter elements in the same group. The first ionization potential (IP1) is a measure of the energy required to remove one valence electron from a neutral atom, and is an atomic property that reflects the outermost electronic configuration. Precise and accurate experimental determination of IP1 gives information on the binding energy of valence electrons, and also, therefore, on the degree of relativistic stabilization. However, such measurements are hampered by the difficulty in obtaining the heaviest elements on scales of more than one atom at a time. Here we report that the experimentally obtained IP1 of the heaviest actinide, lawrencium (Lr, atomic number 103), is electronvolts. The IP1 of Lr was measured with 256Lr (half-life 27 seconds) using an efficient surface ion-source and a radioisotope detection system coupled to a mass separator. The measured IP1 is in excellent agreement with the value of 4.963(15) electronvolts predicted here by state-of-the-art relativistic calculations. The present work provides a reliable benchmark for theoretical calculations and also opens the way for IP1 measurements of superheavy elements (that is, transactinides) on an atom-at-a-time scale.

First Aqueous Chemistry with Seaborgium (Element 106)

For the first time, chemical separations of element 106 (Seaborgium, Sg) were performed in aqueous solutions. The isotopes Sg and Sg were produced in the Cm + Ne reaction at a beam energy of 121 MeV. The reaction products were continuously transported by a He(KCl)-jet to the computer-controlled liquid chromatography system ARCA. In 0.1 M HNO3/5 X ΙΟ -4 M HF, Sg was found to be eluted within 10 s from 1.6X8 mm cation-exchange columns (Aminex A6, 17.5±2 μπι) together with the hexavalent Moand W-ions, while hexavalent U-ions and tetravalent Zr-, Hf-, and element 104 ions were strongly retained on the column. Element 106 was detected by measuring correlated α-decays of the daughter isotopes 78-s 104 and 26-s 102. For the isotope Sg, we have evidence for a spontaneous fission branch. It yields a partial spontaneousfission half-life which is in agreement with recent theoretical predictions. The chemical results show that the most stable oxidation state of Sg in aqueous solution is +6, and that like its homologs Mo and W, Sg forms neutral or anionic oxoor oxohalide-compounds under the present condition. In these first experiments, Sg exhibits properties very characteristic of group 6 elements, and does not show U-like properties.