CHEMICAL
IDENTIFICATION OF ELEMENT 106
( Thermochromatography of Oxochlorides)
I.Zvara, A.B.Yakushev, S.N.Timokhin,
Xu Honggui, V.P.Perelygin, and Yu.T.Chuburkov:(JINRPreprint E12-97-102, Dubna,
1997.; submitted to Radiochimica Acta).
Experiments
performed during past four years have resulted in first chemical identification
of element 106. Bombardments of 249Cf with 18O ions in a
total lasted 90 hours, and as many as 40 atoms of the element (presumably mass
number 263, T1/2 = 1 s) isolated from the mixture
of the products were recorded. Specifically, to prove the chemical individuality
of element 106, it was separated from elements 105, 104 and heavy actinoids.
The element
was detected by its spontaneous fission, and the chemical separation technique
was essentially the thermochromatography of oxochlorides (see Figure). The
thermalized recoils swept from a target chamber by flowing gas are treated by a
gaseous chlorinating agents and oxygen to produce volatile oxochlorides. They
are characteristic of group VI transition metals W, Mo, and Cr, while element
106 is expected to have a character of eka-tungsten. In a silica column with an
imposed negative temperature gradient, volatile compounds of various elements
are deposited in different temperature ranges according to their adsorption
energies. The latter are known to correlate with macroscopic volatility of
the species. The inner wall of the column served as the solid state track
detector of fission fragments from the decay of element 106. The tracks could
be revealed after the end of a long lasting continuous experiment by etching
the surface and scanning it for the tracks with an optical microscope.
The white
histogram demonstrates fission events observed with a cold inert gas all the
atoms are irreversibly deposited near the inlet of the column. The stacked
hatched histogram shows the fission events recorded in three independent
chemical experiments. Now, element 106 produces a zone with a characteristic
profile, as one can see from the peak shape of a simultaneously produced
longer-lived tungsten isotope (in the chemical state of an oxochloride), which
could be traced by its gamma-radiation.
This
first identification was performed with a relatively good statistics. So it
also provides first quantitative data on the difference in properties between
eka-W (106) and W. Such results are of utmost importance in view of the
challenging problem of the so called relativistic effects in the chemical
properties of the heaviest elements.
CHEMICAL IDENTIFICATION OF ELEMENT 108
Hassium confirms its position in the
Periodic Table.
For the first time Element 108 has been
chemically identified by six atoms.
Thanks to
the new experimental techniques developed in the international collaboration -
Paul Scherrer Institute (PSI), the University of Bern in Switzerland, GSI,
Institute of Nuclear Chemistry in Mainz, Germany, LBNL (USA) and FLNR (Dubna,
Russia) - the element named after the Land Hesse (Germany) has found its place
in the Periodic Table.
Element 108
was synthesized at GSI (Darmstadt, Hesse, Germany) in 1984 but only now and thanks
to cooperative efforts of scientists from Switzerland, Germany, Russia, USA and
China its first chemical study has been performed. Hassium (Hs)'s six decay
chains have been registered and two of them belong to the newly discovered in
this experiment 270Hs. It was discovered that hassium like its
nearest homologues Ru and Os forms an extremely volatile compound with oxygen. This
proves that it belongs to the eighth group of the Periodic Table. Its atomic
number is 108 so hassium is for a while the heaviest element studied
chemically.
Hs atoms
have been got in a fusion reaction 248Cm with 26Mg
bombarding particles at UNILAC accelerator in Darmstadt and they exist only for
a few seconds. Formation's small cross-section involved high- intensity 26Mg
beam. To settle this problem the new radiation technology has been realized in
GSI - rotating vacuum window and target separated accelerator's vacuum and
target chamber gas space.
New
gas-chemical separation method developed collectively by chemists from FLNR,
PSI and the University of Bern allowed to convert synthesized atoms to volatile
compound over oxygen and highly effectively transform it to the detector setup
in the gas flow. The detector setup is a narrow gas channel of silicon
detectors with negative temperature gradient from 0oC up to 170oC,
it was created at PSI in cooperation with LBNL.
Successful
experiment opens new and inviting prospects for future chemical experiments
with heavier elements.
Editorial note.
We got this information from a participant in the experiment Alexander Yakushev
who works in Darmstadt at the moment. Press release has been prepared
practically by all collaborators together. As for the FLNR contribution, -
added Alexander in his later message,- chemical extraction method belongs to
us, separation principle is ours as well, detection principle belongs to LBNL. PSI
totalized everything, GSI prepared new construction of the target that allowed
the chemists to accept very high intensity.
Chemical
investigation of hassium (element 108)
Nature 418, 859 - 862 (2002); doi:10.1038/nature00980
CH. E. DULLMANN*, W. BRUCHLE, R. DRESSLER, K. EBERHARDT, B.
EICHLER, R. EICHLER, H. W. GAGGELER*, T. N. GINTER , F. GLAUS, K. E.
GREGORICH , D. C. HOFFMAN , E. JAGER, D. T. JOST, U. W. KIRBACH , D. M. LEE ,
H. NITSCHE , J. B. PATIN , V. PERSHINA, D. PIGUET, Z. QIN#, M. SCHADEL, B.
SCHAUSTEN, E. SCHIMPF, H.-J. SCHOTT, S. SOVERNA*, R. SUDOWE , P. THORLE,
S. N. TIMOKHIN , N. TRAUTMANN, A. TURLER**, A. VAHLE, G. WIRTH, A. B.
YAKUSHEV & P. M. ZIELINSKI
*
Departement fur Chemie und Biochemie, Universitat Bern, CH-3012 Bern,
Switzerland
Labor fur Radio- und Umweltchemie, Paul Scherrer Institut, CH-5232 Villigen,
Switzerland
Gesellschaft fur Schwerionenforschung mbH, D-64291 Darmstadt, Germany
Institut fur Kernchemie, Universitat Mainz, D-55128 Mainz, Germany
Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley,
California 94720, USA
Department of Chemistry, University of California, Berkeley, California
94720-1460, USA
# Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000,
P.R. China
Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research,
141980 Dubna, Russia
** Institut fur Radiochemie, Technische Universitat Munchen, D-85748 Garching,
Germany
Research Center Rossendorf e.V., D-01314 Dresden, Germany
Correspondence and requests for materials should be addressed to H.W.G.
(e-mail: spm111@yandex.ru).
The periodic table provides a classification of the
chemical properties of the elements. But for the heaviest elements, the
transactinides, this role of the periodic table reaches its limits because
increasingly strong relativistic effects on the valence electron shells can
induce deviations from known trends in chemical properties. In the case of the
first two transactinides, elements 104 and 105, relativistic effects do indeed
influence their chemical properties, whereas elements 106 and 107 both behave
as expected from their position within the periodic table. Here we report the
chemical separation and characterization of only seven detected atoms of
element 108 (hassium, Hs), which were generated as isotopes 269Hs
(refs 8, 9) and 270Hs (ref. 10) in the fusion reaction between 26Mg
and 248Cm. The hassium atoms are immediately oxidized to a highly
volatile oxide, presumably HsO4, for which we determine an enthalpy
of adsorption on our detector surface that is
comparable to the adsorption enthalpy determined under identical conditions for
the osmium oxide OsO4. These results provide evidence that the
chemical properties of hassium and its lighter homologue osmium are similar,
thus confirming that hassium exhibits properties as expected from its position
in group 8 of the periodic table
A.
Yakushev's Interview to "Nature" on Element 112
From Kendall Powell's article "Heavy elements: A
very brief encounter"
Nature 418, 815 - 816 (2002); doi:10.1038/418815a
Deviant behaviour
One element, however, looks set to throw
the rulebook away completely. A team led by Alexander Yakushev at the Flerov
Laboratory of Nuclear Reactions in Dubna, Russia, is currently trying to
capture element 112. This element is in group 12, so it ought to behave like a
more volatile version of mercury. But relativistic effects are expected to make
some of its properties more like those of an inert gas such as radon7.
Yakushev and his colleagues decided to hedge their bets by building an
experimental set-up to detect both mercury-like and radon-like activity. Unlike
the hassium experiment, the group is assessing the chemistry of element 112 in
its unbonded state. Calcium ions are smashed into a uranium target, and the
atoms of element 112 that are created are flushed onto two different detectors.
If the element behaves like mercury, it should bind to the gold-covered surface
of one of the detectors. If it doesn't, it will be swept into an ionization
chamber where its radioactive decay chain will be detected. In preliminary,
unpublished results, nothing stuck to the gold surface, but eight atoms were
detected in the chamber, indicating that 112 may display radon-like properties.
Other elements disrupt the trends within their groups, but 112 appears to be
acting as if it belongs to another group altogether.
Like other work on the chemistry of heavy elements, the Flerov team relies
heavily on techniques and predictions developed by researchers around the
world. The hassium study was an equally multinational affair. Teams at Lawrence
Berkeley National Laboratory in Berkeley, California, and the Paul Scherrer
Institute in Villigen, Switzerland - where Dullmann is based - designed the
detectors, Flerov researchers performed preliminary studies of osmium and
various German groups made the target, organized the final experiment and
provided theoretical calculations. "In principle, it was everyone working
in gas-phase chemistry of superheavy elements in the world," says
Yakushev, who is a co-author on the hassium paper. Such collaborative spirit
does not always come easily. The competition between groups to find new
elements is intense, partly because the discoverers get to name the element. But
the complexity of the chemistry experiments forces the groups to work together.
"It requires walking a fine line and tremendous diplomacy," says
Heino Nitsche, a nuclear chemist at Lawrence Berkeley.