Journal of Nuclear and Radiochemical Sciences, Vol. 8, No. 2, pp. 47-53, 2007

Superheavy Element Chemistry — Achievements and Perspectives
M. Schädel*Gesellschaft fü Schwerionenforschung mbH, Planckstr. 1, D-64291 Darmstadt, Germany
Received: October 11, 2006; In Final Form: October 11, 2006
Superheavy elements have been synthesized and chemically characterized one-atom-at-a-time up to element 108.
Presently, the quest for element 112 is one of the hottest topics in this field. The transactinide elements 104 to 108
are members of group 4 to 8 of the Periodic Table and element 112 belongs into group 12. Chemical properties ofsome of these elements, like elements 104 and 105, show stunning deviations from simple extrapolations within
their respective group while others exhibit great similarities with their lighter homologues elements. First
experiments to investigate seaborgium (Sg, element 106) in aqueous solution were performed. Again, in large
international collaborations at the GSI, several gas-phase chemistry experiments were performed with hassium(Hs, element 108). Recently, the highly efficient and very clean separation of Hs was applied for nuclear studies ofvarious Hs nuclides investigating their cross section and their nuclear decay properties in the region of the doublymagic 270Hs (Z = 108, N = 162). To overcome certain limitations of the presently used on-line chemical separations
the new TransActinide Separator and Chemistry Apparatus (TASCA) — with a gas-filled recoil separator as afront-end tool — was designed and built at the GSI in a collaborative effort. Presently in its commissioning phase,
TASCA shall be a key instrument for a big leap into quantitatively and qualitatively new experiments in the regionof superheavy elements.

1. Introduction
The number of chemical elements has considerably increased
over the last decades. But how many elements are sufficiently
chemically characterized to justify their position in the Periodic
Table and are their chemical properties significantly modified
by increasingly strong relativistic effects? These are key questions chemists like to answer in addition to the central questionof how many elements can exist. Already the first pioneeringchemical studies showed that rutherfordium and dubnium (Rf,element 104, and Db, element 105, respectively) belong into
group 4 and 5 of the Periodic Table. These elements, which
can only be produced one-atom-at-a-time in heavy-ion reactions, mark the beginning of a remarkable series of chemicalelements; from a chemical point of view they are transactinide
elements and from a nuclear point of view they can be calledsuperheavy elements (SHE).1 It was only in recent years, that alarge number of experiments did not only shed light on manyfascinating and sometimes surprising chemical properties of
Rf and Db but allowed to stepwise climb up the exceedingly
difficult path to the subsequent elements seaborgium (Sg, element 106), bohrium (Bh, element 107) and hassium (Hs, element 108); see References 1–4 for a comprehensive coverage ofthis development.
Most chemical experiments of lighter transactinides dependon the problematic cluster (aerosol) jet-transport. This technique was applied to investigate Rf (see References 5 and 6 andreferences therein for a large number of very detailed, recent
Rf studies), Db, and Sg in aqueous solution. For Sg, the heaviest element investigated in aqueous solution,7,8 until now only
two studies were performed. These will be described in an
exemplary way. Contrary to the transport of the refractory
lighter transactinides with a cluster jet a rather volatile compound of element 108 is directly formed in the recoil chamber
and is transported to the chemistry/detector device. This
unique approach allowed unprecedented chemical studies of*Corresponding author. E-mail: m.schaedel@gsi.de. Fax: +496159-71-2903.

Hs (References 9 and 10) and yielded exciting nuclear results
for the most neutron-rich Hs isotopes and their daughter
nuclides. Chemical and nuclear aspects of Hs studies will be
discussed in more detail. Recently the quest for element 112
and beyond became one of the hottest and most challenging
topics in heavy element research with chemical methods.11,12
Studies with element 112 constitute a transition from a more
traditional approach in SHE chemistry — to form a chemicalcompound and chemically investigate this compound —towards studies of an element in its atomic state. The successin SHE chemistry was only feasible because of an enormous
progress in many fields. Therefore, experimental developments, their scientific outcome, and perspectives for the future
SHE chemistry research will be discussed in an exemplaryway.
These very successful chemistry experiments, however, atthe same time clearly demonstrated the limits of these techniques. To move on to new frontiers, including heavier elements and so far inaccessible chemical systems, “physical”
recoil separators are presumably ideal front-end “tools” forSHE chemistry. Ground-breaking experiments began at theBerkeley Gas-filled Separator.13,14 A large international community is presently building and commissioning TASCA, theTransActinide Separator and Chemistry Apparatus,15 at the
GSI. Characteristic features of this gas-filled recoil separator,
which will be very instrumental in chemical and in nuclear oriented experiments in the SHE region, will be outlined while
discussing perspectives of SHE research.
2. Nuclear Syntheses and Properties of Superheavy Elements
Heavy-ion fusion reactions of medium-heavy projectiles
with Pb and Bi targets produce short-lived nuclides. They are,maybe with one or two exceptions,13 not useful for chemical
investigations. In contrast to these so-called “cold-fusion”
reactions superheavy element chemistry experiments usually
exploit an advantage of “hot-fusion” reactions which lead to thesynthesis of the most neutron-rich, longest-lived isotopes of agiven element. To this end, the most neutron-rich available iso-© 2007 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 10/19/2007

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SchädelJ. Nucl. Radiochem. Sci., Vol. 8, No. 2, 2007
248

tope of an actinide element, e.g., Cm, is irradiated with aneutron-rich light ion beam like 18O, 22 Ne, and 26 Mg. These
reactions produce SHE one-atom-at-a-time — decreasing fromabout one atom per minute for element 104 and 105, and a few
atoms per hour for element 106, to about one atom per day forelement 108.1,2 This leads to the most extreme situation one canenvision in chemistry; only single atoms or molecules, which
are rapidly vanishing due to their radioactive decay, are at handfor chemical investigations. As all nuclides used and investigated in recent chemical studies of transactinides decay byemission of characteristic α-particles a clear identification of
the separated nuclide (and element) was feasible after chemical
isolation.
More elements and longer-lived nuclides are on the horizon
and a challenge for chemical studies. In reactions between 48Ca
as a projectile and targets made of 233,238U, 242Pu, and 248Cm,
Oganessian et al.16 reported on the observation of elements up
to 116. This opens up a thrilling region for heavy element
chemists to probe the influence of increasingly strong relativistic effects and the structure of the Periodic Table at its extreme
limit; see Figure 1. As all nuclear decay chains observed fromthese 48Ca induced reactions are terminated by spontaneous
fission (SF) no “genetic” link into the region of known nuclides
can be established. Therefore, an unambiguous identificationof these new elements still remains open as the presently available physical techniques do not allow for a clear detection of
the atomic number. Chemistry — in addition to unraveling
exciting chemical properties of these elements — may again
become a crucial tool in elemental identification. The firststeps towards a chemical separation and identification of element 112 — directly produced or as decay product of element
114 — have been made.11,12 Those chemical experiments tosearch for 283112 produced directly in the 48Ca on 238U reaction11
at the GSI will be discussed in the next section in more detail
together with chemical aspects of element 112. While theseexperiments did not identify 283112 (only upper-limit cross sections were obtained),11 a recent report from a similar experiment performed at the Flerov Laboratory of Nuclear Reactions(FLNR), Dubna, making use of the 48Ca on 242Pu reaction andsearching for 283112 as an α-decay daughter of 287114, indicatesthe observation of element 112 after chemical separation.12
Chemistry experiments on Sg and Hs, which were performedat the GSI and will be discussed in more detail, use 22Ne and26
Mg beams to synthesize and investigate 265Sg and 269,270,271Hs

Figure 1. Periodic Table of the Elements. The IUPAC acceptedtransactinide elements 104 through 111 shall take the positions of theseventh period transition metals below Hf in group 4 and Au in group
11. While chemical studies have justified placing the elements Rf
through Hs into group 4 to 8 of the Periodic Table, the “chemicallyunknown” heavier elements (chemical symbols for “known” elements
and open symbols for yet unconfirmed reports) still need to be investigated. The arrangement of the actinides reflects that the firstactinide elements still resemble, to a decreasing extent, the chemistryof d-elements.

248

in reactions with Cm. While the main emphasis in the Sg
experiments7,8 was to unravel chemical properties of Sg, recent
Hs experiments exploited the unique and very clean Hs chemistry to study nuclear reaction and nuclear structure aspects.
The rotating 248Cm target wheel ARTESIA1 was irradiated withhigh intense 26Mg beams at five different energies between Elab=130 MeV and 150 MeV covering the range from below the
maximum of the 4n channel producing the new isotope 270Hs(Reference 17) to an energy well beyond the maximum of the
5n channel (269Hs). Measured cross sections are in good agreement with calculations using the code HIVAP.18 At the lower
irradiation energies, surprisingly enough, evidence for theobservation of 271Hs — produced in the 3n-evaporation channel(!) — was obtained.17 Most interesting, the decay of these Hs
isotopes — their α-decay energies and partial SF half-lives —allows for a crucial test of theoretical model predictions of theN = 162 neutron-shell strength. The deduced Qα -value17 of the
doubly-magic 270Hs162 is in good agreement with macroscopicmicroscopic model predictions.19 In addition, also the decay
properties of the Sg isotopes, observed as the Hs α -decay
daughter nuclides, provide important data for this comparison.
Most recently, a 25 Mg beam was used in a search for the
unknown isotope 268 Hs. The sensitivity of this chemistry
experiment was well below one picobarn for an assumed 268Hs
half-life of one second or longer.
3. Chemical Properties of Superheavy Elements
After the first chemical studies have shown that Rf and Db
are transactinides and member of group 4 and 5 of the Periodic
Table (see Figure 1), more detailed chemical studies were performed over the last two decades; see References 1–4 for acomprehensive summary. It soon became clear that simple
extrapolations of chemical properties within a given group ofelements in the Periodic Table are not trustworthy. Especially
Rf and Db exhibit chemical properties which are often verymuch different from extrapolations in group 4 and 5. Studies
in the liquid phase, which concentrated on the aspects of hydrolysis and complex formation, were mainly performed in pureand mixed mineral acid solutions. First detailed studies of Db
in mixed HCl/HF solutions yielded a surprisingly non-Ta-likebehavior.20 Only subsequent experiments,21 which were carriedout in pure acid solutions, showed a Db behavior in agreementwith theoretical predictions22 including relativistic effects. In
recent years, the aqueous phase behavior of Rf was investigatedin greater detail 5, 6 , 2 3, 2 4 using first the Automated Rapid
Chemistry Apparatus (ARCA) 25 and most recently the much
more advanced AIDA 23,26 which includes automated sample
preparation and transfer of the sample into the detector chamber. For the first time, this allowed to measure a Rf elution
curve.24 A number of surprising results were obtained in a large
number of detailed Rf studies; e.g., the fluoride complexation6
of Rf revealed stunning differences between Rf and Zr and Hf.
These kind of experimental findings still remain a challenge
for theoretical model descriptions.
Aqueous chemistry with ARCA has reached Sg for which
only two very basic chromatographic studies exist;7,8,27 both
performed with a cation-exchange resin. The one carried out
with 0.1 M HNO3/5 × 10 –4 M HF showed that Sg elutes within
10 s from a 1.6 × 8 mm cation-exchange column (Aminex A6,
17.5 ± 2 µm). Therefore, under these conditions Sg behaves
similarly to Mo and W in group 6 of the Periodic Table anddistinctively different from hexavalent U which forms uranylions.27 This return to an expected behavior — after all the surprises with Rf and Db chemistry — was termed occasionally“oddly ordinary seaborgium.” However, this does NOT allow a
statement like “seaborgium reaffirms periodic table’s predictive ability.” As not only relativistic effects but also othereffects, like shell effects, on the atomic and molecular electronsSuperheavy Element Chemistry — Achievements and Perspectives

can cancel each other with the result of surprisingly similar
properties — or, in other cases, they can all act in such a direction that strong deviations from expected properties can beobserved. Already the second Sg experiment,8 which was performed in pure 0.1 M HNO3, indicated a non-W-like behaviorof Sg. Contrary to W, Sg was not eluted from the cationexchange column. From this, it was concluded that neutral oranionic oxofluoride complexes like SgO2 F 2 or SgO2 F 3 – werelikely to be formed and eluted in the first experiment. Without
the presence of complexing fluoride anions Sg was retained on
the resign in cationic form, presumably, as Sg(OH) 4(H2O)22+ or
SgO(OH)3(H2O)2+ present in dilute HNO3 due to the lower tendency of Sg to hydrolyze28 as compared to that of W.
The recent success in SHE chemistry in the liquid phase andin the gas phase was only feasible because of an enormous
progress in many fields to meet a large number of physical,
chemical, technological, and metrological challenges. Intenseand stable heavy ion beams became available and technologies
like the rotating target wheel ARTESIA1 were developed tostand high heat loads on windows, actinide target, and backings. In recent experiments at the GSI, e.g., Mg beams were
produced from the ECR source with very low consumption of
0.5 mg/h or less of isotopically enriched material. This made“pulse” beam intensities of 4 × 1013 particles per second available in the 5-ms long UNILAC macropulse. At a 50 Hz repetition rate this corresponds to 1.5 particle-µA DC beam. With
these high beam intensities traditional He/cluster-jet transportsystems reach their limits and become inefficient as transportyields sharply drop. Not only to circumvent these problems but
to exploit a number of advantages, the formation of a volatileoxide directly in the recoil chamber and its transport to a combined chemistry and detector device29,30 was applied in all Hs
experiments.9,10,17 Before, gas-adsorption chromatographic studies of the lighter transactinides were mainly performed withvolatile halide or oxohalide complexes formed in a remote reaction chamber after a cluster-jet transport; see Reference 31 for acompilation.
Two kinds of gas-adsorption experiments have been performed with HsO4 (References 9 and 10) both showing a typical group 8 behavior of Hs. Firstly and typical for its lighter
homologue Os, all experiments demonstrated, as expected,32
the formation of a stable and at room temperature volatile
tetroxide of Hs in an oxygen containing gaseous environment.
However, in the thermochromatographic experiments9 — inwhich the deposition temperature of Os and Hs compounds
was measured by registering characteristic α-decays in detector arrays mounted along a temperature gradient — a theoretically unexplained32 higher adsorption temperature — or lower
volatility — was measured for HsO4 in comparison with OsO4.
From the observation of seven molecules of HsO 4 and theiradsorption position at (–44 ± 6) °C, in comparison with the oneof OsO 4 at (–82 ± 7) °C, the following adsorption enthalpies(∆Ha°) on silicon nitride were deduced from the first Hs experiment: 9 –∆H a° (T ) (HsO 4 ) = (46 ± 2) kJ/mol for HsO 4 and –∆H a° (T ) (OsO 4 ) = (39 ± 1) kJ/mol for OsO 4 . Although thedifference between the theoretically predicted 32 and experimentally observed and recently confirmed HsO 4 volatility issmall on an absolute scale of adsorption temperatures it
remains unclear why the inverse order of volatilities HsO 4 <OsO4 is observed experimentally as compared with the theoretical prediction OsO4 ≤ HsO4. Most recently, a Hs-chemistry
experiment showed that a sub-picobarn cross section limit canbe reached in superheavy element chemistry — a crucial prerequisite to explore the chemistry of SHE in the region aroundelement 114.
As in the preceding experiment, also in the second Hs
experiment10 tetroxides were formed in a recoil chamber and inits hot (600 °C) outlet section. Contrary to the preceding
experiment, which had to meet the challenge of using very dry

J. Nucl. Radiochem. Sci., Vol. 8, No. 2, 2007

49

gases to avoid early ice formation in the cold part of the detector, in this second experiment water was added (2 g H2O per kg
gas) to the O2 containing He. Within 3–4 s volatile products
were transported to a set of four detector boxes kept at room
temperature. Each box contained a linear array of four PINdiode detectors facing at a NaOH coated stainless steel plate.
Computer controlled, always three detector boxes in a row were
measuring while the fourth box was refurbished and freshly
prepared NaOH was mounted. Simultaneously produced andtransported OsO4 was used as a monitor. Due to the formationof an osmate (VIII) with the chemically reactive NaOH surface
more than 50% of the Os is found in front of detector one andthe rest exhibits a significant tailing. Six decay chains of Hs,
centered at detector number three, were detected in the first
five detectors.10 The low statistics does not allow drawing any
conclusion about a possible lower reactivity of the HsO 4 ascompared to OsO4. However, the observation (i) confirms theformation and stability of the volatile HsO4 compound, and (ii)shows the similarity in chemical reactivity between HsO4 andOsO 4. Presumably, the deposition of Hs is, in analogy to awell-known behavior of Os, the result of the formation of a hassate (VIII) according to: 2NaOH + HsO4 → Na2 [HsO4 (OH) 2].
For the first time, an acid-base chemical reaction was performed with HsO4.
Recent attempts to get a first glimpse on the chemistry ofelement 112 are most exciting and most challenging. Since themid-70’s possible chemical properties of element 112 haveattracted a lot of attention, mainly because of strong relativistic
effects and the 6d107s2 closed-shell configuration. Very earlyon, especially the question how closely element 112 would
resemble the chemistry of Hg — its lighter homologue in group
12 — was in the focus; see Reference 33 for a summary of
early theoretical works. A wide span of volatilities has been
predicted for element 112. One group of predictions is basedon theoretical model calculations including relativistic
effects33–35 while others rest on empirical extrapolations.36,37
While earlier predictions did not exclude a highly volatile andchemically inert element 112, possibly even resembling aninert gas like behavior,34 recent calculations are discussing amore Hg-like behavior35 but still with a higher volatility for element 112. A very recent fully-relativistic treatment of theinteraction of element 112 with metallic surfaces such as Au
and Pd predicts weaker adsorption of 112 than Hg on these
metals.35 These calculations predict that the adsorption temperature of element 112 on (ideal) Au surfaces will be 93 K below
the one for Hg. In addition it is pointed out that element 112
will form some metal-metal bonding with Au and, therefore,
element 112 will adsorb at much higher temperatures than Rn.
Adsorption enthalpies of element 112 on metal surfaces
obtained from an empirical model also indicate a weak chemical bond formed on Au surfaces and a “volatile noble metal”
character of element 112 was predicted.36–38 The element 112
volatility was expected to be much higher than that of Hg.
Recent experiments11,39 on element 112 constitute a transition
from a more traditional approach in SHE chemistry — to forma chemical compound and chemically investigate this compound — to studies of an element in its atomic state. However,
several experiments to study the volatility of element 112 in its
atomic state gave partially controversial and inconclusive
results.11,39 Still unpublished, a most recent press release12
claims a successful chemical separation and identification ofelement 112. Unfortunately, a number of controversial
reports11,16,40–43 from different experiments about the cross section to synthesize 283112 in the 48Ca on 238U reaction and about
the nuclear decay properties of 283112 leave parts of the scientific community in a state of confusion; see Table 1 for a summary.
After first chemistry experiments39 performed at the FLNR
an international collaboration carried out a second series of

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SchädelJ. Nucl. Radiochem. Sci., Vol. 8, No. 2, 2007

TABLE 1: Experiments to synthesize 283112 in the 48Ca + 238U reaction and their results
Eproj / MeV
Events assigned to 283112 E α / MeV(middle of target)
α ; SF
or SF
231
238
231
234

0;2
0:0
0;0
0;2

SF
–
–
SF

233

0;7

SF

230
234
230
236
233
236
239
231
235

TechniqueHalf-life

VASSILISSA(1.4+2.5–0.5 ) mine(5.1+3.5–1.5 ) min

5.0+6.3
–3.2
<7.3
<2.2
3.0+4.0–2.0“Rn-like” chemistry>3 min assumed f

2.0+0.9
–0.7

DGFRS

3.4 s
(4.0+1.3–0.7 ) s+1.2
0.5–0.4
2.5+1.8–1.1
b

VASSILISSA

g

0 ; (1)4 ; (2) g
0;0
0;0
0;0
0 ; (1) h
0;0
–;0
–;0
0;0
0;0

9.54
–
–
–
SF
–
–
–
–
–

Cross sectiona
Reference
/ pb

BGS
SHIP

h
(5.2+25.1–2.4 ) s“Hg-like” chemistry“Rn-like” chemistry“Hg-like” chemistry“Rn-like” chemistry

5 min (SF) assumed f
5 min (SF) assumed f
4 s (α) f ; 5 min (SF) f
4 s (α) f ; 5 min (SF) f<0.8 , <1.6c<0.96b, <2.0c<0.8b+1.6 h
(0.7–0.6
)
<0.6b
<0.8d
<1.9d
<2.3d ; <1.7d<2.7d ; <7.6d

40
41
39
16
43
42

11

a

Error bars and upper limit sensitivities at 68% c.i. if not otherwise specified.
“One-event” limits without statistical fluctuation.
cUpper limit sensitivity at 84% c.i.
dUpper limit sensitivity at 95.45% c.i.
eMean value including previously observed events.
f
T1/2 not measured in chemistry experiment, for cross section calculation assumed T1/2.
gInterpreted as SF from the daughter nucleus after missing the α-event from the mother decay.
h
No assignment made to a specific isotope.
bexperiments at the GSI.11 The 48Ca on 238U reaction was selected
to produce 283112. Simultaneously, 220 Rn was produced as atransfer product from U and 184–186Hg from small amounts of
Nd in the target. These experiments were aiming at measuring
the adsorption behavior of element 112 in comparison with Hg
and Rn on Au. Along the Au surface, a temperature gradientfrom +35 °C to about –185 °C was established in a modified
version of the Cryo On-Line Detector (COLD), which was successful in the Hs experiment.9 A schematic view of this setup is
shown in Figure 2. In the first somewhat slow GSI experiment,
concentrating on a then believed 5-min SF decay for 283112, a
Au-catcher was facing an array of 32 silicon PIN-diodes.
Although some events were observed which could have beeninterpreted as SF from 283112 small imperfections and open

questions led the international collaboration agree to first
repeat this experiment under improved conditions to substantiate the findings. An improved version was developed andapplied in the second experiment which allows measuringmuch more efficiently in (almost) 4 π -geometry.11 Further
improvements made the second experiment also much moresensitive to shorter half-lives in the region of a few seconds.
Also the second experiment, which in addition to longer-lived
SF decays concentrated on shorter-lived α-SF-decay sequences,
did not detect any decay pattern which could be unambiguously
attributed to a superheavy element over a broad range ofadsorption properties between its group 12 homologue Hg andthe noble gas Rn. The upper limit sensitivity levels reached inboth GSI experiments are listed in Table 1 for two different
assumed decay modes and half-lives and for two different
assumed volatilities. The levels reached in these experiments
are not low enough to clarify contradictions between previously
published results on the cross section and on the decay of
283
112.
4. Perspectives

Figure 2. Schematic view of the experimental set up used in the firstexperiment on element 112 at the GSI. The upper left part depicts theIn-situ Volatilization (IVO) part attached to the rotating target wheel.
It is coupled to the Cryo On-Line Detector (COLD) with its Si PINdiodes monitoring the opposite Au-coated side of the thermochromatographic channel. Figure from Reference 1.

Many of the very successful experiments on the chemistryof SHE at the same time clearly demonstrated limits of theapplied techniques. A totally new quality of chemical studies
is on the horizon when combining chemical techniques with
gas-filled recoil separators. They are ideal front-end tool toovercome the unwanted interaction of the primary heavy-ion
beam with anything present in the recoil chamber and to preseparate unwanted nuclear reaction products. Ground-breaking
experiments began at the Berkeley Gas-filled Separator13,14(BGS). Coupled to the BGS, the first Rf separation withSISAK,13,44 which is a fast and continuously operating liquidliquid extraction technique, was successful. Preseparated 4.7-s
257
Rf was stopped in the gas of a Recoil Transfer Chamber14,30

Superheavy Element Chemistry — Achievements and Perspectives(RTC) — the key interface with a thin window between the gas
filled separator and any chemistry set up — and was transported via a He/KCl-jet to the SISAK system. The α decay of257
Rf was registered on-line with a rather unspecific liquidscintillator being part of the flowing organic phase. Though
resolution is very low preseparation enabled a clear Rf identification. The SISAK technique in combination with preseparation allows further improvements to study the extraction
behavior of even heavier elements in aqueous solution. Under
development are also alternative approaches like the use ofcrown ethers45 to widen the scope of chemical investigations or
to extend the studies of SHE in aqueous solution beyond Sg.
For this region electrochemical deposition techniques are underpreparation. In addition, in the field of SHE chemistry previously unknown, completely new techniques and compounds
will become accessible in gas-phase experiments; e.g., the useof organometallic compounds,46 when performing chemical
reactions with preseparated SHE to produce and investigate
volatile species.
Most recently, the TransActinide Separator and Chemistry
Apparatus47 (TASCA) was built at the GSI and a large international community is presently commissioning all componentsof the separator and its peripheral components. The goal ofbuilding TASCA was to provide the community with a gasfilled separator with maximized transmission (efficiency) for
transactinide research making use of hot-fusion reactions andactinide targets to produce the most neutron-rich, longest-lived
nuclides. While chemical investigations of preseparated SHE
are in the focus and shall play a major role in the upcoming
program a rich nuclear reaction and nuclear structure researchis envisaged making use of TASCA. As it can be operated withdifferent gas fillings like, e.g., H2 or N2 as an alternative to He
as the standard gas, basic research on the interaction of slow
moving ions of the heaviest elements in different gases and thedetermination of their charge states may become an interesting
research aspect. Some central components of the 3.5-m longgas-filled separator TASCA use components from a former
separator.48 To optimize all components, ion-optical calculations49 were performed based on the model fusion reaction of
5–6 MeV/u 48Ca on 0.5 mg/cm 2 actinide targets (238U, 244Pu).
The DQQ configuration with a 30-degree dipole magnet and aquadrupole doublet, which was selected as the best choice,allows operation in two possible modes. While the DQ h Q v
mode gives the highest possible transmission the smallest
image size results from the DQ v Qh mode (Qh and Q v denotehorizontally and vertically focusing quadrupoles). New ducts
were designed, built and installed for the dipole and the quadr upoles to maximize the transmission in both modes.
According to first model calculations,47,49 a horizontal and vertical acceptance of about ±110 and ±40 mrad was achieved forthe “high transmission” DQhQv mode which corresponds to asolid angle of ≈14 msr. This is at least 50% higher as comparedwith the solid angle of the Dubna Gas-Filled Recoil Separator(DGFRS) which has a 35–40% transmission16,50 for the Ca on
Pu reaction. From this one can estimate that the TASCA transmission should be about 50% higher than the DGFRS one; i.e.,in the “high transmission” mode of TASCA we are expecting
up to 60% transmission for evaporation residues produced Ca
on U or Pu reactions. This is very similar to the best values
given for the BGS.43 TASCA will combine two advantages ofthese two separators, i.e., the large transmission of the BGS
and the small dispersion of the DGFRS. In the DQvQh mode, areduced horizontal acceptance of ±34 mrad will presumably
reduce the transmission by a factor of ≈0.6. However, an
extraordinarily small image area should be achievable — a key
issue to build small recoil transfer chambers for a fast transportof products into any chemistry setups and something uniquefor TASCA.47,49
To make use of the highest presently obtainable beam inten-

J. Nucl. Radiochem. Sci., Vol. 8, No. 2, 200751

sities at the UNILAC and the even higher intensities which will
become available with the implementation of a new 28 GHz
SC-ECR source in a few years, a windowless differential
pumping section was installed and is successfully in operation. 51 A new target chamber was designed and built whichaccommodates (i) the rotating actinide target wheel in an easily
removable cassette taking care of the safety aspects whileworking with highly radioactive material, (ii) the newly built
drive, (iii) collimators, and (iv) beam diagnostic components.
A beam current transformer upstream of the target shall allow
for continuous monitoring of the beam current. Equipped witha separator like TASCA and combining it with the tools whichwere developed over the last decade to study superheavy elements promises a big leap ahead and gives hope for a new quality in SHE research.
Acknowledgement. The author wishes to thank his groupmembers at the GSI for their support and contributions, his fellow colleagues who prepared, guided, and evaluated so many
experiments at the GSI, all participants in the very successful
and pleasant GSI-JAEA collaboration, especially Y. Nagame
and coworker, and all members of the TASCA collaboration
who are most actively working to get TASCA ready for SHE
experiments.
References(1) M. Schädel, Angew. Chem. 118, 378 (2006); Angew.
Chem. Int. Ed. 45, 368 (2006).
(2) The Chemistry of Superheavy Elements, Ed. M. Schädel,Kluwer Academic Publishers, Dordrecht (2003).
(3) J. V. Kratz, Pure Appl. Chem. 75, 103 (2003).
(4) D. C. Hoffman, D. M. Lee, and V. Pershina, The Chemistryof the Actinide and Transactinide Elements, 3rd ed. Vol. 3,
Eds. L. R. Morrs, N. M. Edelstein, and J. Fuger, Springer,
Dordrecht (2006), p 1652.
(5) Y. Nagame, K. Tsukada, M. Asai, A. Toyoshima, K.
Akiyama, Y. Ishii, T. Kaneko-Sato, M. Hirata, I. Nishinaka,
S. Ichikawa, H. Haba, S. Enomoto, K. Matsuo, D.. Saika,
Y. Kitamoto, H. Hasegawa, Y. Tani, W. Sato, A. Shinohara,
M. Ito, J. Saito, S. Goto, H. Kudo, H. Kikunaga, N.
Kinoshita, A. Yokoyama, K. Sueki, Y. Oura, H. Nakahara,
M. Sakama, M. Schädel, W. Brüchle, and J. V. Kratz,
Radiochim. Acta 93, 519 (2005).
(6) H. Haba, K. Tsukada, M. Asai, A. Toyoshima, K. Akiyama,
I. Nishinaka, M. Hirata, T. Yaita, S. Ichikawa, Y. Nagame,K. Yasuda, Y. Miamoto, T. Kaneko, S. Goto, S. Ono, T.
Hirai, H. Kudo, M. Shigekawa, A. Shinohara, Y. Oura, H.
Nakhara, K. Sueki, H. Kikunaga, N. Kinoshita, N. Tsuruga,
A. Yokoyama, M. Sakama, S. Enomoto, M. Schädel, W.
Brüchle, and J. V. Kratz, J. Am. Chem. Soc. 126, 5219
(2004).
(7) M. Schädel, W. Brüchle, R. Dressler, B. Eichler, H. W.
Gäggeler, R. Günther, K. E. Gregorich, D. C. Hoffman, S.
Hübener, D. T. Jost, J. V. Kratz, W. Paulus, D. Schumann,
S. Timokhin, N. Trautmann, A. Türler, G. Wirth, and A.
Yakushev, Nature 388, 55 (1997).
(8) M. Schädel, W. Brüchle, E. Jäger, B. Schausten, G. Wirth,
W. Paulus, R. Günther, K. Eberhardt, J. V. Kratz, A.
Seibert, E. Strub, P. Thörle, N. Trautmann, A. Waldeck, S.
Zauner, D. Schumann, U. Kirbach, B. Kubica, R. Misiak,
Y. Nagame, and K. E. Gregorich, Radiochim. Acta 83, 163(1998).
(9) Ch. Düllmann, W. Brüchle, R. Dressler, K. Eberhardt, B.
Eichler, R. Eichler, H. W. Gäggeler, T. N. Ginter, F. Glaus,
K. E. Gregorich, D. C. Hofmann, E. Jäger, D. T. Jost, U.
W. Kirbach, D. M. Lee, H. Nitsche, J. B. Patin, V. Pershina,
D. Piquet, Z. Qin, M. Schädel, B. Schausten, E. Schimpf,
H.-J. Schött, S. Soverna, R. Sudowe, P. Thörle, S. N.

52

J. Nucl. Radiochem. Sci., Vol. 8, No. 2, 2007

Timokhin, N. Trautmann, A. Türler, A. Vahle, G. Wirth, A.
B. Yakushev, and P. Zielinski, Nature 418, 859 (2002).
(10) A. von Zweidorf, R. Angert, W. Brüchle, S. Bürger, K.
Eberhardt, R. Eichler, H. Hummrich, E. Jäger, H.-O. Kling,
J. V. Kratz, B. Kuczewski, G. Langrock, M. Mendel, U.
Rieth, M. Schädel, B. Schausten, E. Schimpf, P. Thörle, N.
Trautmann, K. Tsukada, N. Wiehl, and G. Wirth,Radiochim. Acta 92, 855 (2004).
(11) R. Eichler, W. Brüchle, R. Buda, S. Bürger, R. Dressler,
Ch. E. Düllmann, J. Dvorak, K. Eberhardt, B. Eichler, C.
M. Folden, H. W. Gäggeler, K. E. Gregorich, F. Haenssler,
D. C. Hoffman, H. Hummrich, E. Jäger, J. V. Kratz, B.
Kuczewski, D. Liebe, D. Nayak, H. Nitsche, D. Piguet, Z.
Qin, U. Rieth, M. Schädel, B. Schausten, E. Schimpf, A.
Semchenkov, S. Soverna, R. Sudowe, N. Trautmann, P.
Thörle, A. Türler, B. Wierczinski, N. Wiehl, P. A. Wilk, G.
Wirth, A. B. Yakushev, and A. von Zweidorf, Radiochim.
Acta 94, 181 (2006).
(12) H. W. Gäggeler and R. Eichler (private communication,2006); PSI press release (in German), May 31, 2006: http://
www.psi.ch/medien/medien-news.shtml; Reference addedin proof: R. Eichler, N. V. Aksenov, A. V. Belozerov, G. A.
Bozhikov, V. I. Chepigin, R. Dressler, S. N. Dmitriev, H.
W. Gäggeler, V. A. Gorshkov, F. Haenssler, M. G. Itkis, V.
Ya. Lebedev, A. Laube, O. N. Malyshev, Yu. Ts.
Oganessian, O. V. Petrushkin, D. Piguet, P. Rasmussen, S.
V. Shishkin, A. V. Shutov, A. I. Svirikhin, E. E. Tereshatov,
G. K. Vostokin, M. Wegrzecki, and A. V. Yeremin, Nature
447, 72 (2007).
(13) J. P. Omtvedt, J. Alstad, H. Breivik, J. E. Dyne, K.
Eberhardt, C. M. Folden III, T. Ginter, K. E. Gregorich, E.
A. Hult, M. Johansson, U. W. Kirbach, D. M. Lee, M.
Mendel, A. Nähler, V. Ninov, L. A. Omtvedt, J. B. Patin, G.
Skarnemark, L. Stavsetra, R. Sudowe, N. Wiehl, B.
Wierczinski, P. A. Wilk, P. M. Zielinski, J. V. Kratz, N.
Trautmann, H. Nitsche, and D. C. Hoffman, J. Nucl.
Radiochem. Sci. 3, 121 (2002).
(14) Ch. E. Düllmann, C. M. Folden III, K. E. Gregorich, D. C.
Hoffman, D. Leitner, G. K. Pang, R. Sudowe, P. M.
Zielinski, and H. Nitsche, Nucl. Instrum. Methods Phys.
Res. A 551, 528 (2005).
(15) M. Schädel, D. Ackermann, A. Semchenkov, and A. Türler,
GSI Report 2006-1, 262 (2006); http://www.gsi.de/tasca.
(16) Yu. Ts. Oganessian, V. K. Utyonkov, Yu. V. Lobanov, F. Sh.
Abdullin, A. N. Polyakov, I. V. Shirokovsky, Yu. Ts.
Tsyganov, G. G. Gulbekian, S. L. Bogomolov, B. N. Gikal,
A. N. Metsentsev, S. Iliev, V. G. Subbotin, A. M. Sukhov,
A. A. Voinov, G. V. Buklanov, K. Subotic, V. I. Zagrebaev,
M. G. Itkis, J. J. Patin, K. J. Moody, J. F. Wild, M. A.
Stoyer, N. J. Stoyer, D. A. Shaughnessy, J. M. Kenneally, P.
A. Wilk, R. W. Lougheed, R. I. Il’kaev, and S. P.
Vesnovskii, Phys. Rev. C 70, 064609 (2004).
(17) J. Dvorak, W. Brüchle, M. Chelnokov, R. Dressler, C. E.
Duellmann, K. Eberhardt, V. Gorshkov, E. Jäger, R.
Krücken, A. Kuznetsov, Y. Nagame, F. Nebel, Z.
Novackova, Z. Qin, M. Schädel, B. Schausten, E. Schimpf,
A. Semchenkov, P. Thörle, A.Türler, M. Wegrzecki, B.
Wierczinski, A. Yakushev, and A. Yeremin, Phys. Rev. Lett.
97, 242501 (2006).
(18) W. Reisdorf and M. Schädel, Z. Phys. A 343, 47 (1992).
(19) I. Muntian, S. Hofmann, Z. Patyk, and A. Sobiczewski,
Acta Phys. Pol. B 34, 2073 (2003).
(20) J. V. Kratz, H. P. Zimmermann, U. W. Scherer, M. Schädel,W. Brüchle, K. E. Gregorich, C. M. Gannet, H. L. Hall, R.
A. Henderson, D. M. Lee, J. D. Leyba, M. J. Nurmia, D. C.
Hoffman, H. Gäggeler, D. Jost, U. Baltensperger, Ya NaiQi, A. Türler, and Ch. Lienert, Radiochim. Acta 48, 121(1989).
(21) W. Paulus, J. V. Kratz, E. Strub, S. Zauner, W. Brüchle, V.

SchädelPershina, M. Schädel, B. Schausten, J. L. Adams, K. E.
Gregorich, D. C. Hoffman, M. R. Lane, C. Laue, D. M.
Lee, C. A. McGrath, D. A. Shaughnessy, D. A. Strellis, andE. R. Sylwester, Radiochim. Acta 84, 69 (1999).
(22) V. Pershina, B.Fricke, J. V. Kratz, and G. V. Ionova,
Radiochim. Acta 64, 37 (1994).
(23) H. Haba, K. Tsukada, M. Asai, S. Goto, A. Toyoshima, I.
Nishinaka, K. Akiyama, M. Hirata, S. Ichikawa, Y.
Nagame, Y. Shoji, M. Shigekawa, T. Koike, M. Iwasaki, A.
Shinohara, T. Kaneko, T. Maruyama, S. Ono, H. Kudo, Y.
Oura, K. Sueki, H. Nakahara, M. Sakama, A. Yokoyama,
J.V. Kratz, M. Schädel, and W. Brüchle, J. Nucl.
Radiochem. Sci. 3, 143 (2002).
(24) A. Toyoshima, H. Haba, K. Tsukada, M. Asai, K. Akiyama,
I. Nishinaka, Y. Nagame, K. Matsuo, W. Sato, A.
Shinohara, H. Ishizu, M. Ito, J. Saito, S. Goto, H. Kudo, H.
Kikunaga, C. Kato, A. Yokoyama, and K. Sueki, J. Nucl.
Radiochem. Sci. 5, 45 (2004).
(25) M. Schädel, W. Brüchle, E. Jäger, E. Schimpf, J. V. Kratz,
U. W. Scherer, and H. P. Zimmermann, Radiochim. Acta
48, 171 (1989).
(26) Y. Nagame, H. Haba, K. Tsukada, M. Asai, K. Akiyama,
M. Hirata, I. Nishinaka, S. Ichikawa, H. Nakahara, S. Goto,
T. Kaneko, H. Kudo, A. Toyoshima, A. Shinohara, M.
Schädel, J. V. Kratz, H. W. Gäggeler, and A. Türler, Czech.
J. Phys. 53, A299 (2003).
(27) M. Schädel, W. Brüchle, B. Schausten, E. Schimpf, E.
Jäger, G. Wirth, R. Günther, J. V. Kratz, W. Paulus, A.
Seibert, P. Thörle, N. Trautmann, S. Zauner, D. Schumann,
M. Andrassy, R. Misiak, K. E. Gregorich, D. C. Hoffman,
D. M. Lee, E. Sylwester, Y. Nagame, and Y. Oura,Radiochim. Acta 77, 149 (1997).
(28) V. Pershina and J. V. Kratz, Inorg. Chem. 40, 776 (2001).
(29) Ch. Düllmann, B. Eichler, R. Eichler, H. W. Gäggeler, D.
T. Jost, D. Piquet, and A. Türler, Nucl. Instrum. Methods
Phys. Res. A 479, 631 (2002).
(30) U. W. Kirbach, C. M. Folden III, T. N. Ginter, K. E.
Gregorich, D. M. Lee, V. Ninov, J. P. Omtvedt, J. B. Patin,
N. K. Seward, D. A. Strellis, R. Sudowe, A. Türler, P. A.
Wilk, P. M. Zielinski, D. C. Hofmann, and H. Nitsche,Nucl. Instrum. Methods Phys. Res. A 484, 587 (2002).
(31) H. W. Gäggeler and A. Türler, The Chemistry ofSuperheavy Elements, Ed. M. Schädel, Kluwer Academic
Publishers, Dordrecht (2003), p 237.
(32) V. Pershina, T. Bastug, B. Fricke, and S. Varga, J. Chem.
Phys. 115, 792 (2001).
(33) B. Fricke, Struct. Bond. 21, 89 (1975).
(34) K. S. Pitzer, J. Chem. Phys. 63, 1032 (1975).
(35) V. Pershina, T. Bastug, C. Sarpe-Tudoran, J. Anton, and B.
Fricke, Nucl. Phys. A 734, 200 (2004).
(36) B. Eichler, Kernenergie 19, 307 (1976).
(37) B. Eichler and H. Rossbach, Radiochim. Acta 33, 121(1983).
(38) B. Eichler and R. Eichler, The Chemistry of Superheavy
Elements, Ed. M. Schädel, Kluwer Academic Publishers,
Dordrecht (2003), p 205.
(39) A. B. Yakushev, I. Zvara, Yu. Ts. Oganessian, A. V.
Belozerov, S. N. Dmitriev, B. Eichler, S. Hübener, E. A.
Sokol, A. Türler, A. V. Yeremin, G. V. Buklanov, M. L.
Chelnokov, V. I. Chepigin, V. A. Gorshov, A. V. Gulyaev, V.
Ya. Lebedev, O. N. Malyshev, A. G. Popeko, S. Soverna, Z.
Szeglowski, S. N. Timokhin, S. P. Tretyakova, V. M. Vasko,
and M. G. Itkis, Radiochim. Acta 91, 433 (2003).
(40) Yu. Ts. Oganessian, A. V. Yeremin, G. G. Gulbekian, S. L.
Bogomolov, V. I. Chepigin, B. L. Gikal, V. A. Gorshkov,
M. G. Itkis, A. P. Kabachenko, V. B. Kutner, A. Yu.
Lavrentev, O. N. Malyshev, A. G. Popeko, J. Roháchecka,
R. N. Sagaidak, S. Hofmann, G. Münzenberg, M. Veselsky,
S. Saro, N. Iwasa, and K. Morita, Eur. Phys. J. A 5, 63

Superheavy Element Chemistry — Achievements and Perspectives(1999).
(41) Yu. Ts. Oganessian, A. V. Yeremin, A. G. Popeko, O. N.
Malyshev, A. V. Belozerov, G. V. Buklanov, M. L.
Chelnokov, V. I. Chepigin, V. A. Gorshkov, S. Hofmann,
M. G. Itkis, A. P. Kabachenko, B. Kindler, G. Münzenberg,
R. N. Sagaidak, Š. Šáro, H.-J. Schött, B. Štreicher, A. V.
Shutov, A. I. Svirikhin, and G. K. Vostokin, Eur. Phys. J. A
19, 3 (2004).
(42) S. Hofmann, D. Ackermann, S. Antalic, H. G. Burkhard, R.
Dressler, F. P. Heßberger, B. Kindler, I. Kojouharov, P.
Kuusiniemi, M. Leino, B. Lommel, R. Mann, G.
Münzenberg, K. Nishio, A. G. Popeko, S. Saro, H. J.
Schött, B. Streicher, B. Sulignano, J. Uusitalo, and A. V.
Yeremin, J. Nucl. Radiochem. Sci. 7, R25 (2006).
(43) K. E. Gregorich, W. Loveland, D. Peterson, P. M. Zielinski,
S. L. Nelson, Y. H. Chung, Ch. E. Düllmann, C. M. Folden
III, K. Aleklett, R. Eichler, D. C. Hoffman, J. P. Omtvedt, G.
K. Pang, J. M. Schwantes, S. Soverna, P. Sprunger, R.
Sudowe, R. E. Wilson, and H. Nitsche, Phys. Rev. C 72,
014605 (2005).
(44) L. Stavsetra, K. E. Gregorich, J. Alstad, H. Breivik, K.
Eberhardt, C. M. Folden III, T. N. Ginter, M. Johansson, U.
W. Kirbach, D. M. Lee, M. Mendel, L. A. Omtvedt, J. B.
Patin, G. Skarnemark, R. Sudowe, P. A. Wilk, P. M.
Zielinski, H. Nitsche, D. C. Hoffman, and J. P. Omtvedt,
Nucl. Instrum. Methods Phys. Res. A 543, 509 (2005).

J. Nucl. Radiochem. Sci., Vol. 8, No. 2, 200753(45) R. Sudowe, M. G. Calvert, Ch. E. Düllmann, L. M. Farina,
C. M. Folden III, K. E. Gregorich, S. E. H. Gallaher, D. C.
Hoffman, S. L. Nelson, D. C. Phillips, J. M. Schwantes, R.
E. Wilson, P. M. Zielinski, and H. Nitsche, Radiochim.
Acta 94, 123 (2006).
(46) Ch. E. Düllmann, Czech. J. Phys. (in press, 2006).
(47) M. Schädel, D. Ackermann, A. Semchenkov, and A. Türler
for the TASCA collaboration, GSI Report 2006-1, 262(2006). In addition, information on the TASCA project,general information on this community and links to a large
number of related workshop contributions can be found at:
http://www.gsi.de/tasca.
(48) V. Ninov, P. Armbruster, F. P. Heßberger, S. Hofmann, G.
Münzenberg, Y. Fujita, M. Leino, and A. Lüttgen, Nucl.
Instrum. Methods Phys. Res. A 357, 486 (1995).
(49) A. Semchenkov, W. Brüchle, E. Jäger, E. Schimpf, M.
Schädel, A. Türler, A. Yakushev, and K. E. Gregorich, GSI
Report 2005-1, 332 (2005).
(50) K. Subotic, Yu. Ts. Oganessian, V. K. Utyonkov, Yu. V.
Lobanov, F. Sh. Abdullin, A. N. Polyakov, Yu. S. Tsyganov,and O. V. Ivanov, Nucl. Instrum. Methods Phys. Res. A
481, 71 (2002).
(51) A. Semchenkov, W. Brüchle, E. Jäger, E. Schimpf, M.
Schädel, A. Türler, and A. Yakushev, GSI Report 2006-1,
264 (2006).