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Superheavy elements
The existence of SuperHeavy Elements (SHE) is based
on nuclear structure effects. Shell stabilization creates a
barrier against spontaneous fission, which would otherwise
terminate the periodic table just above Z = 100. The
effect of repulsive Coulomb forces and nuclear attraction
delicately balance each other in the region of SHE. Level
densities are high and nucleonic orbitals with high and
low angular momentum occur close together near the
Fermi energy. Small shell gaps may cause shape changes
such that nuclear deformed states may coexist. These
are the main reasons why nuclear-structure effects play
an especially important role in this region. They may also
have a decisive influence on the possibility of producing
these nuclei in fusion reactions. Present SHE research
goes far beyond synthesis studies. It builds on a large
variety of tools and methods, which allow the atomic,
nuclear and chemical properties of SHE to be studied.
Highlights of recent work include the synthesis of elements
up to Cn (Z = 112) and element Z = 114 at GSI. The
chemical study of element 108 (Hs) led to the discovery
of deformed doubly magic 270 Hs. At Dubna new elements
up to Z = 118, produced in complete fusion reactions of
48 Ca projectiles with radioactive transuranium isotopes
as targets, have been reported. They were consistently
assigned, but lack direct Z (and A) identification. Further
Box 3. Superheavy elements
New elements
The long-standing quest for superheavy elements (SHE)
has led to exciting results during the past decade claiming
synthesis of elements up to Z = 118. Confirmation of
these results obtained in Dubna, synthesis of new elements
with Z > 118 and to reach the predicted neutron
shell closure at N = 184 will be the great challenges for
the next decade.
Masses and atomic structure
Masses of 252-254 No, 255 Lr were measured with
SHIPTRAP at GSI. The fundamental challenge is to
extend these mass measurements to neutron rich longlived
transactinides, which terminate the α-decay chains
starting at Z > 113, as well as investigating the complex
atomic structure of stored super-heavy nuclides by
means of laser spectroscopy.
Nuclear structure
Transfermium nuclei can be produced with crosssections
of > 10nb enabling in-beam and focal-plane
studies in tagging experiments. In addition to the
ground-state rotational band, bands built on high-K
isomers have been observed in 254 No and adjacent
nuclei, in experiments carried out at JYFL and GSI.
Chemistry
Strong relativistic effects on the electronic structure
of SHE make them extremely interesting objects for
chemical studies. Copernicium (Cn) is a noble metal
as its sublimation enthalpy and boiling point follow the
trend of the lighter group-12 elements towards high
volatility.
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