Prospects for the Discovery of the
Next New Element, C. Folden, Cyclotron
Institute, Texas A&M University, College Station, Texas USA
− Currently,
fusion-evaporation reactions are the preferred method for
producing the
heaviest elements.These
reactions
involve the complete fusion of the projectile and target into a
thermally
equilibrated compound nucleus in a complex process.The cross sections for
these reactions have
been described by the product of three factors: the cross section
for capture
of the projectile by the target, the probability of forming the
compound
nucleus (PCN), and the probability that the compound nucleus
“survives” against
fission (Wsur).Experiments
are
currently underway worldwide to discover element 120, but the
projectile
which will result in the largest production cross section has not
been
determined.These
element discovery
experiments rely on projectiles heavier than 48Ca, and their
success likely
depends on the magnitude of the decrease in PCN and Wsur when
using these
heavier projectiles.At
the Texas
A&M University Cyclotron Institute, we have begun to
investigate the effect
of projectile atomic number on reaction cross section.Initial experiments have
focused on using
lighter systems as models for new element synthesis by carefully
choosing the
projectile and target so that the projectile energy relative to
the Coulomb
barrier and the resulting excitation energy are comparable to
those expected in
much heavier systems.The
data suggest
that the production of spherical ground-state nuclei is heavily
suppressed by
the large increase in level density that occurs if these nuclei
deform during the
de-excitation process.These
deformations
result in an increase in the probability of fission and a
substantial decrease
in Wsur.These
data suggest
that the reactions which could be used to discover new elements
may have peak
cross sections much less than 1 pb, and may be below the current
limits of
experimental sensitivity.This
talk will
highlight these issues as they relate to the discovery of new
elements.