Above Z=50, the limits of proton excess are defined by the nuclei which
decay by emitting a proton. These so-called proton emitters have been
identified in odd-Z nuclei up to Bismuth (Z=83). A number of new proton
emitters have been identified recently using the FMA, and the lifetimes
in nearly all of these cases can be well reproduced if one assumes that
the nucleus is spherical. Recently, proton radioactivity has been
observed in ^141^Ho and ^131^Eu, however, the decay lifetimes for these
isotopes can only be understood if the nuclei are deformed. By studying
excited states built on top of proton emitters, one should be able to
independently confirm both the deformation and single-particle parentage
of the proton-emitting state. This is especially critical for the
deformed emitters where there are only a few known cases. In addition, a
study of the excited states in these nuclei provide detailed information
on the nuclear structure at the proton drip line, thus providing more
stringent tests of theoretical models. Due to extremely low production
cross-sections for making these proton emitters, excited states in these
nuclei have only been identified using the Recoil Decay Tagging
technique.

A number of proton-unbound systems have been studied with Gammasphere
and the FMA ranging from ^109^I to ^185^Bi. The case of ^141^Ho is
particularly interesting due to its anomalous proton half lives and
subsequent association with decays from a well-deformed system. Two
proton emitting states have been identified in ^141^Ho, and figure 1
shows the γ-ray spectra correlated with the proton decay of each state.
The cross-sections for producing these two states are very small, 300 nb
and 50 nb, respectively, or in other words, ^141^Ho is produced in only
1 out of 5,000,000 reactions between the beam and target nuclei!
Nevertheless, the sensitivity of the RDT technique has allowed for the
isolation of the γ decay for both states. The rotational bands built on
top of the proton emitting states is sketched in figure 2. The
deformation extracted for these bands agrees well with that inferred
from the proton-decay half lives, and the behavior of the bands as a
function of spin supports the original configuration assignments.

While the limits of proton excess are defined by the proton emitters,
these nuclei lie well beyond the proton drip line. Due to the
sensitivity of the proton half life to the spin of the proton emitting
state, the intrinsic structure of the state can be inferred. Because of
this fact, more is known about the structure of the proton emitter than
the heavier isotopes which either alpha or beta decay. Such was the
situation in the Au isotopes

where the ground state of ^171^Au was determined to be spherical from
the study of its proton decay and Au isotopes with A\>180 were found to
be deformed in their ground states. No experimental information was
available concerning how the nuclear structure evolved when going from
the deformed Au isotopes to the spherical proton emitter ^171^Au. In
order to remedy this, excited states built on top of the alpha decaying
states in the proton unbound isotopes ^173,175,177^Au were identified
using the RDT technique. For ^177^Au, the ground-state is found to be
spherical while the excited states are associated with a prolate
deformed nucleus. In ^175^Au, states associated with spherical, oblate
and prolate shapes have been identified and found to \"co-exist\" at low
spin and excitation energy. Finally, in ^173^Au, states associated with
only spherical shapes have been identified. Thus, the evolution of shape
in these Au isotopes has been found to be rather dynamic and sensitively
dependent on the neutron number. These data should prove to be valuable
for testing theoretical models which attempt to calculate the structure
of nuclei at the edges of stability.