  An inelastic $\alpha$-scattering experiment on the unstable $N=Z$,
doubly-magic $^{56}$Ni nucleus was performed in inverse kinematics at an
incident energy of 50 A.MeV at GANIL. High multiplicity for $\alpha$-particle
emission was observed within the limited phase-space of the experimental setup.
This observation cannot be explained by means of the statistical-decay model.
The ideal classical gas model at $kT$ = 0.4 MeV reproduces fairly well the
experimental momentum distribution and the observed multiplicity of $\alpha$
particles corresponds to an excitation energy around 96 MeV. The method of
distributed $m\alpha$-decay ensembles is in agreement with the experimental
results if we assume that the $\alpha$-gas state in $^{56}$Ni exists at around
$113^{+15}_{-17}$ MeV. These results suggest that there may exist an exotic
state consisting of many $\alpha$ particles at the excitation energy of
$113^{+15}_{-17}$ MeV.

Nuclear Experiment