  We study the decay properties of Tonks-Girardeau gases escaping from a
double-well potential. Initially, the gases are constrained between two
infinite $\delta$ barriers with an on-center $\delta$-split potential. The
strength of one of the obstacles is suddenly reduced, and the particles start
to tunnel to the open space. Using the resonance expansion method, we derive
the single-term approximate expression for the $N$-particle survival
probability and demonstrate its effectiveness in both the exponential and
nonexponential regimes. We also predict a parity effect and provide physical
insights into its nature at different stages of the time evolution. We conclude
that only the initial phase of the decay of the many-particle state may comply
with an exponential law. The decay properties are dramatically affected by the
presence of the split barrier. Our results reveal the overall decay mechanism
of unstable Tonks-Girardeau gases from single and double quantum wells.
