  We investigate the feasibility of a high statistics experiment to search for
invisible decay modes in nuclear gamma cascades using 200 kg of %36 Cs(Tl)
scintillators that are presently available at Texas A\&M. The experiment aims
to search for missing energy by robustly establishing the absence of a photon
in a well identified gamma cascade. We report on the experimental demonstration
of the energy resolution necessary for this search. Prior explorations of this
detector concept focused on baryonically coupled physics that could be emitted
in $E_2$ transitions. We point out that this protocol can also search for
particles that are coupled to photons by searching for the conversion of a
photon produced in a gamma cascade into a hidden particle. Examples of these
processes include the oscillation of a photon into a hidden photon and the
conversion of a photon into an axion-like-particle either in the presence of a
magnetic field or via the Primakoff process. This proof-of-concept apparatus
appears to have the ability to search for hitherto unconstrained baryonically
coupled scalars and pseudoscalars produced in $E_0$ and $M_0$ transitions. If
successfully implemented, this experiment serves as a pathfinder for a larger
detector with greater containment that can thoroughly probe the existence of
new particles with mass below 4 MeV that lie in the poorly constrained
supernova ``trapping window'' that exists between 100 keV and 30 MeV.
