  Direct measurements of reaction cross-sections at astrophysical energies
often require the use of solid targets able to withstand high ion beam currents
for extended periods of time. Thus, monitoring target thickness, isotopic
composition, and target stoichiometry during data taking is critical to account
for possible target modifications and to reduce uncertainties in the final
cross-section results. A common technique used for these purposes is the
Nuclear Resonant Reaction Analysis (NRRA), which however requires that a narrow
resonance be available inside the dynamic range of the accelerator used. In
cases when this is not possible, as for example the 13C(alpha,n)16O reaction
recently studied at low energies at the Laboratory for Underground Nuclear
Astrophysics (LUNA) in Italy, alternative approaches must be found. Here, we
present a new application of the shape analysis of primary gamma rays emitted
by the 13C(p,g)14N radiative capture reaction. This approach was used to
monitor 13C target degradation {\em in situ} during the 13C(alpha,n)16O data
taking campaign. The results obtained are in agreement with evaluations
subsequently performed at Atomki (Hungary) using the NRRA method. A preliminary
application for the extraction of the 13C(alpha,n)16O reaction cross-section at
one beam energy is also reported.

Instrumentation and Detectors;Nuclear Experiment