  With the advent of high repetition rate laser facilities, novel diagnostic
tools compatible with these advanced specifications are required. This paper
presents the design of an active gamma-ray spectrometer intended for these high
repetition rate experiments, with particular emphasis on functionality within a
PW level laser-plasma interaction chamber's extreme conditions. The
spectrometer uses stacked scintillators to accommodate a broad range of
gamma-ray energies, demonstrating its adaptability for various experimental
setups. Additionally, it has been engineered to maintain compactness,
electromagnetic pulse resistance, and ISO-5 cleanliness requirements while
ensuring high sensitivity. The spectrometer has been tested in real conditions
inside the PW-class level interaction chamber at the BELLA center, LBNL. The
paper also outlines the calibration process thanks to a $^{60}$Co radioactive
source.
