Commissioning of the LaBr 3 (Ce) detector array at the National Superconducting Cyclotron Laboratory

The timing and energy resolution properties of LaBr${}_3$(Ce) scintillators are well suited for use in $\gamma \gamma$ fast-timing experiments. Using standard ⁶⁰Co, ⁸⁸Y, and ¹⁵²Eu sources, the 16-element array of 1.5 inch $\times$ 1.5 inch right-cylindrical LaBr${}_3$(Ce) detectors and the associated readout electronics at the National Superconducting Cyclotron Laboratory were commissioned by measuring the lifetimes of excited states and the angular correlations of $\gamma$ rays emitted in cascade. Excited-state lifetimes in ¹⁵²Sm and ¹⁵²Gd were measured using the exponential slope of the decay and a method based on the centroids of time-difference spectra. Results for the lifetimes are consistent with the well-known literature values which cover a range from a few picoseconds to several nanoseconds. Furthermore, the $\gamma \gamma$ angular correlations for the $4^{+}\to 2^{+}\to 0^{+}$ cascade in ⁶⁰Ni and the $3^{-}\to 2^{+}\to 0^{+}$ cascade in ⁸⁸Sr were measured and shown to agree with GEANT4 simulations that take into account the expected angular correlations within the cascades as well as the geometry of the array.