GRIFFIN's Fast-Timing Array

The Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei~(GRIFFIN) is the new $\beta$-decay spectrometer facility at TRIUMF-ISAC. Consists of an array of 16 large-volume HPGe clover detectors with an unparalleled efficiency of $19\%$ at 1.33~MeV. Its strongest advantage is the versatility of the ancillary detectors that can be coupled to the main array to tag on $\beta$ particles, neutrons or precisely measure conversion electron spectra. An ancillary array of 8 LaBr$_3$(Ce) detectors for $\gamma$-rays and a fast plastic scintillator for $\beta$-particles has been optimized for fast-timing experiments with GRIFFIN. The 51 mm x 51 mm cylindrical LaBr$_3$(Ce) crystals are coupled to Hamamatsu R2083 photomultipliers. Timing resolutions as good as FWHM$\sim200$~ps and time-walks below $\pm30$~ps have been obtained for individual crystals using analog electronics. There is also an ongoing project to develop an active BGO shield for the LaBr$_3$(Ce) crystals. The LaBr$_3$(Ce) array commissioning experiment to measure the $^{145,146}$Cs decay to $^{145,146}$Ba will test its capabilities over a wide range of lifetimes. Preliminary results on the lifetimes of some of the low-laying states will be presented.