A simple procedure for γ - γ lifetime measurements using multi-element fast-timing arrays

The lifetimes of nuclear excited states are important observables in nuclear physics. Their precise measurement is of key importance for developing and testing nuclear models as they are directly linked with the quantum nature of the nuclear system. The $\gamma$-$\gamma$ timing technique represents a direct lifetime determination by means of time-difference measurements between the $\gamma$ rays which directly feed and decay from a nuclear excited state. Using arrays of very-fast scintillator detectors, picosecond-sensitive time-difference measurements can be performed. We propose to construct a symmetric energy–energy–time cube as is usually done to perform $\gamma$-$\gamma$ coincidence analyses and lifetime determination with high-resolution germanium detectors. By construction, a symmetric mean time-walk characteristics is obtained, that can be precisely determined and used as a single time correction for all the data independently of the detectors. We present the results of timing characteristics measurements of an array with six LaBr${}_3$(Ce) detectors, as obtained using a ¹⁵²Eu point $\gamma$-ray source. Compared with a single detector pair, the time resolution of the symmetrised time-difference spectra of the array is nearly unaffected.