High intensity lasers (>1019 W/cm2) produce relativistic electrons when they interact with matter. The high energy electrons upon incidence on a solid target produce secondary emissions like protons, neutrons, positrons, x-ray emission and γ-rays1. Gamma rays produce from this interaction can be used to induce photoneutron reaction in a material, thereby producing short-lived isotopes or isomers2. The isotopes or isomers produced can be used for diagnosing the radiation flux and directionality3. Materials with short half-lives (in μs to ms time scale) are of interest as a diagnostic for shot to shot measurement of parameters in high repetition lasers (10 Hz), since they decay well before the incidence of the subsequent pulse on the material. For understanding the working of this diagnostic, systematic studies of decay of the isotopes/isomers produced and the attenuation of γ-rays in the material are necessary. The design and efficiency of a diagnostic for characterizing γ-rays using the method of nuclear activation for 10 Hz high repetition laser is presented. © 2021 Author(s).