Abstract Pulse height and timing characteristics of CsI(Tl)-Si(PIN) detector have been investigated for γ ‐rays and fission fragments (FFs). Energy dependence of the scintillation light output has been studied for FFs from a 252Cf source by degrading their energy in P-10 gas at different pressures. It is seen that the light output for both heavy and light mass groups increases linearly with energy in the interval of 0.2–0.9 MeV/A. At a given energy, the light output is more for the heavy mass fragments than for light mass fragments. The time resolution for γ ‐rays was determined to be 134±3 ns using a BaF 2 as start and CsI(Tl)-Si(PIN) as stop detector.