A new-concept gamma calorimeter at ELI-NP

ELI-NP is an European Research Infrastructure that will provide a monochromatic, high brilliance gamma beam with tunable energy up to 19.5MeV. The time structure of the beam consists of 32 high intensity gamma bunches separated by a time interval of 16 ns and delivered at a repetition rate of 100 Hz. In order to match such unprecedented beam specifications, specific devices and techniques have been developed to measure and monitor the beam parameters during the commissioning and the operational phase. This paper presents an overview of the gamma beam characterization system, with particular focus on a new-concept sampling calorimeter made of silicon detectors and polyethylene absorbers.