[en] The implosion of an inertial fusion target generates a flux of X-radiation that is characteristic of target heating and thus important to know. The harsh radiation environment implies that measuring instruments should be away from the target which imposes the conversion of X-rays into visible light (380 - 780 nm) easier to carry. The new scintillator should operate in a spectral range away from the blue to avoid detecting Cerenkov light. A plastic scintillator has been selected: a matrix of polystyrene will make the conversion X-ray to UV radiation. This matrix will contain molecules of 2.5-diphenyloxazole and of Nil to assure the conversion of UV into red light through a cascade of absorption-emission processes. Di-isopropyl-ethylamine molecules are also present to accelerate fluorescence. (A.C.)