A method for controlling the quality of a 
mass density measurement of a multiphase fluid mixture FM comprising a plurality of fluid fractions and a plurality of constituting elements, the method comprises the steps of: submitting a measuring 
pipe 3 to a flux of 
high energy photons and measuring count rates, the measuring 
pipe being arranged to let the photons pass through the multiphase fluid mixture. determining S3a a 
mass density ρma<sub2>—< / sub2>mix of the multiphase fluid mixture based on count rate measurements S2a, S2b in a first E32 and second E81 
energy window, the first E32 and second E81 energy windows being chosen so that the measurements in said energy windows are mainly sensitive to the fluid fractions, determining S4 an 
electronic density ρma<sub2>—< / sub2>mix of the multiphase fluid mixture based on count rate measurements S2c in a third 
energy window E356, the third 
energy window E356 being chosen so that the measurements in the third energy window E356 are substantially sensitive to the density of the constituting elements, and comparing S5 the 
electronic density ρel<sub2>—< / sub2>mix to the 
mass density ρma<sub2>—< / sub2>mix of the multiphase fluid mixture, one of said densities being corrected with a factor depending on the 
atomic number Z and the 
mass number A of the multiphase fluid mixture prior to comparison, a difference between both densities indicating the quality of the mass density measurement of the multiphase fluid mixture.