A method for correct averaging in transmission radiometry

Transmission radiometry with photon or particle radiation is a common technique for the measurement of thickness, density and composition of materials, e.g. in production lines and in multiphase flow metering. Moreover, radiation transmission measurement is the basis for many imaging techniques, such as x-ray and gamma ray tomography. A common problem associated with transmission measurement is correct temporal averaging for time-varying material properties. Averaging the intensity signal at the detector over time and taking this mean to calculate average ray attenuation leads to incorrect results when attenuation changes within the integration period. This paper discusses the implications of this systematic error and introduces a methodology for correct averaging which is applicable even to very low intensity measurements.