Neutron signal transfer analysis

A new method called neutron signal transfer analysis has been developed for quantitative determination of hydrogenous distributions from neutron radiographic measurements. The technique is based on a model which describes the detector signal obtained in the measurement as a result of the action of three different mechanisms expressed by signal transfer functions. The explicit forms of the signal transfer functions are determined by Monte Carlo computer simulations and contain only the distribution as a variable. Therefore an unknown distribution can be determined from the detector signal by recursive iteration. This technique provides a simple and efficient tool for analysis of this type while also taking into account complex effects due to the energy dependency of neutron interaction and single and multiple scattering. Therefore this method provides an efficient tool for precise quantitative analysis using neutron radiography, as for example quantitative determination of moisture distributions in porous building materials. A comparison between neutron signal transfer analysis and conventional methods has been made by simulating an experiment with a sample containing a known moisture distribution by Monte Carlo calculation. By using the neutron signal transfer method the error is less than 3%. Whereas the calibration curve method overestimates the moisture content by a factor in the range around 10% and the exponential attenuation method underestimates the moisture content by a factor in the range of 2.