Determination of minimum detectable mass of impurities in industrial objects using neutrons in transmission

The elemental analysis method presented is based on the change in the neutron macroscopic cross section of an object due to the introduction of impurities. Equations have been derived to calculate the minimum detectable mass and length fractions of these impurities distributed in a matrix for tomographic applications. Best results (5 μg/g) were obtained, as expected, for the detection of hydrogen in elements which comprise commonly used industrial materials. Impurities of certain elements as little as 10−2 μm in length could be detected by neutron transmission with a contrast of 0.01. The minimum required number of neutrons required for the detection of impurities in iron for a given relative error of 5% and a neutron flux of 5×104 n cm−2s−1 have been calculated as an example. Optimum sample thickness for a minimum counting time was also calculated and compared for sample matrices of iron, aluminium and water using cold, thermal and fast neutrons. These optimum values were found to be 1.8, 9 and 198 mm for water, 579, 209 and 173 mm for aluminium and 32, 16.8 and 194 mm for iron matrix at the three neutron energies, respectively.