Quantification of cement hydration through neutron radiography with scatter rejection

The unique capabilities of neutrons to penetrate materials opaque to X-rays and at the same time to interact with hydrogen make neutron radiography a technique of choice for the quantification of hydrogen-containing substances. However, the interaction of neutrons with hydrogen is through scattering, not absorption and unwanted scattered neutrons can be responsible for a considerable fraction of the registered events, reducing the accuracy of hydrogen quantification, especially in imaging experiments where the sample has to be placed close to the detector to avoid image blurring due to the finite beam divergence. Various post-experiment data processing techniques were developed to correct and mitigate the effects of scattering. Another complementary ´hardware´ solution described in this paper, is to simply eliminate the detrimental scattering component from the detected signal through the use of neutron collimators. Development of compact polycapillary collimators, merely a few mm thick, now enables accurate, high spatial resolution quantification of a wide range of materials which tend to strongly scatter neutrons. This paper demonstrates how it is now possible to substantially improve the accuracy of the measured water content in cement samples. A compact polycapillary neutron collimator (2 mm thick, 5 cm diameter, with ~8 μm pores hexagonally packed on ~10 μm centers) used for scatter rejection in our experiments. The water content within the 1×1×2 cm3 cement samples is measured by neutron transmission radiography, performed with sub-100 μm spatial resolution. The measurement of water concentration is markedly improved through the use of this collimator, proving those can be attractive for the experiments where samples must be placed in quite close proximity (e.g., only few centimeters or closer), from the neutron detector active surface.