This proposal combines small-angle neutron scattering with novel deuteration strategies to investigate amyloid protein fibrils. Variations in dynamics of elongation and breakage underpin phenomena ranging from non-genetic heredity in yeast, to diseases such as Alzheimers, BSE and CJD. However, solution methods to monitor growth dynamics only give information on the overall % of material transformed from non-fibrillar to fibrillar forms. They cannot determine elongation rate directly, instead convoluting it with length distribution; and so cannot distinguish a few long fibrils growing quickly from many short fibrils growing slowly. We have developed a SANS approach to measure elongation rate, with isotope labelled ends growing on contrast-matched "seed" fibrils, demonstrated by proof -of-concept data on SANS2D in 2016. This proposal will enable us to finish the study, to allow publication