[en] Comparison of the possibilities for analyzing light elements in heavy matrix by two methods: by the line intensities of fluorescent spectrum (XFA) and by the ratio of Compton and Rayleigh scattering intensities, for the example of iron-carbon system in the carbon concentration range from 0.03 to 1.4 mas.% was carried out. Both the methods provide almost similar thresholds of detectability 0.03...0.07 mas.% for this system. In XFA at low background intensity, it was possible to obtain high concentration sensitivity to provide the measurement accuracy ± 0.025mas.%. For measurements by the scattering peak ratio, the concentration sensitivity 1.86 %mas.% was obtained (theoretical value is 2.05). Thus, to provide 0.024 mas.% sensitivity, it is necessary to accumulate not less than 107 counts for each peak that needs the measurement time 500...1000 s using Si(Li) detector. It was shown that concentration sensitivity jump with decreasing atomic number of light element offers good perspectives of the method for analysis of hydrogen with m=10...100 %mas.% and ∼10-4 mas.% threshold of detectability for hydrogen in metals.