Radiocarbon analysis is used to determine the age of coal and organic residues. The basic principle of radiocarbon analysis is to determine the concentration of radioactive 14С in a sample. 14С is naturally formed in the atmosphere in the nuclear reaction of nitrogen with cosmic neutrons. Since a constant amount of 14С is always formed in The earth's atmosphere, it is in equilibrium with the carbon in the plants, after the death of the plant and the formation of coal, 14С ceases to enter the material and its amount begins to decrease due to the decay of the 14С nuclei. Since the half-life of carbon 14 is 5700 years, by measuring the concentration of 14С in the coal, it is possible to determine how long the decay of 14С occurred. The problem is that in very old samples there is too little 14С to measure. Samples older than 60,000 years, contain so little 14С that they undergo less than one decay of the 14С nucleus per hour, it is too small to measure, so the radiocarbon method has limitations.