They have masses of 13 and 14 respectively and are referred to as "carbon-13" and "carbon-14." If two atoms have equal numbers of protons but differing numbers of neutrons, one is said to be an "isotope" of the other.

Carbon-13 and carbon-14 are thus isotopes of carbon-12.

So, objects older than that do not contain enough of the isotope to be dated.

Libby and others (University of Chicago) devised a method of estimating the age of organic material based on the decay rate of carbon-14.

Carbon-14 is produced in the atmosphere when neutrons from cosmic radiation react with nitrogen atoms: C ratio of 0.795 times that found in plants living today. Solution The half-life of carbon-14 is known to be 5720 years. Radioactive decay is a first order rate process, which means the reaction proceeds according to the following equation: is the quantity of radioactive material at time zero, X is the amount remaining after time t, and k is the first order rate constant, which is a characteristic of the isotope undergoing decay.

(Since this is a decay problem, I expect the constant to be negative.

If I end up with a positive value, I'll know that I should go back and check my work.) In Its radiation is extremely low-energy, so the chance of mutation is very low.

Conversely, the method doesn't work on objects that are too young.

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