Sulfur-32 is a stable isotope of sulfur whose atomic nucleus contains 16 protons and 16 neutrons. Its mass number is , the sum of those counts. The measured relative atomic mass is approximately ; a mass number is an integer count, whereas a relative atomic mass is a mass ratio.[ref]
The same NIST table gives a representative isotopic abundance of , or , making sulfur-32 the predominant natural sulfur isotope. This is a representative composition, not an immutable percentage in every sample. Using the listed sulfur-34 fraction , the corresponding isotope ratio is : about 4.47 sulfur-34 atoms per 100 sulfur-32 atoms.[ref]
Atomic Weights and Isotopic Compositions for All Elements by National Institute of Standards and Technology. Sulfur isotope rows 32–36
An isotope ratio and a percentage of all sulfur atoms have different denominators.Sulfur-32 is also the daughter of phosphorus-32 beta-minus decay. One nuclear neutron becomes a proton, changing to while retaining mass number .[ref] This connects a radioactive tracer to a stable daughter without turning their chemical identities into the same thing.
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