= Sulfur-34
{title2=$^{34}\mathrm S$}
<Sulfur-34> is a stable <isotope> of <sulfur> with 16 <protons> and 18 <neutrons> in its <atomic nucleus>. Its <mass number> is $34$, while its relative <atomic mass> is approximately $33.967867004$. NIST lists a representative <isotopic abundance> of $0.0425$, or $4.25\%$, alongside $0.9499$ for <sulfur-32>.<Atomic Weights and Isotopic Compositions for All Elements by National Institute of Standards and Technology>[Sulfur rows 32 and 34, isotope masses and compositions]{ref} The representative composition does not require every natural sample to have exactly those fractions.
Comparing <sulfur-34> with <sulfur-32> illustrates how an <isotope ratio> differs from a fraction of all sulfur. The representative ratio is
$$
R=\frac{N_{34}}{N_{32}}=\frac{0.0425}{0.9499}\approx0.04474.
$$
In an idealized measurement that has already corrected differences in response and interferences, suppose the inferred atom counts are $N_{34}=450$ and $N_{32}=10000$. Their ratio is $0.045$, about $0.58\%$ higher than that representative ratio. This compares two isotopes; calculating the sulfur-34 fraction of all sulfur additionally needs the other isotopes in the denominator. Raw <mass spectrometer> signals are not automatically corrected atom counts.
<Sulfur-34> and <sulfur-32> have the same <atomic number>, so replacing one with the other preserves the element while changing nuclear <mass>. This makes isotope composition an additional descriptor of a sulfur-containing sample, distinct from its <chemical formula>. A stable isotope also provides a different kind of label from radioactive <sulfur-35>: its usefulness does not depend on detecting <radioactive decay>.
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