Sulfur (16S) has 23 known isotopes with mass numbers ranging from 27 to 49, four of which are stable: 32S (94.85%), 33S (0.76%), 34S (4.37%), and 36S (0.016%). The preponderance of sulfur-32 is explained by its production from carbon-12 plus successive fusion capture of five helium-4 nuclei in the alpha process of nucleosynthesis.