Editing Sulfur (section)

===Isotopes===
{{Main|Isotopes of sulfur}}
Sulfur has 23 known [[isotope]]s, four of which are stable: <sup>32</sup>S ({{val|94.99|0.26|u=%}}), <sup>33</sup>S ({{val|0.75|0.02|u=%}}), <sup>34</sup>S ({{val|4.25|0.24|u=%}}), and <sup>36</sup>S ({{val|0.01|0.01|u=%}}).<ref name="CIAAWsulfur"/><ref name="CRC-2011">{{RubberBible92nd|page=1.14}}</ref> Other than <sup>35</sup>S, with a [[half-life]] of 87 days, the [[radioactivity|radioactive]] isotopes of sulfur have half-lives less than 3&nbsp;hours.

The preponderance of <sup>32</sup>S is explained by its production in the so-called alpha-process (one of the main classes of nuclear fusion reactions) in exploding stars. Other stable sulfur isotopes are produced in the bypass processes related with <sup>34</sup>Ar, and their composition depends on a type of a stellar explosion. For example, proportionally more <sup>33</sup>S comes from [[novae]] than from [[supernovae]].<ref>{{Cite web |title=Searching for the Origins of Presolar Grains |url=https://www.energy.gov/science/np/articles/searching-origins-presolar-grains |access-date=2023-02-04 |website=Energy.gov |language=en}}</ref>

On the planet Earth the sulfur isotopic composition was determined by the Sun. Though it was assumed that the distribution of different sulfur isotopes would be more or less equal, it has been found that proportions of the two most abundant sulfur isotopes <sup>32</sup>S and <sup>34</sup>S varies in different samples. Assaying of the isotope ratio ([[Δ34S|δ<sup>34</sup>S]]) in the samples suggests their chemical history, and with support of other methods, it allows to age-date the samples, estimate temperature of equilibrium between ore and water, determine pH and oxygen [[fugacity]], identify the activity of sulfate-reducing bacteria in the time of formation of the sample, or suggest the main sources of sulfur in ecosystems.<ref>{{Cite book |last1=Paytan |first1=Adina |title=Geologic Time Scale |last2=Yao |first2=Weiqi |last3=Faul |first3=Kristina |last4=Gray |first4=E.T. |year=2020 |pages=259–278 |language=en |chapter=Sulfur Isotope Stratigraphy |doi=10.1016/B978-0-12-824360-2.00009-7 |isbn=9780128243602 |chapter-url=https://www.researchgate.net/publication/347656764}}</ref> However, there are ongoing discussions over the real reason for the δ<sup>34</sup>S shifts, biological activity or postdeposit alteration.<ref>{{Cite web |title=NASA Astrobiology |url=https://astrobiology.nasa.gov/news/the-first-sulfur-eaters/ |access-date=2023-02-04 |website=astrobiology.nasa.gov |language=en-EN}}</ref>

For example, when [[sulfide mineral]]s are precipitated, isotopic equilibration among solids and liquid may cause small differences in the δ<sup>34</sup>S values of co-genetic minerals. The differences between minerals can be used to estimate the temperature of equilibration. The [[Δ13C|δ<sup>13</sup>C]] and δ<sup>34</sup>S of coexisting [[carbonate minerals]] and sulfides can be used to determine the [[pH]] and oxygen fugacity of the ore-bearing fluid during ore formation.

Scientists measure the [[Sulfur isotope biogeochemistry|sulfur isotopes]] of [[Mineral|minerals]] in rocks and [[Sediment|sediments]] to study the [[redox]] conditions in past oceans. [[Sulfate-reducing microorganism|Sulfate-reducing bacteria]] in marine sediment fractionate [[Sulfur isotope biogeochemistry|sulfur isotopes]] as they take in [[sulfate]] and produce [[sulfide]]. Prior to the 2010s, it was thought that sulfate reduction could fractionate [[Sulfur isotope biogeochemistry|sulfur isotopes]] up to 46 [[permil]]<ref>{{Cite journal |last1=Goldhaber |first1=M.B. |last2=Kaplan |first2=I.R. |date=April 1980 |title=Mechanisms of sulfur incorporation and isotope fractionation during early diagenesis in sediments of the gulf of California |url=https://linkinghub.elsevier.com/retrieve/pii/0304420380900638 |journal=Marine Chemistry |language=en |volume=9 |issue=2 |pages=95–143 |doi=10.1016/0304-4203(80)90063-8|bibcode=1980MarCh...9...95G }}</ref> and fractionation larger than 46 permil recorded in sediments must be due to [[disproportionation]] of sulfur compounds in the sediment. This view has changed since the 2010s as experiments showed that [[Sulfate-reducing microorganism|sulfate-reducing bacteria]] can fractionate to 66 permil.<ref>{{Cite journal |last1=Sim |first1=Min Sub |last2=Bosak |first2=Tanja |last3=Ono |first3=Shuhei |date=July 2011 |title=Large Sulfur Isotope Fractionation Does Not Require Disproportionation |url=https://www.science.org/doi/10.1126/science.1205103 |journal=Science |language=en |volume=333 |issue=6038 |pages=74–77 |doi=10.1126/science.1205103 |pmid=21719675 |bibcode=2011Sci...333...74S |s2cid=1248182 |issn=0036-8075}}</ref> As substrates for disproportionation are limited by the product of [[Sulfate-reducing microorganism|sulfate reduction]], the isotopic effect of disproportionation should be less than 16 permil in most sedimentary settings.<ref>{{Cite journal |last1=Tsang |first1=Man-Yin |last2=Böttcher |first2=Michael Ernst |last3=Wortmann |first3=Ulrich Georg |date=August 2023 |title=Estimating the effect of elemental sulfur disproportionation on the sulfur-isotope signatures in sediments |url=https://linkinghub.elsevier.com/retrieve/pii/S0009254123002334 |journal=Chemical Geology |language=en |volume=632 |pages=121533 |doi=10.1016/j.chemgeo.2023.121533|s2cid=258600480 }}</ref>

In [[forest]] ecosystems, sulfate is derived mostly from the atmosphere; weathering of ore minerals and evaporites contribute some sulfur. Sulfur with a distinctive isotopic composition has been used to identify pollution sources, and enriched sulfur has been added as a tracer in [[hydrology|hydrologic]] studies. Differences in the [[natural abundance]]s can be used in systems where there is sufficient variation in the <sup>34</sup>S of ecosystem components. [[Rocky Mountain]] lakes thought to be dominated by atmospheric sources of sulfate have been found to have measurably different <sup>34</sup>S values than lakes believed to be dominated by watershed sources of sulfate.

The radioactive <sup>35</sup>S is formed in [[cosmic ray spallation]] of the atmospheric [[argon-40|<sup>40</sup>Ar]]. This fact may be used to verify the presence of recent (up to 1 year) atmospheric sediments in various materials. This isotope may be obtained artificially by different ways. In practice, the reaction [[Chlorine-35|<sup>35</sup>Cl]] + [[neutron|n]] → <sup>35</sup>S + [[proton|p]] is used by irradiating [[potassium chloride]] with neutrons.<ref>{{Cite conference |last1=Kim |first1=Ik Soo |last2=Kwak |first2=Seung Im |last3=Park |first3=Ul Jae |last4=Bang |first4=Hong Sik |last5=Han |first5=Hyun Soo |date=2005-07-01 |title=Production of Sulfur-35 by the Cation Exchange Process |conference=2005 autumn meeting of the KNS, Busan (Korea, Republic of), 27–28 Oct 2005 |url=https://www.osti.gov/etdeweb/biblio/20765660 |language=en}}</ref> The isotope <sup>35</sup>S is used in various sulfur-containing compounds as a [[radioactive tracer]] for many biological studies, for example, the [[Hershey-Chase experiment]].

Because of the weak [[Beta decay|beta activity]] of <sup>35</sup>S, its compounds are relatively safe as long as they are not ingested or absorbed by the body.<ref>{{Cite web |title=Sulfur-35 (35 S) safety information and specific handling precautions |url=https://ehs.yale.edu/sites/default/files/files/radioisotope-s35.pdf |website=Yale Environmental Health & Safety}}</ref>