Editing Mendelevium (section)

===Isotopes===
{{main|Isotopes of mendelevium}}

Seventeen isotopes of mendelevium are known, with mass numbers from 244 to 260; all are radioactive.<ref name="Silva16301">Silva, pp. 1630–1</ref> Additionally, 14 [[nuclear isomer]]s are known.<!--244m,245m,246m,247m,249m,250m,251m,252m,253m,254m,255m,256m1,256m2,258m, too many to list-->{{NUBASE2020|ref}} Of these, the longest-lived isotope is <sup>258</sup>Md with a half-life of 51.59&nbsp;days, and the longest-lived isomer is <sup>258m</sup>Md with a half-life of 57.0&nbsp;minutes.{{NUBASE2020|ref}} Nevertheless, the shorter-lived <sup>256</sup>Md (half-life 1.295&nbsp;hours<!--77.7 minutes-->) is more often used in chemical experimentation because it can be produced in larger quantities from [[alpha particle]] irradiation of einsteinium.<ref name="Silva16301" /> After <sup>258</sup>Md, the next most stable mendelevium isotopes are <sup>260</sup>Md with a half-life of 27.8&nbsp;days, <sup>257</sup>Md with a half-life of 5.52&nbsp;hours, <sup>259</sup>Md with a half-life of 1.60&nbsp;hours, and <sup>256</sup>Md with a half-life of 1.295&nbsp;hours. All of the remaining mendelevium isotopes have half-lives that are less than an hour, and the majority of these have half-lives that are less than 5&nbsp;minutes.{{NUBASE2020|ref}}<ref name="Silva16301" />

The half-lives of mendelevium isotopes mostly increase smoothly from <sup>244</sup>Md onwards, reaching a maximum at <sup>258</sup>Md.{{NUBASE2020|ref}}<ref name="Silva16301" /> Experiments and predictions suggest that the half-lives will then decrease, apart from <sup>260</sup>Md with a half-life of 27.8&nbsp;days,{{NUBASE2020|ref}}<ref name="Silva16301" /> as [[spontaneous fission]] becomes the dominant decay mode{{NUBASE2020|ref}} due to the mutual repulsion of the protons posing a limit to the island of relative stability of long-lived nuclei in the [[actinide]] series.<ref name="Nurmia">{{cite journal|first = Matti|last = Nurmia|date = 2003 |title = Nobelium|journal = Chemical and Engineering News|url = http://pubs.acs.org/cen/80th/nobelium.html|volume = 81|issue = 36|page = 178|doi = 10.1021/cen-v081n036.p178}}</ref> In addition, mendelevium is the element with the highest atomic number that has a known isotope with a half-life longer than one day.{{NUBASE2020|ref}}

Mendelevium-256, the chemically most important isotope of mendelevium, decays through [[electron capture]] 90% of the time and [[alpha decay]] 10% of the time.<ref name="Silva16301" /> It is most easily detected through the [[spontaneous fission]] of its electron capture daughter [[fermium-256]], but in the presence of other nuclides that undergo spontaneous fission, alpha decays at the characteristic energies for mendelevium-256 (7.205 and 7.139&nbsp;[[electronvolt|MeV]]) can provide more useful identification.<ref name="Silva16313" />