Editing Lead (section)

=== Isotopes ===
{{Main|Isotopes of lead}}
Natural lead consists of four stable [[isotope]]s with mass numbers of 204, 206, 207, and 208,{{sfn|IAEA - Nuclear Data Section|2017}} and traces of six short-lived radioisotopes with mass numbers 209–214 inclusive. The high number of isotopes is consistent with lead's [[atomic number]] being even.{{efn|An even number of either protons or neutrons generally increases the nuclear stability of isotopes, compared to isotopes with odd numbers. No elements with odd atomic numbers have more than two stable isotopes; even-numbered elements have multiple stable isotopes, with tin (element 50) having the highest number of isotopes of all elements, ten.{{sfn|IAEA - Nuclear Data Section|2017}} See [[Even and odd atomic nuclei]] for more details.}} Lead has a [[magic number (physics)|magic number]] of protons (82), for which the [[nuclear shell model]] accurately predicts an especially stable nucleus.{{sfn|Stone|1997}} Lead-208 has 126 neutrons, another magic number, which may explain why lead-208 is extraordinarily stable.{{sfn|Stone|1997}}

With its high atomic number, lead is the heaviest element whose natural isotopes are regarded as stable; lead-208 is the heaviest stable nucleus. (This distinction formerly fell to [[bismuth]], with an atomic number of 83, until its only [[primordial nuclide|primordial isotope]], bismuth-209, was found in 2003 to decay very slowly.){{efn|The half-life found in the experiment was 1.9{{e|19}} years.{{sfn|de Marcillac|Coron|Dambier|Leblanc|2003|pp=876–78}} A kilogram of natural bismuth would have an activity value of approximately 0.003 [[becquerel]]s (decays per second). For comparison, the activity value of natural radiation in the human body is around 65 becquerels per kilogram of body weight (4500 becquerels on average).{{sfn|World Nuclear Association|2015}} }} The four stable isotopes of lead could theoretically undergo [[alpha decay]] to isotopes of [[mercury (element)|mercury]] with a release of energy, but this has not been observed for any of them; their predicted half-lives range from 10<sup>35</sup> to 10<sup>189</sup> years{{sfn|Beeman|Bellini|Cardani|Casali|2013}} (at least 10<sup>25</sup> times the current age of the universe).

[[File:Holsinger Meteorite.jpg|thumb|left|The Holsinger meteorite, the largest piece of the [[Canyon Diablo (meteorite)|Canyon Diablo]] meteorite. [[Uranium–lead dating]] and [[lead–lead dating]] on this meteorite allowed refinement of the [[Age of Earth|age of the Earth]] to 4.55&nbsp;billion ±&nbsp;70&nbsp;million years.|alt=A piece of a gray meteorite on a pedestal]]
Three of the stable isotopes are found in three of the four major [[decay chain]]s: lead-206, lead-207, and lead-208 are the final decay products of [[uranium-238]], [[uranium-235]], and [[thorium-232]], respectively.{{sfn|Radioactive Decay Series|2012}} These decay chains are called the [[uranium chain]], the [[actinium chain]], and the [[thorium chain]].{{sfn|Committee on Evaluation of EPA Guidelines for Exposure to Naturally Occurring Radioactive Materials|Commission on Life Sciences|Division on Earth and Life Studies|National Research Council|1999}} Their isotopic concentrations in a natural rock sample depends greatly on the presence of these three parent uranium and thorium isotopes. For example, the relative abundance of lead-208 can range from 52% in normal samples to 90% in thorium ores;{{sfn|Smirnov|Borisevich|Sulaberidze|2012}} for this reason, the standard atomic weight of lead is given to only one decimal place.{{sfn|Greenwood|Earnshaw|1998|p=368}} As time passes, the ratio of lead-206 and lead-207 to lead-204 increases, since the former two are supplemented by radioactive decay of heavier elements while the latter is not; this allows for [[lead–lead dating]]. As uranium decays into lead, their relative amounts change; this is the basis for [[uranium–lead dating]].{{sfn|Levin|2009|pp=40–41}} Lead-207 exhibits [[nuclear magnetic resonance]], a property that has been used to study its compounds in solution and solid state,{{sfn|Webb|2000|p=115}}{{sfn|Wrackmeyer|Horchler|1990}} including in the human body.{{sfn|Cangelosi|Pecoraro|2015}}

Apart from the stable isotopes, which make up almost all lead that exists naturally, there are [[trace radioisotope|trace quantities]] of a few radioactive isotopes. One of them is lead-210; although it has a half-life of only 22.2 years,{{sfn|IAEA - Nuclear Data Section|2017}} small quantities occur in nature because lead-210 is produced by a long decay series that starts with uranium-238 (that has been present for billions of years on Earth). Lead-211, −212, and −214 are present in the decay chains of uranium-235, thorium-232, and uranium-238, respectively, so traces of all three of these lead isotopes are found naturally. Minute traces of lead-209 arise from the very rare [[cluster decay]] of radium-223, one of the [[Decay product|daughter products]] of natural uranium-235, the rare beta-minus-neutron decay of thallium-210 (a decay product of uranium-238), and the decay chain of neptunium-237, traces of which are produced by [[neutron capture]] in uranium ores. Lead-213 also occurs in the decay chain of neptunium-237. Lead-210 is particularly useful for helping to identify the ages of samples by measuring its ratio to lead-206 (both isotopes are present in a single decay chain).{{sfn|Fiorini|2010|pp=7–8}}

In total, 43 lead isotopes have been synthesized, with mass numbers 178–220.{{sfn|IAEA - Nuclear Data Section|2017}} Lead-205 is the most stable radioisotope, with a half-life of around 1.70{{e|7}}&nbsp;years.{{NUBASE2020|ref}}{{efn|Lead-205 decays solely via [[electron capture]], which means when there are no electrons available and lead is fully ionized with all 82 electrons removed it cannot decay. Fully ionized thallium-205, the isotope lead-205 would decay to, becomes unstable and can decay into a [[beta decay#Bound-state β− decay|bound state]] of lead-205.{{sfn|Takahashi|Boyd|Mathews|Yokoi|1987}} }} The second-most stable is lead-202, which has a half-life of about 52,500&nbsp;years, longer than any of the natural trace radioisotopes.{{sfn|IAEA - Nuclear Data Section|2017}}

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