Editing Lead (section)

=== In space ===

Lead's per-particle abundance in the [[Solar System]] is 0.121&nbsp;[[Parts-per notation|ppb]] (parts per billion).{{sfn|Lodders|2003|pp=1222–1223}}{{efn|Abundances in the source are listed relative to silicon rather than in per-particle notation. The sum of all elements per 10<sup>6</sup> parts of silicon is 2.6682{{e|10}} parts; lead comprises 3.258 parts.}} This figure is two and a half times higher than that of [[platinum]], eight times more than [[Mercury (element)|mercury]], and seventeen times more than [[gold]].{{sfn|Lodders|2003|pp=1222–1223}} The amount of lead in the [[universe]] is slowly increasing{{sfn|Roederer|Kratz|Frebel|Christlieb|2009|pp=1963–1980}} as most heavier atoms (all of which are unstable) gradually decay to lead.{{sfn|Lochner|Rohrbach|Cochrane|2005|p=12}} The abundance of lead in the Solar System since its formation 4.5&nbsp;billion years ago has increased by about 0.75%.{{sfn|Lodders|2003|p=1224}} The Solar System abundances table shows that lead, despite its relatively high atomic number, is more prevalent than most other elements with atomic numbers greater than 40.{{sfn|Lodders|2003|pp=1222–1223}}

Primordial lead—which comprises the isotopes lead-204, lead-206, lead-207, and lead-208—was mostly created as a result of repetitive neutron capture processes occurring in stars. The two main modes of capture are the [[s-process|s-]] and [[r-process]]es.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|pp=608–615}}

In the s-process (s is for "slow"), captures are separated by years or decades, allowing less stable nuclei to undergo [[beta decay]].{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|p=551}} A stable thallium-203 nucleus can capture a neutron and become thallium-204; this undergoes beta decay to give stable lead-204; on capturing another neutron, it becomes lead-205, which has a half-life of around 17&nbsp;million years. Further captures result in lead-206, lead-207, and lead-208. On capturing another neutron, lead-208 becomes lead-209, which quickly decays into bismuth-209. On capturing another neutron, bismuth-209 becomes bismuth-210, and this beta decays to polonium-210, which alpha decays to lead-206. The cycle hence ends at lead-206, lead-207, lead-208, and bismuth-209.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|pp=608–609}}

[[File:S-R-processes-atomic-mass-201-to-210.svg|thumb|right|upright=1.15|Chart of the final part of the [[s-process]], from [[mercury (element)|mercury]] to [[polonium]]. Red lines and circles represent [[neutron capture]]s; blue arrows represent [[beta decay]]s; the green arrow represents an [[alpha decay]]; cyan arrows represent [[electron capture]]s.|alt=Uppermost part of the nuclide chart, with only practically stable isotopes and lead-205 shown, and the path of the s-process overlaid on it as well that of the cycle on lead, bismuth, and polonium]]
In the r-process (r is for "rapid"), captures happen faster than nuclei can decay.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|p=553}} This occurs in environments with a high neutron density, such as a [[supernova]] or the merger of two [[neutron star]]s. The neutron flux involved may be on the order of 10<sup>22</sup> neutrons per square centimeter per second.{{sfn|Frebel|2015|pp=114–115}} The r-process does not form as much lead as the s-process.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|pp=608–610}} It tends to stop once neutron-rich nuclei reach 126 neutrons.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|p=595}} At this point, the neutrons are arranged in complete shells in the atomic nucleus, and it becomes harder to energetically accommodate more of them.{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|p=596}} When the neutron flux subsides, these nuclei beta decay into stable isotopes of [[osmium]], [[iridium]], [[platinum]].{{sfn|Burbidge|Burbidge|Fowler|Hoyle|1957|pp=582, 609–615}}