Editing Nuclear weapon design (section)

==== Designs with lead tampers ====
[[File:Bassoon Prime.jpg|right|thumb|upright|Bassoon, the prototype for a 9.3-megaton clean bomb or a 25-megaton dirty bomb. Dirty version shown here, before its 1956 test. The two attachments on the left are ''[[#Light pipes|light pipes]]''; see below for elaboration.]]
On March 1, 1954, the largest-ever U.S. nuclear test explosion, the 15-megaton [[Castle Bravo]] shot of [[Operation Castle]] at Bikini Atoll, delivered a promptly lethal dose of fission-product fallout to more than {{convert|6000|sqmi|km2}} of Pacific Ocean surface.<ref>See [[:File:Bravo fallout2.png|map]].</ref> Radiation injuries to [[Castle Bravo#Inhabited islands affected|Marshall Islanders]] and [[Daigo Fukuryū Maru|Japanese fishermen]] made that fact public and revealed the role of fission in hydrogen bombs.

In response to the public alarm over fallout, an effort was made to design a clean multi-megaton weapon, relying almost entirely on fusion. The energy produced by the fissioning of [[uranium-238|unenriched natural uranium]], when used as the tamper material in the secondary and subsequent stages in the Teller-Ulam design, can far exceed the energy released by fusion, as was the case in the Castle Bravo test. Replacing the [[fissionable]] material in the tamper with another [[Atomic number|high-Z]] material ([[lead]]) is essential to producing a "clean" bomb. In such a device, the tamper no longer contributes energy, so for any given weight, a clean bomb will have less yield. This was called the "materials substitution method".<ref name="q320" /> The earliest known incidence of a three-stage device being tested, with the third stage, called the tertiary, being ignited by the secondary, was May 27, 1956, in the Bassoon device. This device was tested in the Zuni shot of [[Operation Redwing]]. This shot used non-fissionable tampers; an inert substitute material such as tungsten or lead was used. Its yield was 3.5 megatons, 85% fusion and only 15% fission.{{Citation needed|date=June 2021}}

On July 19, 1956, AEC Chairman Lewis Strauss said that the [[Operation Redwing|Redwing Zuni]] shot clean bomb test "produced much of importance ... from a humanitarian aspect." However, less than two days after this announcement, the dirty version of Bassoon, called Bassoon Prime, with a [[uranium-238]] tamper in place, was tested on a barge off the coast of Bikini Atoll as the [[Operation Redwing|Redwing Tewa]] shot. The Bassoon Prime produced a 5-megaton yield, of which 87% came from fission. Data obtained from this test, and others, culminated in the eventual deployment of the highest-yielding US nuclear weapon known, and the highest [[nuclear weapon yield|yield-to-weight weapon]] ever mass produced, a three-stage thermonuclear weapon with a maximum "dirty" yield of 25 megatons, designated as the [[B41 nuclear bomb]], which was to be carried by U.S. Air Force bombers until it was decommissioned; this weapon was never fully tested.{{Citation needed|date=June 2021|reason=also relevancy}}

In the Soviet [[peaceful nuclear explosion]] program "Nuclear Explosions for the National Economy", "clean" bombs were used for a 1971 triple salvo test related to the [[Pechora–Kama Canal]] project. It was reported that about 250 nuclear devices might be used to get the final goal. The ''Taiga'' test was to demonstrate the feasibility of the project. Three of these devices of 15&nbsp;kiloton yield each were placed in separate boreholes, simultaneously detonated, catapulting a radioactive plume into the air that was carried eastward by wind. The resulting trench was around {{convert|700|m|ft}} long and {{convert|340|m|ft}} wide, with an unimpressive depth of just {{convert|10|to|15|m|ft|sigfig=1}}.<ref>{{cite journal |last1=Ramzaev |first1=V. |last2=Repin |first2=V. |last3=Medvedev |first3=A. |last4=Khramtsov |first4=E. |last5=Timofeeva |first5=M. |last6=Yakovlev |first6=V. |date=July 2011 |title=Radiological investigations at the "Taiga" nuclear explosion site: Site description and in situ measurements |url=https://linkinghub.elsevier.com/retrieve/pii/S0265931X11000750 |journal=Journal of Environmental Radioactivity |language=en |volume=102 |issue=7 |pages=672–680 |bibcode=2011JEnvR.102..672R |doi=10.1016/j.jenvrad.2011.04.003 |pmid=21524834}}</ref> Despite their "clean" nature, the area still exhibits a noticeably higher (albeit mostly harmless) concentration of [[fission products]], the intense [[Neutron irradiation|neutron bombardment]] of the soil, the device itself and the support structures also activated their stable elements to create a significant amount of man-made radioactive elements like [[60Co|<sup>60</sup>Co]]. A larger scale project as was envisioned, however, would have had significant consequences both from the fallout of radioactive plume and the radioactive elements created by the neutron bombardment.<ref>{{cite journal |last1=Ramzaev |first1=V. |last2=Repin |first2=V. |last3=Medvedev |first3=A. |last4=Khramtsov |first4=E. |last5=Timofeeva |first5=M. |last6=Yakovlev |first6=V. |date=July 2012 |title=Radiological investigations at the "Taiga" nuclear explosion site, part II: man-made γ-ray emitting radionuclides in the ground and the resultant kerma rate in air |url=https://linkinghub.elsevier.com/retrieve/pii/S0265931X11003043 |journal=Journal of Environmental Radioactivity |language=en |volume=109 |pages=1–12 |bibcode=2012JEnvR.109....1R |doi=10.1016/j.jenvrad.2011.12.009 |pmid=22541991}}</ref>

Other high fusion yield fraction tests include the 50-megaton [[Tsar Bomba]] at 97% fusion,<ref>[https://nuclearweaponarchive.org/Nwfaq/Nfaq4-5.html 4.5 Thermonuclear Weapon Designs and Later Subsections] {{webarchive|url=https://web.archive.org/web/20160303170957/https://nuclearweaponarchive.org/Nwfaq/Nfaq4-5.html|date=March 3, 2016}}. Nuclearweaponarchive.org. Retrieved on 2011-05-01.</ref> the 9.3-megaton [[Operation Hardtack I|Hardtack Poplar]] test at 95%,<ref>[https://nuclearweaponarchive.org/Usa/Tests/Hardtack1.html Operation Hardtack I] {{webarchive|url=https://web.archive.org/web/20160910232153/https://nuclearweaponarchive.org/Usa/Tests/Hardtack1.html|date=September 10, 2016}}. Nuclearweaponarchive.org. Retrieved on 2011-05-01.</ref> and the 4.5-megaton [[Operation Redwing|Redwing Navajo]] test at 95% fusion.<ref>[https://nuclearweaponarchive.org/Usa/Tests/Redwing.html Operation Redwing] {{webarchive|url=https://web.archive.org/web/20160910232205/https://nuclearweaponarchive.org/Usa/Tests/Redwing.html|date=September 10, 2016}}. Nuclearweaponarchive.org. Retrieved on 2011-05-01.</ref>