Castle Bravo: Difference between revisions

|picture = File:CastleBravo1.gif

|next_test = [[Castle Romeo]]| map_type = Pacific Ocean

[[Fallout]], the heaviest of which was in the form of pulverized surface coral from the detonation, fell on residents of [[Rongelap Atoll|Rongelap]] and [[Utirik Atoll|Utirik]] atolls, while the more [[particulate]] and gaseous fallout spread around the world. The inhabitants of the islands were not evacuated untilonly three days later and suffered [[radiation sickness]]. Twenty-three crew members of the Japanese fishing vessel ''[[Daigo Fukuryū Maru]]'' ("Lucky Dragon No. 5") were also contaminated by the heavy fallout, experiencing [[acute radiation syndrome]], including the death six months later of Kuboyama Aikichi, the boat's chief radioman. The blast incited a strong international reaction over atmospheric thermonuclear testing.<ref>{{Cite book |last=Foster |first=John Bellamy |title=The Ecological Revolution: Making Peace with the Planet |date=2009 |publisher=Monthly Review Press |page=73}}</ref>

The primary device was a ''COBRA'' [[boosted fission weapon|deuterium-tritium gas-boosted]] atomic bomb made by [[Los Alamos Scientific Laboratory]], a very compact MK 7 device. This boosted fission device washad been tested in the ''[[Upshot -Knothole]]'' ''Climax'' event and yielded {{convert|61|ktonTNT|abbr=~}} (out of 50–70 kt expected yield range). It was considered successful enough that the planned operation series ''Domino'', designed to explore the same question about a suitable primary for thermonuclear bombs, could be canceled.<ref name="swordsoarIII" />{{refpage|197}} The implosion system was quite lightweight at {{convert|900|lb|abbr=on}}, because it eliminated the aluminum pusher shell around the [[Tamper (nuclear weapon)|tamper]]{{refn|group=Note|In the Mark 7 HE system, the irregularities in the implosion front were relatively small rendering the pusher component unnecessary.<ref name="weaponactivity">{{Cite book |last=Glasstone |first=Samuel |title=LA-1632: Weapons Activities of Los Alamos Scientific Laboratory |date=1954 |volume=Part I |author-link=Samuel Glasstone}}</ref>{{refpage|60}}}} and used the more compact ring lenses,{{refn|group=Note|Ring Lenses were used in conjunction with 1E23 type bridge-wire detonators. The ring lenses reduced weapon's external diameter by making the HE layer thinner, and their simultaneity of shock wave emergence was considerably higher compared to previous hyperboloid lenses, enabling better and more accurate compression (LA-1632, table 4.1). At the same time, since the [[high explosive]] layer was thinner it was less opaque for the [[X-ray]]s emitted by the pit.<ref name="weaponactivity" />{{refpage|86}}{{refpage|98}}}} a design feature shared with the Mark 5, 12, 13 and 18 designs. The explosive material of the inner charges in the MK 7 was changed to the more powerful [[Cyclotol]] 75/25, instead of the [[Composition B]] used in most stockpiled bombs at that time, as Cyclotol 75/25 was denser than Composition B and thus could generate the same amount of explosive force in a smaller volume (it provided 13 percent more compressive energy than Comp B).<ref name="weaponactivity" />{{refpage|86}}{{refpage|91}} The composite uranium-plutonium ''COBRA'' core was levitated in a type-D pit. ''COBRA'' was Los Alamos' most recent product of design work on the "new principles" of the hollow core.<ref name="swordsoarIII">{{Cite book |last=Hansen |first=Chuck |url=http://www.uscoldwar.com/ |title=Swords of Armageddon |date=1995 |volume=III |author-link=Chuck Hansen |access-date=December 28, 2016}}</ref>{{refpage|196}} A copper pit liner encased within the weapon-grade plutonium inner capsule prevented DT gas diffusion into the plutonium, a technique first tested in ''[[Greenhouse Item]]''.<ref name="swordsoarIII" />{{refpage|258}} The assembled module weighed {{convert|1840|lb|abbr=on}}, measuring {{convert|30.5|in|abbr=on}} across. It was located at the end of the device, which, as seen in the declassified film, shows a small cone projecting from the ballistic case. This cone is the part of the paraboloid that was used to focus the radiation emanating from the primary into the secondary.<ref name="nucweaparch">{{Cite web |title=The Nuclear Weapon Archive&nbsp;– A Guide to Nuclear Weapons |url=https://nuclearweaponarchive.org/ |access-date=September 23, 2017 |website=nuclearweaponarchive.org}}</ref>

The device was called '''SHRIMP,''', and had the same basic configuration (radiation implosion) as the ''[[Ivy Mike]]'' wet device, except with a different type of [[nuclear fusion|fusion]] fuel. ''SHRIMP'' used [[lithium deuteride]] (LiD), which is solid at room temperature; ''Ivy Mike'' used [[cryogenic]] liquid [[deuterium]] (D₂), which required elaborate cooling equipment. ''Castle Bravo'' was the first test by the United States of a practical deliverable [[hydrogen bomb|fusion bomb]], even though the TX-21 as proof-tested in the Bravo event was not weaponized. The successful test rendered obsolete the cryogenic design used by ''Ivy Mike'' and its weaponized derivative, the [[Mark 16 nuclear bomb|''JUGHEAD'']], which was slated to be tested as the initial ''Castle Yankee''. It also used a {{Convert|9.5|cm|in|-thick|adj=mid|order=flip}} [[7075 aluminum alloy|7075 aluminum]] ballistic case. Aluminum was used to drastically reduce the bomb's weight and simultaneously provided sufficient radiation confinement time to raise yield, a departure from the heavy stainless steel casing (304L or MIM 316L) employed by other weapon-projects at the time.<ref name="swordsoarIII" />{{refpage|54}}{{refpage|237}}<ref name="ThePhysicsFactbook">{{Cite book |last=Sutherland |first=Karen |url=https://hypertextbook.com/facts/2004/KarenSutherland.shtml |title=Density of Steel |date=2004 |author-link=Karen Sutherland |access-date=December 28, 2016}}</ref>

The ''SHRIMP'' was at least in theory and in many critical aspects identical in geometry to the [[Mark 17 nuclear bomb|''RUNT'']] and [[Mark 17 nuclear bomb|''RUNT II'']] devices later proof-fired in ''[[Castle Romeo]]'' and ''[[Castle Yankee]]'' respectively. On paper it was a scaled-down version of these devices, and its origins can be traced back to the spring and summer of 1953. The [[United States Air Force]] indicated the importance of lighter thermonuclear weapons for delivery by the [[B-47 Stratojet]] and [[B-58 Hustler]]. [[Los Alamos National Laboratory]] responded to this indication with a follow-up enriched version of the ''RUNT'' [[Dimensional analysis|scaled down]] to a 3/4 scale radiation-implosion system called the ''SHRIMP''. The proposed weight reduction (from TX-17's {{convert|42000|lb}} to TX-21's {{convert|25000|lb}}) would provide the Air Force with a much more versatile deliverable [[gravity bomb]].<ref name="swordsoarIII" />{{refpage|237}} The final version tested in ''Castle'' used partially enriched [[lithium]] as its fusion fuel. Natural lithium is a mixture of lithium-6 and lithium-7 [[isotopes of lithium|isotopes]] (with 7.5% of the former). The enriched lithium used in ''Bravo'' was nominally 40% lithium-6 (the remainder was the much more common lithium-7, which was incorrectly assumed to be inert). The fuel slugs varied in enrichment from 37 to 40% in {{sup|6}}Li, and the slugs with lower enrichment were positioned at the end of the fusion-fuel chamber, away from the primary. The lower levels of lithium enrichment in the fuel slugs, compared with the [[Mark 14 nuclear bomb|''ALARM CLOCK'']] and many later hydrogen weapons, were due to shortages in enriched lithium at that time, as the first of the ''Alloy Development Plants'' (ADP) started production byin the fall oflate 1953.<ref name="swordsoarmIII">{{Cite book |last=Hansen |first=Chuck |url=http://www.uscoldwar.com/ |title=Swords of Armageddon |date=1995 |volume=III |author-link=Chuck Hansen |access-date=May 20, 2016}}</ref>{{refpage|208}} The volume of LiD fuel used was approximately 60% the volume of the fusion fuel filling used in the wet ''SAUSAGE'' and dry ''RUNT I'' and ''II'' devices, or about {{convert|500|L|sp=us}},{{refn|group=Note|Both SAUSAGE and the two RUNTs (SAUSAGE's "lithiated" versions) had fusion fuel volumes of 840 [[liter]]s. SAUSAGE used an 840-liter version of a cryogenic vessel developed for the PANDA committee (PANDA was SAUSAGE's unclassified name) and in part by the [[National Bureau of Standards]] (see more information [https://nvlpubs.nist.gov/nistpubs/jres/58/jresv58n5p243_A1b.pdf here]). This vessel fits the description of Richard Rhodes in ''Dark Sun'' (p. 490) and Mike's fusion fuel volume assumed by Andre Gsponer and Jean-Pierre Hurni in their paper "The physical principles of thermonuclear explosives, inertial confinement fusion, and the quest for fourth generation nuclear weapons", p. 68.}} corresponding to about 400&nbsp;kg of lithium deuteride (as LiD has a density of 0.78201 g/cm³).<ref name="T4">{{Cite book |last=Holian |first=Kathleen S. |title=T-4 Handbook of Material Properties Data Bases |date=1984 |volume=Ic |author-link=Kathleen S. Holian}}</ref>{{refpage|281}} The mixture cost about 4.54&nbsp;[[USD]]/g at that time. The fusion burn efficiency was close to 25.1%, the highest attained efficiency of the first thermonuclear weapon generation. This efficiency is well within the figures given in a November 1956 statement, when a DOD official disclosed that thermonuclear devices with efficiencies ranging from 15% to up about 40% had been tested.<ref name="swordsoarIII" />{{refpage|39}} [[Hans Bethe]] reportedly stated independently that the first generation of thermonuclear weapons had (fusion) efficiencies varying from as low as 15% to up about 25%.

Attached to the cylindrical ballistic case was a natural-uranium liner, the radiation case, that was about 2.5&nbsp;cm thick. Its internal surface was lined with a [[copper]] liner that was about 240 μm thick, and made from 0.08-μm thick copper foil, to increase the overall albedo of the [[hohlraum]].<ref name="X-Ray Albedo">{{Cite journal |last=Pruitt |author-link=J. S. Pruitt |date=1963 |title=High Energy X-Ray Photon Albedo |journal=Nuclear Instruments and Methods |volume=27 |issue=1 |pages=23–28 |bibcode=1964NucIM..27...23P |doi=10.1016/0029-554X(64)90131-4}}</ref><ref name="γ-Ray Albedo">{{Cite book |last=Bulatov and Garusov |title={{sup|60}}Co and {{sup|198}}Au γ-ray albedo of various materials |date=1958 |author-link=B. P. Bulatov and E. A. Garusov}}</ref>{{check|type=0.08 μm?? -|date=January 2021}} Copper possesses excellent reflecting properties, and its low cost, compared to other reflecting materials like gold, made it useful for mass-produced hydrogen weapons. Hohlraum albedo is a very important design parameter for any inertial-confinement configuration. A relatively high albedo permits higher interstage coupling due to the more favorable azimuthal and latitudinal angles of reflected radiation. The limiting value of the albedo for high-''Z'' materials is reached when the thickness is 5–10&nbsp;g/cm{{sup|2}}, or 0.5–1.0 free paths. Thus, a hohlraum made of uranium much thicker than a free path of uranium would be needlessly heavy and costly. At the same time, the angular anisotropy increases as the atomic number of the scatterer material is reduced. Therefore, hohlraum liners require the use of copper (or, as in other devices, [[gold]] or [[aluminium]]), as the absorption probability increases with the value of ''Z''{{sub|eff}} of the scatterer. There are two sources of X-rays in the hohlraum: the primary's irradiance, which is dominant at the beginning and during the pulse rise; and the wall, which is important during the required radiation temperature's (''T''{{sub|r}}) plateau. The primary emits radiation in a manner similar to a [[Flash (photography)|flash bulb]], and the secondary needs constant ''T''{{sub|r}} to properly implode.<ref name="IC">{{Cite book |title=Current Trends in International Fusion Research Proceedings of the Third Symposium |date=2002}}</ref> This constant wall temperature is dictated by the ablation pressure requirements to drive compression, which lie on average at about 0.4 keV (out of a range of 0.2 to 2 keV){{refn|group=Note|This temperature range is compatible with a hohlraum filling made of a low-''Z'' material because the fission bomb's tamper, pusher and high-explosive lenses as well as interstage's plastic foam strongly [[attenuation|attenuate]] the radiation emitted by the core. Thus, [[X-ray]]s deposited into the hohlraum liner from primary's interface with the interstage (i.e. the primary's outer surface) were "cooler" than the maximum temperature of a fission device.<ref name="Gsponer">{{Cite book |title=The physical principles of thermonuclear explosives, inertial confinement fusion, and the quest for fourth generation nuclear weapons |date=2009}}</ref>{{refpage|25}}<ref name="nucl">https://nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html. {{dead link|date=February 2022}}</ref>}}, corresponding to several million [[kelvin]]s. Wall temperature depended on the temperature of the primary's [[Pit (nuclear weapon)|core]] which peaked at about 5.4 keV during boosted-fission.<ref name="Pritz">{{Cite journal |last=Pritzker |first=Andreas |author-link=A. Pritzger and W. Halg |last2=Hälg |first2=Walter |date=1981 |title=Radiation dynamics of nuclear explosion |journal=Zeitschrift für Angewandte Mathematik und Physik |volume=32 |issue=1 |pages=1–11 |bibcode=1981ZaMP...32....1P |doi=10.1007/BF00953545 |s2cid=122035869}}</ref>{{refpage|1-11}}<ref name="Gsponer" />{{refpage|9}} The final wall-temperature, which corresponds to energy of the wall-reradiated X-rays to the secondary's pusher, also drops due to losses from the hohlraum material itself.<ref name="X-Ray Albedo" />{{refn|group=Note|These losses were associated with material's properties like back-scattering, [[quantum tunneling]], [[Radiant exitance|exitance]] etc.<ref name="X-Ray Albedo" />}} [[Natural uranium]] nails, lined to the top of their head with copper, attached the radiation case to the ballistic case. The nails were bolted in vertical arrays in a double-shear configuration to better distribute the shear loads. This method of attaching the radiation case to the ballistic case was first used successfully in the ''Ivy'' ''Mike'' device. The radiation case had a parabolic end, which housed the [[Mark 15 nuclear bomb|''COBRA'']] primary that was employed to create the conditions needed to start the fusion reaction, and its other end was a [[cylinder]], as also seen in Bravo's declassified film.

The yield of 15 (+/-± 5) Mt<ref>{{Cite web |date=March 6, 1954 |title=Commander Task Group 7.1 Eniwetok to U.S. AEC |url=https://nsarchive.gwu.edu/document/31248-document-3-commander-task-group-71-eniwetok-us-aec-1-march-1954-attached-2-and-6 |access-date=March 1, 2024 |website=National Security Archive}}</ref> was triple that of the 5 Mt predicted by its designers.<ref name="nuclearweaponarchive.org" /><ref name="Rhodes" />{{refpage|541}} The cause of the higher yield was an error made by designers of the device at [[Los Alamos National Laboratory]]. They considered only the lithium-6 isotope in the lithium- deuteride secondary to be reactive; the lithium-7 isotope, accounting for 60% of the lithium content, was assumed to be inert.<ref name="Rhodes" />{{refpage|541}} It was expected that the lithium-6 isotope would absorb a [[neutron]] from the fissioning plutonium and emit an [[alpha particle]] and [[tritium]] in the process, of which the latter would then fuse with the [[deuterium]] and increase the yield in a predicted manner. Lithium-6 indeed reacted in this manner.

:{{sup|7}}Li + {{sup|2}}H → 2 {{sup|4}}He + {{sup|1}}n + 15.123 MeV

Following the test, the [[United States Department of Energy]] estimated that 253 inhabitants of the [[Marshall Islands]] were impacted by the radioactive fallout.<ref>{{Cite journal |last=Lauerman |first=John F. |last2=Reuther |first2=Christopher |date=September 1997 |title=Trouble in Paradise |journal=Environmental Health Perspectives |volume=105 |issue=9 |pages=914–917 |doi=10.2307/3433870 |jstor=3433870 |pmc=1470349 |pmid=9341101}}</ref> This single test exposed the surrounding populations to varying levels of radiation. The fallout levels attributed to the Castle Bravo test are the highest in history.<ref name=":2">{{Cite journal |date=January 1, 1966 |title=Fallout Radiation And Growth |journal=The British Medical Journal |volume=1 |issue=5496 |page=1132 |doi=10.1136/bmj.1.5496.1132-a |jstor=25407693 |pmc=1844058 |pmid=20790967}}</ref>{{failed verification|date=August 2018}} Populations neighboring the test site were exposed to high levels of radiation resulting in mild radiation sickness of many (nausea, vomiting, diarrhea). The unexpected strength of the detonation, combined with shifting wind patterns, sent some of the radioactive fallout over the inhabited atolls of [[Rongelap_Atoll|Rongelap]] and [[Utrik_Atoll|Utrik]]. Within 52 hours, the 86 people on Rongelap and 167 on Utrik were evacuated to [[Kwajalein_Atoll|Kwajalein]] for medical care.<ref>{{cite web |title=The Legacy of U.S. Nuclear Testing and Radiation Exposure in the Marshall Islands |url=https://mh.usembassy.gov/the-legacy-of-u-s-nuclear-testing-and-radiation-exposure-in-the-marshall-islands/ |publisher=[[United States Embassy|U.S. Embassy]] in the Republic of the Marshall Islands |access-date=8 July 2024 |date=15 September 2012}}</ref> Several weeks later, many people began suffering from [[alopecia]] (hair loss) and skin lesions as well.<ref>{{Cite journal |date=January 1, 1955 |title=Radioactive Fallout in the Marshall Islands |journal=Science |volume=122 |issue=3181 |pages=1178–1179 |bibcode=1955Sci...122.1178. |doi=10.1126/science.122.3181.1178 |jstor=1749478 |pmid=17807268}}</ref>