Castle Bravo: Difference between revisions

|picture = Castle-bravo-detonationFile:CastleBravo1.ogggif

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.