how to make and dismantle an atomic bomb
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HowtoBuildandDismantleNuclearBombs
Dr.CharlesD.FergusonPresident,Federa<onofAmericanScien<sts
DepartmentofPhysicsColloquium
AmericanUniversityFebruary15,2012
Agenda
• Howdonuclearbombswork?
• Whathavescien<stsdonetoreducenucleardangersandinformgovernmentpolicyandthepublicdebateaboutthisandotherna<onalsecurityissues?
• Whatcanweinthescien<ficcommunityfurtherdo?
NuclearFission• “SpliNng”ofanucleus• Fissileisotopes:thosethat
fissionaPercapturinganeutronofalmostanyenergy;e.g.,U‐233,U‐235,Pu‐239,Pu‐241,Np‐237,Am‐241
• Fissionableisotopes:thosethatfissionaPercapturinganeutronwithenergiesaboveathreshold;e.g.,U‐238,Pu‐238
• Fer/leisotopes:thosethatcanbeusedtoproducefissilematerialaPerabsorbinganeutron;e.g.,Th‐232andU‐238
A neutron can: 1. Cause fission 2. Be absorbed without resulting in fission 3. Escape
ChainReac<on
NuclearFusion
CurveofBindingEnergy
Fusion Fission
GrowthofNuclearChainReac<on
Number of Fissions = 2Generation After 80 generations, 280 fissions or about 1024 have occurred. This number of fissions is required to produce the explosive energy in a typical nuclear weapon – within a small fraction of a second – within microseconds.
Time or # Generations
# F
issi
ons
Exponential growth
Two Traditional Paths to Nuclear Weapons: Make Highly Enriched Uranium (HEU) or
Produce Plutonium
NuclearWeaponsTypes
• Simple: Gun‐type Implosiontype
• Sophis<cated Boosted(fission‐fusion) Thermonuclear
ExplosiveYields
• Typicalconven<onalmilitarybomb:
1,000poundsofTNTexplosiveequivalent,or½ton.• “Low‐yield”nuclearweapon:5kilotonsor5,000tons
• Hiroshimabomb:13kilotonsor13,000tons• TypicalnuclearweaponinU.S.arsenal:100to300kilotonsor100,000to300,000tons
Gun‐TypeNuclearWeapon
Final assembly is supercritical without change in density Need greater than critical mass of material – inefficient use of materials; Requires HEU – spontaneous fission rate of Pu is too great.
HiroshimaBomb–“LieleBoy”
Gun Type – Easiest to design and build (Hiroshima bomb was never tested)
About 13 kiloton explosive yield
ImplosionBomb
FirstNuclearTest:“Trinity”device:July16,1945
Hiroshima:August6,1945
Nagasaki:August9,1945
HansBethe,LosAlamos,andtheFoundingoftheFedera<onofAtomic/American
Scien<sts
“Fat Man”: Nagasaki Bomb
Schema<cofPrimaryPartofBomb
Aluminum case (1 cm) Source: Steve Fetter et al., “Detecting Nuclear Weapons,” 1990
High explosive (10 cm)
Tamper (tungsten or uranium) (3 cm)
Beryllium reflector (2 cm)
Fissile material (WgU or WgPu) WgU: 12 kg, 7 cm outside,
1.23 cm thick WgPu: 4 kg, 5 cm outside,
0.75 cm thick
Hollow core, where D and T are injected for boosting.
ThermonuclearWeapons:Scien<sts’Advice(ForandAgainst)totheGovernment
NuclearTes<ng:SurpriseResultsfromThermonuclearTests
Contamina<onfromNuclearTes<ng
NuclearTestBanDebate:Bethe,EdwardTeller,LinusPauling,andAndreiSakharov
MissileDefenseAnalysisin1960sthrough1980s:BetheandRichardGarwin
ObamaAdministra<on’sMissileDefenseSystem
“UpseNngtheReset,”2011Federa<onofAmericanScien<stsReportbyYousafBueandTedPostol
Dual-Use Dilemma: Atoms for Peace and Atoms for War are Intertwined
DeathbyClimateChangeorNuclearWar?
SnapshotofNuclearPowerToday• about15%ofglobalelectricitydemandandabout6%oftotalglobalenergyuse
•30countries+Taiwanopera/ngabout430reactors(370GW)[dozenscurrentlyshutdowninJapan]
•11countriesenrichinguranium
•5countriesreprocessingspentfuelcommercially
•0countrieswithgeologicrepositoriesfornuclearwaste
Predic<onsinthePastWereVeryDifferent
Source: Frank von Hippel, Princeton University and FAS
Sources:IAEAPRISandMycleSchneiderConsul<ng
*Sources:U.S.StateDepartmentandC.D.FergusonandM.Smith,ForeignPolicy,Jan/Feb2009
?
*
BarrierstoNewBuild
Manyfactorscomplicatenewnuclearbuild– Cost– Time
– Personnel
Sources:IAEAPRISandForeignPolicy
“WedgeModel”forCounteringClimateChange
Source:S.PacalaandR.Socolow,Science,August14,2004.
Sources:EIA,OakRidgeNa<onalLaboratory,andFerguson&Smith,ForeignPolicy
• Risk=ProbabilityXSeverity• Riskcanbesignificantwhenuncertaintyislarge• Riskcanbehighwhenprobabilityislow
Uncertainty and Risk
Prob
abili
ty
Severity
Uncertainty Range
(housefire)
Source: Jay Gulledge, Pew Center on Climate Change and FAS member
RichardFeynman:ChallengerInves<ga<on
• hep://www.youtube.com/watch?v=8qAi_9quzUY
• Applyourresearchskillstopublicpolicyandsocietalissues
• Writepopularar<clesaboutscienceforthepublicandpolicymakers
• Educatethenewsmediaaboutgoodscienceandconceptssuchasriskanduncertainty
• Getinvolvedwithschoolboardsandothergovernmentins<tu<onsthatdeterminesciencecurriculaandtextbookselec<on
• Writetopoli<cianstoinformthemaboutscienceaspectsofpolicydecisions
WhatCanWe—intheScien<ficCommunity—Do?
WhatCanWe,Scien<sts,Do?• Educatethenextgenera<onofpolicymakers:giveguestlecturesorteachadjunctcoursestopoli<calsciencestudents
• InteractwiththeEduca<onDepartmentattheuniversity
• Talktostudentsinmiddleandhighschoolsaboutcareersinscience
WhatWe,Scien<sts,CanDo?
• Joinscience‐basedNGOs:Federa<onofAmericanScien<sts(www.fas.org),UnionofConcernedScien<sts,e.g.
• Workforscience‐basedNGOs
• JointheAPSunitForumonPhysicsandSociety
• ApplyforgovernmentfellowshipsthroughAPS,AIP,orAAAS
Thankyouverymuchforyouraeen<on
• Anyques<ons?• FormoreaboutFAS,seeFAS.org
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