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