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ThefirstnuclearweaponWhatisnuclearweapon？Anuclearweaponisanexplosivedevicethatderivesitsdestructiveforcefromnuclearreactions,eitherfissionoracombinationoffissionandfusion.Bothreactionsreleasevastquantitiesofenergyfromrelativelysmallamountsofmatter.ThephysicistAlbertEinsteindidnotdirectlyparticipateintheinventionoftheatomicbomb.Butasweshallsee,hewasinstrumentalinfacilitatingitsdevelopment.In1905,aspartofhisSpecialTheoryofRelativity,hemadetheintriguingpointthatalargeamountofenergycouldbereleasedfromasmallamountofmatter.Thiswasexpressedbytheequation

E=mc2(energy=masstimesthespeedoflightsquared).Theatomicbombwouldclearlyillustratethisprinciple.Trinitywasthecode

nameofthefirstnuclearweaponstestofanatomicbomb.ThistestwasconductedbytheUnitedStatesArmyonJuly16,1945intheJornadadelMuertodesertabout35miles(56

km)southeastofSocorro,NewMexico,atthenewWhiteSandsProvingGround,whichincorporatedtheAlamogordoBombingandGunneryRange.(ThesiteisnowtheWhiteSandsMissileRange.)ThedateofthetestisusuallyconsideredtobethebeginningoftheAtomicAge.

ThefirstnuclearweaponbombOnAugust6,1945，thefirstatomicweaponcalledLittleBoybombedonHiroshima.ThenonAugust9,1945,anotherweaponcalledfatmandroppedonNagasaki-shi.Purefissionweaponswerethefirstnuclearweaponsbuiltandhavesofarbeentheonlytypeeverusedinwarfare.Theactivematerialisfissileuranium(U-235)orplutonium(Pu-239),explosivelyassembledintoachain-reactingcriticalmassbyoneoftwomethods

Fusion-boostedfissionweaponsimproveontheimplosiondesign.Thehighpressureandtemperatureenvironmentatthecenterofanexplodingfissionweaponcompressesandheatsamixtureoftritiumanddeuteriumgas(heavyisotopesofhydrogen).Thehydrogenfusestoformheliumandfreeneutrons.Theenergyreleasefromthisfusionreactionisrelativelynegligible,buteachneutronstartsanewfissionchainreaction,speedingupthefissionandgreatlyreducingtheamountoffissilematerialthatwouldotherwisebewastedwhenexpansionofthefissilematerialstopsthechainreaction.Boostingcanmorethandoubletheweapon'sfissionenergyrelease.Two-stagethermonuclearweaponsareessentiallyachainoffission-boostedfusionweapons(nottobeconfusedwiththepreviouslymentionedfusion-boostedfissionweapons),usuallywithonlytwostagesinthechain.Thesecondstage,calledthe"secondary,"isimplodedbyx-rayenergyfromthefirststage,calledthe"primary."Thisradiationimplosionismuchmoreeffectivethanthehigh-explosiveimplosionoftheprimary.Consequently,thesecondarycanbemanytimesmorepowerfulthantheprimary,withoutbeingbigger.Thesecondarycanbedesignedtomaximizefusionenergyrelease,butinmostdesignsfusionisemployedonlytodriveorenhancefission,asitisintheprimary.Morestagescouldbeadded,buttheresultwouldbeamulti-megatonweapontoopowerfultoserveanyplausiblepurpose.Apartfromtheiruseasweapons,nuclearexplosiveshavebeentestedandusedforvariousnon-militaryuses,suchasnuclearplant.Nuclearpowerplant

Becauseoftheimmensemilitarypowertheycanconfer,thepoliticalcontrolofnuclearweaponshasbeen