GMAT网络课堂阅读笔记-王昆嵩主讲8

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1、Passage1Virtuallyeverythingastronomersknownaboutobjectsoutsidethesolarsystemisbasedonthedetectionofphotons-quantaofelectromagneticradiation.Yetthereisanotherformofradiationthatpermeatestheuniverse:(5)neutrinos.With(asitsnameimplies)noelectriccharge,andnegligiblemass,theneutrinointeractswith

2、otherparticlessorarelythataneutrinocancrosstheentireuniverse,eventraversingsubstantialaggregationsofmatter,withoutbeingabsorbedorevendeflected.Neu-(10)trinoscanthusescapefromregionsofspacewherelightandotherkindsofelectromagneticradiationareblockedbymatter.Furthermore,neutrinoscarrywiththemi

3、nformationaboutthesiteandcircumstancesoftheirproduction:therefore,thedetectionofcosmicneutrinos(15)couldprovidenewinformationaboutawidevarietyofcosmicphenomenaandaboutthehistoryoftheuni-verse.Buthowcanscientistsdetectaparticlethatinteractssoinfrequentlywithothermatter?Twenty-fiveyears(20)pa

4、ssedbetweenPauli'shypothesisthattheneutrinoexistedanditsactualdetection:sincethenvirtuallyallresearchwithneutrinoshasbeenwithneutrinoscreatedartificiallyinlargeparticleacceleratorsandstudiedunderneutrinomicroscopes.Butaneutrinotelescope,(25)capableofdetectingcosmicneutrinos,isdifficulttoco-

5、nstruct.Noapparatuscandetectneutrinosunlessitisextremelymassive,becausegreatmassissynonymouswithhugenumbersofnucleons(neutronsandprotons),andthemoremassivethedetector,thegreaterthepro-(30)babilityofoneofitsnucleon'sreactingwithaneutrino.Inaddition,theapparatusmustbesufficientlyshieldedfromt

6、heinterferingeffectsofotherparticles.Fortunately,agroupofastrophysicistshasproposedameansofdetectingcosmicneutrinosbyharnessingthe(35)massoftheocean.NamedDUMAND,forDeepUnder-waterMuonandNeutrinoDetector,theprojectcallsforplacinganarrayoflightsensorsatadepthoffivekilo-metersundertheoceansurf

7、ace.Thedetectingmediumistheseawateritself:whenaneutrinointeractswitha(40)particleinanatomofseawater,theresultisacascadeofelectricallychargedparticlesandaflashoflightthatcanbedetectedbythesensors.Thefivekilometersofsea-waterabovethesensorswillshieldthemfr