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A.SpontaneousFission自发裂变源1)Themostcommonspontaneousfissionsourceis252Cf;2)Half-time:2.65y;3)thedominantdecaymechanismisαdecay;4)theenergyspectrumofneutronsisplottedinfig.1-10.Severaldifferenttargetmaterialscanleadto(α,n)reactionsforthealphaparticleenergieswhicharereadilyavailableinradioactivedecay.ThemaximumneutronyieldisobtainedwithBeasthetarget:Someradioisotopegamma-rayemitterscanalsobeusedtoproduceneutronswhencombinedwithanappropriatetargetmaterial.Theresultingphotoneutronsourcesarebasedonsupplyingsufficientexcitationenergytoatargetbyabsorptionofgamma-rayphotontoallowtheemissionoffreeneutron.Onlytwotargetnuclei,9Beand2H,areofanypracticalsignificationforradioisotopesource.1)Themaindisadvantageofphotoneutronsources:Itisneededthatverylargegamma-rayactivitiesmustbeusedinordertoproduceneutronsourcesofattractiveintensity.onegammaray(105or106)→oneneutron2)Someofthemorecommongamma-rayemittersare226Ra,124Sb,72Ga,140Laand24Na.Becausealphaparticlesaretheonlyheavychargedparticleswithlowzconventientlyavailablefromradioisotopes,reactionsinvolvingincidentprotons,deuterons,andsoon,mustrelyonartificallyacceleratedparticles.Twoofthemostcommonreactionofthistypeusedtoproduceneutronsare:2中子的分类与性质(2)中子的性质3中子与物质的相互作用反冲质子在实验室座标系中的能量分布的概率密度函数为:(2)中子的俘获2)发射带电粒子的中子核反应4中子探测的基本方法(1)核反应法反应均为放热反应,反应能Q在生成核与出射粒子之间分配。由于反应能Q比较大,又主要用于慢中子探测,即:(2)核反冲法(3)核裂变法(4)活化法照射冷却4小时后测量有8种痕量元素,4周后测量发现其他元素存在。核技术基础知识中子-伽马测井原理及应用:不同岩性的地层和不同的孔隙液体,热中子寿命τ不一样,可以利用它来区分油水层,划分油、气、水界面。谢谢!2中子源2)(,n)型中子源。2、加速器中子源