放射性核素的衰变规律VIP免费

第三章放射性核素的衰变规律Radioactivedecay目的•熟悉各种衰变的特点•掌握衰变规律与活度计算•了解放射性平衡及放射系内容•α衰变•β衰变•γ衰变•衰变规律•放射性平衡•放射系引言•放射性的发现：贝可勒尔与居里夫妇•放射线的分类及本质•放射性与放射性核素的概念•自发的含义•核衰变的概念与分类•各种放射性核素通过衰变趋向β稳定线•对各类衰变，要求熟悉其含义、方程、对象、能量和纲图HenriBecquerel•1852~1908,France•Frenchphysicistwhodiscoveredradioactivitythroughhisinvestigationsofuraniumandothersubstances.In1903hesharedtheNobelPrizeforPhysicswithPierreandMarieCurieMarieCurie•bornNov.7,1867,Warsaw,Poland,RussianEmpirediedJuly4,1934,nearSallanches,France•Polish-bornFrenchphysicistfamousforherworkonradioactivityandtwiceawinneroftheNobelPrize.WithHenriBecquerelandherhusband,PierreCurie,shewasawardedthe1903NobelPrizeforPhysics.Shewasthensolewinnerofthe1911NobelPrizeforChemistry.ShewasthefirstwomantowinaNobelPrizePierreCurie•bornMay15,1859,Paris,FrancediedApril19,1906,Paris•FrenchphysicalchemistandcowinneroftheNobelPrizeforPhysicsin1903.Heandhiswife,MarieCurie,discoveredradiumandpoloniumintheirinvestigationofradioactivity.放射线的分类及本质放射性(radioactivity)•原子核自发放出α、β、γ等粒子的性质•thespontaneousdisintegrationofatomicnuclei,withtheemissionofusu.penetratingradiationorparticles(Oxford)•propertyexhibitedbycertaintypesofmatterofemittingenergyandsubatomicparticlesspontaneously.Itis,inessence,anattributeofindividualatomicnuclei.(EB)•Note:amajorsourceofheatintheinteriorofboththeEarthandtheMoonisprovidedbyradioactivedecay.(EB)放射性核素(radionuclide)•具有放射性的核素•aradioactivenuclide(Oxford)•aradioactivenuclide(Merriam-Webster)•radioactiveisotope(radioisotope):anyofseveralspeciesofthesamechemicalelementwithdifferentmasseswhosenucleiareunstableanddissipateexcessenergybyspontaneouslyemittingradiationintheformofalpha,beta,andgammarays(EB)（核，放射性）衰变(decay,disintegration)•原子核自发放出α、β、γ等粒子的过程•(ofasubstanceetc.)undergochangebyradioactivity(Oxford)•anyprocessinwhichanucleusemitsaparticleorparticlesordividesintosmallernuclei(Oxford)•原子核自发的结构或能量转变过程α衰变Alphadecayα衰变的定义•放射性原子核自发放出α粒子而变为另一种原子核的过程•typeofradioactivedisintegrationinwhichsomeunstableatomicnucleidissipateexcessenergybyspontaneouslyejectinganalphaparticle•α粒子的实质：高速运动的氦原子核α衰变的方程或：•例：注：衰变过程满足质量数守恒、电荷守恒、能量守恒以及动量守恒αYX4A2ZAZHeYX424A2ZAZαPoRn2188422286α衰变的衰变能和衰变条件•衰变能：•衰变条件：即：只有比较重(A>140)的原子核才可能发生α衰变MMMZZ222)(cmmmQZZ22)(cMMMZZα衰变的对象•丰质子的核素α衰变的动能分配•α粒子的动能远大于子核的反冲动能或：衰变能绝大部分被α粒子带走•原子核的基态与激发态•α粒子的能谱是分立的线状谱•短射程α粒子与长射程α粒子讨论和提问（1~3分钟）α衰变的纲图(decayscheme)一个问题•从Ra-226的衰变纲图看，只有α和γ粒子的发射，为何在发自镭源的射线（图3-1）中显示有β粒子的发射？β衰变betadecayβ衰变的定义•β-衰变、β+衰变和电子俘获(EC)的统称•同量异位跃迁(isobarictransition)•anyofthreeprocessesofradioactivedisintegrationbywhichsomeunstableatomicnucleispontaneouslydissipateexcessenergyandundergoachangeofoneunitofpositivechargewithoutanychangeinmassnumber.•Thethreeprocessesareelectronemission,positron(positiveelect...