核科学起源.pptx
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1、RadiochemistryRadiochemistry放射化学放射化学 Chapter1 Origin of Nuclear ScienceChapter1 Origin of Nuclear Science第一章第一章 核科学起源核科学起源杨金玲杨金玲Wilhelm Conrad Roentgen(1845-1923)In 1895 W.Roentgen 伦琴伦琴discovered that when cathode rays 阴极射线阴极射线(i.e.electrons)struck the wall of anevacuated glass tube,it caused the wa
2、ll material to emit visible light(fluoresce荧光荧光),while at thesame time a very penetrating radiation 穿透辐射穿透辐射was produced.The name X-ray was given to this radiation.发现发现x x射线射线Antoine Henri Becquerel(1852-1908)Becquerel 贝克勒尔贝克勒尔soon found that the radiation causing the blackening wasnot a transformat
3、ion of solar energy because it was found to occur even with assemblies thathad not been exposed to light;the uranyl(铀酰铀酰)salt obviously produced radiation spontaneously.Thisradiation,which was first called uranium rays(or Becquerel rays)but later termed radioactiveradiation(or simply radioactivity)1
4、,was similar to X-rays in that it ionized air,as observedthrough the discharge of electroscopes.研究研究x x射线产生原因时,发现射线产生原因时,发现硫酸钾复盐具有的自发射线硫酸钾复盐具有的自发射线Becquerel Becquerel 的发现的发现vRoentgenRoentgen(伦琴)发现了令人费解的(伦琴)发现了令人费解的 射线,这种射线在玻璃壁和其它一些射线,这种射线在玻璃壁和其它一些材料中会产生荧光(当时称为磷光);材料中会产生荧光(当时称为磷光);v18801880年年Becquere
5、lBecquerel,受他祖父和父亲的影响,对磷光现象感兴趣,制备出硫,受他祖父和父亲的影响,对磷光现象感兴趣,制备出硫酸铀酰钾(酸铀酰钾(K K2 2UOUO2 2(SO(SO4 4)2 2.2H.2H2 2O O););v18961896年,年,Becquerel Becquerel 提供了第一批实验结果:硫酸铀酰复盐晶体受强烈阳提供了第一批实验结果:硫酸铀酰复盐晶体受强烈阳光照射后,放出一种穿透能力很强的辐射;光照射后,放出一种穿透能力很强的辐射;(1 1)在强光、弱光、无光的条件下,铀盐都具有感光现象;)在强光、弱光、无光的条件下,铀盐都具有感光现象;(2 2)其它铀盐、亚铀盐、铀盐溶
6、液、金属铀都能产生这种辐射,且与)其它铀盐、亚铀盐、铀盐溶液、金属铀都能产生这种辐射,且与铀含量成正比;铀含量成正比;Marie Curie(1867-1934)Marie Curie 玛丽居里玛丽居里subsequently showed that all uranium and thorium compounds produced ionizingradiation independent of the chemical composition of the salts.This was convincing evidencethat the radiation was a propert
7、y of the element uranium or thorium.Moreover,she observedthat some uranium minerals such as pitchblende沥青铀矿沥青铀矿 produced more ionizing radiation than pureuranium compounds.发现发现U U,ThTh也有类似的性质,也有类似的性质,进一步研究时发现某些矿物进一步研究时发现某些矿物中的放射性比其中所含中的放射性比其中所含U U,ThTh的放射性要强的多的放射性要强的多vAfter hard working,the Curies d
8、iscovered polonium钋钋(1898,7)v1898,9 the Curies,together with G.Bemont,isolated another radioactive substance for which they suggested the name radium镭镭.vIn order to prove that polonium and radium were in fact two new elements,large amounts of pitchblende were processed,and in 1902 M.Curie announced
9、that she had been able to isolate about 0.1 g of pure radium chloride from more than one ton of pitchblende waste.The determination of the atomic weight of radium and the measurement of its emission spectrum provided the final proof that a new element had been isolated.CurieCurie夫妇夫妇 的成就的成就v发现钍发出与铀具
10、有相似的射线;发现钍发出与铀具有相似的射线;v天然铀矿石的放射性比纯铀、人工合成铀矿石的强;天然铀矿石的放射性比纯铀、人工合成铀矿石的强;v在天然铀矿石的分离过程,发现了钋和镭元素,并经光谱法证实;在天然铀矿石的分离过程,发现了钋和镭元素,并经光谱法证实;测定了镭的分子量测定了镭的分子量226.5226.5;v建立了首个镭和钡分离的化学分离方法;建立了首个镭和钡分离的化学分离方法;v测定了浓缩铀式样的热效应,发出测定了浓缩铀式样的热效应,发出100cal/g.h100cal/g.h。W.Crookes and Becquerel madean important discovery.Preci
11、pitating a carbonate salt from a solution containing uranyl ions铀酰铀酰离子离子,they discovered that while the uranium remained in the supernatant liquid 上层清液上层清液in the form of the soluble uranyl carbonate complex,the radioactivity originally associated with the uranium was now present in the precipitate,w
12、hich contained no uranium.Moreover,the radioactivity of the precipitate slowly decreased with time,whereas the supernatant liquid showed a growth of radioactivity during the same period(Fig.1.1).vSimilar results were obtained by E.Rutherford and F.Soddy when investigating the radioactivity of thoriu
13、m.vLater Rutherford and F.E.Dorn found that radioactive gases(emanation射气射气)could be separated from salts of uranium and thorium.After separation of the gas from the salt,the radioactivity of the gas decreased with time,while new radioactivity grew in the salt in a manner similar to that shown in Fi
14、g.1.1.vThe rate of increase with time of the radioactivity in the salt was found to be completely independent of chemical processes,temperature,etc.Rutherford and Soddy concluded from these observations that radioactivity was due to changes within the atoms themselves.They proposed that,when radioac
15、tive decay occurred,the atoms of the original elements(e.g.of U or of Th)were transformed into atoms of new elements.RutherfordRutherford和和SoddySoddy的转化假说的转化假说v18991899年发现在钍、镭和锕的化合物都可以释放出放射性的射气,这种射气是年发现在钍、镭和锕的化合物都可以释放出放射性的射气,这种射气是惰性的。惰性的。v在射气的研究中,得到两个重要的结论:在射气的研究中,得到两个重要的结论:(1 1)放射性物质的放射性活度不是永远不变的,是
16、随时间而衰减的,其)放射性物质的放射性活度不是永远不变的,是随时间而衰减的,其时间特性因物质而异;时间特性因物质而异;(2 2)放射性过程伴随有放射性原子的化学性质而变化。)放射性过程伴随有放射性原子的化学性质而变化。v19031903年,年,RutherfordRutherford和和SoddySoddy才对放射性的本质有十分深入的了解:才对放射性的本质有十分深入的了解:v(1 1)放射性元素不断地自发地从一种化学元素转变为另一种元素;)放射性元素不断地自发地从一种化学元素转变为另一种元素;v(2 2)上述转化过程中伴随着放射性辐射;)上述转化过程中伴随着放射性辐射;v(3 3)这种放射性过
17、程是原子内部的亚原子变化。)这种放射性过程是原子内部的亚原子变化。vThe radioactive elements were called radioelements.Lacking names for these radioelements,letters such as X,Y,Z,A,B,etc.,were added to the symbol for the primary(i.e.parent)element.Thus,UX was produced from the radioactive decay of uranium,ThX from that of thorium,et
18、c.These new radioelements(UX,ThX,etc.)had chemical properties that were different from the original elements,and could be separated from them through chemical processes such as precipitation沉淀沉淀,volatilization挥发挥发,electrolytic deposition电解沉积电解沉积,etc.The radioactive daughter elements decayed further
19、to form still other elements,symbolized as UY,ThA,etc.vA careful study of the radiation emitted from these radioactive elements demonstrated that it consisted of three components which were given the designation alpha(),beta(),and gamma().vAlpha-radiation was shown to be identical to helium ions(He)
20、,whereas beta-radiation was identical to electrons.Gamma-radiation had the same electromagnetic nature as X-rays but was of higher energy.vThe decay rate could be expressed in terms of a half-life半衰期半衰期,which is the time it takes for the radioactivity of a radioelement to decay to one-half of its or
21、iginal value.vHalf-lives for the different radioelements were found to vary from fractions of a second to millions of years;e.g.that of ThA is 0.1 of a second,of UX it is 24.1 days(Fig.1.1),and of uranium,millions of years.射线性质的早期研究过程射线性质的早期研究过程v18991899年,年,RutherfordRutherford利用静电计研究了射线的自身性质:利用静电计研
22、究了射线的自身性质:结论:一种射线被结论:一种射线被千分之几的厘米千分之几的厘米的铝箔表面吸收(的铝箔表面吸收(););一种在铝箔厚度增加到一种在铝箔厚度增加到100100倍才被倍才被大量吸收大量吸收 ();铝的吸收系数为铝的吸收系数为15cm15cm-1-1,射线的电离效应被减弱的量与初始值之间按照指数射线的电离效应被减弱的量与初始值之间按照指数 衰减公式:衰减公式:e e d d。vCurieCurie夫人发现,夫人发现,射线的射线的 值不是常数,随着射线进入吸收体的深度增加而增加。值不是常数,随着射线进入吸收体的深度增加而增加。vBraggBragg提出并证实了提出并证实了 粒子具有一定
23、的射程;并发现一些放射性物质放出的粒子具有一定的射程;并发现一些放射性物质放出的 射线具有不射线具有不同的特征射程;同的特征射程;v其它科学家研究:通过磁场和静电场的偏转实验证实其它科学家研究:通过磁场和静电场的偏转实验证实 和和 射线是高速运动的离子流;射线是高速运动的离子流;证实证实 粒子就是氦粒子;粒子就是氦粒子;发现了发现了 射线,但是其性质和射线,但是其性质和 射线相似,只是能量不同,在随后一射线相似,只是能量不同,在随后一 段时间内,没有区分段时间内,没有区分 射线射线 射线。射线。Discovery of isotopesvBy 1910 approximately 40 dif
24、ferent chemical species had been identified through their chemical nature,the properties of their radiation,and their characteristic half-lives.The study of the generic relationships in the decay of the radioactive species showed that the radioelements could be divided into three distinct series.vU系
25、系 4n+2 238U-206PbvTh系系 4n 232Th-208PbvAc系系 4n+3 235U-207PbvSoddy proposed the name isotopes 同位素同位素to account for different radioactive species which have the same chemical identity.年代年代现代核科学发展的重要步骤现代核科学发展的重要步骤490-430B.CEmpedocles提出万物是由气、土、水和火四种元素组成。任何物质都是提出万物是由气、土、水和火四种元素组成。任何物质都是通过它们之间的转化而形成的。(四种元素
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