中国科学技术大学：《物理学》课程教学资源（科普报告）正电子在材料科学中的应用

正电子技术的在材料科学 中应用 @ e 中国科学技术大学 核固体物理实验室 Laboratory of Nuclear Solid State Physics,USTC

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内容提要 正电子概况 正电子湮灭探测技术 正电子技术的应用 LN PDF created with pdfFactory Pro trial version www.pdffactory. com

正电子发现 1928 Predicted by Dirac 1930 Found by Z.Y.Zhao 1932 Found in osmic Radiations by Anderson 1940s rstudiesctronic structures 1950's Establishment of ROsitron Annihilation Spectroscopy 1968 First LINAC based Positron Generation 1982 Slow positron beams

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Relativity Quantum Theory =Antimatter e 5-m平0 Paul A.M.Dirac (1928) 0 0 10 0 1 0 0 +1m 111 1 0 0 0 0 Electron:spin 1/2 Another spin-1/2 particle?? For v#0,upper and lower components mix 1929:Positive electron proton ??? 1931:m(e-)=m(e+)!Annihilation possible

1930年春天，赵尧先生© CT实验时发现，y射线被铅散射时， 除康普顿散射外，伴随着反常吸收 还有一种特殊的光辐射出现。当时 测定的这种特殊辐射的强度是大致 各向同性的，并且每个光子的能量 汽一个电子质量的相当能量很接近。 花揭示了一种新的反应机制。赵忠 赵忠尧 尧这乔实验结果写成第二篇论文， (1902-1998) 题目为飞硬y射线的散射》，并于 1930年10月在美国《物理评论》杂 中国科学技术大学 志上发表。 近代物理系的创建 者和首任系主任

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Cloud Chamber Photograph Positron Lead plate Larger curvature Carl Anderson of particle 1905-1991 above plate MARC1H15,1923 PHYSICAL REVIEW VOLUME 43 means it's moving slower (lost energy as it The Positive Electron CARL D.ANDERSON,Californie Institule of Tecknology,Pasudend,California passed through) (Received February 28,1933) Out of a group of 1300 photographs of cosmic-ray tracks curvatures and ionizations produced require the mass to be in a vertical Wilson chamber 15 tracks were of positive less than twenty times the electron mass.These particles particles which could not have a mass as great as that of will be called positrons.Because they occur in groups the proton.From an examination of the energy-loes and associated with other tracks it is concluded that they must ionization produced it is coneluded that the charge is less be secondary particles ejected from atomie nuclei. than twice,and is probably exactly equal to,that of the Editor proton.If these particles carry unit positive charge the N Auguot名1932，during the coureof eleetrons happened to produce two tracko co photographing cosmic-ray tracks produced placed as to give the impression of a single in a vertical Wilson chamber (magnetic field of particle shooting through the lead plate.This

正电子的性质© ●质量：等于电子质量 电荷：与电魂荷数量相等 ● 磁矩： 与电子磁想等，ge/2mc ●寿命： 在真空无电子郵超。 >2×1021年 正电子属轻子族， 所以它是费米子，遵守Fermi-Dirac:统计： 不直接参与强相互作用

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正电子产生 B+-decay (22Na -22Ne et v.+y(1.28 MeV)) pair prodc) Some Cyclotron-produced Radionuclides Common Production Natural abundance Product Decay Mode Reaction of Target Isotope(%) C B 10B(d,n)C 19.7 B(p,n)C 80.3 I3N B+ 12C(d,n)13N 98.9 0 B+ 14N(d,n)15O 99.6 18F B*,EC 20Ne(d,a)18F 90.9 22Na B*,EC 23Na(p,2n)2Na 100

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2.602a 22Na B*(90.4% EC(9.5%) B*(0.1%) 3.7ps y(1.274MeV) 22Ne 100000 22Na 10000 1000 100 10 0.000010.0001 0.001 0.010.1 10 100 P(E)

22-Na 0.511MeV 'e Ba 1.27MeV Energy