80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...
Radioactivity
1. ATOMIC NUCLEUS AND RADIOACTIVITY E.H.ANNEX Medical Physicist Batra Hospital and Medical Research Centre New Delhi 62
2. 1896 – Henry Becquerel – studied phosphorescence with Uranyl sulfate – discovered the Uranium Radioactivity. Nobel Prize in Physics – 1903 for discovery of radioactivity Becquerel investigated whether there was any connection between X-rays and naturally occurring phosphorescence. He had inherited from his father a supply of uranium salts, which phosphoresce on exposure to light. When the salts were placed near to a photographic plate covered with opaque paper, the plate was discovered to be fogged. The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom. Later, Becquerel showed that the rays emitted by uranium, which for a long time were named after their discoverer (‘Becquerel rays’), caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields.
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7. Summary of Masses 0.511 5.486x10 -4 9.109 x 10 -31 Electron 939.57 1.008665 1.6750 x 10 -27 Neutron 938.28 1.007276 1.6726 x 10 -27 Proton MeV/c 2 u kg Particle Masses
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19. Nuclear Energy Our everyday life units for energy and mass are not suitable for atoms. The atomic mass unit (unified mass unit): 1u = 1.66 x10 27 kg Mass of a hydrogen atom is 1.0078 u The energy unit is the electronvolt (eV). 1eV = 1.60 10 19 J 1Mev = 1.60 10 13 J E (1 u) = mc 2 = 931 MeV
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22. Binding Energy Einstein’s famous equation E = m c 2 Deuteron: mc 2 = 1875.6MeV Difference is Binding energy , 2.2MeV Proton: mc 2 = 938.3MeV Neutron: mc 2 = 939.5MeV Adding these, get 1877.8MeV
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26. Types of Radioactivity particles: electrons : photons (more energetic than x-rays) penetrate! Easily Stopped Stopped by metal particles: nucleii Radioactive sources B field into screen detector
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28. -decay Emission of an -particle or 4 He nucleus (2 neutrons, 2 protons) This is the preferred decay mode of nuclei heavier than 209 Bi with a proton/neutron ratio along the valley of stability The parent decreases its mass number by 4, atomic number by 2
29. -decay Emission of an electron (and an antineutrino) during conversion of a neutron into a proton The mass number does not change, the atomic number increases by 1. Example: 87 Rb -> 87 Sr + e – + This is the preferred decay mode of nuclei with excess neutrons compared to the valley of stability
30. -decay and electron capture Emission of a positron (and a neutrino) or capture of an inner-shell electron during conversion of a proton into a neutron The mass number does not change, the atomic number decreases by 1. Examples: 40 K -> 40 Ar + e + + 50 V+ e – -> 50 Ti + + These are the preferred decay modes of nuclei with excess protons compared to the valley of stability
43. The Decay Constant N/ t N(t) N number of radionuclides at some moment of time t N number of nuclei that decay in a time interval t decay constant N 0 initial number of nuclei T 1/2 half-life e = 2.718 N = N t N(t) = N 0 e t N 0 /2 = N 0 e T 1/2 T 1/2 = 0.693/
The isotope shown here is Dysprosium The lecturer can point out that not decay is mentioned but transition - this is due to the fact that the isotope remains from the same element. Just some internal energy is lost and emitted in the form of electromagnetic radiation.
