S117Lecture22011

S117Lecture22011 - Radioactivity 1896 Henri Becquerel discovers that a Uranium ore emitted"rays that exposed a photographic plate(in the absence of

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Radioactivity 1896 Henri Becquerel discovers that a Uranium ore emitted “rays” that exposed a photographic plate (in the absence of sunlight). The original ore after emission of the rays has a component that has a different chemical properties (is a different element). The emitted rays can also be characterized by how they behave in electric and magnetic fields. Recall that charged particles are deflected by electric and magnetic fields. These emissions are determined to be charged particles! Alpha ( ) particles : Charge = +2 determined to be the same as He nuclei. Beta ( ) rays : Charge = +1 and -1 Those with -1 charge determined to be the same as the electron. Those with +1 charge are called positrons . Gamma ( ) rays : neutral and have no mass Radioactivity is a spontaneous, naturally occurring process!
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“Rutherford’s“ Gold foil experiment (1910-1911) http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf Most of the time the incident alpha particles passed directly through the gold foil and were detected on the ZnS coated screen which scintillated when the alpha particles struck it. Sometimes however the alpha particles were detected through large angles. The animation is an idealized version of the Rutherford experiment. For a realistic picture of how the experiment was carried out, see the link below. See also http://web.lemoyne.edu/~giunta/ruth1920.html for more information. R H = 37 pm = 37 x 10 -12 m = 3.7 x 10 -9 cm R Au nucleus = 7 x 10 -13 cm (Rutherford first reported 5 x 10 -13 cm !) R proton = 1 x 10 -13 cm 4 13 9 10 7 . 3 10 1 10 7 . 3 p H R R The radius of hydrogen is 37,000 times larger than the radius of the proton! (actually Geiger and Marsden)
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Atomic Numbers and Mass Numbers Atomic number is the number of protons in a nucleus. All atoms of the same element have the same atomic number. It is the atomic number that is the basis of periodicity in the periodic table. The atomic number is always an integer. It is designated by Z . Mass number
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This note was uploaded on 01/17/2012 for the course S 117 taught by Professor Stephenjacobson during the Fall '11 term at Indiana.

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S117Lecture22011 - Radioactivity 1896 Henri Becquerel discovers that a Uranium ore emitted"rays that exposed a photographic plate(in the absence of

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