PHY122_L26 - PHY122 Physics for the Life Sciences II...

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PHY122 – Physics for the Life Sciences II Lecture 26 Applications and Biological Effects of Radioactivity Final Review: Ch 17-19, 28-30 Note: Clicker Channel 21 12/08/2011 Lecture 26 1
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Content Nuclear components: the proton (mass m p ) and the neutron (mass m n ) – masses, spin, neutron decay, … – the strong nuclear force – the nuclear shell model – binding energy m (He) – 2 m H –2 m n < 0 (The bound whole has less mass than the sum of its parts! This is true for any bound system.) – binding energy/nucleon – fission and fusion Radioactivity – Isotopes and stability – from instability towards stability – types of radiation – decay activity, half-life and decay constant Applications and Effects of Radiation – radiation effects and radiation sources in nature – nuclear medicine – nuclear energy 12/08/2011 Lecture 26 2
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Radioactivity As we saw, possible radiation from nuclear decays is … α -radiation: • highly ionizing • typical for large- Z nuclear decays and fission • short range: not very penetrating; will stop in fraction of a mm of solid • VERY damaging for live tissue (lung, intestinal tissue) β -radiation: • moderately ionizing • penetrating (cm’s in solids) γ -radiation: • non-ionizing • VERY penetrating (10s of cm’s in solids) n radiation: • multiple n eutrons emitted in fission • non-ionizing, but kicks up ionizing protons • VERY penetrating and damaging (many 10s of cm’s in solids) 12/08/2011 Lecture 26 3 44 22 XY AA ZZ Q  1 eQ * XX Q Q released binding energy: Q= ( M Y + m α M X ) c 2 depending on energy : more energetic, more penetrating! Y α energy & momentum conservation: Q=K Y +K α , M Y v Y = m α v α
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Detecting Ionizing Radiation – Geiger Counter Many detection instruments have been developed … Geiger counter for ionizing radiation 12/08/2011 Lecture 26 4 HV Cylindrical electric field of the wire is E=kQ/r The ejected electrons cause an avalanche of ionization in the high field near the wire
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you have three radioactive cookies, all with the same activity. A is an α -source, B a β -source, and G a γ -source. You must eat one (1) , put one cookie in your pocket (2) , and place one in a lead box (3) . What do you do? (example ABG = eat A, put B in pocket, put G in box) 12/08/2011 Lecture 26 5 A. ABG B. AGB C. BAG D. BGA E. GAB F. GBA 1 2 3
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