15.Nucl_chem_Part_3_

15.Nucl_chem_Part_3_ - Chapter 15, Nuclear Chemistry Part 3...

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Chapter 15, Nuclear Chemistry Part 3 Skip Archeological dating Skip Geological dating NOTE: subsequent to lecture slides, you will find several solved problems A Bonus Quiz will be posted on Blackboard On Thursday March 30, at 5:00 PM ---
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Decay of radioactive elements In unstable nuclide, (Table 15.2) excess mass often favors α emission High N/Z favors beta emission Low N/Z favors o positron emission o Electron capture High-energy nuclides may also lose excess energy through emission of γ rays ---------------
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Example (For light elements N/Z close to one is favored) C-14 has 6 protons and 14-6 = 8 neutrons N/Z = 1.3 N-14 has 7 protons and 14 – 7 = 7 neutrons N/Z = 1 C-14 has a high N/Z ratio, beta emission is favored to produce an element that falls within the stability band (also see example 15.5 on page 597) --- 14 14 0 6 7 1 C N β - +
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Decay of Heavy elements Very heavy elements often undergo a series of α and β decays Example Decay of U-238 (next slide) -
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Decay of U-238 238 92 U 234 90 Th + 4 2 α 234 90 Th 234 91 Pa + 0 1 - β Stable Decaying series <----
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Actinium-227 decays and emits five alpha particles and three beta particles in eight steps. What is the final product? For that type of problem, as long as we know the number of particles emitted, we do not have to know the order of their emissions We just setup the net equation to identify the final product: Balance mass to solve for A 227 = 5(4) +3 (0) + A (we get A = 207) Balance charge to solve for Z 89 = 5(2) +3 (-1) + Z (we get Z = 82) periodic table: the element with 82 protons is Pb Final product ----- Problem 227 4 89 2 5 Ac X α β 0 Α -1 Ζ + 3 + 207 82 Pb
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Radiation Detectors Geiger Counter detects ionization caused by radiation Specific films react to radiation as films do to light the greater the radiation the more exposed the film becomes Scintillation counters and computerized equipments for accurate measurement of the amount of a radioactive sample ---
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Measuring Radioactivity The amount of exposure to radiation is measured in Roentgen (R) The extent of ionization in human tissue is measured in rad The rate of disintegration of a radioactive sample is measured in Curies, Ci 1Ci mCi = 0.001 Ci = 10 -3 Ci μ Ci = 10 -6 Ci ----
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15.Nucl_chem_Part_3_ - Chapter 15, Nuclear Chemistry Part 3...

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