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NUCLEAR CHEMISTRY

NUCLEAR CHEMISTRY. An Energetic Concept. WHO DID WHAT. Wilhelm Roentgen Laboratory generated phosphorescence X-rays. WHO DID WHAT. Henri Becquerel Inherited U salts (pitchblende) Natural phosphorescence Discovered spontaneous phosphorescence. WHO DID WHAT. Marie & Pierre Curie

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NUCLEAR CHEMISTRY

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  1. NUCLEAR CHEMISTRY An Energetic Concept

  2. WHO DID WHAT • Wilhelm Roentgen • Laboratory generated phosphorescence • X-rays

  3. WHO DID WHAT • Henri Becquerel • Inherited U salts (pitchblende) • Natural phosphorescence • Discovered spontaneous phosphorescence

  4. WHO DID WHAT • Marie & Pierre Curie • Studied Becquerel phosphorescence and named it • Discovered Po, Ra

  5. ISOTOPE REVIEW A X Z A—mass number Z—atomic number A – Z = number of neutrons

  6. SO, WHAT IS RADIATION? • Instability due to n:p+ • Radioisotopes • Goal is stability

  7. SO, WHAT IS RADIATION?

  8. TYPES OF RADIATION • Rutherford • Electric field effect on radioactivity • Alpha • Beta • Gamma

  9. TYPES OF RADIATION

  10. TYPES OF RADIATION • Alpha () • Same as a He-4 nucleus • A decreases by 4 • Z decreases by 2

  11. TYPES OF RADIATION • Alpha • Not very penetrating • Stopped by a sheet of paper • Very ionizing

  12. TYPES OF RADIATION • Beta () • Same as an electron • A remains the same • Z increases by 1 e

  13. TYPES OF RADIATION • Beta • More penetrating than  • Stopped by a thin sheet of metal • Less ionizing than 

  14. TYPES OF RADIATION • Gamma () • Pure energy • Usually accompanies  and  • More penetrating than  and  • Somewhat blocked by several inches of Pb or several feet of concrete • Less ionizing than  and 

  15. TYPES OF RADIATION • Positron (+) • Same mass as  • Opposite charge of  F  O + e 18 18 0 9 8 +1

  16. TYPES OF RADIATION • Electron capture • The opposite of  emission • A remains the same • Z decreases by 1 0 40 40 K + e  Ar 19 -1 18

  17. DECAY SERIES • Continued radiation until stable • Fr-221 undergoes the following decay series: ,,,,, 209 83 221 87 209 82 217 85 209 81 213 83 217 85 213 83 205 81 209 81 209 83 209 82 4 2 4 2 4 2 0 -1 4 2 0 -1 Fr  At + He Tl  Pb + e Pb  Bi + e At  Bi + He Bi  Tl + He Bi  Tl + He

  18. RATE OF RADIOACTIVE DECAY • Half-Life • t½ = 0.693/k • k = rate law constant • First-order Kinetics • lnN = –kt + lnNo • N…amount after elapsed time • t = elapsed time • No = amount originally

  19. UNITS OF RADIOACTIVE DECAY • curie (Ci) • 1 Ci = 3.7 x 1010 disintegrations per second • ~activity of 1 g of Ra-226 • becquerel (Bq) • SI unit • 1 Bq = 1 dis/s…37 GBq = 1 Ci

  20. UNITS OF RADIATION EXPOSURE • sievert (Sv) • Dose absorbed by specific tissue • Replaced röntgen equivalent to man (rem) • 1 Sv…nausea • 2-5 Sv…hair loss, hemorrhage • 3 Sv…death in 50% of people in 30 days • >6 Sv…unlikely survival • Typical background exposure is 2.4 mSv/year

  21. RATE OF RADIOACTIVE DECAY • The half-life of F-18 is 2 hours. If you receive a dose of 200 mCi at 8:00 AM, how long will it take for 10 mCi to remain in your body? At what time will you have 10 mCi in you? • Solve for the value of k • Plug into the linear equation and solve for t

  22. RATE OF RADIOACTIVE DECAY 2 h = 0.693/k… k = 0.3465 h-1 ln(10 mCi) = –(0.3465 h-1)(t) + ln(200 mCi) ln(10 mCi) – ln(200 mCi) = –(0.3465 h-1)(t) – 2.996= –(0.3465 h-1)(t) 8.65 h = t at 4:39 PM, you will have 10 mCi in you

  23. RADIOACTIVE DATING • C-14 is a beta emitter with a half-life of 5730 years • Used to determine the age of carbon-based substances

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