1. Nuclear Reactions Nuclear Reactions involve the nucleus of atoms When a nuclear reaction occurs, the element is changed completely into another element As a result, nuclear reactions are also known as Transmutations

2. The Nucleus d  10 -13 cm (d  10 -8 cm for an atom)

3. The Nucleons mass (AMU)charge (esu) proton1+1 neutron10

4. In case you forgot... many elements have several isotopes U 238 92 U 235 92 92 protons 143 neutrons 92 protons 146 neutrons Identical chemistries, different nuclear reactions

5. Chemical vs. Nuclear Energies CH 4(g) + 2 O 2(g)  CO 2(g) + 2 H 2 O (g)  H = -896 kJ/mol = -56 kJ/g 235 U nuclear fission other nuclei  H = -8.2 x 10 7 kJ/g

6. Why do nuclear reactions occur? Naturally, some atoms are stable while others are unstable Usually, when the ratio of neutron:proton is greater than 1.3, the nucleus is unstable Examples, 236 U, 209 Po, 14 C, 230 Th An unstable nucleus is radioactive and naturally emits certain radiations and is converted to a more stable isotope

7. proton (p) neutron (n) the nuclear force Forces in the Nucleus electrostatic repulsion

8. Nuclear Stability protons (Z) neutrons (N) 090 0 140 N/Z=1................................................................................................................................................................................................... “Island of Stability”   decay    EC decay  decay neutrons needed for stability

9. Determine if any of the following isotopes is stable or unstable Isotope Protons (P) Neutrons (N) N/P ratioStable or unstable 218 Po 14 C 214 Pb 206 Pb

10. Types of Radiation There are 4 main types of radiation: RadiationChargeMassSymbol Alpha rays (  -particles) +24 4 2 He Beta rays (  -particles) 0 0 -1  Gamma rays (  -rays) 00 0000 Positrons+10 O +1 

11. The Discovery of Radioactivity U - +    ++

12.  Particles positively charged massive accurate measurements  4 He nuclei 2 protons 2 neutrons

13. Emission of  particles Some unstable nuclide decay by emitting only  -particles Examples: 226 88 Ra → 222 86 Rn + 4 2 He 210 84 Po → 206 82 Pb + 4 2 He 230 90 Th → 226 88 Ra + 4 2 He Using Table N, identify 4 nuclide that undergo alpha decay and write the nuclear equation

14.  Decay U 238 92 He + 4 2 234 90 Th nucleons are conserved (238) charge is conserved (92) identities of atoms are not!

15. Emission of  particles Some unstable nuclide decay by emitting only  -particles Examples: 239 92 U → 239 93 Np + 0 -1  239 93 Np → 239 94 Pu + 0 -1  14 6 C → 14 7 N + 0 -1  Using Table N, identify 4 nuclide that undergo beta decay and write the nuclear equation

16. TABLE N Selected Radioisotopes

17.   Particles negatively charged small mass accurate measurements  electrons

18.   Decay 234 90 Th e - + 0 234 91 Pa i.e. a neutron is turned into a proton + an electron 90 p 144 n 91 p 143 n

19. Electron Capture 55 26 Fe + e - 55 25 Mn 26 p 29 n 25 p 30 n i.e. a proton captures an electron and is turned into a neutron

20. Electron Capture (EC) + ++ + + + + + + + + - -

21. Decay Series A  B  C  D ...  Ž non-radioactive nuclide There are three such series: A = 238 U, A = 232 Th, A = 235 U and

22. 238 U Decay Series 238 U Ž 234 Th Ž 234 Pa Ž 234 U Ž 230 Th     226 Ra  222 Rn (g) Œ  218 Po Œ  214 Pb Œ   214 Bi Ž 214 Po Ž 210 Pb Ž 210 Bi     210 Po 206 Pb Œ  non-radioactive 

23. Nuclear Reactions A + B Ž C [mass (A) + mass (B)]  mass (C) e.g. Fe 56 26 26 p + 30 n ŽFe 56 26 find mass before and after reaction

24. Nuclear Reactions mass before = 26 m p + 30 m n = 26(1.00728 amu) + 30(1.00866 amu) = 56.44908 amu mass after = mass 56 Fe atom - 26 m e = 55.9349 amu - 26(.0005486 amu) = 55.92070 amu “mass defect” = 0.52838 amu

25. Nuclear Reactions The mass is converted to energy!

26. "It followed from the special theory of relativity that mass and energy are both but different manifestations of the same thing -- a somewhat unfamiliar conception for the average mind. Furthermore, the equation E is equal to m c-squared, in which energy is put equal to mass, multiplied by the square of the velocity of light, showed that very small amounts of mass may be converted into a very large amount of energy and vice versa. The mass and energy were in fact equivalent, according to the formula mentioned before. This was demonstrated by Cockcroft and Walton in 1932, experimentally."

27. Nuclear Reactions The mass is converted to energy!  E =  mc 2  m = 0.52838 amu / 56 Fe nucleus = 0.52838 g/mol = 0.52838 x 10 -3 kg/mol c = 3.00 x 10 8 m/s

28. Nuclear Reactions  E =  mc 2 = 0.52838 x 10 -3 kg/mol (3.00 x 10 8 m/s) 2 = 4.75 x 10 13 (kg m 2 s -2 ) / mol = 4.75 x 10 13 J/mol = 4.75 x 10 10 kJ/mol = the “binding energy” of 56 Fe

29. Binding Energy is a maximum at 56 Fe lighter elements become more stable upon fusion heavier elements become more stable upon fission

30. Nuclear Fission n 235 U unstable 236 U 92 Kr 36 141 Ba 56 + 3 1 n 0

31. Nuclear Fission 1 n + 235 U  141 Ba + 92 Kr + 3 1 n Many other fission “pathways” exist: 1 n + 235 U  137 Te + 97 Zr+ 2 1 n

32. Exercises Page 814: questions 8, 9, 10, 11 and 12

33. Artificial Transmutations Aim: What is Artificial Transmutation and how do Artificial Transmutations occur? Do Now Write Nuclear Equations for the following natural transmutations: (a)U-235 → Th-234 (b) Th-230 → Ra-226 (c) Po-214 → Pb-210 (d) Pb-214 → Bi-214 (e) U-234 → Th-230 (e) Pa-234 → U-234

34. What is Artificial Transmutation? Artificial Transmutation is where a stable isotope is made to disintegrate This is usually done by bombardment with high speed particles Examples: 4 2 He + 14 7 N → 17 8 O + 1 1 p 27 13 Al + 4 2 He → 30 15 P + 1 0 n 32 15 P + 0 -1  → 32 14 Si

35. Individual Practice Page 816: Problems 15 and 16 Page 837: Problems 73-76 Group Practice Examine the Figure on page 814. Write a series of nuclear equations showing the transmutations from U-238 to Po-214