Chapter 22 Nuclear Reactions

2. Chapter 22Nuclear Reactions

3. Nuclear Rxns • Nuclear reaction-a reaction that involves a change in an atom’s nucleus. • Therefore, an atom of one element changes into an atom of another element.

4. Nuclear Rxns • Nuclide (Nucleus of an atom) • Contains nucleons(protons and neutrons)

5. Chemical vs. Nuclear Rxns. Chemical Rxns Nuclear Rxns • Occur when bonds are broken and formed • Occur when nuclei emit particles and/or rays • Atoms remain unchanged, just rearranges • Atoms are often converted into atoms of another element. • Involve only outer electrons • May involve p, n • Associated with small energy changes • Associated with large energy changes

6. Radiation • Radiation-The rays and particles that are emitted by radioactive materials.

7. Alpha Radiation • Alpha radiation-radiation deflected towards the negatively charged plate and gives off alpha particles • Alpha particles, He or α : 2p, 2n so +2 charge, largest mass (4 amu)

8. Beta Radiation • Beta radiation-radiation deflected towards the positively charged plate and gives off beta particles (electrons). • Beta particles, β or e: 1e so -1 charge, mass is between alpha and gamma particles

9. Gamma Radiation • Gamma radiation-radiation deflected towards no plate and gives off gamma rays • Gamma rays, γ : no mass and no charge, usually occupied by α and β decay.

10. Nuclear Rxns • (1) Ra → Rn + He • α decay • (2) C → N + e • β decay • (3) U → Th + He + 2γ • γ decay

11. Types of Radiation (Memorize) Consists Charge Mass Stopped w/ symbol Alpha Beta Gamma

12. Types of Radiation • Positron emission-radioactive decay that involves the emission of a positron from a nucleus • Positron-particle with the same mass as the electron but opposite charge • Symbol:

13. Types of Radiation • Electron Capture- nucleus of an atom draws in a surrounding electron and an X-ray photon is emitted • Symbol:

14. Nuclear Reactions • Nuclear Rxn- a rxn that changes the nucleus • Transmutation-a change in the identity of the nucleus, change in # of protons in nucleus.

16. Nuclear Stability • The smaller stable nuclides have a neutron-proton of 1:1 to the larger nuclides of 1.5:1. • If the nuclei ratio falls above/below the band of stability, the nuclides will undergo decay until they are within the band of stability.

17. Nuclear Stability Mass of p, n, e for helium should be the mass of the atom 2p (2 x 1.007276 amu) = 2.014552 amu 2e (2 x 1.008665 amu) = 2.017330 amu 2n (2 x 0.0005486 amu) = 0.001097 amu Total = 4.032979 amu

18. Total = 4.032979 amu Mass from periodic table = 4.00260 amu Difference of 0.03038 amu

19. Mass defect – difference between mass of an atom and sum of masses for p, n, e.

20. Why loss of mass? Caused by conversion of mass to energy upon formation of nucleus

21. Nuclear Binding energy – energy released upon formation of nucleus

22. Radioactive decay • Radioactive decay-spontaneous disintegration of an unstable nucleus to a smaller nucleus by giving off nuclear radiation. • Radioactive nuclide- unstable nucleus that will undergo radioactive decay

23. Nuclear Rxns Identify the product that balances the following nuclear rxns. • 212Po →4He + ____ • 230Th → _____ + 4He • 238U + 4He → ____ + 1n • 27Al + 1n →24Na + ____

24. Radioactive decay Alpha Emission 210Po 206Pb + ____ Beta Emission 14C 14N + ____ Electron Capture (reverse of beta) 106Ag + _____ 106Pd Positron emission 11C →11B + _____

25. 1. 216Bi decays by beta emission. 2. 204Pb undergoes radioactive decay to form 200Hg. What particle is given off?

26. Half-life • Half-Life- t1/2 - the time required for half the atoms of a radioactive element to decay into another element. • Fluorine-21 has a half life,t1/2, of 5 seconds 1000 atoms F-21500 atoms F-21  250 atoms F-21 1(whole amt)  ½ left  ¼ left 100 g F-21 50 g F-21 25 g F-21

27. Oxygen-15 decays by positron emission. Write a balanced nuclear reaction.

28. Half-Life Problems Formulas: To determine the number of half-lives that past: #half-lives past = total time t1/2 To determine amount remaining: Amount remaining = (Initial amt)1n 2 n= # of half lives past

29. Half-Life Problems • If the radioactive sample of I-131 was 18.5g, what amt is left after 32 days? (t1/2 = 8 days)

30. Half-Life Problems 2.Iron-59 is used in medicine to diagnosis blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days?

31. Half-Life Problems 3. If gallium-68 has a half-life of 68.3 minutes, how much of a 10.0 mg sample is left after two half-lives?

32. Half-Life 4. After 15 days only 2 grams remain of a sample that has a half life of 5 days. How many grams were in the original amount? 5. What is the half life of K-42 if a 750 gram sample decays to 93.75 grams in 24 hours?

33. 6. The half-life of carbon-14 is 5715 years. A sample has only ¼ of its original amount. What is the age of the sample?

34. Decay Series • Decay Series-a series of radioactive nuclides produced by successive radioactive decay until a stable nuclide is reached

35. Decay Series Questions Use pg. 814 • Write the four nuclear equations of the uranium-238 decay series. • What stable nuclide does U-238 finally become? • How long is the half life of U-238?

37. U-238 • U-238 is found in small amounts in soil and rock, particularly, shale and granite. • Rn is one of the daughter nuclide of U-238(parent nuclide) decay. • Rn is a radioactive gas that can be a health hazard trapped in homes from cracks and holes in foundation. It can cause lung cancer and birth defects. • Ra-226, Po-210, Pb-210 are found in cigarettes and the lungs of smokers.

38. Induced Transmutation • Induced Transmutation- bombardment of stable nuclei with charged and uncharged particles. • This process is used to make radioactive nuclides not found nature, like our newly discovered elements.

40. Induced Transmutation 1. Write a balanced nuclear equation for the induced transmutation of aluminum- 27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom.

41. Induced Transmutation 2. Write the balanced nuclear equation for the induced transmutation of aluminum-27 into sodium-24 by neutron bombardment. An alpha particle is released in the rxn.

42. Induced Transmutation What element would be formed in the following nuclear rxn? 3. 242Cm + 4He  ______ + 1n

43. Nuclear Radiation • Radiation Exposure • Rem-a unit used to measure radiation damage to human tissue like x-rays… (Complete personal radiation wkst)

44. Nuclear Radiation • Radiation Detection • Geiger Muller counters -measures electrical pulses on gas ionized by radiation • Film Badge • Scintillation counter

45. Film Badge

47. Applications of Nuclear Radiation • Radiochemical Dating: 14C 0e + 14N t1/2 = 5715 yrs • Living organisms absorb 14C through food. This C-14 is a constant amt. When the organism dies, there is no new absorption of C-14. The C-14 decays to N-14. By measuring the amount of C-14 the age may be approximated.

48. The half-life of carbon-14 is 5715 years. A sample has only ¼ of its original amount. What is the age of the sample?

49. Applications of Nuclear Radiation • Radioactive Nuclides in Medicine • Radioactive tracers are radioactive atoms incorporated into substances so they can be followed by radiation detectors. • Ex. Tc-99 used to detect bone cancer, I-131 to detect thyroid problems

50. Applications of Nuclear Radiation • Radioactive Nuclides in Agriculture • Radioactive tracers are used to determine effectiveness of fertilizers. • Cobalt-60 is used to irradiate food, to kill bacteria and insects. It is also used to kill cancer cells.