Marie Curie discovered radioactivity through her work on atoms and their structure. Nuclear reactions involve changes to the nucleus through loss of particles and rearrangement of protons and neutrons, releasing significant energy. There are three main types of radiation emitted in radioactive decay: alpha, beta, and gamma. Half-life refers to the time it takes for half of a radioactive sample to decay and is used in radioactive dating. Radiation is dangerous as it can ionize atoms and damage DNA, disrupting cells.

1. Nuclear Chemistry

2. Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934). She discovered radioactivity: the spontaneous disintegration of the nucleus of some elements into smaller pieces.

3. Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleus The nucleus loses particles, and protons and neutrons are rearranged The disintegration of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy “ Normal” Chemical Reactions involve electrons, not protons and neutrons

5. Types of Radiation Alpha ( ά ) – a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons Beta ( β ) – an electron Gamma ( γ ) – pure energy; called a ray rather than a particle

6. Alpha Decay When a radioactive nucleus emits an alpha particle , a new nucleus forms that has: a mass number that is 4 less than that of the initial nucleus. an atomic number that is decreased by 2.

7. Alpha Decay Nuclear Equation Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

8. In a balanced nuclear equation, the sum of the mass numbers and the sum of the atomic numbers for the nuclei of the reactant and the products must be equal. MASS NUMBERS Total = 251 = 251 251 Cf 247 Cm + 4 He 98 96 2 Total = 98 = 98 ATOMIC NUMBERS Balancing Nuclear Equations

9. Equation for Alpha Decay Write an equation for the alpha decay of 222 Rn. STEP 1 Write the incomplete equation 222 Rn ?s + 4 He 86 2 STEP 2 Determine the mass number 222 – 4 = 218 STEP 3 Determine the atomic number 86 – 2 = 84 STEP 4 Determine the symbol of element 84 = Po STEP 5 Complete the equation 222 Rn 218 Po + 4 He 86 84 2

10. Beta Decay A beta particle is an electron emitted from the nucleus. forms when a neutron in the nucleus breaks down. 1 n 0 e + 1 H 0 -1 1

11. STEP 1 Write an equation for the decay of 42 Potassium,a beta emitter. 42 K new nucleus + 0 e 19 -1 STEP 2 Mass number : (same) = 42 STEP 3 Atomic number: 19 + 1 = 20 STEP 4 Symbol of element 20 = Ca STEP 5 42 K 42 Ca + 0 e 19 20 -1 Writing An Equation for Beta Decay

12. Other Nuclear Particles Neutron Positron – a positive electron Proton – usually referred to as Hydrogen +1 Any other elemental isotope

15. Half Life The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay.

16. Half Lives for Radioactive Elements Radioactive Parent Stable Daughter Half life Potassium 40 Argon 40 1.25 billion yrs Rubidium 87 Strontium 87 48.8 billion yrs Thorium 232 Lead 208 14 billion years Uranium 235 Lead 207 704 million years Uranium 238 Lead 206 4.47 billion years Carbon 14 Nitrogen 14 5730 years

17. Half Life and radioactive dating

18. Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?

19. Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?

20. In gamma radiation energy is emitted from an unstable nucleus, indicated by m following the mass number. the mass number and the atomic number of the new nucleus are the same. 99m Tc 99 Tc +  43 43 Gamma (  ) Radiation

21. In position emission , a proton is converted to a neutron and a positron. 1 p 1 n + 0 e 1 0 +1 the mass number of the new nucleus is the same, but the atomic number decreases by 1. 49 Mn 49 Cr + 0 e 25 24 +1 Positron Emission

22. Why radiation is dangerous Radiation ionizes atoms in cell tissue and causes chemical reactions akin to decomposition / combustion. disrupts nucleotide sequences (your DNA is mutated)

23. Why radiation is dangerous

24. Measuring Radiation How radioactive a substance is refers to the number of nuclear disintegrations per second that occur in a sample. SI unit is the Becquerel (Bq) which is 1 disintegration/second The older unit, the Curie(Ci) : 1 Ci = 3.7 x 10 10 disintegrations per second

25. Measuring Radiation The 'rad ' is used to describe the energy quantity or dose of radiation absorbed. rad (rd) stands for “radiation absorbed dose” One rad defined as 10 -5 J/g of material.

26. Measuring Radiation Damage The rad does not account for the kind of damage done, only for how much radiation goes in. To take into account this fact the REM was derived To find the dose in REMS the dosage in rads is multiplied by a conversion factor that reflects the effectiveness of the kind of radiation causing the damage

27. Dosage in REMS Biological Effect : 25 notable change in blood cell components 100 radiation sickness - nausea, vomiting, decrease in white blood cell count, diarrhea, dehydration, prostration, hemorrhaging and loss of hair 200 the same as above but more pronounced in a shorter period of time 400 ½ of any population exposed to this dosage will be dead in 60 days 600 all exposed to this level will be dead in one week

29. Chernobyl Anyone near the Chernobyl plant when it melted down received 400 rems also immediately. The day after 1 rem/hr was found in the nearest city. Normal background radiation is 1,000 times lower than this

31. Detecting radiation

32. Detecting radiation

33. Protection from radiation Wear lead infused suit. Keep your distance. Inverse square law. Intensity of radiation is inversely proportional to the square of the distance from the source

34. Nuclear Fuel Uranium “Yellow Cake” U 3 O 8

35. Fission Neutron

36. Fission Chain Reaction

37. Representation of a fission process.

38. Nuclear Fission

39. Diagram of a nuclear power plant.

41. Nuclear Fission & POWER Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. 17% of the world’s energy comes from nuclear.

42. Fusion A process by which multiple like-charged atomic nuclei join together to form a heavier nucleus

43. Nuclear Fusion Fusion: small nuclei combine 2 H + 3 H 4 He + 1 n + 1 1 2 0 Occurs in the sun and other stars Energy

44. What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He ? + 1 n 5 2 0 Fusion

45. Nuclear Fusion Fusion Excessive heat can not be contained Attempts at “cold” fusion have FAILED. “ Hot” fusion is difficult to contain

46. Artificial Nuclear Reactions New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4 He and 11 B. Reactions using neutrons are called  reactions because a  ray is usually emitted. Radioisotopes used in medicine are often made by  reactions .

47. Artificial Nuclear Reactions Production of radioactive 31 P for use in studies of P uptake in the body. 31 15 P + 1 0 n ---> 32 15 P + 

48. Transuranium Elements Elements beyond 92 (transuranium) made starting with a  reaction 238 92 U + 1 0 n ---> 239 92 U +  239 92 U ---> 239 93 Np + 0 -1  239 93 Np ---> 239 94 Pu + 0 -1 

49. Nuclear Medicine: Imaging Thyroid imaging using Tc-99m

50. Food Irradiation Food can be irradiated with  rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats and eggs.