Nuclear Chemistry

1. Nuclear Chemistry The weird world of the nucleus

2. Isotope Refresher • Atoms of the same element all have the same number of protons • Atoms of the same element may have different neutrons and therefore mass numbers (p+ + n0)

3. Nuclear Instability • Not all combinations of protons and neutrons are created equal • Some are more unstable than others. • If they are unstable they will do one of the following: • Radioactive decay • Nuclear fission • Nuclear fusion

4. Nuclear “Reactions” • Nuclear “reactions” must still be balanced. • Notice 238 = 4 + 234 “Mass balanced” • Notice 92 = 2 + 90 “Charge balanced”

5. Radioactive Decay

6. Radioactive Decay • Radioactive decay – the nucleus of an atom undergoes a change so that it is no longer the same element • Decay is a totally random event. Nothing has an effect when an atom decays Two Main Types of Radioactive Decay • Alpha decay • Beta decay

7. Alpha Decay • Alpha decay – emission of an alpha particle from the nucleus • Alpha (α) particle - a helium-4 nucleus • Uranium-235, “enriched uranium,” decays by alpha decay

8. Beta Decay • Beta decay – emission of a beta particle from the nucleus • Beta (β) particle – electron • Thorium-231 decays by beta decay

9. Practice Decay Reactions • Beta decay by cesium-137 • Alpha decay by polonium-210

10. Decay Series • Some atoms require multiple decays to become stable • Most decay series of naturally occurring isotopes end in lead.

12. Half Life

13. Half Life • Half life – the amount of time it takes for ½ of a radioactive isotope to decay into something else. • Notice the atoms don’t disappear, they just change their identity.

14. Half Life Problem • A 100.0g radioactive sample decays for 5 hours. Only 12.5g of the original isotope remains after 5 hours. How long is the half life? • 3 half lives = 5 hours • 5hours/3half lives = 1.67hours/halflife

15. Half Life Problem Selenium-72 has a half life of 8.40 days. How much of a 450.0g sample of selenium-72 will remain after 42.0 days? 25.2 days

16. Radiocarbon Dating Technique • Uses the known half life of C-14 to estimate death of organic matter • Based on the known ratio of C-14 to C-12

18. Nuclear Fission and Fusion

19. Nuclear Fission • Nuclear fission – one atom’s nucleus splits apart. • A neutron strikes a nucleus causing it to split into small pieces • Releases lots of energy. • Extra neutrons are also produced.

20. Nuclear Fission • The extra neutrons can cause a chain reaction

21. Uses of Nuclear Fission • Nuclear power • Energy produced by fission is transferred as heat to a coolant

22. Nuclear Power

23. Uses of Nuclear Fission Mushroom cloud from Nagasaki

24. Uses of Nuclear Fission • Nuclear weaponry • “Atomic bomb” • “A-bomb” • Runaway fission reaction resulting in an explosion.

26. Nuclear Fusion • Fusion – combining of nuclei • Above reactions describe fusion in the Sun. • Releases more energy than fission. • Also requires very high temperatures.

27. Uses of Nuclear Fusion

28. Uses of Nuclear Fusion • Fusion weapons • Hydrogen bomb • “H-bomb” • Thermonuclear bomb • Uses a fission reaction to start the fusion reaction • “A-bomb” is the detonator for an “H-bomb”

29. Radiation

30. 3 Primary Types of Radiation • Alpha radiation – α – alpha particles • Low energy • Result of alpha decay • Low penetration • Stop with a sheet of paper • Beta radiation – β –beta particles (electrons) • Higher energy • Result of beta decay • Some penetration ability • Stop with several sheets of aluminum foil • Gamma radiation – γ –high energy gamma rays • Very high energy • Can result from any type of decay • Very highly penetrating and damaging • Stop with several centimeters of lead or very thick concrete

31. 3 Primary Types of Radiation

32. Sources of Human Exposure