Fission

1. Fission • Splitting a nucleus into smaller fragments • Happens with atoms larger than Iron (Fe) • Usually far more massive • Can release A LOT of energy • Think: atomic bomb • Nuclear reactors use fission as source of energy http://www.atomicarchive.com/Fission/Fission1.shtml

2. http://www.spiritofbaraka.com/images/koyaanisqatsi/fullsize/koyanisa320.jpghttp://www.spiritofbaraka.com/images/koyaanisqatsi/fullsize/koyanisa320.jpg

3. Why does fission happen? • Addition of a neutron to the nucleus • Neutrons can also be emitted when an unstable nucleus breaks down • Why a neutron? (Why won’t an alpha particle work?) • What effect will this neutron have on the forces in the nucleus? http://reactor.engr.wisc.edu/fission.htm

4. Fission’s good side • Used in nuclear power plants • Has to be controlled

5. Fusion • Two nuclei combine • Happens with elements smaller than (Iron) Fe • Usually much smaller • The Sun: hydrogen nuclei combine to form helium • Release large amounts of energy, but requires very high temperatures • Ex: hydrogen bomb http://www.noaanews.noaa.gov/stories2005/images/ http://reactor.engr.wisc.edu/fission.htm

6. The dream of Fusion • Yet to be harnessed • Would provide even MORE energy than fission • No system of control unlike fission

7. Fusion - the Sun http://www.atpm.com/7.12/sewickley/images/sun.jpg http://zebu.uoregon.edu/~soper/Light/fusion.html

8. Fusion – the hydrogen bomb

9. The relationship between energy and matter • What is the law of conservation of matter? • Fission & fusion seem to break this law • Mass of products is less than the mass of the starting material • Matter (or mass) not destroyed but converted into another form… • Energy • E = m c2

10. What is radiation? • Certain elements or isotopes are unstable, and will decay over time.

11. 3 types of Radiation Alpha (a) Radiation Beta (b) Radiation Gamma (g) radiation

12. 1. AlphaRadiation (a) • Nuclear decay which releases alpha particles • Alpha particle: two protons and two neutrons • Results: • What happens to the atomic number? • What happens to the mass number? • Notice: atom becomes a different element http://education.jlab.org/glossary/alphaparticle.html

13. 2. Beta Radiation (b) • Nuclear decay in which beta particles – high energy electrons – are released • A neutron is a collapsed proton and electron. • Neutron  proton + electron • Results: • What happens to the atomic number? • What happens to the mass number? • Notice: atom becomes a different element http://www.physics.isu.edu/radinf/beta.htm

14. 3. Gamma Radiation (g) • High energy “light” (electromagnetic radiation) • No mass or charge • Often emitted along with beta or alpha radiation • Results: • How does gamma radiation effect the… • atomic number? • mass number? http://www.epa.gov/radiation/understand/ionize_nonionize.htm

15. Alpha particles. Alpha particles are the least penetrating form of radiation. They do not penetrate the outer layer of skin, however, may be a risk to an open wound. • Beta particles. Beta particles can burn the skin and damage eyes. • Gamma rays. Gamma rays are the most penetrating kind of radiation, can travel long distances and penetrate through the body. (excerpt from Mayo clinic website) (EPA website) http://www.epa.gov/radiation/docs/ionize/402-f-98-009.htm

16. Writing nuclear equations Symbol Meaning: • X = element type • A = mass # or protons + neutrons • Z = atomic # or # of protons

17. Conservation of Mass • According to the Law of Conservation of Mass: • Matter cannot be created nor destroyed. • The total starting mass must equal the total resulting mass. http://web.fccj.org/~ethall/1025/scale3.gif

18. Alpha Decay • Atom releases an alpha particle. • Atomic # decreases becoming new element. + • Notice: • total starting mass equals total resulting mass: 238 = 234 + 4 • total starting charge equals total resulting charge: 92 = 90 + 2

19. Using alpha decay, properly complete the following nuclear equations. + + +

20. Did you notice… • when an atom undergoes alpha decay, its atomic number decreased by ______? • when an atom undergoes alpha decay, its mass number decreased by _______?

21. Beta Decay • Atom releases a beta particlewith zero mass & negative charge • Atomic number increases (becomes new element!) + • Notice: • total mass stays the same: 14 = 14 + 0 • total charge stays the same: 6 = 7 - 1

22. Using beta decay, properly complete the following nuclear equations. + +

23. Did you notice… • when an atom undergoes beta decay, its atomic number is increased by ______? • when an atom undergoes beta decay, its mass number _________________?

24. Often multiple steps must occur for a radioactive element to reach a stable form. http://www.uic.com.au/ral.htm

25. Properties of Reactions

26. Half-Life HALF-LIFE is the time it takes for 1/2 a sample is disappear. For 1st order reactions, the concept of HALF-LIFE is especially useful.

27. Half-Life • Reaction is 1st order decomposition of H2O2.

28. Half-Life • Reaction after 654 min, 1 half-life. • 1/2 of the reactant remains.

29. Half-Life • Reaction after 1306 min, or 2 half-lives. • 1/4 of the reactant remains.

30. Half-Life • Reaction after 3 half-lives, or 1962 min. • 1/8 of the reactant remains.

31. Half-Life • Reaction after 4 half-lives, or 2616 min. • 1/16 of the reactant remains.

32. Half-Life Sugar is fermented in a 1st order process (using an enzyme as a catalyst). sugar + enzyme --> products Rate of disappear of sugar = k[sugar] k = 3.3 x 10-4 sec-1 What is the half-life of this reaction?

33. Half-Life Rate = k[sugar] and k = 3.3 x 10-4 sec-1. What is the half-life of this reaction? Solution [A] / [A]0 = fraction remaining = 1/2 when t = t1/2 Therefore, ln (1/2) = - k • t1/2 - 0.693 = - k • t1/2 t1/2 = 0.693 / k So, for sugar, t1/2 = 0.693 / k = 2100 sec = 35 min

34. Half-Life Rate = k[sugar] and k = 3.3 x 10-4 sec-1. Half-life is 35 min. Start with 5.00 g sugar. How much is left after 2 hr and 20 min (140 min)? Solution 2 hr and 20 min = 4 half-lives Half-life Time Elapsed Mass Left 1st 35 min 2.50 g 2nd 70 1.25 g 3rd 105 0.625 g 4th 140 0.313 g

35. Half-Life Radioactive decay is a first order process. Tritium ---> electron + helium 3H 0-1e 3He t1/2 = 12.3 years If you have 1.50 mg of tritium, how much is left after 49.2 years?

36. Half-Life Start with 1.50 mg of tritium, how much is left after 49.2 years? t1/2 = 12.3 years Solution ln [A] / [A]0 = -kt [A] = ? [A]0 = 1.50 mg t = 49.2 y Need k, so we calc k from: k = 0.693 / t1/2 Obtain k = 0.0564 y-1 Now ln [A] / [A]0 = -kt = - (0.0564 y-1) • (49.2 y) = - 2.77 Take antilog: [A] / [A]0 = e-2.77 = 0.0627 0.0627 = fraction remaining

37. Half-Life Start with 1.50 mg of tritium, how much is left after 49.2 years? t1/2 = 12.3 years Solution [A] / [A]0 = 0.0627 0.0627 is the fraction remaining! Because [A]0 = 1.50 mg, [A] = 0.094 mg But notice that 49.2 y = 4.00 half-lives 1.50 mg ---> 0.750 mg after 1 half-life ---> 0.375 mg after 2 ---> 0.188 mg after 3 ---> 0.094 mg after 4

38. Half-Lives of Radioactive Elements Rate of decay of radioactive isotopes given in terms of 1/2-life. 238U --> 234Th + He 4.5 x 109 y 14C --> 14N + beta 5730 y 131I --> 131Xe + beta 8.05 d Element 106 - seaborgium263Sg 0.9 s