1. The Atomic Nucleus & Radioactive Decay (Chapter 10)

2. Student Learning Outcomes Analyze radioactive decay processes Differentiate between nuclear Fission & Fusion

3. How do we know the number of neutrons?  Atomic number = number of protons  Mass number = protons + neutrons 17 8 O −2

4. Practice Classify each atom. Is it an ion? Is it an isotope?

5. What is the limit for the Strong Nuclear Force?  The protons and neutrons in the core of an atom are held together by the strong nuclear force. Diameter < 10 -15 m  The strong nuclear force balances the electric force in a stable atom. FEFE FNFN

7. Nuclear Force vs. Electric Force Strong Nuclear ForceElectric Force AttractionRepulsion Protons & NeutronsProtons Range < 10 -15 mRange > 10 -15 m

8. Practice 1)Would a helium (He) atom or a bismuth (Bi) atom tend to be more unstable? 2)What about a 3 2 He atom?

9. What does radioactivity mean?  Radioactivity is the transformation of an unstable atom into a different type of atom.  Over 60 radioactive elements can be found in nature.  There are 3 general sources of radioactivity. Earth Cosmic Rays Human Produced

10. How do we determine the new isotope?  Atoms radioactively decay by emitting high energy particles. X  Y +  (alpha decay) X  Y +  (beta decay) X  Y +  (gamma decay)

11. Can cause damage on the surface of matter  Alpha radiation: particle (He + ) is a positively charged particle that leaves the nucleus.

12.  Beta radiation: (e − ) is a negatively charged particle that leaves the nucleus. Can penetrate through several millimeters of matter 8 4 Be 8 3 Li Beta Particle

13.  Gamma Rays: (  ) are high energy photons. High Energy Gamma Ray released No change to nucleus High Energy Atom Can pass through all types of matter

14. The Rules Unstable Condition NameSymbol The Rules 83+ ProtonsAlpha 4 2 He + +2+2   Mass #) = – 4  Atomic #) = – 2 Neutron/Proton Ratio Betae–e– –1–1   Mass #) = – 0  Atomic #) = + 1 Excited Nucleus Gammaphoton0  No Change

15. Practice 1. 226 88 Ra  X + e − 2. 226 88 Ra  X +  3. 222 86 Rn  X + 4 2 He 4. 14 6 C  X +  5. 36 18 Ar  X +  Is the atom an isotope? What makes it unstable? What is the new atom?

16. What does the half-life of an element indicate?  Half-life is the time it takes for one half of an unstable substance to decay into a different substance. IsotopeHalf Life 15 6 C2.449 seconds 14 6 C5,730 years

17. Practice 1. An isotope of radium (Ra) has a half-life of 1620 years. If 1000 grams were placed in a barrel, how much of the material in the barrel would be radium after 6480 years? 2. 225 89 Ac (Actinium) has a half-life of 10.0 days. How many days would it take to decrease the original amount placed in a barrel to 1/8 th of the original amount?

18. What is carbon dating?  Carbon dating is the process of using the known half-life of carbon to determine age of a sample.  Living plants and animals take in CO 2 (Carbon-14)  Carbon-14 is a radioactive isotope 14 6 C  14 7 N + 

19. Practice The half-life of carbon-14 is 5730 years. 1. If a piece of wood has 1/2 as much carbon-14 as compared to a living tree, how old is the wood? 2. If a piece of wood has 1/32 as much carbon-14 as compared to a living tree, how old is the wood?

20. A Question to Ponder 3. It is assumed the relative abundance of carbon-14 in our atmosphere has remained constant for the last 50,000 years. How do you think this assumption could affect carbon dating?

21. What is Nuclear Fission?  Nuclear fission is splitting apart a nucleus.  Electric force wins  Nucleus flies apart  Huge amounts of energy released  Nuclear fission is used in atomic bombs & nuclear reactors.  Atomic bombs produce a chain reaction.  Nuclear reactors control the rate of fission.

22. A little Uranium yields a lot of energy 8.4 x 10 10 Joules per atom

23. A Question Nuclear energy is a clean fuel. It does not pollute the atmosphere. What reasons may people have for not wanting to utilize nuclear energy?

24. What is Nuclear Fusion?  Nuclear fusion is the process of forcing atoms together into a new type of atom.  Requires very high temperatures and pressures  Nuclei must overcome Coulomb Barrier  Some mass is converted into energy

25.  Nuclear Fusion occurs naturally in stars. Image Credit: NASA

26. 1 Second In The Sun 10 38 Reactions 600 Billion kg H  He 4 Billion kg Mass  Energy 4 x 10 26 Watts http://csep10.phys.utk.edu/astr162/lect/energy/ppchain.html

27. How is radiation measured?  Radiation is energy.  The rem: radiation absorbed and the possible biological damage Lethal doses begin at about 400 – 500 rems Human exposure is about 0.2 rems/year Food39 mrems Electronics11 mrems Tobacco1,300 – 9,000 mrems