Radioactivity

1. Radioactivity

2. Radioactivity is the spontaneous decay of unstable nuclei to release either alpha or beta particles or gamma rays and energy

3. 1 Which is not one of the three types of radiation? • Gamma particles • Alpha particles • Beta particles • Gamma waves

4. Many elements (red) exist primarily as radioactive elements, while others have both radioactiveand stable isotopes. After U, all are radioactive and manmade.

5. 2 All atoms with atomic number ___ & above are radioactive. • 58 • 86 • 92 • 104

6. Why are some isotopes unstable (radioactive), while others are not? Larger elements have protons & neutrons too far apart to be held together by the strong nuclear force—acts at small distances. (Remember, p+ are repelled by each other)

7. Neutrons are held together by strong nuclear force, and they shield p+ from each other. So, stable isotopes of atoms with large protons numbers usually have more neutrons than protons—but if the nucleus gets too high in diameter, the strong nuclear force is too weak to hold it together. e.g., hydrogen-1 is stable, but Hydrogen-2 deuterium and Hydrogen-3 tritium are radioactive

8. The ratio of p+/no determines whether atoms of an isotope will be stable or radioactive. Green elements are stable, but yellow ones are radioactive.

9. 3 Why are some isotopes of an element radioactive, while others are not? • Wrong ratio of protons to neutrons • Nuclear diameter too high • Proton to proton repulsion too high • Strong nuclear force not sufficiently high • All of the above

10. Three main types of radioactive decay exist: Alpha α, Betaβ, Gamma Ɣ 224Ra --> 220Rn + 4 He2+ 2 alpha α particles are He nuclei (2 protons and 2 neutrons, mass 4; they have a positive 2 charge because they have no electrons 4 He 2+ 2 The large size of alpha particles makes them sluggish and slow and low in energy. You can protect yourself from α radiation by holding up a sheet of paper.

11. Beta decay: Gain or loss of a proton through conversion of neutrons to a proton or protons to a neutron—whichev er confers the stable ration; during the conversion, β particles about the size of an electron are released. β particles low masses allow them to travel at higher speed and to have higher energy—to protect yourself from these, you must use a plastic sheet ¼ inch thick. Gamma Ɣ decay—high energy waves, no particles; the highest energy of radiation—to protect yourself, you must use a 1/8 inch lead shield—like in the heavy apron at the dentist’s office from when you have Xrays.

12. 4 Which type of radiation is comprised of He2+ ions, having a mass of 4 amu? • Alpha particles α • Beta particles β • Gamma particles Ɣ • Gamma rays Ɣ

13. 5 Which type of radiation is comprised of tiny positively (positrons) or negatively (electrons) charged particles? • Alpha particles α • Beta particles β • Gamma particles Ɣ • Gamma rays Ɣ

14. 6 Which type of radiation is comprised only of energy traveling as an electromagnetic wave? • Alpha particles α • Beta particles β • Gamma particles Ɣ • Gamma rays Ɣ

15. 7 Which type of radiation has the highest energy and can be blocked (shielded) only by a ¼ inch or more of lead? • Alpha particles α • Beta particles β • Gamma particles Ɣ • Gamma rays Ɣ

16. 8 Which type of radiation travels so rapidly that it requires at least ¼ inches of plastic for protective shielding, even though the particles are incredibly tiny? • Alpha particles α • Beta particles β • Gamma particles Ɣ • Gamma rays Ɣ

17. 9 Which type of radiation is comprised of large particles move slowly and have the least energy of the types of radiation? • Alpha particles α • Beta particles β • Gamma particles Ɣ • Gamma rays Ɣ

18. 10 Which type of radiation can be stopped (shielded) by a piece of paper? • Alpha particles α • Beta particles β • Gamma particles Ɣ • Gamma rays Ɣ

19. Writing balanced chemical equations to represent nuclear decay.Reactants products Equations obey Law of conservation of matter & energy: Total mass of reactants = total mass products Total charge of reactants = total charge products Total charge of reactants = total charge products For α & β nuclear decay ONLY: Total #s and identities of elements on reactant side = totals & identities for product side. Why? Transmutation—creation of new elements when neutrons are lost are gained

20. Why can you know whether α or β decay occurred in each? Look at mass numbers & atomic numbers! thorium-232 --> radium-228 + α reduced mass radium-228 --> actinium-228 + β mass same, ↑atomic # actinium-228 --> thorium-228 + βmass same, ↑atomic # thorium-228 --> radium-224 + α reduced mass radium-224 --> radon-220 + α ? radon-220 --> polonium-216 + α ? polonium-216 --> lead-212 + α ? lead-212 --> bismuth-212 + β ? bismuth-212 --> polonium-212 + β ? polonium-212 --> lead-208 + α ?

21. 11 As radioactive elements decay they become new, more stable elements and isotopes, through a process called ____. • mutation • transmutation • Atomic number shift • Mass number shift

22. Radioactive isotopes emit radiation that destroys or causes mutation of DNA. The energy emitted by radiation causes breaks in the DNA molecules.When DNA damage is minor, then it can be repaired, but mistakes (mutations) may occur during the repair (e.g., instead of A to T pairing, T to T pairing When very large or numberousbreaks occur, then cells may die via programmed cell death calledapoptosis (cell suicide).

23. Cell suicide, Apoptosis, after large scale damage of DNA (due to either a short exposure to a high level of radiation OR long exposure to a low level of radiation. Alpha and Beta emitters can cause mutation OR apoptosis if they are ingested.

24. When DNA damage is spread over many parts of the body, then death can occur within days due to multi-organ failureas the result of radiation sickness.Early symptoms of radiation sickness* Mild exposure (1-2Gy) Moderate(2-6Gy) Severe(6-8 Gy)Very severe (8-10 Gy +)Nausea & vomiting Within 6 hours --2 hours -- 1 hour -- 10 minutes Diarrhea – Within 8 hours -- 3 hours -- 1 hour Headache -- Within 24 hours --4 hours -- 2 hours Fever -- Within 3 hours -- 1 hour Later symptoms of radiation sickness*Dizziness and disorientation -- -- Within 1 week --immediateWeakness, fatigue Within 4 –1 to 4 weeks --1 week -- Immediate Hair loss, bloody vomit and stools, infections, poor wound healing, low blood pressure -- Within 1-4 weeks -- 1 week -- Immediate

25. 12 Radiation sickness is due to widespread ___: • mutation • transmutation • apoptosis • burns

26. Nuclear energy takes advantage of the huge amount of heat energy released during radioactive decay Pros Cheap Lots of U-238 available Cons Long half life of wastes—no where to store them Accident possibility Cost of building and maintaining, even after closing Weapon grade plutonium Terrorist obtaining waste Heat water, release steam

27. Energy from decay heats water to turn turbines that generate electricity. Pellet (1 penny)=2 tons coal equivalent!

28. Biggest problem is storage of wastes with long half lives: time for half of a sample to become nonradioactive. After 10 half lives, safe disposal is possible.

29. If an isotope has a half life of 37,000 years, then how much of a 100 kg sample of it will still beradioactive after: 37000 years ____ ½ or 50Kg_ 74000 years __ ½ X ½ or ¼, 25 Kg 111000 years _ ½ X ½ X½ =1/8 or 12.5 Kg Ten half lives allows disposal—370,000 years!

30. 13. How many years must pass before a 1000 Kg sample of Cesium, half life 37 days, decays to only 1/16 being radioactive? • 16 days • 37 days • 148 days • 1000 days

31. Plutonium needs storage for 400,000 years! Why so hard to store it? Heat decays containers & breaks rocks, allowing the waste to reach ground water and thus the food chain! High cost of protection from theft No long term site yet! Highest risk waste stored on site at the plants in swimming pools! (theft waiting to happen or spills)

32. 14. Plutonium is produced as a bi-product of nuclear fission for nuclear power generation. It is a necessary component for production of nuclear weapons. Why is this waste particulary difficult to dispose? • Risk of theft by terrorists • Tremendous heat produced during decay can destroy containers & crack surrounding rock in storage facilities • Risks contamination of water • It’s 40,000 year half life makes 10 half life storage very difficult. • All of the above

33. Why possible accidents at nuclear reactors? Fission chain reactions get out of control. Normally, collisions with heavy water slow the reactions.

34. 15 Nuclear power today primarily uses: • Fission of U-238 • Fusion of He • Fission of Pu-245 • Fusion of U-235

35. Retired power plants (30 years old or so) require as large a staff and as much protection as a working plant. Yet they generate no money or electricity! There’s not yet a place safe enough to store the used fuel rods. Now they’re stored under water at the plants! (also, transport is very dangerous)

36. Nuclear bombs use chain reactions to create huge shock waves: heat compresses air together to create blast & radiation damages DNA and RNA.

37. Why do we have greater risk from dirty bombs than from traditional atom bombs? Easier to build Any radioactive materials will work—long half lives work best Can detonate with explosives by blowing a plane up in the air and contaminate huge area Cost of clean up is massive—maybe not possible Move out of area to avoid long term exposure that can cause cancer and birth defects Unguarded waste and submarine fuel rods are scattered in large amounts in the former USSR. It’s hard to detect wastes—most ports, airports, borders don’t screen with geiger counters!

38. Fusion energy is the ultimate: fuse atoms together at high temperatures Would generate energy in enormous amounts starting with water as fast moving positrons released increase motion of water and increase its temperature steam to run electrical turbines. No wastes made Free! Problem: all materials melt at lower temperature—hard to reach the temperature to start it—magnetic “bottles” are the only container to hold the reaction mix!

39. 16. Why would fusion a better source of electricity? • No radioactive wastes generated • Source of fuel is water • Limitless, nearly free electricity • All of the above