1. Radiation ALPHA, BETA, AND GAMMA

2. Science Park HS -- Honors Chemistry Early Pioneers in Radioactivity Roentgen: Discoverer of X-rays 1895 Becquerel: Discoverer of Radioactivity 1896 The Curies: Discoverers of Radium and Polonium 1900- 1908 Rutherford: Discoverer Alpha and Beta rays 1897

3. Radioactivity  Scientists quickly learned that there were three different kinds of radiation given off by radioactive materials.  Alpha rays  Beta rays  Gamma rays  The scientists called them “rays” because the radiation carried energy and moved in straight lines, like light rays.

4. Radioactivity  We now know that radioactivity comes from the nucleus of the atom.  If the nucleus has too many neutrons, or is unstable for any other reason, the atom undergoes radioactive decay.  The word decay means to "break down."

5. Radioactivity  In alpha decay, the nucleus ejects two protons and two neutrons.  Beta decay occurs when a neutron in the nucleus splits into a proton and an electron.  Gamma decay is not truly a decay reaction in the sense that the nucleus becomes something different.

6. Alpha-particle production  Alpha particle – helium nucleus  Examples  Net effect is loss of 4 in mass number and loss of 2 in atomic number.

7. Beta-particle production  Beta particle – electron  Examples  Net effect is to change a neutron to a proton.

8. Gamma ray release  Gamma ray – high energy photon  Example  Net effect is no change in mass number or atomic number.

9. Three Common Types of Radioactive Emissions - Penetrability Alpha particles may be completely stopped by a sheet of paper, beta particles by aluminum shielding. Gamma rays, however, can only be reduced by much more substantial obstacles, such as a very thick piece of lead.

10. Radioactivity  Radioactive decay gives off energy.  The energy comes from the conversion of mass into energy.  Because the speed of light (c) is such a large number, a tiny bit of mass generates a huge amount of energy.  Radioactivity occurs because everything in nature tends to move toward lower energy.

11. Detection of Radioactivity Geiger-Muller counter – instrument which measures radioactive decay by registering the ions and electrons produced as a radioactive particle passes through a gas-filled chamber Scintillation counter instrument which measures the rate of radioactive decay by sensing flashes of light that the radiation produces in the detector

12. Radioactivity  Radioactive decay depends on chance.  It is possible to predict the average behavior of lots of atoms, but impossible to predict when any one atom will decay.  One very useful prediction we can make is the half-life.  The half-life is the time it takes for one half of the atoms in any sample to decay.

13. Half-life  The half-life of carbon-14 is about 5,700 years.  If you start out with 200 grams of C-14, 5,700 years later only 100 grams will still be C-14.  The rest will have decayed to nitrogen-14.

14. Where are the Sources of Radioactivity?  Naturally Occurring Sources:  Radon from the decay of Uranium and Thorium  Potassium -40 – found in minerals and in plants  Carbon 14 – Found in Plants and Animal tissue  Manmade Sources:  Medical use of Radioactive Isotopes  Certain Consumer products –(eg Smoke detectors)  Fallout from nuclear testing  Emissions from Nuclear Power plants

15. Nuclear Reactions and Energy  A nuclear reaction is any process that changes the nucleus of an atom.  Radioactive decay is one form of nuclear reaction.

16. Nuclear Reactions and Energy  If you could take apart a nucleus and separate all of its protons and neutrons, the separated protons and neutrons would have more mass than the nucleus did.  The mass of a nucleus is reduced by the energy that is released when the nucleus comes together.  Nuclear reactions can convert mass into energy.

17. Fission reactions  A fission reaction splits up a large nucleus into smaller pieces.  A fission reaction typically happens when a neutron hits a nucleus with enough energy to make the nucleus unstable.

18. Nuclear Fission  U-235 is bombarded with neutrons  The nucleus absorbs neutrons  It becomes unstable and splits into 2 neutrons  2-3 neutrons are emitted and bombard another U-235 atom  Chain reaction

19. How Electricity is Produced

20. Fusion reactions  A fusion reaction is a nuclear reaction that combines, or fuses, two smaller nuclei into a larger nucleus.  It is difficult to make fusion reactions occur because positively charged nuclei repel each other.

21. Fusion  Fuel= isotopes of hydrogen

22. Fusion  Way of the future??  Produces no high-level waste  Fuel is hydrogen (plenty of it!)  Problems  It takes very high temperatures (millions of degrees) to make atoms fuse  Confining the plasma after it is formed  Scientists have yet to be able to create energy from fusion

23. Rules for nuclear reactions  Nuclear reactions obey conservation laws.  Energy stored as mass must be included in order to apply the law of conservation of energy to a nuclear reaction.  Nuclear reactions must conserve electric charge.  The total baryon number before and after the reaction must be the same.  The total lepton number must stay the same before and after the reaction.

24. Applications of radioactivity  Many satellites use radioactive decay from isotopes with long half-lives for power because energy can be produced for a long time without refueling.  Isotopes with a short half-life give off lots of energy in a short time and are useful in medical imaging, but can be extremely dangerous.  The isotope carbon-14 is used by archeologists to determine age.

25. Carbon dating  Living things contain a large amount of carbon.  When a living organism dies it stops exchanging carbon with the environment.  As the fixed amount of carbon-14 decays, the ratio of C-14 to C-12 slowly gets smaller with age.

26. Pros and Cons of Nuclear Energy Pros  Less of an immediate environmental impact compared to fossil fuels  Carbon-free source of electricity- no greenhouse gases emitted  May be able to generate H-fuel Cons  Generates radioactive waste  Many steps require fossil fuels (mining and disposal)  Expensive

27. Pros and Cons of Nuclear Energy

28. Cost of Electricity from Nuclear Energy  Cost is very high  20% of US electricity is from Nuclear Energy  Affordable due to government subsidies  Expensive to build nuclear power plants  Long cost-recovery time  Fixing technical and safety issues in existing plants is expensive

29. Safety Issues in Nuclear Power Plants  Meltdown  At high temperatures the metal encasing the uranium fuel can melt, releasing radiation  Probability of meltdown or other accident is low  Public perception is that nuclear power is not safe  Sites of major accidents:  Three Mile Island  Chernobyl (Ukraine)

30. Three-Mile Island  1979- most serious reactor accident in US  50% meltdown of reactor core  Containment building kept radiation from escaping  No substantial environmental damage  No human casualties  Elevated public apprehension of nuclear energy  Led to cancellation of many new plants in US

31. Chernobyl  1986- worst accident in history  1 or 2 explosions destroyed the nuclear reactor  Large amounts of radiation escaped into atmosphere  Spread across large portions of Europe  Radiation spread was unpredictable  Radiation fallout was dumped unevenly  Death toll is 10,000-100,000

32. Nuclear Energy and Nuclear Weapons  31 countries use nuclear energy to create electricity  These countries have access to spent fuel needed to make nuclear weapons  Safe storage and handling of these weapons is a concern

33. Radioactive Waste  Low-level radioactive waste-  Radioactive solids, liquids, or gasses that give off small amounts of ionizing radiation  High-level radioactive waste-  Radioactive solids, liquids, or gasses that give off large amounts of ionizing radiation

34. Radioactive Wastes  Long term solution to waste  Deep geologic burial –Yucca Mountain  As of 2004, site must meet EPA million year standard (compared to previous 10,000 year standard)  Possibilities:  Above ground mausoleums  Arctic ice sheets  Beneath ocean floor

35. Radioactive Waste  Temporary storage solutions  In nuclear plant facility (require high security)  Under water storage  Above ground concrete and steel casks  Need approved permanent options soon.

36. Case-In-Point Yucca Mountain  70,000 tons of high-level radioactive waste  Tectonic issues have been identified

37. Decommissioning Nuclear Power Plants  Licensed to operate for 40 years  Several have received 20-year extensions  Power plants cannot be abandoned when they are shut down  Three solutions  Storage  Entombment  Decommissioning (dismantling)