Energy Changes in Nuclear Reactions

1. Energy Changes in Nuclear Reactions BY…

2. E=mc² • Einstein’s equation that relates mass and energy • E=Energy • m=mass • c=speed of light, 3.00 x 108 m/s • States that mass and energy are proportional • If a system loses mass, it loses energy, and vice versa • Mass and energy changes are much greater in nuclear reactions than in chemical reactions

3. Example of E=mc² • 238 U 234Th + 4 He • Mass U=238.0003 amu, mass Th=233.9942 amu, mass He=4.0015 amu • Δm=233.9942g+4.0015g-238.0003=-0.046 • Lost mass=exothermic • Energy change calculated through Einstein’s equation, E=mc²: • ΔE=Δ(mc2)=c2Δm =(2.9979 x 108 m/s)2(-0.0046 g)(1 kg/100o g) =-4.1 x 1011 kg-m2/s2 = -4.1 x 1011 J (Note: Δm is converted to kg, SI unit of mass, to get ΔE in joules, SI unit for energy.)

4. Nuclear Binding Energies • Energy required to separate a nucleus into its individual nucleons • Masses of nuclei are always less than the masses of individual nucleons • Mass defect- difference between a nucleus and its constituent nucleons • Addition of energy to a system must be joined by a proportional increase in mass • Larger the binding energy is, the more stable the nucleus is towards decomposition

5. Nuclear Binding Energies Continued • Binding energies per nucleon initially increases in magnitude as mass number increases • Nuclei of intermediate mass numbers are more tightly bonded (more stable) than other nuclei that is smaller or has larger mass numbers • Trend has two consequences • Heavy nuclei gain stability and give off energy if they divide into two mid-sized nuclei • Fission • Greater amounts of energy is release when very light nuclei are combined or fused together to give larger nuclei • Fusion

6. Biological Effects of Nuclear Radiation By: Kayla Seider and Hannah Cherry

7. Radioactivity • We are continually being bombarded by artificial and natural radiation • Infrared, UV, visible radiation from the sun, radio waves, microwaves, and x-rays • There is radioactivity in the soil and other materials

8. Types of Radiation • If matter absorbs radiation, it can cause either excitation or ionization of the matter • Excitation occurs when absorbed radiation excites electrons to a higher energy state or increases the motion of molecules • Causes them to move, vibrate, or rotate • Ionization occurs when the radiation removes an electron from an atom or molecule • Is more harmful than radiation that doesn’t cause ionization • Non-ionization is lower in energy or slower moving neurons • Radiofrequency electromagnetic radiation • Most of the energy is absorbed by water molecules in tissue • Most tissue is 70% water by mass • Can define ionizing radiation as radiation that can ionize water • X-rays, higher-energy UV, alpha, beta, and gamma rays

10. What Happens • When ionization radiation passes through living tissue, electrons are removed from water molecules, forming highly reactive H2O+ • An H2O+ can react with another water molecule to form H3O+ and a neutral OH • OH becomes a free radical • A free radical is a substance with one or more unpaired electrons • In cells and tissues, these particles can attack a host of surrounding biomolecules to produce new free radicals • These new free radicals can initiate a large number of chemical reactions that are able to disrupt the normal operation of cells • Can contribute to cancer, diabetes, stroke, heart attack, Parkinson's, Alzheimer's, schizophrenia, and hemochromatosis

11. The Damage • Damage depends on the activity and energy of the radiation, the length of exposure, and whether the source is inside or outside the body • Gamma rays are harmful outside of the body • They can penetrate human tissue very easily • Can cause organ damage and genetic damage • Dangerous • Alpha rays are stopped by skin • In the body, alpha rays are particularly dangerous because they transfer their energy efficiently to the surrounding tissue causing considerable damage • Beta rays can penetrate about a cm beyond the skin • Tissue that shows the greatest damage are those that reproduce at a rapid rate • Bone marrow, blood-forming tissues, and lymph nodes

12. Radiation Doses • Radiation is measured in the gray (Gy) and the rad (radiation absorbed dose) • The gray is equivalent to the absorption of 1 J of energy per kilogram of tissue • The rad is equivalent to the absorption of .01 J of energy per kilogram of tissue • 1 gray= 100 rads • A rad of alpha radiation causes more damage than a rad of beta radiation • To correct these differences, the radiation dose is multiplied by a factor that measures the relative biological effectiveness (RBE) of radiation • The exact RBE value varies with dose rate, total dose, and the type of tissue affected • RBE is approximately 1 for gamma and beta and 10 for alpha • The product of radiation dose and the RBE gives you the effective dosage in units of rem (roentgen equivalent for man) • Number of rems= (number of rads)(RBE) • The siervert (Sv) is the unit for effective dosage • 1 Sv= 100 Rem

13. Radiation Doses • 600 rem will cause death • Dental x-rays is .5 mrem • The average exposure for a person in one year due to natural sources of ionizing radiation is about 360 mrem

15. Radiation Therapy • Both healthy and unhealthy cells can be destroyed by radiation • Can lead to physiological disorders • Cancer is the growth of abnormal cells, that growth produces malignant tumors • The tumors can be destroyed by exposing them to the same radiation because rapidly reproducing cells are susceptible to radiation damage • Therefore, cancerous cells are easier to destroy than healthy ones • That’s why radiation is used in cancer treatment • Side effects • Fatigue, nausea, hair loss, weakened immune system, even death • Because of these side effects, radiation therapy is a last resort for treatments

16. True or False • Radiation in Japan is equal to 38,000 bananas • True • About 1,200 radioactive isotopes have been produced in all the known elements • True • You get little amounts of radiation while on a nuclear submarine • True • Burning coal releases more radiation than a nuclear plant does • True

17. Questions • What is ionizing radiation? • Radiation that can ionize water and it can remove an electron from a molecule • What is a free radical? Why is it so bad? • A substance with one or more unpaired electrons. They disrupt the normal operations of cells • Which is smaller the rad or the gray and how are they related to eachother? • The rad is smaller than the gray. 1 gray= 100 rads • What dose of rems cause death? • 500-600 rems

18. 21.8: Nuclear Fusion Kyle, Suraj, Brian

19. Energy is produced when light nuclei fuse into heavier ones Talked about in 21.6 (don’t write this part down) Type of reactions responsible for energy produced by sun Nuclear Fusion Intense workouts Nuclear fusion = Equal in hottness (write this equation down)

20. Nuclear Fusion • Several different types of fusion processes: 1/1H+1/1H 2/1H+ 0/1e 1/1H+2/1H 3/2He 3/2He+3/2He 4/2He+2(1/1H) 3/2He+1/1H 4/2He+0/1e

21. Fusion Energy • Appealing as an energy source • Nonradioactive products • Light isotopes of hydrogen are easily available • Currently not used • Extremely high energies are needed to overcome repulsion of nuclei

22. Overcoming Nuclei Repulsion • In order to achieve the required energies, high temperatures must be maintained • Thus, fusion reactions are known as thermonuclear reactions • Lowest temperature required for fusion is 40 million Kelvin • This temperature has only been achieved by hydrogen bombs • Uncontrolled power generation -Requires 40,000,000 K to initiate

23. Fusion as energy • Numerous problems must be overcome before fusion becomes a practical source for energy • High Temperatures to start reaction • Confining the reaction • No known material is able to withstand the temperature needed for fusion • Researches try to use tokomaks to achieve fusion • Also use lasers

24. Tokamak • Uses strong magnetic fields to contain and to hear a fusion reaction • Have reached 3million degrees Kelvin • http://www.youtube.com/watch?src_vid=E2-Y8bYtvX4&annotation_id=annotation_49072&feature=iv&v=IU7oMISRS2Y

25. Nuclear Fission Jake Wiley, James Haeckel, Sergio Machaca

26. Fission • Extremely exothermic • Uranium-233, -235, and Plutonium-239 are main practical sources • 1 neutron hits a heavy nuclei and causes it to split • Average of 2.4 neutrons are released • Various and unpredictable products, typically radioactive

27. Chain Reactions • Each neutron released can cause another nucleus to split • Critical Mass • Enough mass of the material is present to sustain the reaction at a constant rate • Uranium ~ 1kg • Subcritical Mass • Less than critical mass, neutrons escape without hitting any nuclei • Supercritical Mass • More than critical mass, reaction proceeds unchecked, typically with violent results

28. Which one is Subcritical? Supercritical?

29. Nuclear Arms • Gun-type • Two subcritical masses are shot together into a supercritical mass • Implosion • Subcritical mass of P-239 is compressed by explosives to supercritical mass

30. Nuclear Reactors • Fuel rods typically use 3% U-235 • Encased in stainless steel or zirconium tubes • Control rods regulate amount of neutrons • Typically boron or cadmium • A moderator is used to slow the neutrons as to be more readily absorbed by fuel • A cooling liquid is used to carry off excess heat • Often the moderator and cooling liquid are one in the same

31. Nuclear Reactors (Cont.) • Excess heat is used to turn water to steam • Used to turn a turbine • Steam is cooled and condensed • Often cooled with water from a stream or lake • All incased in reinforced concrete • Prevents radiation leak • Protects reactor from external forces

32. Nuclear Waste • Estimated at 20 half-lives before safe exposure • Puts used fuel at about 600 years • Dangerous to handle and transport • Originally stored in pools at reactor and transported to reprocessing plants • Transportation incredibly unpopular and reprocessing too hazardous • Spend fuel rods are presently stored on site • Yucca Mountain, Nevada is a possible long term storage facility

33. Thorium • Silvery metal • Topic of energy source discussions • Thorium reactors are considered safer • No chain reaction • Must be bombarded with neutrons to drive the fission process • Reactor halts process by itself in case of overheat • No room for mechanical or electrical failure • Thorium is as abundant as lead

34. Continued • Thorium poses fewer environmental hazards • Cleaner than uranium or other radioactive materials used in other reactors • Can burn up plutonium and toxic waste from old reactors • Saves money • Does not require isotope separation • High neutron yield, better fission rating, longer fuel cycles • ~100% of recovered thorium is fit for reactors

35. Nuclear Reactor Meltdowns • Three Mile Island, Pennsylvania • Partial Meltdown • March 28, 1979 • Fuel rods liquefied • Chernobyl, Russia • Complete Meltdown • April 26, 1986 • Experiment on core failed causing two explosions • Town remains uninhabited

36. Questions • Is Fission an exothermic or endothermic process? • What is critical mass and the two types? • What do the control rods and the moderator do in a Nuclear reactor? • Explain this process:

37. Answers • Exothermic: the process releases energy • The amount of fissionable large enough to maintain a chain reaction, Sub- less than critical mass and Super- more than • Control rods regulate neutrons to keep up chain reaction, while preventing overheating; Moderator slows neutrons to be used more readily by fuel • 1 Neutron splits an Uranium nucleus into a Krypton and Barium nucleus and 3 Neutrons

40. Patterns of Nuclear Stability Melissa Ross, LexySmyles, Kevin Miner

41. Neutron-to-Proton Ratio • Strong nuclear force- strong force of attraction that exists between nucleons at close distances • Nucleons= protons and neutrons • Overcomes the repulsive forces of protons • Nuclei with two or more protons contain neutrons • More protons = more neutrons • Required to bind nucleus together

42. Neutron-to-Proton Ratio • Atomic number 20 and lower • 1:1 ratio of protons and neutrons • Higher atomic number • More neutrons than protons *Neutron to proton ratio of stable nuclei increases with increasing atomic number* http://www.youtube.com/watch?v=H8Yd2T9MQBU

43. 0 0 Neutron-to-Proton Ratio + + + 0 0 0 0 + + + + 0 0 0 0 • In heavier nuclei, the number of protons increases the proton-proton repulsions which outweighs sum of: • proton-proton attractions • proton-neutron attractions • neutron-neutron attractions • THEREFORE… number of neutrons must increase at more rapid rate than number of protons + + 0 0 0 + 0 0 0 0 + 0 0 + 0 0 0 0 0 0 + DEMO 0 0 + 0 0 + + 0 0 0 0 + 0 0 0 + 0 0 0 0 + 0 0 0 0 0 0 0 0 0 + 0 0 + + + 0 0 + 0

44. Belt of Stability – Area where all stable nuclei lie • Ends at element 83 • *All elements with 84 or more protons are radioactive*

45. Radioactive Decay • Nuclei above belt of stability • High neutron to proton ratio • Move toward belt by emitting beta particle • Decreases number of neutrons and increases number of protons

46. Nuclei below belt of stability • Low neutron to proton ratio • Move toward belt by positron emission or electron capture • Decrease protons and increase neutrons • Positron emission more common in lighter elements • Electron capture more common in heavier elements

47. http://www.youtube.com/watch?v=VJZuY3_aLnI • Nuclei outside belt of stability • Atomic number 84 or higher • Undergo alpha emission • Decreases both protons and neutrons by two • Moves diagonally towards belt of stability

48. Radioactive Series • Some nuclei can’t gain stability through a single emission, so a series of successive emissions occur • Radioactive series (nuclear disintegration series) – begins with an unstable nucleus and ends with a stable one • Three exist: • Uranium 238 – lead 206 • Uranium 235 – lead 207 • Thorium 232 – lead 208

49. Radioactive series example Net Reaction: