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NUCLEAR REACTIONS

NUCLEAR REACTIONS. TOPICS IN THIS LESSON. Stability of the Nucleus Alpha Radiation Beta Radiation Gamma Radiation Balancing Nuclear Eqns Half-Life Nuclear Fission Nuclear Fusion Radiation in Your Life & Uses of Radioactivity. NUCLEAR STABILITY.

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NUCLEAR REACTIONS

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  1. NUCLEAR REACTIONS

  2. TOPICS IN THIS LESSON • Stability of the Nucleus • Alpha Radiation • Beta Radiation • Gamma Radiation • Balancing Nuclear Eqns • Half-Life • Nuclear Fission • Nuclear Fusion • Radiation in Your Life & Uses of Radioactivity

  3. NUCLEAR STABILITY • Almost all atoms we’ve encountered have stable nuclei • Not radioactive • Radioactive atoms are relatively rare, which is fortunate since radiation can be harmful • Radioactive atoms have nuclei that are disintegrating • So why are some nuclei stable and others unstable?

  4. The fundamental force that holds the nucleus together is called the Strong Nuclear Force. • If the force is strong enough the nucleus will be stable • One reason the force might not be strong enough is the number of protons and neutrons in the nucleus. • Not all combinations of protons and neutrons are stable. • There must be a “magic” number of each particle to ensure stability

  5. The first 20 stable nuclei follow a distinct pattern. • For elements with atomic numbers between 1 and 20 stable nuclei have almost equal numbers of protons and neutrons. • Beyond 20 protons, nuclei need increasingly more neutrons than protons to be stable. • Nuclei are unstable not only if they contain too few neutrons, but also if they contain too many.

  6. DISCUSSION QUESTIONS What force is holding together the nucleus? What seems to be the common factor that influences whether an atom will be radioactive or not? Using the graph on the previous slide, how many neutrons does it take for an atom to be stable that has 70 protons?

  7. Particles emitted from nucleus AKA: ionizing radiation • Radioactive elements/isotopes are responsible for producing what we think of as radiation. • There are three different forms of nuclear radiation • Alpha • Beta • Gamma • Spontaneous emission of radiation from an atom is known as radioactivity.

  8. 4 He a or 2 Alpha Particles • Alpha radiation consists of a stream of high-energy alpha particles • Consists of 2 protons and 2 neutrons and is identical to a helium-4 nucleus • Can be represented by the symbol

  9. Alpha Particles • Alpha particles do not have much penetrating power. • They are able to travel only a few centimeters through air and are easily stopped by paper or clothing • Not normally harmful to humans • Can be very dangerous if source is ingested

  10. 4 226 222 He Ra Rn 2 88 86 Alpha Decay Equations • An alpha particle is emitted spon-taneously from some unstable nuclei. • With each expulsion of an alpha particle from the atom’s nucleus the atom loses 4 units of mass & 2 protons (+2 charged particle) • Any change in #’s of protons changes the type of atom, this is transmutation. +

  11. DISCUSSION QUESTIONS What nucleus is left of a radioactive isotope of Actinium-231 after an alpha decay? What is the original nucleus that produces a nucleus of Radon-222 after 2 consecutive alpha decays?

  12. 0 e -1 b or Beta Particles • Beta radiation consists of a stream of high-speed electrons • A neutron changes into a proton and an electron • The proton remains in the nucleus and the electron is expelled from the nucleus • Beta radiation is represented by the symbol

  13. Beta Particles • The mass number is zero • 100 times more penetrating then alpha radiation • Can damage the skin and tissues • Ionizing radiation can cause damage to DNA, which might lead to… • Apoptosis (cell death) • Mutation

  14. 131 0 131 e I Xe 54 53 -1 Beta Decay Equations • A beta particle is emitted spon-taneously from some unstable nuclei. • The beta electron is the result of one of the atom’s neutrons decomposing into a proton and an electron. • This results in the atom having one more proton which causes it to transmutate into a different atom. +

  15. Beta Decay

  16. DISCUSSION QUESTIONS How is a beta particle produced? What nucleus will be the result of a beta decay of Bismuth-210? If the nucleus from question 2 continues to decay by emitting an alpha particle and then immediately undergoes a beta decay, what is the resulting nucleus?

  17. Gamma Rays • A Gamma ray is highly energetic light, similar to x-rays • Does not consist of particles • Gamma radiation is energy given off during alpha and beta decay • Much more penetrating than either of a or b • It is able to penetrate deeply into solid material, including body tissue • Symbolized by: g

  18. 4 0 2 -1

  19. Properties of Some Radiations Property Alpha Radiation Beta Radiation Gamma Radiation Common source Radium-226 Carbon-14 Cobalt-60 Appox. energy 5 MeV 0.05 to 1 MeV 1MeV Power Low (0.05mm body tissue) Moderate (4mm body tissue) Very high (penetrates body easily) Shield-ing Paper, clothing Metal foil Lead, concrete

  20. The antimatter equivalent to a beta particle is called a positron ( ) • The absorption of an electron by a nucleus, a.k.a. electron capture 0 e +1 Other Nuclear Decay Particles… • There are 2 other types of radioactive decays observed.

  21. DISCUSSION QUESTIONS How is a positron produced? Which of the three basic types of radiation (alpha, beta, and gamma) is the most energetic most penetrating? Start with a Seaborgium-263 nucleus, perform each of the types of decays mentioned so far.

  22. Balancing Nuclear Eqns • A rxn equation can be written for any transmutation • These rxn eqns must be “balanced” • The total of the mass numbers on the left hand side must equal the total of the mass numbers on the right of the arrow • Same must be true of atomic numbers • There might be coefficients needed to indicate more than one identical nucleus

  23. For example: 241+4 = 245 2(1)+? = 245 95+2 = 97 2(0)+? = 97 Our goal should be to fill in the missing information and the nuclei that corresponds to that information

  24. For example: 241+4 = 245 2(1)+243 = 245 95+2 = 97 2(0)+97 = 97 Now what atom has an atomic number of 97?

  25. For example: 241+4 = 245 2(1)+243 = 245 95+2 = 97 2(0)+97 = 97 Notice that the total mass numbers on both sides are equal and the total atomic numbers on both sides are equal…it is balanced.

  26. DISCUSSION QUESTIONS Balance the following nuclear reactions:

  27. Half-Life • Every radioactive isotope has a unique rate of decay or half-life • A half life is the time required for ½ of nuclei of a radioactive sample to decay • After 1 half-life, ½ of the original nuclei have undergone transmutation • Half lives may be as as short as a fraction of a second or as long as billions of years

  28. Half-Life • Most artificially produced radioactive isotopes have very short half-lives • Rapidly decaying isotopes do not pose long term bio-radiation hazards to med patients • A simple half-life equation:

  29. Half-Life • One radioactive isotope that has a long half-life is U-238 (4.47x109 yrs) • It is the most common isotope of U • It decays into Th-234 • However, the process continues in a series of radioactive intermediates to the eventual stable isotope of Pb-206 • A stable isotope is finally reached when Lead-206 results • There are 13 intermediate products between U-238 and Pb-206

  30. DISCUSSION QUESTIONS What is the half-life of Pa-234? (hint: use the graphic on the previous slide) If 100.0 g of C-14 decays until only 25.0 g of carbon is left after 11,460 years, what is the half-life of C-14? Thallium-208 has a half-life of 3.053 min. How long will it take for 120.0 g to decay to 7.50 g?

  31. Other Nuclear Reactions • Radioactive decay occurs when a nucleus disintegrates spontaneously • A nuclear reaction is a reaction that involves the collision of nuclear particles • These rxns deal with the interaction of nuclear particles not a decay of a nucleus • There are two types of nuclear reactions • fission & fusion

  32. Nuclear Fission • Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing free neutrons and other smaller fission products • The pieces the nucleus splits into have less mass collectively than the original nuclear material (mass lost is converted to energy) • Fissioning produces huge amounts of energy. • More energy than chemical reactions

  33. Nuclear Fission • One fission rxn produces enough neutrons to start 3 more fission rxns, which in turn produces the neutrons needed to start 3 morerxns, and so on, in a series called a nuclear chain reaction. • Control rods absorb some of the neutron products in nuclear reactors to control these chain rxns • Uncontrolled chain reactions are atomic bombs

  34. In a nuclear reactor, the fission of 4.5g of U-235 will satisfy a person’s energy needs for 1 year. • Fission reactors are used for a clean & efficient source of power.

  35. DISCUSSION QUESTIONS Briefly research the pros and cons of nuclear fission, and in Word construct a table (with two columns one for Pros and one for Cons) and provide 6 pros for nuclear fission and 6 cons for nuclear fission. Under the table copy and paste the sources you used for the table. Print it out to turn in with your other discussion questions.

  36. Nuclear Fusion • Fusion is the process of two nuclei colliding with each other hard enough to fuse into a larger nuclei • some of the mass of the original nuclei into energy- a great deal of energy • According to the eqn: E=mc2 • Fusion naturally occurs in stars, but artificial fusion has been accomplished, just not controlled. • On a large scale…hydrogen bomb

  37. Fusion that takes place in stars the size of the sun. It’s called the proton-proton chain.

  38. Nuclear Fusion • Fusion rxns are hard to initiate and to control • So far it takes a tremendous amount of heat to start • Cold fusion is a natural research opportunity, • The goal is to harness the power of the sun

  39. Nuclear Fusion • With fusion we get a large amount of energy, without as many of the waste products of fission. • There are currently 2 types of nuclear fusion reactors being researched • Magnetic Confinement • Tokamak reactor • Inertial Confinement • NOVA reactor

  40. DISCUSSION QUESTIONS • Research the concepts behind the 2 types of nuclear fusion reactors (inertial & magnetic confinement) & in Word generate a 2 column table, 1 for inertial and 1 for magnetic confinement. In the table include these points for each type of reactor. • Basic design • How it works • Practicality • Advantages

  41. Radiation in Your Life • Radiation emitted from radioisotopes is called ionizing radiation • Radiation with enough energy to knock electrons out of atoms • It can’t be seen, smelled, heard, nor felt • Due to this, we can use instruments to detect the presence of radiation • Geiger counter • Scintillation counters • Film badges

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