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NUCLEAR PHYSICS

NUCLEAR PHYSICS. Know the following: Differences between mass number, atomic number, atomic mass. Definition of Binding Energy Mass Defect MeV 1 u = 931.5 MeV How to find Binding Energy of a nucleus Decay Modes (alpha, Beta-, Beta+, gamma, capture) Stability Measuring Nuclear Decay

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NUCLEAR PHYSICS

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  1. NUCLEAR PHYSICS

  2. Know the following: • Differences between mass number, atomic number, atomic mass. • Definition of Binding Energy • Mass Defect • MeV • 1 u = 931.5 MeV • How to find Binding Energy of a nucleus • Decay Modes (alpha, Beta-, Beta+, gamma, capture) • Stability • Measuring Nuclear Decay • Rates, activity, decay constant, becquerel • Half-life • Difference Between Fission and Fusion • A little about particles (different types, anti-matter, quarks)

  3. Z

  4. A

  5. N

  6. Albert Einstein said: • Mass and Energy are the same thing! • From Al’s Special Theory of Relativity • This theory also states that the speed of light is a universal speed limit and length and time are relative. • Most famous equation in Physics: • E = mc2 • E=Rest energy, m=mass, c=speed of light • In class, we will use this: • 1 u = 931.5 MeV/c2 (or MeV c-2 for IB)

  7. Atomic Mass Unit • Also known as the unified mass unit; u • Is defined as 1/12 the mass of a Carbon-12 nucleus’ mass. • Is used because its easier than using kilograms at this small scale • 1 u = 1.6605402 x 10-27 kg

  8. Electron-Volt • A unit of energy • Used in place of Joules due to small scale • Is defined as the energy an electron gains as it is accelerated through a potential difference of one volt. • 1 eV = 1.6 x 10-19 J • An MeV is a mega-electron-volt which is one million electron-volts, 1MeV=1x106eV

  9. Particle u MeV Proton 1.007825 938.3 Neutron 1.008665 939.6 Electron 0.000549 0.5110 • Only for free particles (not in nucleus) • Strong Force: interaction that binds nucleons together in a nucleus

  10. Binding Energy: The energy involved when nucleons bind together to form a stable nucleus • Purpose of BE problems: to find the amount of energy within the nucleus or amount per nucleon • Basicconcept: Free nucleons have more mass than nucleons within a nucleus. • Called “Mass Defect”---where did all the mass go? It turned into Energy! Binding Energy! Al was right! Mass turns into energy!

  11. Examplify! • Find Binding Energy for Tm-169: • A few things: use the charts on page 966 – 971 • First find the total mass of the nucleons as if they are free. (multiply # of neutrons by the mass of one and the same with protons. Combine these) • Second, subtract the mass of the nucleus from the free nucleon mass. • this mass from The difference is the “Mass Defect”. Convert this to energy.

  12. Nuclear Decay • Nuclear decay: a natural or artificial process by which an unstable nucleus breaks apart. This usually results in a new element: the daughter. Original nucleus is called the parent! • Radioactivity: spontaneous emission of energy during nuclear decay • Three types of radiation:

  13. αβγ

  14. Particle Symbol Composition Charge Effect on Alpha α 2protons +2 mass loss 2 neutrons new element Beta β- electron -1 new element β+ positron +1 Gamma γ photon 0 energy loss

  15. Half-life • Decay constant: λ. Not to be confused with wavelength. This indicates the rate at which the isotope decays. • ΔN = - λ NΔt • N= # of radioactive parent nuclei; ΔN = # of parent nuclei that decayed into daughter nuclei; Δt= time interval of decay. • Activity = - ΔN / Δt = λ N • This means the # of decays per time, or decay rate. Measured in Becquerel (Bq) • Half-life is the time required for half the original nuclei of a radioactive material to undergo radioactive decay. • T1/2 = 0.693/ λ

  16. A new element called Spiffexium is discovered. 200 kg are all the is known to exist in the universe. After 9 hours, 25 kg are left. Carp! Hurry! What is the half-life of Spiffexium?

  17. A sample of Ra-226 contains 3x1016 nuclei. What is the decay constant? How many will decay per second? • It’s decay-tastic!

  18. Beta Decay • Neutrinos and antineutrinos are emitted in beta decay. These account for the “missing” energy in the decay equation. They are massless particles that barely interact with matter. • β+ decay (positron): 127N  126C + 01e + ν • A proton turns into a neutron and creates a high energy anti-electron (positron) and a neutrino • β- decay (negatron): 146C  147N + 0-1e + ν • A neutron turns into a proton and creates a high energy electron (negatron) and an antineutrino

  19. Proof of positrons: WOW!

  20. Neutrino detectors: Shine work with windex, dude, I’m gonna go, y’know, party…..

  21. Alpha and Gamma It’s decay-tastic! • γ decay: • This involves no changes to the nucleus, but decreases its energy after the nucleus is left in an excited state: 126C* 126C + γ • α decay: 23892U  23490Th + 42He Helium nucleus is alpha particle

  22. Fission and Fusion • Fission: a nucleus splits into two or more nuclei plus energy • Fusion: two or more nuclei combine and thus releases energy • You can make stable nuclei unstable by blasting it with energetic particles like neutrons. This is fission. This can then create a chain reaction: 10n + 23592U  23692U  14056Ba + 9336Kr + 310n

  23. Chain Reaction

  24. TMI

  25. USS Enterprise

  26. Fusion • Power source of stars • Works with light nuclei, more energy than fission • Benefits of a fusion reactor include cheap energy (water is fuel), no radioactive waste, lots of energy, no dangers • Unfortunately, fusion only works at extremely high temperatures. Research is underway for “cold fusion”, or fusion at doable temperatures

  27. Spacemaster Spiff found some wood. The wood was pretty old, but Spiff needed to find out how old exactly for his science. He showed Timemaster Timmy the old wood. Timmy said: “carbon-14 date it” Spiff measured the C-14 in the old wood to be 6.25 % compared to fresh wood. How old is the wood? (Half-life of C-14 is 5730 years)

  28. E=mc2

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