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The Atomic Nucleus

The Atomic Nucleus. Review…the nucleus. The nucleus is composed of particles called nucleons..__ & __ Neutrons and protons have the same mass, with ___ being slightly greater. Neutrons have nearly 2000 times the mass of _____. protons and neutrons neutrons electrons. Review…the atom.

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The Atomic Nucleus

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  1. The Atomic Nucleus

  2. Review…the nucleus • The nucleus is composed of particles called nucleons..__ & __ • Neutrons and protons have the same mass, with ___ being slightly greater. • Neutrons have nearly 2000 times the mass of • _____. • protons and neutrons • neutrons • electrons

  3. Review…the atom • The mass of an atom is almost equal to the mass of the _____ alone • Nucleons are bound together by an attractive nuclear force called the ____ force • The positively charged protons in the nucleus hold the negatively charged electrons in their ____ • nucleus • strong • orbits

  4. Review…the atom • The number of ___ in the nucleus determines the chemical properties of the atom • The # of protons determines the # of ____ that orbit the atom • The # of ___ has no direct effect on the # of electrons • protons

  5. Review…the atom • The principal role of the neutrons in the nucleus is to act as a sort of ____ to hold the nucleus together • The electrical force acts as a ____ force between protons • The atom needs a certain balance of neutrons and protons for ___ • cement • repulsive • stability

  6. The symbol was created in 1946 UC- Berkeley to represent “activity coming out of a atom”

  7. What is Radioactivity? • Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. • There are numerous types of radioactive decay. The general idea: • An unstable nucleus releases energy to become more stable

  8. Radioactive Decay

  9. Radioactive Decay • A neutron is very unstable. A lone neutron will spontaneously decay into a proton + an electron. • If you have a lot of neutrons, within 11 minutes ½ of them will have decayed • Particles that decay are said to be radioactive • A lone neutron is radioactive

  10. All the elements heavier than Bismuth (At # 83)

  11. Their atoms emit 3 things…alpha, beta particles and gamma rays

  12. Which is more penetrating?

  13. Radioactive Isotope • Iodine-131, a beta emitter, is taken as sodium iodide in drinking water. Almost all of it will find its way to the thyroid

  14. Isotopes • They are atoms of the same element that have different numbers of neutrons.

  15. Radioactive Half-life

  16. Radioactive Half-Life • The half-life of an element is the time it takes for half of the material you started with to decay Remember, it doesn’t matter how much you start with. After 1 half-life, half of it will have decayed. • Each element decays into a new element • C14 decays into N14 while U238 decays into Pb206 (lead), etc • The half-life of each element is constant. It’s like a clock keeping perfect time

  17. Half-life

  18. Half-life

  19. Half-life

  20. Half-life

  21. “How much of this element remains after 4 half-lives? Just remember that at the end of one half-life, 50% of the element will remain. Find 50% on the vertical axis, Follow the blue line over to the red curve and drop straight down to find the answer:

  22. Carbon Dating • The radioactivity of once living things decreases at a predictable rate

  23. Uranium Dating • The dating of older, non-living things (like rocks) is accomplished by radioactive minerals, such as Uranium. Uranium decays very slowly. • Rocks on Earth have been dated to 3.7 bil yrs old • Rocks on Moon dated to 4.2 bil yrs old • The Earth has been dated to 4.6 bil yrs old

  24. Review…whew! • https://archive.org/details/NASARealWorldMath_WhatIsRadioactiveDecay_HD • http://en.wikipedia.org/wiki/Barium_swallow

  25. Radiation Penetrating Power

  26. 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.

  27. Radiation Penetrating Power • http://www.passmyexams.co.uk/GCSE/physics/penetrating-properties-of-radiation.html

  28. Radiation and You (and me)! • http://people.chem.duke.edu/~jds/cruise_chem/nuclear/exposure.html

  29. Is there radon in your home?

  30. Sources of Radioactivity • Primordial - from before the creation of the Earth • Cosmogenic - formed as a result of cosmic ray interactions • Human produced - enhanced or formed due to human actions (minor amounts compared to natural)

  31. Radiation Exposure to Americans

  32. Review • Name three of the science pioneers in the study of Radioactivity.? • Why does a nucleus decay? • Order these emissions from least to greatest penetrability: Gamma, Alpha, Beta. • What is the greatest source of exposure to radioactivity in our everyday lives?

  33. Nuclear Fusion - Energy released when two light nuclei combine or fuse • However, a large amount of energy is required to start a fusion reaction: • Need this energy to overcome ________ forces of protons. • Extremely high temperatures can provide start-up energy. repulsion More energy in fusing hydrogen that fission of uranium

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