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PS 101

PS 101. Kim Cohn Email address Kcohn@academic.csubak.edu. How to Obtain Slides. A CD-R disc can be checked out from the library – 2 hour reserve. The disc can be duplicated at the library. The disc can be duplicated at your house. I have a few for sale. $5.00 - need bills, not checks.

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PS 101

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  1. PS 101 Kim Cohn Email address Kcohn@academic.csubak.edu

  2. How to Obtain Slides • A CD-R disc can be checked out from the library – 2 hour reserve. • The disc can be duplicated at the library. • The disc can be duplicated at your house. • I have a few for sale. • $5.00 - need bills, not checks. Chapter 14-The Atomic Nucleus

  3. Comments- Norah Jones • Fusion somewhere between Jazz, Country and Popular. • Incredible voice. • “Come Away with Me” Chapter 14-The Atomic Nucleus

  4. Comments- Today’s Demo • Both balloons were filled with a gas less dense than air. • Consequently both balloons will float in air. • One balloon was filled with Helium. • The other was filled with Hydrogen. • Hydrogen has one proton and one electron. • Helium has two protons and two electrons. Chapter 14-The Atomic Nucleus

  5. 4th Grade Standards 1 • Students know how to design and build simple series and parallel circuits by using components such as wires, batteries, and bulbs. • Students know how to build a simple compass and use it to detect magnetic effects, including Earth's magnetic field. • Students know electric currents produce magnetic fields and know how to build a simple electromagnet. Chapter 14-The Atomic Nucleus

  6. Alpha, Beta and Gamma Rays 1 – Review • Atoms themselves are made up of three smaller particles, the electron, the neutron and the proton. • The electron is the smallest of the three, has a charge of –1 and a relative weight of 1. • The proton and neutron have a relative weight of about 2000 and a charge of +1 and 0 respectively. Chapter 14-The Atomic Nucleus

  7. Alpha, Beta and Gamma Rays 2 • If the atomic number (number of protons) is greater than 82 element emits radiation. • Alpha particles – 2 protons and two neutrons (he atom) charge +2 • Beta particles – an electron, charge –1 • Gamma rays – “light” whose wavelength is very short and energy very high. Chapter 14-The Atomic Nucleus

  8. Alpha, Beta and Gamma Rays 3 • Alpha rays are stopped by paper. • Beta rays are stopped by aluminum. • Gamma rays are stopped by lead. • Unless you ingest a radioactive compound most radiation damage is caused by gamma rays. Chapter 14-The Atomic Nucleus

  9. Effects of Radiation on Humans • Natural radiation from bricks, stones and cosmic rays is always present. • The higher you go the more radiation you get. • We tolerate most this radiation. • Naturally occurring radon (222) heavy gas is dangerous. • Coal industry contributes more radiation than nuclear power. Chapter 14-The Atomic Nucleus

  10. Tracers • Can make elements radioactive by bombarding elements with neutrons and other particles. • Can use radioactive elements to trace path of materials in plants and humans. • Fertilizer uptake. • CAT scans. Chapter 14-The Atomic Nucleus

  11. Nucleus Revisited • Review- the nucleus of an atom (the total number of protons and neutrons at the center of an atom) is surrounded by electrons. • Protons and neutrons are composed of even more elementary particles such as quarks and leptons. Chapter 14-The Atomic Nucleus

  12. Second Demo • Here is a Geiger counter. • The frequency of the beeps is an indication of how much radiation is being detected. • It always beeps. • Thorium is a pretty good emmitter. Chapter 14-The Atomic Nucleus

  13. Isotopes • The number of protons (atomic number) determines the element. One proton atoms are hydrogen, an element with 20 protons is calcium. • The number of neutrons may vary. • Hydrogen (one proton) may have, for example, no neutrons, one neutron or two neutrons. • The number of neutrons plus the number of protons determines the atomic mass. • Atoms with the same number of protons but different numbers of neutrons are isotopes. Chapter 14-The Atomic Nucleus

  14. Isotopes - 2 • The atomic number of an atom that contains 32 protons, 30 neutrons and 31 electrons is? • How many protons and neutrons are there in U235? • What is the difference in chemistry between an atom with one proton and no neutron to that which contains one proton and one neutron? Chapter 14-The Atomic Nucleus

  15. Half-Life • A radioactive isotope emits particles and changes. This is called decay. • The amount of time it takes an original quantity of a radioactive element to decline by on half is called the half-life. Chapter 14-The Atomic Nucleus

  16. Half-Life 2 • If you start with 1.00 gram of element x that has a half life of 1 day, how much will be left after three days? • Which gives a higher count on a radiation detector, an isotope with a short half life or one with a long half life? Chapter 14-The Atomic Nucleus

  17. Transmutation of Elements. • How many protons and neutrons are there in U235? • If U235 emits an alpha particle (review – this is a particle that consists of 2 neutrons and 2 protons), what becomes of the original U235? Chapter 14-The Atomic Nucleus

  18. Isotopic Dating • In the upper atmosphere cosmic rays bombard nitrogen and transmute it to radioactive carbon. • Plants take up the radioactive carbon. • Animals eat plants until the animals die. • At death the animals no longer eat and the radioactive carbon decays. • We know the half life of radioactive carbon. • Therefore we can tell when the animal died by measuring the amount of radioactive carbon. Chapter 14-The Atomic Nucleus

  19. Isotopic Dating - 2 • The half life of radioactive carbon (carbon 14) is 5730 years. • If I dig up an animal that has 25% (or ¼) of the amount of radioactive carbon as a recently killed animal, when did the animal I dug up die? Chapter 14-The Atomic Nucleus

  20. Nuclear Fission • Fission means breaking apart. • When uranium 235 is hit by a neutron, it breaks apart into an atoms of barium 142, and atom of krypton 91 and three neutrons. • The diagram on page 346 is wrong. • If there is a large enough amount of uranium 235 the neutrons that are produced will continue to break apart more and more uranium atoms (a chain reaction). • Illustrate on board. Chapter 14-The Atomic Nucleus

  21. Nuclear Fission Reactors • Produce about 20% of power in US. • Atoms split, produce heat energy, boil water, turn turbine to make electricity. • Consist of three parts, nuclear fuel, control rods to absorb neutrons, water to transfer heat. • Biggest problem is disposing of waste. Chapter 14-The Atomic Nucleus

  22. Questions • Is there a greater proportion of C14/C12 in new or old bones? • Most of the radioactivity we encounter comes from what source? • How do astronomers determine what elements are present in a star? • Which ray, alpha, beta or gamma, is the heaviest? Chapter 14-The Atomic Nucleus

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