PS 101 - PowerPoint PPT Presentation

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PS 101

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PS 101 Kim Cohn Email address Kcohn_at_academic.csubak.edu – PowerPoint PPT presentation

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Title: PS 101


1
PS 101
  • Kim Cohn
  • Email address
  • Kcohn_at_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.

3
Comments- Norah Jones
  • Fusion somewhere between Jazz, Country and
    Popular.
  • Incredible voice.
  • Come Away with Me

4
Comments- Todays 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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?

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.

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?

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?

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.

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?

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.

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.

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?
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