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.

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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.

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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.

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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.

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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?