This activity will allow you to explore the nature of the interactions between photons and gas atoms in a stellar interior. We've been told that it takes a long time for photons released in the stellar core to reach the surface to be emitted. You should be able to recognize the complex effects of aborption and re-emission by individual atoms and the effect that a photon's energy has on the rate of absorption by a particular gas.

Equipment Needed:

        electronic calculator
        pencil and graph paper
        Clea Computer Program on Energy Transport
      

Introduction:

     Absorption in the Atmosphere - Some photons are absorbed and re-emitted by atoms in the stellar atmosphere. This causes us to see absorption  or dark lines in the stellar spectrum. In the interior photons zig and zag throughout the interior, interacting with particles in the interior and taking literally hundreds of thousands of years to reach the surface. That's a long time.

Exercises:

        1.    Interaction of the sub-microscopic study of some photon/atom interactions:

    From the Simulation menu choose Interaction. You'll see an electron cloud around the atom and its nucleus. This is NOT to scale. In fact, you can change the scale  from the View menu. Select Line (or Continuum) from Photon type menu. Line photons have the right amount of energy to be absorbed by an electron. This kicks the electron to a higher level and shortly thereafter the electron returns, emitting a photon characteristic of that transition. These are called Bound-Bound Transitions since electrons are bound to the atoms. Continuum photons on the other hand, have the wrong energy to be absorbed so they pass through unaffected.

    Choose line photons and click run. Stop after 20 photons are sent. Record:

            1. How many photons were scattered? _________________________

Repeat the activity with continuum photons.

            2. How many continuum photons were scattered? _________________

        2. LINE FORMATION

    Select Line formation from the simulation menus. Each time you run it photons are sent through a cloud of gas (test-tube)They come from the left and your detector is on the right side of the tube.Use 20 photons for the run.
            What percentage made it to the detector?   ____________________