
This window provides a simulation of the interactions of continuum
photons with the atoms of a gas, in a laboratory setting.  (Continuum
photons have an energy that does not correspond to an available energy
level in the gas atoms.) The following features are provided to control
and vary the simulation and record the results:

Menu Selections

    Parameters - One parameter may be set by the user:

        # of Photons (for "Run") - The number of photons to be sent
        through the gas (in succession) when "Run" is pressed.

    Quit - Terminates the simulation and closes the window.

Control Buttons

    Step - Sends one photon through the gas.  The photon comes from the
    light source on the left and is initially moving horizontally across
    the field toward the detector (eye) on the right.  The current
    counters are not reset, and are incremented as appropriate.

    Run - Clears the counters and sends one photon through the gas.
    Whenever a photon leaves the field another is issued, until the
    indicated number of run photons have been sent or the Stop button is
    pressed.  When Run is selected the Stop button is activated, all
    other buttons and all menu items except Quit are deactivated.

    Stop - Stops issuing photons.  The current photon remains active
    until it leaves the field.  When Stop is selected, the other buttons
    and all menu items are activated.  The simulation cannot be
    restarted at the stop point (pressing Run will reset the counters
    and restart), but the Step button can be used to continue without
    resetting the counters.  The Stop button is deactivated until Run is
    pressed.

    Reset - Resets the counters to zero.

Display

    Run Photons - The number of photons to be sent consecutively when
    the Run button is pressed (set via menu).

Counters

    Photons Sent - The number of photons sent, including the current
    one.

    Detected - The number of photons that have passed undeflected
    through the gas into the "eye".

    Not Detected - The number of photons that have been deflected by
    interactions with the gas atoms and did not pass though the "eye".

    Note that the counts are not complete until the last photon leaves
    the field.

