(comments to: moloney@nextwork.rose-hulman.edu)

(CUPS = Consortium
for Upper Level
Physics Software,
published by John Wiley)

Modern Physics Suggestions from the CUPS project

- Rutherford Scattering
- Electron Diffraction
- Special Relativity
- Laser Cavities and Dynamics
- Nuclear Properties and Decays
- Quantum Mechanics
- Hydrogenic Atoms and the H2+ Molecule

- Geiger and Marsden used 8.1 MeV alpha particles, scattered from a gold
foil.

Calculate the closest approach of such an alpha particle to a gole (Z=79) nucleus.

Is it within range (10^-15 m) of the nuclear force? - Calculate the deBroglie wavelength of an 8.1 MeV alpha particle.

Is this large or small compared to the distance of closest approach? - Run the simulation of the Geiger-Marsden scintillation experiment.

If time is available, get enough points to observe a number of backscattered (>150 degrees) alphas.

- Repeat the Davisson-Germer experiment. Use the (111) plane and do runs for accelerating voltages of 40,44,48,54,60, and 64 V. Record the height of the peak at 130 degrees for each run.

- Beam of particles incident on a barrier. Run the 'barrier' section
of the program.

Observe the qualitative difference when the beam energy is above the 2 eV height of the barrier, and when the incoming beam energy is below the 2 eV barrier height.

Write down what you see for the wave function in each case, and give an explanation for the difference in behavior. - Run the 'Uncertainty Principle' part of the program.

Describe what happens to the spread in momentum as you make the particle 'smaller'.

Make a sketch of the momentum spread for a 'narrow' and a 'wide' electron wave function.

- In 'Geiger Tube Counting', do a run with the default parameters.

Press 'Poisson' to bring up a poisson distribution curve which you can drag around on the screen. Since the GMT (geiger-muller tube) is 'dead' for a period after each count, you should be able to explain why the GMT distribution has a peak which is smaller than would be true for an 'ideal' counting tube. - Predict which way must you move the incoming count rate from its initial value of 250/s so that the ideal and GMT curves will be closer together. Make the change in count rate, do the run, and record the peak values of each distribution.
- Change the incoming count rate to 8000/s. Now the counts are coming in with an average spacing of 125 microseconds. Leave the geiger tube dead time at 200 microseconds. Do a run and record the peak values of each distribution.
- Does the GMT distribution have the same 'width' as the ideal distribution?
- Bring up the poisson distribution and drag it over to the ideal distribution. How does it fit?
- Drag the poission distribution over the GMT distribution. How does it fit?
- Can you predict the peak of the GMT distribution if the count rate were set to an enormous rate, like 1 million per second? [ Every time the tube 'woke up' after being dead, bang! there would be another particle to count.]