PHYS 361
Homework due Friday, November 12
10 Points
1. Let’s do some data analysis from Geiger and Marsden’s famous 1913 experiment which
proved that atoms have a positive nucleus and a negative electron cloud. Geiger and Marsden
scattered 6.5 MeV alpha particles through a gold foil of thickness 1 µm. A 1 mm x 1 mm square
zinc sulfide detector was located 1 cm away from the gold foil on a goniometer. If 6x106 alpha
particles are incident on the gold each second, and a 1 µm thick gold foil has 5.9x1022 scattering
centers per m2
a. Find an expression for the differential scattering cross section, dσ/dΩ, as a function
only of alpha particle energy, E, and scattering angle, θ.
b. Make a graph of dσ/dΩ versus θ for these scattered alpha particles. (Maple could be
useful for this.)
c. How many alpha particles does the detector see each second if it is located at 90o?
25o? 50?
2. Symon 4-10