1. Introduction

At the end of the nineteenth century, physicists believed that the structure of atoms could best be described by Sir J. J. Thompson’s "plum pudding" model. This model stated that negatively charged electrons were thought to vibrate at fixed equilibrium points within a cloud of positively charged "pudding". While this produced a stable atom it did not predict the correct spectral lines observed in experiments. Lord Rutherford conducted a series of experiments that showed that the plum pudding model could not be correct. Instead, his experiment supported a planetary model of the atom that had already been proposed but had been rejected on the grounds that it was unstable. The fact that the planetary model agreed with his experiments drove others (in particular Bohr) to the development of Quantum Mechanics.

During your experiment you will be doing the following:

1. Firing alpha particles into gold foil and observing that large angle backscattering (scattering at angles larger than 90 degrees) does occur.
2. Verifying the Rutherford scattering formula by showing that the number of deflected α particles goes as 1/sin⁴(θ/2).
3. Using the data from part B to calculate the atomic number of the foil material.

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