Today we are here with Mr. Ernest Rutherford, who has kindly agreed to come here and enlighten us about his Gold Foil Experiment in 1906.
Question:Would you like to start us off with a description of your Gold Foil Experiment?
Rutherford: Sure. What my partners, Hans Geiger and Ernest Marsden, and I did was to set up a very thin piece of gold foil set up on a glass plate to hold it up. Behind the foil was a detecting screen made of zinc sulfide that emitted a flash of light when it was struck by alpha particles given off by a few milligrams of radium (radon 222).
Q: What happened in this experiment?
R: Most of the alpha particles from the radium, which emitted the particles, went right through the gold foil. This was what we expected because the alpha particles had more velocity/power than the atoms in the gold foil. This means that the electrons and their atoms would be the particles to move out of the way. We were surprised that some of the alpha particles were deflected by a degree or two. In fact, there were particles all over the paper, but most of them were in the center because they hadn’t been deflected by anything.
Q: When you saw these results, did you wonder if there were any other alpha particles deflected away from the detecting screen?
R:Yes, my partners and I did question that, so we set up the experiment with a larger detecting screen that almost encircled the gold foil, leaving a little space for the alpha particles to get through. Through this new experiment, we saw that some of the alpha particles were even deflected backwards so that they went away in the same direction that they had come from to hit the gold foil. In this picture, the arrows are the alpha particles and the orange circles are the gold foil atoms. The little black dots are the nuclei. Here you can see what I was explaining with the alpha particles being deflected.
Q:Why did this happen?
R: The reason for this is something within the atom, called a nucleus. We knew that atoms were made up of electrons, which were in a type of cloud, protons, and neutrons. We thought that the mass of the atom was spread out evenly through the whole atom, but we were wrong. The Gold Foil Experiment proved that all of the mass had to be in a smaller, more condensed area than that of the whole atom, to be able to deflect the alpha particles. These particles would have been able to move through the atoms if all of the mass was spread out evenly because of their velocity. The alpha particles were still able to move the electrons out of their way, but something else bared their way if they hit it. That was the nucleus.
Q: What were some of the other theories about the atom before you did this experiment?
R: A widespread theory was that there were thousands of electrons in each atom and that they held most of the mass of the atom. Then J.J. Thomson published his Plum Pudding Theory which suggested that there were as many electrons as the atomic number. My experiment proved both of these, among others, wrong.
Q: What is the significance of your research? How does it affect us today?
R: We would not be able to know the things that we do about the atom if we didn’t have my research. We would not know about the nucleus. We would still not know how mass is held in atoms, if it was spread out evenly, all together, etc. We would also not have the Bohr Model to give us an idea of how an atom is laid out, even though his model is not entirely correct.
Q: So, basically, without you, we would still not know much about the atom?
R: Correct.
Q: Wow! Well, thank you for talking time to come and talk to us.
It is now time to end our show. Thank you everyone for listening and we will talk to you again tomorrow.
You can see the setup in this picture. In our initial setup, the detecting screen was much smaller because we did not think that the particles would be deflected by the gold foil.
Other guests
Ned the Neutron
Patty the Proton
Ernie the Electron
