Gold foil can be used for a lot of things, especially if you are a creative person, and I am. However, one thing I never thought about doing with gold foil was to use it to conduct a scientific experiment. Ernest Rutherford, though, used it to do just that. His experiment produced amazing results (and not just gold foil angel halos); in fact, his experiment actually ushered in the atomic age!
In Rutherford’s time, the idea of the existence of atoms was not a new idea. In fact, the ancient Greeks had predicted the existence of atoms around 500 B.C. (of course ancient Greeks were also the first to measure the earth’s circumference, so those people got around – forgive the pun). However, at the end of the nineteenth century, scientists still believed the atom to be an inconsequential player in chemical events (you know, kind of like the kid who plays the sheep in the Christmas play and has no lines). However, a little gold foil changed all that.
We can’t really tell the story of Rutherford’s experiment, though, without mentioning a few other actors in this drama who came first and who did have speaking parts – Roentgen, Becquerel, and the Curies. Wilhelm Roentgen took a picture of his wife’s hands using x-rays he had created, which showed her skeleton (thus demonstrating that, yes, there were skeletons in her closet, or at least in her hand). Antoine Becquerel put his photographic plates in a drawer (instead of the closet) with some crystal-containing uranium, and found that these crystals produced x-rays on their own without any outside energy source. These two men thought that their experiments were pretty cool, but they were in essence just dabbling until Marie and Pierre Curie came along. The Curies decided to not only dabble, but to devote their lives to the study of radiation, and in fact they coined the phrase, “radioactive.” Their discovery that radiation is an atomic property of matter, rather than an independent phenomenon, led the way for Rutherford’s experiment.
Now enters Rutherford and his gold foil! Rutherford carried out a multitude of experiments in which a piece of minutely thin gold foil was bombarded with alpha particles, while screens coated with zinc sulfide were used to detect them. In 1909, Hans Geiger and Ernest Marsden, two researchers in Rutherford’s laboratory at the University of Manchester (and why don’t they get any credit?), under the direction of Rutherford, fired a beam of alpha particles at the foil. Rutherford, who had identified alpha particles a decade earlier, thought they would be a good probe of the atomic structure of matter. When positively charged alpha particles were directed at the foil, the researchers found that most of them passed right through, but there were some that actually bounced back.
Rutherford concluded from this experiment that atomic particles consist mostly of empty space with a central core called a nucleus (it didn’t take a scientist to figure that out – oh wait, he was a scientist). Anyway, Rutherford is credited with defining atomic structure, and he was actually the first person to do experiments in which he “split the atom,” and we all know where that led.
Rutherford later said, “It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive centre carrying a charge.” (David C. Cassidy, Gerald James Holton, Gerald Holton, Floyd James Rutherford, (2002) Understanding Physics ISBN 9780387987569).
In summary, the significance of Rutherford’s gold foil experiment was that it disproved the current model of the atom, J. J. Thompson’s plum-pudding model (I don’t have time to go into why it was called that – look it up) and led the way to our current understanding of atoms. Although it took quantum physics to understand in full detail the structure of the atom, Rutherford’s central conclusion regarding the nucleus (which he called the central charge) is still used in current atom models.