Running head: PHYSICS 335 FINAL PAPER 1. Summary and Examination of Rutherford s Gold Foil Experiment. Ryan Jeffers

Transcription

1 Running head: PHYSICS 335 FINAL PAPER 1 Summary and Examination of Rutherford s Gold Foil Experiment Ryan Jeffers University of North Carolina Wilmington

2 PHYSICS 335 FINAL PAPER 2 Abstract This paper focuses on the history, execution and future impacts of Rutherford s Gold Foil Experiment. The primary goal of the experiment was originally to see how alpha particles scattered while being blasted through a small screen of gold foil. The results of the experiment were what Rutherford expected however there was an aspect of the results that he did not expect. This small change in the outcome changed the course of science and created the foundation of the Nuclear model.

3 PHYSICS 335 FINAL PAPER 3 Summary and Examination of Rutherford s Gold Foil Experiment Atomic structure throughout time has changed drastically. Different scientists and physicist have all had different discoveries and breakthroughs that changed the way we look at the atom. In the early 1900 s the plum pudding model was the recognized as the correct way to picture the atom. This model described an atom as being a large positively charged body that contained small, free-floating, negatively charged particles called electron negative charge of the electrons is equivalent to the positive charge of the rest of the atom (Hight). The plum pudding model lacked a proper acceptance by most physicists at the time and this model was consistently getting challenged with new theories and experiments trying to prove something different (Staff, 2016). In the end, the faulty aspect of this model was that it was created before the discovery of the nucleus, proton, and neutron. This is the point at which an x-ray and gamma ray specialist, Ernest Rutherford, stumbled upon a ground-breaking discovery. The gold foil experiment was part of the amazing work done by scientists Hans Geiger and Ernest Marsden all under the guidance of world renown physicist Ernest Rutherford. The intended results of the experiment weren t to find and recreate the model of the atom however that did end up being what came out of the gold foil experiment. Here s how it worked: The scientists bombarded a thin gold foil of thickness approximately 8.6 x 10-6 cm with a beam of alpha particles in vacuum. They used gold since it is highly malleable, producing sheets that can be only a few atoms thick, thereby ensuring smooth passage of the alpha particles. A circular screen coated with zinc sulphide surrounded the foil. Since the positively charged alpha particles possess mass and move very fast, it was

4 PHYSICS 335 FINAL PAPER 4 hypothesized that they would penetrate the thin gold foil and land themselves on the screen, producing fluorescence in the part they struck (Staff, 2016). The results that Rutherford hypothesized are exactly what he received just with one minor change. Rutherford was expecting for the particle to penetrate the gold foil and have a small scattering effect on the surrounding screen and this is exactly what he received. However, when two of his lab assistants did the experiment again they found that most of the particles did in fact have small scattering effect, but a small fraction of the particles shot through the gold foil would bounce back with an angle larger than ninety degrees. With this taken in to account Rutherford concluded that the positive charge Fig 1: Gold Foil Experiment Set up and the mass of an atom are concentrated in a small fraction of the total volume and then derived mathematical equations for the scattering that would occur ( The Gold Foil Experiment ). The formula and further predictions that Rutherford made where verified by experiments completed by his lab assistants, Geiger and Marsden. Rutherford published his results in The model that he came up with for the atom is one that is still accepted today. Rutherford s model includes the fact that all positive charge and essentially all of the mass of the atom Fig 2: Rutherford s Scattering Angle Equation

5 PHYSICS 335 FINAL PAPER 5 is concentrated in an infinitesimally small fraction of the total volume of the atom, which he called the nucleus (from the Latin for little nut) ( The Gold Foil Experiment ). It is more commonly known as the Bohr model due to the refinements and perfecting that Neils Bohr did to the outer structure. Scientists have continued to improve and make slight alterations to the model that Rutherford came up with, but the main concept remains invariant through time. After he published his paper, Rutherford decided that he needed to come up with some Fig 3: Rutherford/Bohr Model names for the particles that he included in his nucleus. So, shortly after WWI, in 1920, Rutherford proposed the name proton for the positively charged particles that are in the nucleus ( The Gold Foil Experiment ). At the same time that he created the name of the proton, Rutherford also theorized that there is a neutral particle that resides alongside the proton in the center of the atom. This had not been proven at the time that he named the particle a neutron but would eventually be tested and proven by James Chadwick in 1932 ( The Gold Foil Experiment ). This experiment has played a huge roll in the way we see modern physics today. So many future experiments and discoveries stemmed from the work that Rutherford put in. This experiment is one of the most important and influential of all time. It is probably true that a fellow scientist would have most likely come across the same type of findings that Rutherford did given the same opportunity but Rutherford had the intelligence and the incite to put the

6 PHYSICS 335 FINAL PAPER 6 ideas together when he did (Hight). These types of discoveries don t come around very many times in ones existence. Scientists everywhere thank Rutherford for the tremendous work and knowledge that he brought to the Physics field and for all of eternity.

7 PHYSICS 335 FINAL PAPER 7 References Hight, M. (n.d.). The Gold Foil Experiment. Retrieved from Staff. (2016, January 19). Gold Foil Experiment. Retrieved from The Gold Foil Experiment. (n.d.). (n.a.). Retrieved from