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Ernst Rutherford was a scientist who studied the absorption of radioactive rays by using thin metal foil sheets in 1899. Based on this observation, he found two major radiations named alpha radiation and beta radiation. Every radiation has its capabilities of passing through the foil sheets. Later, he also observed a third radiation named beta radiation.
Among all these successful observations, Hans Geiger, his assistant, joined him in the study of alpha particles emitted by uranium metal and its compounds. Later on, in 1911, this experimental study was further recognised as the “Gold foil experiment” or “Rutherford model”.
Gold foil experiment
The gold foil experiment is an experimental study done by Ernst Marsden under the guidance of Rutherford and Hans Geiger and published in 1911. This experimental study was the asset to prove that the atom consists of a big positively charged particle having a mass called a nucleus with many electrons circulating it. Along with it, he derived mathematical equations for the scattering of the number of alpha particles.
Experimental working of Gold Foil experiment
In the given experiment, a radioactive source (just like uranium) generated and projected the rays of positively charged alpha particles to the screen, which was coated with the ZnS (Zinc sulphide) to detect alpha particles.
These emitted alpha particles were focused on a narrow beam and passed through the slit in a lead screen. A gold foil of small thickness was placed in front of the slit. Beyond the gold foil, a Zinc sulphide coated screen is placed to detect alpha particles by generating a fluorescent effect on interacting with the time alpha particles.
When the beam of alpha particles passed through the entire setup and struck the ZnS coated screen, it produced a bombardment effect with a burst of light at the screen. This entire process, titled scintillation, was observed by the microscope placed on the backside of the screen. Conclusive evidence about the alpha particles was procured and discussed based on this experiment.
Effects on alpha particles in Gold Foil Experiment
While performing this experiment, it was found that the major fraction of alpha particles pass through the foil undeflected, which proves that most of the space in the atom is open space. In contrast with the above observation, it was also found that a few alpha particles were scattered by very small angles, which resembles the fact that there must be a positively charged particle which interacted with the alpha particles and there must also be a repulsive force that creates the deflection of alpha particles.
A very small number of particles were deflected back by 1800, which was also observed in the experiment. This defined the presence of a big heavy positive particle in the atom, which was further recognised as the “nucleus”. It created a strong repulsive force and made the alpha particles go back through the same path. Based on the above study, Rutherford stated that the atom consists of big positively charged particles in the centre named the nucleus and the space around which the alpha particles go undeflected confirms the presence of oppositely charged particles termed electrons.
Gold Foil Experiment’s Major Findings
- A major fraction of alpha particles passed through the foil undeflected, which confirms that there is plenty of open space exists inside the atom, which comprises oppositely charged particles to alpha particles.
- A few alpha particles were scattered by very small angles predicting that there is some same charged particle as alpha particles inside the atom. It creates an equivalent repulsive force on the alpha particles resulting in a deflection in their path.
- A very small number of particles were deflected back by 1800, depicting the presence of a big positively charged particle “nucleus ”, which forces the movement of alpha particles to go back through the same path. It also created 1800 bounce back effects on alpha particles. At that time, no alpha particles were detected on the zinc sulphide screen.
- Based on the study, Rutherford stated that the structure of an atom consists of a big nucleus present at the centre of the atom along with a circulatory motion of the negatively charged electron around the nucleus. The presence of electrons offers zero resistance to the movement of alpha particles.
Conclusion
The entire article captured glimpses of the gold foil experiment performed by Ernst Marsden under the light of Rutherford and Hans Geiger. A major fraction of alpha particles passes through the foil undeflected, confirming that plenty of space is open space. A few alpha particles were scattered by very small angles confirming the presence of some positively charged particles and a very small number of particles were deflected back by 1800. This brought some evidence of the presence of positively charged particles as nucleus along with the circulatory planetary motion of the electron around it in the atom.
