Alpha Particles

In case any one hasn't noticed, the previous page did not focus on the discoveries of Ernest Rutherford (the topic scientist of this site). Such attention was given to the discoveries of other scientists because the subject of radiation and radioactivity can not be attributed to just one person. For example, the research of Röntgen prompted Becquerel's research, which prompted Rutherford's research. In other words, I provided the general history of the discoveries in this field in hopes that Rutherford's research could be more easily understood. Now that this background has been established, Rutherford's discoveries and contributions can be discussed with the attention that they deserve.

Rutherford began measuring the electric current of gases ionized by Röntgen's X-rays and ultraviolet light soon after he began collaborating with J.J. Thomson (who acted as a mentor to the young and promising scientist for many years). After committing himself to this study for some time, Rutherford began to wonder if the uranium rays that Becquerel discovered would ionize the gas just as X-rays and ultraviolet light were observed to do. With this inquiry in mind, he devised an experiment to test the characteristics of uranium rays by placing two metal plates parallel to one another (with one of course being above the other). The two plates were connected to a battery and the lower plate was coated with uranium powder. Rutherford proceeded to measure the electric current between the plates and discovered that the rays were in fact ionizing the gas.

To further characterize the rays, Rutherford covered the uranium with metal foils of various degrees of thickness to see whether the rays would be blocked by the foil or just pass right through it. While several of the rays were in fact blocked by the foil, some of them still managed to pass through with relative ease. This was perhaps the most crucial point of Rutherford's experiment because it showed that uranium radiation was composed of two different types of rays: one that was easily absorbed and another that was more penetrative.

In 1898 Rutherford published a scientific article in which he described the existence of the two different uranium rays. He also termed the easily absorbed rays as alpha and the more penetrating rays as beta. Upon additional experimentation, Rutherford discovered that these rays were actually composed of tiny alpha and beta particles.

Even though Rutherford worked with both alpha and beta particles (which were later identified as being helium nuclei, He^(+2), and electrons; respectively), his work with alpha particles tends to be emphasized since they were primary components of several of his more commonly known experiments. In fact, the foundation for his Gold Foil Experiment (perhaps one of his greatest scientific achievements) was laid down when he began measuring the specific charge of alpha particles by deflecting them in electric and magnetic fields.

*Note- Above is an image that depicts alpha particle radiation. Even though the process at which these particles are formed wasn't necessarily described by Rutherford, the image provides some incite as to what exactly Rutherford was working with.

Rutherford's initial desire for these tests was to find the deflection of the alpha particles by measuring their position on a photographic film. However, while he was making the appropriate measurements he noticed that the images on the film became blurred when the particles passed through a thin piece of mica. The images were clear and distinct when the mica plate was removed, but became slightly blurred every time the plate was inserted in the particle pathway. Seeing how Rutherford had an extremely inquisitive mind, he could not help but ask the all important question of "why?".

Incidentally, the images that Rutherford saw were blurred because the small alpha particles were being deflected at slight angles by the nuclei of the atoms in the mica sheet. At this point in time the nucleus of an atom had not been discovered, so Rutherford had no way of explaining why he was seeing what he was seeing. However, Rutherford was by nature a scientist and could not be content with just not knowing. Thus in his quest for knowledge he performed the most well known of all of his experiments: The Gold Foil Experiment.