Alpha -scattering experiment, Rutherford

Sir Ernest Rutherford (1871-1937 Nobel Prize for chemistry 1908, which as a physicist he puzzled over) was a brilliant experimentalist endowed with an equal genius of being able to interpret the results. He recognized three types of radiation (alpha, beta, and gamma). He used scattering experiments with alpha radiation, which consists of helium nuclei, to prove that the atom is almost empty. The diameter of the atomic nucleus is about 10 000 times smaller than the atom itself. Furthermore, he proved that atoms are not indivisible and that in addition to protons, there must also be neutrons present in their nucleus. With Niels Bohr he developed the core-shell model of the atom. 

FIGURE 2.5 The Rutherford scattering experiment, (a) When a beam of alpha particles is directed at a thin gold foil, most particles pass through the foil undeflected, but a small number are deflected at large angles and a few bounce back toward the particle source. 

Knowledge Required The general features of Ernest Rutherford s alpha-particle-scattering experiment. 

Geiger, Hans Wilhelm (1882-1945) German physicist, who carried out research with Rutherford at Manchester University before returning to Germany in 1912. In 1908 he and Rutherford produced the Geiger counter, improved in 1928 as the Geiger-Mtiller counter. In 1909 his scattering experiments with alpha particles led to Rutherford s nuclear theory of the atom. 

He did some pioneer work in the field of radioactivity, discovering and characterizing alpha and beta particles — and received a Nobel Prize in chemistry for this work. But he s perhaps better known for his scattering experiments in which he realized that the atom was mostly empty space and that there had to be a dense, positive core at the center of the atom, which is now known as the nucleus. Inspired by Rutherford, many of his former students went on to receive their own Nobel Prizes. 

The alpha-particle scattering experiments of Rutherford established that the atom contains a dense, positively charged nucleus. The later work of Chadwick demonstrated that the atom contains neutrons, which are particles with mass, but no charge. Rutherford also noted that light, negatively charged electrons are present and offset the positive charges in the nucleus. Based on this experimental evidence, a model of... 

On the basis of these results, Rutherford in 1911 postulated that the atom consists of a tiny central positively charged region, which he subsequently termed the nucleus. The nuclear positive charge was balanced by electrons revolving round the nucleus at a considerable distance. The results of the alpha particle scattering experiments were thereby explained the positive alpha particle would experience little or no deviation unless it happened to approach very close to the positively charged nucleus. 

How can we account for the fact that, in the Rutherford scattering experiment, some of the alpha particles were deflected from their paths through the gold foil, and some were even bounced back at various angles ... 

In 1911, Rutherford s alpha-particle scattering experiments were controversial. In the Rutherford model of the atom, all of the positive charge was crammed into the dense, tiny nucleus. Like charges repel, so the nucleus of the atoms should not be stable, yet it was. The relationships of classical physics that worked so well in explaining large-scale systems did not work on atom-sized systems. Thus, someone had to develop a new approach to understanding the atom. The breakthrough that was needed was the development of the field of study now known as quantum mechanics. 

During 1910-1911, Sir Ernest Rutherford suggested ail experiment, carried out by Geiger and Maisden, in which alpha panicles from a radioactive source were scattered from thin foils, The angles at which the alpha particles were scattered were found to be such as could best be... 

In 1911, the British physicist and Nobel laureate Ernest Rutherford (1871-1937) published the article The Scattering of Alpha and Beta Particles by Matter and the Structure of the Atom in Philosophical Magazine. In this article, Rutherford reported the results of an experiment that demonstrated that the protons and electrons in atoms are not distributed homogeneously. Instead, the protons are concentrated in a relatively tiny region Rutherford called the nucleus (from the Latin, meaning kernel ). The electrons are extranuclear electrons are located in a relatively much larger volume of space surrounding the nucleus. Rutherford s discovery of the nucleus was immediately accepted within the scientific community. However, the relationship, if any, between atomic structure and properties was still unclear. 

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