At the beginning of the 20th century, the only news, in the area of Physics, that was known was that in the structure of the atom there were electrons.
Despite being discovered by Thomson in 1897, the mass of the atom was still unknown, making it impossible to say how many electrons an atom contained.
Physicists already knew that atoms were electrically neutral and therefore had to contain positive charges, but these were still unknown.
In 1911 Rutherford suggested, based on the experimental results of his team, that this charge was present in the center of the atom, forming a nucleus, responsible for most of the mass of the atom.
At that time Rutherford already knew that certain elements considered radioactive spontaneously transform into other elements, emitting alpha particles (α), with an approximate energy of 5.5 MeV. It is now known that these are particles of the helium atom.
The idea was to make the alpha particles strike a thin sheet of metal in order to measure the deviation of the particles’ trajectory as they passed through the material. The result obtained was extremely high scattering, close to the temperature of 180°, which was a big surprise, since the scattering angle is small for most particles.
Rutherford’s surprise was such, because at the time the experiment was carried out, most physicists believed in the model known as “plum pudding”, proposed by Thomson, where the positive charge of the atom was uniformly distributed throughout the atom, and the electrons vibrated around fixed positions within this positively charged sphere.
The force experienced by an alpha particle passing an atom-sized sphere of positive charge would produce a deflection of less than 1°. In order to undergo a deflection greater than 90°, Rutherford reasoned that the alpha particle would have to be subjected to a considerable force, his explanation being possible if the positive charge, instead of spreading throughout the atom, was concentrated in a small central region, this alpha particle could approach the positive charge without crossing it, which would make this approach a considerable force.
The current branches of study of Nuclear Physics are basically the atomic nucleus and its properties, because these nuclei have properties that can be classified as static and dynamic, and they are analyzed through nuclear models based on quantum mechanics, relativity and quantum field theory. . The discovery that nuclei (protons and neutrons) are, in fact, composite systems, redirected the interest of nuclear physicists to the investigation of the degrees of freedom of quarks and, with this, currently the research domains of Nuclear Physics and Physics. of Elementary Particles have become interconnected.