Alpha particles or alpha rays are a form of radiation with high ionizing, corpuscular energy and with a low penetration capacity due to the high cross section. Alpha particles consist of two protons and two neutrons joined by a strong force. From a chemical point of view, alpha particles can also be identified with the symbol 4 He ++. Along with the 3 He isotope, the alpha particles belong to the elion family. The beta decay is mediated by a weak force, while the alpha decay is mediated by a strong force.
Definition of alpha particle
An alpha particle is a positively charged particle emitted by various radioactive materials during decomposition. It consists of two neutrons and two protons, and is therefore identical to the nucleus of a helium atom.
Characteristics of alpha particles
Alpha particles are typically emitted by heavy element radioactive nuclides, for example, the uranium isotopes of nuclear fuel, thorium plutonium, radio, etc., in a process called alpha decay. Sometimes, this decomposition leaves the atomic nuclei in an excited state and, consequently, the excess of nuclear energy can be eliminated with the emission of gamma rays.
Alpha rays, due to their electrical charge, interact strongly with matter and, therefore, are easily absorbed by materials. Alpha particles can only travel a few centimeters in the air. Alpha rays can be absorbed by the outermost layers of human skin and, therefore, are not life threatening unless the source is inhaled or ingested. In this case, the damages would be, on the other hand, greater than those caused by any other ionizing radiation. If the dose of alpha rays were high enough, all the typical symptoms of radiation poisoning would appear.
In 1909, Ernest Rutherford with his assistants Hans Wilhelm Geiger and Ernest Marsden, exploited the properties of alpha particles to confirm their studies on atoms. Rutherford measured the angle at which a beam of these particles reflected on a thin gold plate (0.00004 cm thick, containing about 1400 atoms) and found that only a small percentage of these particles (1 in 20,000) it was reflected at an angle greater than 90 °. These were the particles that hit the atomic nuclei, while the others continued their displacement linearly: this shows how the radius of an atom (nucleus-electron distance) is approximately 10,000 times higher than the radius of the single nucleus (protons and neutrons) .
This experiment changed the vision of the atom that was held at that moment (Thomson's atomic model also called panettone model) in the new model called, precisely, Rutherford's atomic model that, in turn, formed the basis for the proposed model. by Niels Bohr in 1913 (Bohr's atomic model.