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 helium nuclei.
From a more technical point of view, alpha particles or alpha rays are a form of ionizing particle high energy radiation.
Alpha particles are typically emitted by radioactive nuclei of heavy elements on the periodic table in a process called alpha decay. These heavy elements can be, for example, the isotopes of uranium (U), plutonium (Pu), thorium (Th) or radium (Ra).
What Is Alpha Radiation?
Alpha radiation occurs when an atom undergoes radioactive decay, emitting an alpha particle. In alpha radiation, the original atom is transformed to another element in the periodic table, reducing its atomic weight by 4 daltons and its atomic number by 2 units.
Due to their charge and mass, alpha particles interact strongly with matter and only travel a few centimeters in the air.
What Is the Composition of the Alpha (α) Particles?
Alpha particles consist of two protons and two neutrons held together by a strong force.
From a chemical point of view, alpha particles can also be identified with the symbol He-4.
Along with the He-3 isotope, alpha particles belong to the elion family. Beta decay is mediated by a weak force, while alpha decay is mediated by a strong force.
How Does Alpha Radiation Affect Health?
Alpha rays, due to their electrical charge, strongly interact with matter and are therefore 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 cannot penetrate this layer. However, they are capable, if an alpha-emitting substance is ingested in food or air, of causing serious cellular damage .
If alpha particles are ingested or inhaled, the damage would be greater than that caused by any other ionizing radiation. If the dose of alpha rays were high enough, all the typical symptoms of radiation poisoning would appear.
Differences with Beta and Gamma Radiation
Beta radiation particles are more penetrating than alpha particles but are less harmful. They travel greater distances in the air and with higher kinetic energy but can be easily stopped with certain materials.
Some beta particles are capable of penetrating the skin and causing damage. However, as with alpha particles, beta particles are more dangerous if inhaled or ingested.
On the other hand, gamma rays are photons without mass but with a lot of energy. This type of radiation can pass through the body easily and pose a significant health hazard.
The Importance of Alpha Particles in Rutherford's Atomic Model
Rutherford's experimentation with alpha particles had a major impact on the development of atomic models in the future.
In 1909, Ernest Rutherford and his assistants exploited the properties of alpha particles to confirm their studies on the structure of the atom.
This experiment changed the vision of the atom that was had at that time (Thomson's atomic model) in the new model called, precisely, Rutherford's atomic model. This model was the basis for Bohr's atomic model in 1913.