Modern Physics

Alpha Particles: Discovery, Resources, Applications

The alpha particles (or alpha particles) are nuclei of helium atoms ionized electrons therefore lost. Helium nuclei are made up of two protons and two neutrons. So, these particles have a positive electric charge whose value is twice the charge of the electron and their atomic mass is 4 atomic mass units.

Alpha particles are spontaneously emitted by certain radioactive substances. In the case of Earth, the main known natural source of alpha radiation emission is radon gas. Radon is a radioactive gas present in soil, water, air and some rocks.


It was throughout the years of 1899 and 1900, when physicists Ernest Rutherford (who worked at McGill University in Montreal, Canada) and Paul Villard (who worked in Paris) differentiated three types of radiation, called by Rutherford himself as: alpha, beta and range.

The distinction was made on the basis of the ability to penetrate objects and the deflection due to the effect of a magnetic field. Because of these properties, Rutherford defined alpha rays as those that were less capable of penetrating common objects.

Thus, Rutherford’s work included measurements of the mass ratio of an alpha particle to its charge. These measurements led him to hypothesize that the alpha particles were double-charged helium ions.

Finally, in 1907, Ernest Rutherford and Thomas Royds managed to prove that the hypothesis established by Rutherford was true, thus demonstrating that the alpha particles were doubly ionized helium ions.


Some of the main characteristics of alpha particles are as follows:

atomic mass

4 atomic mass units; that is, 6.68 ± 10-27 kg.

To load

Positive, twice the charge of the electron, or what is the same: 3.2 × 10-19 C.


From the order of 1.5 x 10 7 m / s and 3 x 10 7 m / s.


They have a high ability to ionize gases, turning them into conductive gases.

Kinetic energy

Its kinetic energy is very high as a result of its great mass and speed.

Penetration capability

They have a low penetration capability. In the atmosphere, they quickly slow down when interacting with different molecules as a result of their large mass and electrical charge.

alpha decay

Alpha decay or alpha decay is a type of radioactive decay that involves the emission of an alpha particle.

When this happens, the radioactive nucleus sees its mass number reduced by four units and its atomic number by two units.

In general, the process is as follows:

Z X → A-4 Z-2 Y + 2 He

Alpha decay normally occurs in heavier nuclides. Theoretically, this can only occur in cores slightly heavier than nickel, where the overall binding energy per core is no longer minimal.

The lightest nuclei known to emit alpha particles are the smallest mass tellurium isotopes. Thus, tellurium 106 ( 106 Te) is the lightest isotope in which alpha decay occurs in nature. However, exceptionally 8 Be can be split into two alpha particles.

Because alpha particles are relatively heavy and positively charged, their average free path is very short, so they quickly lose their kinetic energy at a short distance from the emitting source.

Alpha decay of uranium nuclei

A very common case of alpha decay occurs in uranium. Uranium is the heaviest chemical element present in nature.

In its natural form, uranium occurs in three isotopes: uranium-234 (0.01%), uranium-235 (0.71%) and uranium-238 (99.28%). The alpha decay process for the most abundant uranium isotope is as follows:

238 92 U → 234 90 thousand + 2 he


All the helium that currently exists on Earth originates from the alpha decay processes of different radioactive elements.

For this reason, it is usually found in mineral deposits rich in uranium or thorium. Likewise, it also appears to be associated with natural gas extraction wells.

Toxicity and Health Risks of Alpha Particles

In general, external alpha radiation does not pose a health risk, as alpha particles can only travel distances of a few centimeters.

In this way, alpha particles are absorbed by gases present in just a few centimeters of air or by the thin outer layer of a person’s dead skin, thus preventing them from posing any risk to people’s health.

However, alpha particles are very dangerous to health if they are swallowed or inhaled.

This is because, although they have little penetration power, their impact is very large, as they are the heaviest atomic particles emitted by a radioactive source.


Alpha particles have different applications. Some of the most important ones are as follows:

– cancer treatment.

– Elimination of static electricity in industrial applications.

– Use on smoke detectors.

– Fuel source for satellites and spacecraft.

– Power source for pacemakers.

– Power source for remote sensing stations.

– Power source for seismic and oceanographic devices.

As can be seen, a very common use of alpha particles is as an energy source for different applications.

Furthermore, one of the main applications of alpha particles today is as projectiles in nuclear research.

First, alpha particles are produced by ionization (ie, separating electrons from helium atoms). These alpha particles are later accelerated to high energies.

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