Alpha, Beta and Gamma Particles

Alpha particles are agglomerates composed of two neutrons and two protons. They are emitted following the decay of unstable nuclei and are completely identical to the nuclei of helium atoms (atomic number: Z = 2). Lacking electrons, alpha particles have a positive electric charge (e = +2).

There are three types of radiation called alpha, beta and gamma that can be separated by a magnetic field or an electric field:

Alpha radiation (α): also called alpha particles or alpha rays, they are particles charged by two protons and two neutrons, therefore being helium nuclei. They present positive charge +2 and mass number 4.

Beta radiation (β): beta rays or beta particles, are electrons, negative particles with charge – 1 and mass number 0.

Gamma radiation (γ): or gamma rays. The wavelength of this radiation varies from 0.5? at 0.005? (unit of measure: angstron). Gamma radiation is electromagnetic waves, has zero charge and mass, continuously emits heat and has the ability to ionize the air and make it conductive of electric current.

Mind Map: Radiations


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A radioactive nucleus emits alpha or beta radiation, and gamma radiation is always present. The beta particle can reach a speed of up to 95% of the speed of light, whereas the alpha particle is slower and reaches a speed of 20,000 km / s, and gamma rays reach the speed of electromagnetic waves (300,000 km / s).

To better understand the speed and power of alpha, beta and gamma particles in relation to matter, here are some examples of the penetrating power of radiation:

– Despite being quite energetic, alpha particles are easily blocked by a sheet of paper;

– Beta particles are more penetrating and less energetic than alpha particles, they can pass through sheets of lead up to 2 mm or aluminum up to 5 mm in the air, but are blocked by a 2.5 cm thick wooden board;

– Gamma particles travel thousands of meters in the air, they are more dangerous, when emitted for a long time they can cause malformation in the cells. Gamma rays can pass through steel sheets up to 15 cm thick, but are blocked by thick lead plates or concrete walls.

We can conclude that the alpha particles have a relatively greater mass and electric charge than the others, however, they are easily blocked by a sheet of paper. Gamma radiation, on the other hand, is not so energetic, but it is extremely penetrating and can pass through the human body, it is only stopped by a thick concrete wall or some type of metal.

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