Alpha Radiation

The Difference Between Alpha, Beta and Gamma Radiation

Alpha Radiation


Physical Origin

Alpha radiation is released when an atom undergoes radioactive decay, giving off a particle (called an alpha particle) consisting of two protons and two neutrons (essentially the nucleus of a Helium-4 atom).

Image 3 - The alpha particle consists of 2 neutrons and 2 protons

It transforms the originating atom to a different element with an atomic number 2 less and atomic weight 4 less than it started with.


Process of Decay

Image 4 - Alpha decay and recoil

Size, speed and range

Due to their positive electric charge and heavy mass, alpha particles interact strongly with matter and travel slowly. Alpha particles have an extremely short range reaching only a few centimeters in air and are unable to penetrate the natural protective barriers of our skin (clothing can stop alpha particles). Inside cell tissue, alpha particles have a range of only 50-90 μm (equivalent to a few cell diameters).[i]

Effect on cells

Typically, alpha particles have a LET that is about 100 to 1000 times greater than the average of beta particles. This provides a much greater potential for biological damage. As a result of alpha particles higher Relative Biological Effectiveness (RBE), a significantly lower dose of alpha radiation is needed to achieve the same amount of biological damage compared to other radiation forms.​[ii]

When alpha particles hit a cell nucleus, they cause DNA double-strand breaks. These breaks result in changes in the normal structure of chromosomes, that carry our genetic information and prevent cells from replicating. The DNA double-strand breaks created by alpha particles have been found to be highly complex, more concentrated and more resistant to cell repair mechanisms, and thus more destructive than double-strand breaks caused by other modalities. [iii]

However, thanks to the alpha particles’ short range in tissue, there is a very low risk of healthy cells being affected by an alpha-radiation based treatment.

Image 5 - Alpha particles destroy cancer by causing DNA double-strand breaks


Shielding is the placement of an “absorber” between you and the radiation source – as ionizing radiation passes through matter, the intensity of the radiation is diminished. Alpha, beta, and gamma radiation can all be stopped by different thicknesses of absorbers.

Alpha particles are stopped after traveling through only a few centimeters in air. Due to its short range, no shielding is required. For example, a thin piece of paper, or even the dead cells in the outer layer of human skin, provides adequate shielding.

Image 6 - The range of alpha particles, alpha particles can be stopped by a sheet of paper

Moreover, as a result of its high potency to cause biological damage, a much lower dose of alpha radiation is required, reducing the risk from radiation exposure and the need for shielding.

Alpha Tau

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