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Alpha Radiation | Explanation, Use of α Particles and Health Impact

Alpha Radiation (α Rays)

Alpha rays (or alpha particles or alpha radiation) are a form of radiation emitted by highly ionized and poorly penetrating particles. They consist of two protons and two neutrons combined into a particle identical to a helium nucleus; therefore they can be written He2+. The mass of the alpha particle is 6.644656 × 10-27 kg, which is equivalent to an energy of 3.72738 GeV. Alpha particles are emitted from radioactive nuclei such as uranium or radium through a process called alpha decay.

This process sometimes leaves the nucleus in an excited state; Gamma ray emission allows the nucleus to evacuate this excess energy and return to the ground state. When an alpha particle is emitted, the atomic mass of an element is reduced by about 4.0015 atomic mass units due to the loss of four nucleons. After losing two protons, the atom sees its atomic number decrease by two, turning into a new element. One example is the transformation of radium into radon gas by alpha decay.

Alpha radiation is low penetrating radiation.

Alpha radiation is emitted by atoms with too many protons or neutrons. This corresponds to the emission of a helium atomic nucleus, consisting of two protons and two neutrons: an alpha particle. Its reach in the air was only a few centimeters. It can be stopped with a simple sheet of paper.

Example: A radium 226 atom is converted to a radon 222 atom. Its decay causes the emission of alpha particles.

Use of Alpha Radiation

Most smoke detectors in professional environments are ionic technology and contain small amounts of americium 241, an alpha particle emitter. This isotope is very dangerous by inhalation or ingestion, but the harm is minimal if the source is kept closed. Advances in optical (LED based) technology tend to make them obsolete. Their full withdrawal in France is scheduled for 2021 at the latest.

The fact that alpha particles occur naturally and that they have a sufficiently high energy to participate in nuclear reactions has made possible, through their study, certain advances in the field of nuclear physics.

Alpha decay can provide energy for spacecraft and pacemakers. Alpha particles are easy to catch. The plutonium-238 alpha emitter, for example, requires only 2.5 mm of lead to shield the radiation.

The polonium-210 alpha transmitter is widely used to dissipate static electricity.

Read also: Beta Radiation β (Beta Rays) | Beta-minus and Plus Radio radioactivity

Alpha particles can be used as radiotherapy to fight tumors. Alpha radiation from sources near the tumor damages tumor tissue, but is easily absorbed, leaving healthy tissue harmless.

“Alpha rays” from sources other than radioactive

In physics, the term alpha particle is usually used to describe any fully ionized helium-4 nucleus, even if it did not originate from radioactive decay. For example, about 12% of all particles in galactic cosmic rays are alpha particles. This is not surprising because helium is one of the most abundant elements in the universe. However, this part of the cosmic rays never reaches the ground.

Alpha particles can also be created artificially from helium gas in an ion source. If they are in a particle accelerator that accelerates the rays they are sometimes appropriately called Alpha jets.

The impact of radiation or alpha rays on health

Alpha radiation hitting the human body from the outside is relatively harmless, because alpha particles, due to their low depth of penetration, mostly penetrate only the upper layers of dead skin and remain there. On the other hand, alpha emitters embedded in organisms by inhalation or otherwise (combined) are very dangerous, because their radiation damages living cells. In particular when alpha emitters accumulate in an organ, the radiation dose is concentrated in a small space and, under certain circumstances, has an effect on important body cells. The radiation weighting factor for alpha radiation is set to 20, while only 1 for beta and gamma radiation. For the same energy input, 20 times the harmful effect is assumed for alpha radiation.

In radon balneology, low-dose alpha radiation is assumed to have a healing effect due to the radon content of some bath therapies (eg Badgastein).

Due to the large mass of alpha particles, daughter nuclei also receive a significant share of the energy released when alpha decays. It was discovered in 1909 by Lise Meitner and Otto Hahn and corresponds to the kinematics of the decay of two particles. The daughter’s core energy reaches about 200 keV. By including an alpha emitter, the retreating core also contributes to tissue damage.


Alpha particles are harmful if they work on the network; they trigger chemical reactions in them. However, alpha particles are easy to stop: a sheet of paper will suffice. Therefore, alpha emitters are only harmful if they are absorbed into the body, for example when alpha emitters are ingested through food or injection (Aleksandr Litvinenko poisoning, he died of poisoning with polonium 21, a very rare and very difficult to detect the radioactive substance).

Once inside the body, they can wreak havoc (cause destruction) in their immediate environment, as all the energy released during their decay is concentrated in a small area around the decaying core.

Another route of infection is exposure to an alpha emitting gas, such as the noble gas radon. When radium loses two protons through alpha decay, radon is formed, an alpha emitter. Because radon can be inhaled, it is very dangerous. Very strong alpha radiation hits the inside of the lungs and can cause a lot of damage there. In addition, the radioactive decay products are also no longer volatile and therefore settle in the lungs.

Another example of an alpha emitter that becomes harmful if inhaled is polonium-210, a radioactive isotope, which is found in cigarette smoke. Smoking one and a half packs of cigarettes a day provides the same dose in a year as 300 chest X-rays.

Lung cancer and alpha radiation

How does radon affect the lungs?
It is of course the alpha radiation emitted during the decay of radon, but also the descendants of radon also present in the air, which are harmful to health and damage the lungs. This is because the solid descendants of radon sometimes aggregate on particles in the air that we inhale every day. They thus become blocked in the micro-alveoli of the lungs. These particles are also radioactive in the same way as all the descendants of radon. As a result, ionizing radiation in turn bombards the cells of the lungs until they are finally eliminated by the body.

Why is radon dangerous for health?

When radon is inhaled in large quantities, alpha ionizing radiation has the power to alter the DNA molecules of cells in its path. Thus leading to genetic mutations, ultimately causing cancer.
In addition, the descendants of radon are solid particles that are also radioactive. This means that once inhaled, not only radon but also its descendants will continue to emit ionizing radiation until these particles are finally completely eliminated by the body.

The effects of radon have long been overlooked in the face of the risk of smoking even though prolonged exposure to radon is the second leading cause of lung cancer development after smoking. In France about 5 to 12% of lung cancers are thought to be due to radon. This corresponds to 1900 to 2500 lung cancers which would be caused each year by radon.

Sources: PinterPandai, National Library of Medicine (PubMed), Health Physics SocietyMinistry of the Environment Government of JapanOccupational Safety & Health AdministrationNational Center for Biotechnology Information (NCBI)

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