Alpha Rays (Alpha Particles) | Definition, Uses, Properties

Definition of Alpha Rays

alpha rays

Alpha rays is made up of alpha particles. An alpha particle, structurally equivalent to the nucleus of a helium atom, consists of two protons and two neutrons

Other Definition of Alpha Rays

  • During nuclear decay, the liberated energy (decay energy) is shared between the daughter nucleus and the alpha particle. The two neutrons of an alpha particle give it additional mass that further facilitates ionization by coulombic interaction or even direct collision of the alpha particle with atomic electrons.
  • Alpha particles and other types of charged particles dissipate their energy during these collisions mainly by two mechanisms: ionization and electron excitation. The high mass and charge of an alpha particle, relative to other nuclear radiation forms, gives it greater ionization power but a poorer ability to penetrate matter
  • However, electron excitation occurs when the alpha particle fails to impart sufficient energy to an atomic electron for it to be ejected from the atom. Rather, the atoms or molecules of a given material absorb a portion of the alpha-particle energy and become elevated to a higher energy state. Depending on the absorbing material, the excited atoms or molecules immediately fall back to a lower energy state or ground state by dissipating the absorbed energy as photons of visible light. 

Source of Alpha Particles

Source of Alpha Particles

The source of alpha particles is alpha decay:

The alpha decay of heavier (> 106 u atomic weight) atoms is the best-known source of alpha particles. When an atom emits an alpha particle in alpha decay, the atom’s mass number decreases by four due to the loss of the four nucleons in the alpha particle. The atom’s atomic number goes down by two.

As a result of the loss of two protons – the atom becomes a new element.

Examples of this sort of nuclear transmutation by alpha decay are the decay of uranium to thorium and radium to radon.

Alpha particles are commonly emitted by larger radioactive nuclei such as uranium, thorium, actinium, radium, and transuranic elements. Unlike other types of decay, alpha decay as a process must have a minimum-size atomic nucleus that can support it.

The smallest nuclei that have to date been found to be capable of alpha emission are beryllium-8 and the lightest nuclides of tellurium (element 52), with mass numbers between 104 and 109.

The alpha decay sometimes leaves the nucleus in an excited state; the emission of a gamma-ray then removes the excess energy.

Mechanism of Production in Alpha Decay

Mechanism of Production in Alpha Decay

In contrast to beta decay, the fundamental interactions responsible for alpha decay are a balance between electromagnetic and nuclear forces. Alpha decay results from the Coulomb repulsion between the alpha particle and the rest of the nucleus, which both have a positive electric charge, but which is kept in check by the nuclear force.

In classical physics, alpha particles do not have enough energy to escape the potential well from the strong force inside the nucleus (this well involves escaping the strong force to go up one side of the well, which is followed by the electromagnetic force causing a repulsive push-off down the other side).

           However, the quantum tunnelling effect allows alphas to escape even though they do not have enough energy to overcome the nuclear force. This is allowed by the wave nature of matter, which allows the alpha particle to spend some of its time in a region so far from the nucleus that the potential from the repulsive electromagnetic force has fully compensated for the attraction of the nuclear force. From this point, alpha particles can escape.

Uses of Alpha Rays


There are many ways in which science successfully beneficially uses alpha radiation.

1. Cancer Treatment

Alpha radiation is used to treat various forms of cancer. This process, called unsealed source radiotherapy, involves inserting tiny amounts of radium-226 into cancerous masses. The alpha particles destroy cancer cells but lack the penetrating ability to damage the surrounding healthy cells. Radium-226 has mostly been replaced by Safer, more effective radiation sources, such as cobalt-60. Xofigo, the brand name of Radium-223, is still used to treat bone cancer.

2. Static Eliminator

Alpha radiation from polonium-210 is used to eliminate static electricity in industrial applications. The positive charge of the alpha particles attracts free electrons, thus reducing the potential for local static electricity. This process is common in paper mills, for example.

3. Smoke Detector

Alpha radiation is used in some smoke detectors. The alpha particles from americium-241 bombard air molecules, knocking electrons free. These electrons are then used to create an electrical current. Smoke particles disrupt this current, triggering an alarm.

4. Spacecraft Power

Radioisotope thermoelectric generators are used to power a wide array of satellites and spacecraft, including Pioneer 10 and 11 and Voyager 1 and 2. Because, these devices function as a battery, with the benefit of a long life span. Plutonium-238 serves as the fuel source, producing alpha radiation resulting in heat, which is converted to electricity.

5. Pacemaker Battery

Alpha radiation is used as an energy source to power heart pacemakers. Plutonium-238 is used as the fuel source for such batteries; with a half-life of 88 years, this source of power provides a long lifespan for pacemakers. However, due to their toxicity, difficulties with patients in travelling, and problems with disposal, they are no longer used.

6. Remote Sensing Stations

The United States Air Force uses alpha radiation to power remote sensing stations in Alaska. Strontium-90 is typically used as the fuel source. These alpha-powered systems enable unmanned operations for long periods of time without the need for servicing. Local opposition to the use of radiation is prompting the air force to replace many of these devices with alternative power sources, such as diesel-solar hybrid generators.

7. Heating Devices

Alpha radiation is used to provide heating for spacecraft. Unlike radioisotope thermoelectric generators that convert heat to electricity, radioisotope thermal generators directly use the heat generated by alpha decay.

8. Coast Guard Buoys

The U.S. Coast Guard uses alpha radiation to power some of their oceanic buoys. Like in many of the other applications, alpha radiation provides a power source with a long lifespan. Strontium-90 is the typical power source for these buoys.

9. Oil Well Equipment

The oil industry uses alpha radiation to power some of its offshore equipment. Because this provides a long-lasting power source for remotely located devices that have limited access to crews. Strontium-90 is the typical fuel source for such batteries.

10. Seismic and Oceanographic Devices

Alpha radiation is also used to power a wide array of seismic and other oceanographic devices. These unmanned devices are often located in isolated locations, such as on the ocean floor, limiting short-term batteries’ practicality. Strontium-90 is the most common material used in these alpha decay batteries.

Properties of Alpha Rays

Properties of Alpha Rays

These are some properties of alpha rays:

  1. Alpha rays are positively charged particles. Alpha-particle is a highly active and energetic helium atom that contains two neutrons and protons.  
  2. These particles have the minimum penetration power and highest ionization power. 
  3. They can cause serious damage if they get into the body due to their high ionization power. 
  4. They are capable of numerous ionizing atoms by a short distance. It is because the radioactive substances that release alpha particles are required to be handled after wearing rubber gloves.

Also Read:

Leave a Comment