Shielding of Alpha Radiation

 
Radiation Protection Principles - Time, Distance, Shielding
In radiation protection there are three ways how to protect people from identified radiation sources:
  • Limiting Time. The amount of radiation exposure depends directly (linearly) on the time people spend near the source of radiation. The dose can be reduced by limiting exposure time.
  • Distance. The amount of radiation exposure depends on the distance from the source of radiation. Similarly to a heat from a fire, if you are too close, the intensity of heat radiation is high and you can get burned. If you are at the right distance, you can withstand there without any problems and moreover it is comfortable. If you are too far from heat source, the insufficiency of heat can also hurt you. This analogy, in a certain sense, can be applied to radiation also from radiation sources.
  • Shielding. Finally, if the source is too intensive and time or distance do not provide sufficient radiation protection, the shielding must be used. Radiation shielding usually consist of barriers of lead, concrete or water. There are many many materials, which can be used for radiation shielding, but there are many many situations in radiation protection. It highly depends on the type of radiation to be shielded, its energy and many other parametres. For example, even depleted uranium can be used as a good protection from gamma radiation, but on the other hand uranium is absolutely inappropriate shielding of neutron radiation.
radiation protection pronciples - time, distance, shielding
Principles of Radiation Protection – Time, Distance, Shielding

Shielding of Alpha Radiation

The following features of alpha particles are crucial in their shielding.

  • Alpha particles are energetic nuclei of helium and they are relatively heavy and carry a double positive charge.
  • Alpha particles interact with matter primarily through coulomb forces (ionization and excitation of matter) between their positive charge and the negative charge of the electrons from atomic orbitals.
  • Alpha particles heavily ionize matter and they quickly lose their kinetic energy. On the other hand they deposit all their energies along their short paths.
  • The stopping power is well described by the Bethe formula.

The stopping power of most materials is very high for alpha particles and for heavy charged particles. Therefore alpha particles have very short ranges. For example, the ranges of a 5 MeV alpha particle (most have such initial energy) are approximately only 0,002 cm in aluminium alloy or approximately 3.5 cm in air. Most alpha particles can be stopped by a thin piece of paper. Even the dead cells in the outer layer of human skin provides adequate shielding because alpha particles can’t penetrate it. 

Therefore the shielding of alpha radiation alone does not pose a difficult problem. On the other hand alpha radioactive nuclides can lead to serious health hazards when they are ingested or inhaled (internal contamination). When they are ingested or inhaled, the alpha particles from their decay significantly harm the internal living tissue. Moreover pure alpha radiation is very rare, alpha decay is frequently accompanied by gamma radiation which shielding is another issue.

See also: Interaction of Heavy Charged Particles with Matter

Alpha Particle - Cloud Chamber
Alpha particles and electrons (deflected by a magnetic field) from a thorium rod in a cloud chamber.
Source: wikipedia.org
Shielding of Alpha and Beta Radiation
Basic materials for alpha particles shielding.

See above:

Shielding of Ionizing Radiation

See next:

Shielding of Beta Radiation