Module 5: Basic Concepts in Radiation Physics - Types Of Radiation

TYPES OF RADIATION

Most ionizing radiation is classified into five types:

• Alpha (a)
• Beta (b)
• Gamma (g)
• Neutron (n)
• X-ray (X)

Alpha radiation:

Alpha radiation consists of a-particles, which are high energy helium nuclei emitted from heavy elements, such as uranium

Alpha radiation has a very short penetration:

• a few centimeters in air,
• a few microns in tissue (less than the outer dead cell layer).

Consequently, this type of radiation is easily shielded.

Beta radiation:

Beta radiation consists of high-energy electrons, emitted from certain radioactive nuclei, such as tritium (³H), carbon-14 (¹⁴C) and phosphorus-32 (³²P). They are moderately penetrating:

• up to a few meters in air,
• millimeters in tissue.

Gamma radiation:

Gamma radiation consists of high energy electromagnetic radiation, emitted by the radioactive nuclei of certain isotopes, such as cobalt-60 (⁶⁰Co). The radiation has specific energies, depending on the source, and this can be used in the identification of that source. Gamma radiation is very penetrating, and hence difficult to shield. Lead is frequently used as a shielding material.

Neutron radiation:

Neutron radiation arises from the emission of neutrons from the nuclei of certain atoms, such as uranium-235 (²³⁵U). This can be very penetrating, and requires special consideration for shielding.

This type of radiation can induce radioactivity when absorbed by stable (non-radioactive) elements

X-ray radiation:

X-ray radiation is electromagnetic energy emitted from outside the nucleus. It may be "machine-produced" by bombarding high energy electrons on a metal target (the basics of an x-ray machine), or it may be emitted from certain radioactive materials. X-rays have the same magnitude of penetration as gamma rays, and require similar shielding.