The following table provides practical information to allow the design and implementation of radiation protection in laboratory and industrial environments. Additional information and details can be found in the references.
Type (symbol) | Physical properties | Range | Shielding | Biological hazards | Comments |
Alpha particle (α) | Very large mass (2 protons, 2 neutrons, 0 electrons) +2 charge | Very short 3 cm to 6 cm (∼ 1 inch to 2 inches) in air | Few centimeters of air Sheet of paper Dead (outer) layer of skin | Internally, the source of alpha radiation is in close contact with live body tissue. It can deposit large amounts of energy in a small amount of body tissue Rarely an external hazard | Alpha particles of at least 7.5 MeV are required to penetrate the epidermis, the protective layer of skin, which is about 0.07 mm (70 µm) thick The range R of most particles of common emitters (4.5 MeV to 5.5 MeV) is 3 cm to 4 cm in air Range in air = 0.322 E3/2 cm, when E is expressed in MeV |
Beta particle (β) | Small mass -1 or +1 charge -1 charge particle is an electron; +1 charge particle is a positron | Short 6 cm to 600 cm (1 inch to 20 feet) in air | Low atomic number materials Plastic Glass Aluminum | Internal hazard Externally, may be hazardous to the skin and eyes | Beta particles of at least 70 keV are required to penetrate the epidermis. Rair ≈ 3.65 m/MeV The range of beta particles in material in g cm-2 (thickness in cm multiplied by the density in g cm-3) is approximately half the maximum energy in MeV. (R ≈ Emax/2) Dose rate (in rad/hr) at 1 cm from a beta point source; ≈ 300 rad/hr per Curie Dose rate (in rad/hr) in a solution ≈ 2.12 E̅C/ρ; where E̅ = average energy in MeV, C = concentration in µCi cm-3, and ρ = density of the solution in g cm-3; the dose rate is about one-half this value at the surface An aqueous solution of 1 Curie 32P in a glass vial typically produces 3 mrad/hr at 1 meter from Bremsstrahlung Shielding causes Bremsstrahlung radiation similar to x-rays and gamma rays; generally the higher the atomic number of a material, the more intense is the Bremsstrahlung radiation |
Neutron (n or n0) | Large mass No charge | Very far in air Easily travel several hundred meters High penetrating power due to lack of charge | High hydrogen content material Water Concrete Plastic | External whole body exposure hazard May be external and/or internal hazard Depends on whether source is inside or outside the body Energy dependent | Shielding can be provided by hydrogen-rich materials such as hydrocarbons, water, waxes, high water concrete Can cause neutron activation, in which radionuclides are formed Particularly damaging to soft tissue such as the cornea |
X-Ray, Gamma ray (γ) | No mass No charge Electromagnetic wave X-rays and gamma rays are similar, but place of origin and energy levels may differ | Very far in air Easily travel several hundred meters Very high penetrating power since it has no mass & no charge | High atomic number materials Depleted uranium Lead Steel Concrete Water | Whole body exposure hazard May be external and/or internal hazard Can be a skin and/or eye hazard Depends on whether source is inside or outside the body Energy dependent | Shielding requires large mass and density materials; lead or depleted uranium are commonly used Doubling the distance from a point source will result in a reduction of exposure (or dose) by a factor of four Protective clothing and other PPE can effectively guard against ingestion or absorption of radioactive material but is not usually practical for protecting against x-rays or gamma rays |