Radioactivity Hazards - cont'd
Ionizing Radiation
The most common types of radiation are particulate radiation of alpha ( ) particles, beta ( ) particles and neutrons, electromagnetic gamma ( ) radiation, and x-rays. All of these ionizing radiation sources can be hazardous to human health unless adequate safeguards are provided. Click here for more information on protection from ionizing radiation.
Neutrons are particles released upon the disintegration of radioactive isotopes. Neutron particles are highly penetrating and require heavy shielding. They are capable of penetrating the human body to several centimeters. Within the body the neutrons release excess energy which can cause tissue damage. Secondary releases of energy may also occur from alpha, beta, and gamma emitters released from the neutrons.
Alpha particles are emitted from the nuclei of radioactive atoms. They have high speeds and high energy and are the least penetrating. Their maximum range in air is about 10 cm and can be stopped by a sheet of paper or the outer layer of skin. If they enter the body, alpha emitters are hazardous to human health. They tend to concentrate in bones and body organs like the lung, liver, or kidney. As they disintegrate, they can damage tissue. The normal route of entry by alpha particles are inhalation, digestion and through wounds.
Beta particles are also emitted from the nuclei of radioactive atoms, but they are much smaller in mass than alpha particles and have considerably more penetrating power. Beta emitters are capable of penetrating wood to 4 cm and the human body to 1 cm. Like alpha emitters, they are internal radiation hazards and have the same routes of body entry. They can be stopped by ordinary wall or a 1.3-cm thick sheet of aluminum.
Gamma radiation originates in the nucleus of an atom. It can penetrate deeply into tissue, and may produce burns similar to deep sunburn, alter genes to cause mutations, and reduce the white blood cell count and encourage infections.
X-rays cause cancer by inducing mutations. X-rays are a form of electromagnetic radiation that is produced when high-speed electrons strike the target material inside the x-ray tube. The quality of the x-ray, which is the power to penetrate through matter, depends upon the wavelength and the material being irradiated. Hard x-rays with short wavelengths will penetrate thick steel plate. Soft x-rays with long wavelengths are less penetrating.
The degree of toxicity of radioactive sources depends upon the amount and kind of radiation material. Radioactive materials are classified according to their relative toxicity as shown below:
Radioactive materials retain their radiation properties for extended period of time. This reduction in radiation occurs naturally and results from the decay of radioactivity. The half-life is the time rate of decay for a radioactive material to lose one-half of its beginning intensity or strength. Some materials lose their radioactivity in days or even minutes, others in years. The half-life of a radioactive isotope is specific for that isotope, as shown in the Table.
Several basic units are used to quantify radiation, as shown below.
