Low Level Radioactive Contamination in the Environment

Radiation is defined as the release of energy from an atom in the form of electromagnetic radiation or as radioactivity. As such, the energy is released as either a wave or a particle. When energy is released as a waveform, electromagnetic radiation results. Visible light, heat, ultraviolet radiation, radio waves, infrared waves, X rays, cosmic rays and gamma rays generate electromagnetic radiation. When energy is released as particulate matter, radioactivity exists. Radioactivity is generated when an atomic nucleus experiences decay and takes on the form of alpha and beta particles. However, this type of atomic decay may also cause waves of energy to be released as gamma rays.

While some forms of radiation are necessary and naturally occurring in life, others are artificially generated from various sources. Electromagnetic radiation that occurs naturally with heat, visible light and ultraviolet light is not typically known to cause danger or death to living tissue. Most harmful radiation results from radioactivity or electromagnetic radiation with frequencies in excess of those in visible light, such as with X rays or gamma rays. This type of harmful electromagnetic radiation is known as ionizing radiation. With ionizing radiation, atoms are stripped of some electrons leaving free radicals, which are highly reactive ions that may damage living tissue and other genetic material.

Detection of Low Level Radioactive Contamination by Geiger Counter

Since radiation cannot be detected by any of the human senses, several devices have been developed to detect radiation. One of the most widely used detection devices is the Geiger counter, also known as the Geiger-Muller counter. This device has been configured using a number of design variations, but the overall purpose is to identify types of radiation and characteristics of particulates that are introduced to the counter. While just about all Geiger counters detect the presence of gamma and x rays, specialized counters must be acquired to detect alpha and beta particles.

Types and Sources of Low Level Radioactive Contamination

Radioactive contamination is considered to be the uncontrolled emission of radioactive material. Natural sources of radiation include naturally occurring emissions from the human body, underground gas emissions, cosmic rays from space and radioactive particulate matter that is emitted from soil and rocks. Radon, a radioactive gas, is thought by many scientists to be responsible for most naturally occurring doses of radiation absorbed by humans. Radon is released as the uranium in earth decays. Radon enters buildings and structures through cracks in basement floors and walls, around piping and through the pores of block walls. The EPA estimates that dangerous levels of radon contaminate tens of millions of U.S. homes and radon may contribute to more than 20,000 cases of lung cancer death. While Geiger counters have shown to provide accuracy in radiation detection, they are not able to detect radon. A specialized device, known as a radon detector, must be acquired. Radon detectors may be purchased at most hardware and department stores.

Radioactive contamination is usually the result of emissions of radioactive material from artificial sources, which are not contained. Containment involves the storage of radioactive materials in designated and sealed containers. A radioactive monitor is usually used to determine if content is properly contained. These artificial sources of radiation include emissions from medical x rays, nuclear medicine, consumer products, the production and testing of nuclear weapons and the manufacture of nuclear fuels. Variations of Geiger counters are used to measure and monitor radiation from these sources.

Artificial sources of radioactive contamination include the earliest use of nuclear warfare during the bombings of Hiroshima and Nagasaki, Japan by U.S. forces in 1945. In the bombing of Hiroshima, an atomic bomb known as the “Little Boy” bomb was used. Three days later, the bombing of Nagasaki also involved an atomic bomb known as the “Fat Man” bomb. The “Fat man” bomb was a plutonium-based bomb, which was less radioactive (outside of the moment of critical mass) than the uranium-based “Little Boy” bomb.

Artificial sources of radioactive contamination raise two primary concerns. Firstly, such contamination is avoidable and secondly, geographic and occupation nuances pose higher levels of exposure for certain segments of the population. During the 1950s and 1960s more than 600 nuclear tests were conducted at a Nevada testing site. The overall increase in radiation dosage for residents downwind to the site was as much as 7%. After the testing was moved underground, radiation detectors indicate that the overall increase in dosage dropped to less than 1%.  

Radioactive fallout is also a source of artificial contamination. Radioactive fallout is contamination from nuclear activities in the atmosphere. During the 1950s and 1960s nuclear bombs were detonated in the upper atmosphere as weapons testing was performed in the U.S., the Soviet Union, Britain, China and France. Radioactive dust and debris were transported by wind and then settled to contaminate water, land and food supplies around the globe. Radiation monitoring indicated that while lighter particles tended to remain in the atmosphere for years beyond the testing, heavier particles tended to settle downwind of the explosions. Radioactive fallout has been detected at the Windscale plutonium processing plant in Britain, Three Mile Island in Pennsylvania and the Chernobyl Nuclear Reactor facility in the Ukraine. During the cold war era, fallout shelters were established in many U.S. urban communities to provide shelter, minimize risk to either accidental or deliberate radioactive fallout and provide treatment for contamination.

Dirty bombs, more formally known as Radiological Dispersal Devices (RDD) are weapons developed during the 1950s and 1960s that include a combination of radioactive materials and conventional explosives. These weapons were designed to disperse radioactive material over large areas without causing severe illness or death. The design provided for the conventional explosive components to have the most lethal and immediate effect. The radioactive component was designed to incite psychological damage, such as panic and fear, rather then physical damage. Geneva Protocol prohibits the use of any weapon designed to induce biological damage. Subsequent tests and analysis of detected radiation levels indicates that radiation exposure was high in individuals if they remained in the affected area for a period of one year. Further analysis of the effects of radiation detected after the Chernobyl fallout indicates that effects after five or more years are minimal.

Other sources of low level radiation as indicated by the EPA include the following:

Amounts of Low Level Radioactive Contamination

Contamination may exist on surfaces or in volumes of material or air. Radiation that contaminates living tissue is usually measured as volume contamination. Radiation monitors and radiation meters are used to determine the amount or volume of contamination.

Volume Contamination

The energy released during radiation is measured in rads. A rad is a measure of the absorbed radiation dose deposited in tissue. One rad is equivalent to an absorbed dose of 0.01 joules of energy per kilogram of tissue. Another measure of absorbed radiation dose is a gray. One gray is equivalent to 1 joule of energy per kilogram of tissue. As such, one gray is equal to 100 rad.

A measure used to assess damage to living tissue by a particular type or energy of radiation is known as the relative biological effectiveness (RBE). Measures of the RBE of radiation are also known as quality factors or potency factors and it is denoted as Q. This factor is used determining the risk of radiation. Such risk is measured in rem, which is short for Roentgen. A rem is equivalent to one rad times the RBE of radiation. Another measure of risk is the Sievert (Sv), which is equivalent to one gray times the RBE of radiation. As such, one Sv is equal to 100 rem.

Measures of Sv are used to differentiate the biological effects of radioactivity from the physical aspects measured in gray and described in terms of absorbed dosages. Some established Q values are as follows:

More information about the Gamma-Scout® Geiger counter.