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Moisture and Density "Nuclear" Gauges Used in Road Construction

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  Use of Radioactive Materials:
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This page descibes how radioactive material is used in moisture and density gauges.

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Quality control is an important aspect of any construction project. Building roads is no exception, and the moisture content and density of the materials used are very important. Gauges containing radioactive sources are used for determining the density of asphalt, soil, aggregate (usually gravel or crushed rock), and concrete as well as the moisture content of the soil or aggregate.

These gauges work by measuring either the "backscatter" or the "direct transmission" of radiation directed at a material. "Backscatter" is the amount of radiation that is deflected by the material and is measured by placing the gauge on the surface of the material. "Direct transmission" is the amount of radiation that passes through the material and is measured by drilling a hole in the material and inserting the gauge.

Various kinds of sources are used in moisture and density gauges, and each gives off specific types of radiation. One source often used is cesium-137, which emits both beta and gamma radiation. Another is a compound of americium-241 and beryllium, which emits neutron radiation. (Although americium-241 emits alpha radiation, when mixed with beryllium (a non-radioactive metal), the mixture emits neutrons.)

The radioactive sources in the gauge are surrounded by shielding. It is only when the gauge is mishandled or damaged that it becomes a significant radiological hazard to the operator. Extensive experience with these gauges over many years indicates that radiation exposure to workers is generally low and that accidents involving the gauges are infrequent. When these gauges are used properly, radiation exposure of the general public is not an issue.

Nuclear gauges containing licensed radioactive sources must be disposed of properly. They must not be treated as ordinary trash, recycled as scrap metal, or abandoned. Contact the manufacturer or your state radiation control program for disposal instructions. Some manufacturers also accept gauges for disposal.

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Who is protecting you

U.S. Department of Labor(DOL),Occupational Safety and Health Administration(OSHA)

DOL's Occupational Safety and Health Administration issues regulations and standards for the safety of workers in a wide range of occupational settings including construction and demolition. One area of potential hazard to workers is the improper handling of radioactive material or radiation-generating equipment.

U.S. Nuclear Regulatory Commission(NRC)

NRC issues licenses to companies to use nuclear gauges and requires specific safety measures for their use, storage, and disposal.

The States

Each State has one or more programs to address radiation protection issues and respond to and investigate incidents involving gauges with sealed radioactive sources.

Thirty-four states have signed formal agreements with the Nuclear Regulatory Commission, delegating to the states regulatory responsibility over small quantities of special nuclear material and its source and by-products (americium-241 and cesium-137 are by-product materials). These states are known as NRC-Agreement States.

U.S. Environmental Protection Agency(EPA)

EPA's Alternative Technologies Initiative is investigating the use of new and non-radioactive alternative technologies to reduce the amount of radioactive materials used in industrial gauges.

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What you can do to protect yourself

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Promoting the Use of Alternative Technologies 
April 2, 2012. U.S. Environmental Protection Agency.
On this page, you can read about EPAs work with industry to find nonnuclear substitutes for nuclear technologies such as density gauges.
Orphan Sources
April 2, 2012. U.S. Environmental Protection Agency.
This page describes orphan sources and special challenges surrounding them.
May 2009. U.S. Environmental Protection Agency
On this page, you can learn the basic facts about americium. It is used in fluid density gauges.
April 2, 2012. U.S. Environmental Protection Agency.
On this page, you can learn the basic facts about cesium. Cesium is a radioactive element used in moisture-density gauges.
Radiation: Facts, Risks and Realities (PDF) (17pp, 998 K [about pdf format]) [EPA 402-K-10-008]
April 2, 2012. U.S. Environmental Protection Agency.
This booklet offers basic information on ionizing radiation.
Safety and Health Topics: Ionizing Radiation
April 2, 2012. U.S. Department of Labor, Occupational Safety & Health Administration.
On this page, you can learn about health and safety standards for people who work with or around ionizing radiation sources.
Medical, Industrial, Academic Uses of Nuclear Materials Regulations, Guidance, and Communications
April 2, 2012. U.S. Nuclear Regulatory Commission.
This page has links to NRC’s regulations and guidelines for the medical, industrial and academic uses of nuclear materials.
Directory of Agreement State and Non-Agreement State Directors and State Liaison Officers 
April 2.2012. U.S. Nuclear Regulatory Commission.
This page provides a list of the Nuclear Regulatory Commission Agreement State contacts.

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