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Moisture and Density "Nuclear" Gauges Used in Road Construction
RadTown USA Topics
This page descibes how radioactive material is used in moisture and density gauges.
On this page:
Overview
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.
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.
What you can do to protect yourself
- Handle moisture and density gauges only if you are qualified to do so.
- Keep such gauges under strict supervision when in use and in a secure location when not in use.
- Do not remove the shielding from the sources.
- Dispose of moisture and density gauges according to NRC guidelines.
Resources
| Alternative Technologies for Industry 10 October 2007. U.S. Environmental Protection Agency This page has information on EPA’s Alternative Technologies Initiative, which is working with industry and other stakeholders to develop non-nuclear alternative technologies. |
| Orphan Sources 10 October 2007. U.S. Environmental Protection Agency This page describes the problem of orphan sources and what is being done about it. |
| Americium
- The Basics 8 March 2006. U.S. Environmental Protection Agency This page provides the basic facts about americium, a radioactive element used in moisture and density gauges. |
| Cesium
- The Basics 8 March 2006. U.S. Environmental Protection Agency This page provides the basic facts about cesium, a radioactive element used in moisture and density gauges. |
| Ionizing
Radiation Fact Book (PDF)(22pp, 1.12Mb) [EPA 402-F-06-061] March 2007. U.S. Environmental Protection Agency This booklet offers basic information on ionizing radiation, including in-depth definitions of alpha particles, beta particles, and gamma rays. |
| Ionizing
Radiation - 1910.1096 1996.U.S. Department of Labor,Occupational Safety and Health Administration This page both gives and leads to additional information on worker health and safety standards for working with or around ionizing radiation sources. |
| Black, Kevin. “Materials Notebook: The Nuclear Asphalt Content
Gauge for Measuring Asphalt Content in Mixes.” May 1994.U.S. Department of Transportation, Federal Highway Administration This page gives specific information on the methods for determining asphalt content. |
| Medical,
Industrial, Academic Uses of Nuclear Materials Regulations,
Guidance, and Communications 15 July 2005. U.S. Nuclear Regulatory Commission This page has links to NRC’s regulations, guidance and communications materials that are most relevant to the medical, industrial and academic uses of nuclear materials. |
| Directory
of Agreement State and Non-Agreement State Directors and State
Liaison Officers 7 February 2006. U.S. Nuclear Regulatory Commission This page provides a list of U.S. Nuclear Regulatory Commission Agreement State contacts. |