Radioactive substances (radionuclides) are known health hazards that emit energetic waves and/or particles that can cause both carcinogenic and non-carcinogenic health effects. Radionuclides pose unique threats to source water supplies and water treatment, storage, or distribution systems because radiation emitted from radionuclides in water systems can affect individuals through several pathways - by direct contact with, ingestion or inhalation of, or external exposure to, the contaminated water. While radiation can occur naturally in some cases due to the decay of some minerals, intentional and non-intentional releases of man-made radionuclides into water systems is also a realistic threat.

Threats to water and wastewater facilities from radioactive contamination could involve two major scenarios. First, the facility or its assets could be contaminated, preventing workers from accessing and operating the facility/assets. Second, at drinking water facilities, the water supply could be contaminated, and tainted water could be distributed to users downstream. These two scenarios require different threat reduction strategies. The first scenario requires that facilities monitor for radioactive substances being brought on-site; the second requires that water assets be monitored for radioactive contamination. While the effects of radioactive contamination are basically the same under both threat types, each of these threats requires different types of radiation monitoring and different types of equipment. This document provides a general discussion of radiation and radiation monitoring. Specific information on radiation monitoring equipment designed for these two different threat scenarios is provided in the two documents below:

The most common types of radiation are alpha, beta and gamma radiation.

Alpha emitters emit heavy, positively-charged alpha particles. Many alpha emitters are naturally occurring, but some are man-made. Examples include plutonium, radon, radium, uranium, and thorium. Alpha radiation is short range (i.e., it can only travel a few centimeters from the source through air) and it cannot penetrate human skin. Alpha emitters can be a serious health hazard if they are ingested, such as if they are consumed from water contaminated with radioactive materials.

Beta emitters emit lightweight, negatively-charged particles (electrons). Beta emitters are primarily man-made and include strontium-90, carbon-14, tritium (H-3), and sulfur-35. Beta radiation has a medium range (i.e., it can travel several feet from its source through air) and it has moderate capabilities to penetrate through objects.

Gamma emitters emit very long range electromagnetic radiation, and can be both man-made and naturally-occurring. Examples of man-made gamma emitters generated by the nuclear industry include iodine-131, cesium-137, and cobalt-60. Gamma radiation is highly penetrating, and it can travel through many types of objects, including human skin and clothing. It is effectively shielded or absorbed by materials such as concrete, steel, or lead.

Different types of radiation monitoring instruments have been designed for different purposes. In general, this equipment is designed to measure either:

For example, if a utility wished to determine whether there was elevated radiation from some source, they would most likely use some type of "screening"-type equipment to measure the gross radiation from the source. If a high level of radiation was detected, the utility may identify individual species of radionuclides and their energy levels using equipment specifically designed for this purpose. This would allow the calculation of radiation doses and exposure levels and an evaluation of the potential health effects of the radiation exposure.

While the goals of the radiation monitoring influence the type of analysis to be done, other factors also affect the specific type of equipment to be used to conduct the monitoring. Different types of radiation have unique properties (i.e., particle vs. wave radiation, ability of different types of radiation to penetrate different materials, distance that different forms of radiation travel from their source, interaction of radiation with matter, and the unique energy signatures of different types of radiation), and therefore radiation detection instrumentation is somewhat specific to the radiation to be detected. For example, survey meters such as Geiger-Mueller (GM) counters allow the rapid evaluation of different types of radiation from solid surfaces. Therefore, these GM meters are appropriate for evaluation of radioactive spills. However, due to the fact that water is not a smooth surface, and because alpha and beta emissions are relatively short range and can be attenuated within the water, these types of instruments are not suitable for measuring alpha or beta radiation in water samples. A more appropriate method for measuring alpha and beta radiation in water is in a laboratory setting with a liquid scintillation counter. While field measurements of gamma radiation in water may be easier to accomplish than field measurements of alpha or beta radiation in water, they still may not be highly accurate. For example, gamma emissions may be attenuated by the sample container and/or the water itself, reducing the efficiency of the detection device.


With all of these factors affecting the appropriate choice of radiation monitoring equipment, choosing the appropriate instrument to achieve an individual's monitoring goals can be a daunting task. Therefore, it may be appropriate to consult an expert in radiation monitoring to ensure that the goals of any radiation monitoring program are met (i.e., to ensure that the appropriate type of radiation is measured and that the appropriate type of instrumentation is used).

As discussed above, different equipment has been developed to evaluate gross radiation vs. specific radionuclides. For security monitoring purposes, it may be most appropriate to initially evaluate the overall radiation from a source, whether it be a package coming into the plant or a water sample from a drinking water reservoir. Should elevated levels of radiation be detected, additional measurements can be made to identify the specific radionuclides present. Therefore, this document will focus on detection devices that are used to perform screening-type measurements for gross levels of radiation.

Radioactivity is expressed in the number of disintegrations per unit time. For example, 1 becquerel (Bq) is 1 disintegration per second, and 1 curie (Ci) is 3.7 x 1010 disintegrations per second. However, due to various physical and statistical factors related to detection efficiency, determining the actual number of disintegrations per unit time is almost impossible. For example, measuring the actual radiation from a source would require one hundred percent efficiency in measuring all alpha, beta, and gamma emissions, which are radiating in every direction from the source. This would require a detector that would completely surround the sample and could capture a large range of energies from an unlimited number of sample shapes and physical properties within a defined distance from the sample. Therefore, radiation emissions are typically measured as counts per minute (cpm), which takes into account the detection efficiency of the instrument.

As discussed above, the most important factor in purchasing any radiation monitoring equipment is ensuring that the equipment is appropriate for the type of survey being conducted. There are many different detection methods available for different types of radiation, and thus individual users must determine the appropriate equipment for their needs. Other factors in choosing the appropriate equipment are the local conditions at the site (i.e., temperature, humidity), and the specific properties of the radionuclides at the site.

The U.S. DOE is working with the U.S. DOJ to make older-generation equipment available to emergency preparedness organizations in major U.S. cities. Types of radiological instrumentation redeployed through this program include portable instrument probes (e.g., GM counters and alpha and gamma scintillators) and self-reading pocket dosimeters (dosimeters are used to track an individual's exposure levels, and they are not discussed in this document). Starting in April 2003, DOE formally transferred excess radiological detection instrumentation to cities across the country through the Homeland Defense Equipment Reuse (HDER) Program.