Radiation Detection of Air and Water in the United States

Hoi Ng
March 4, 2014

Submitted as coursework for PH241, Stanford University, Winter 2014


Fig. 1: Geiger-Müller radiation detector.(Source: Wikimedia Commons)

The detection of radiation and the measurement of its properties are required in all aspects of the nuclear field - in scientific research, in the operation of nuclear-power plants, in medical applications, and even in counterterrorism. [1] Radiation detectors enable humans to determine the radioactivity of nuclear waste, the severity of nuclear fallout, and the amount of radionuclides in the air, water, soil, and food etc. Since radiation has detrimental impact on human health and ecosystems, it is crucial to constantly monitor the radiation level around people, to set dose limits for personnel working in high radioactivity environments, and to strictly regulate the amount of radionuclides encountered in everyday life. In the United States, RadNet, managed by EPA, is the nationwide system that continuously monitors ambient environmental radiation levels and those resulting from major nuclear accidents. Nonetheless, many individuals and private non-profit groups volunteer for radiation monitoring, thanks to the ready availability of detector technologies. [2] As radiation detection is a huge subject, this paper will limit its focus to detectors used for measuring radionuclide levels in air and water.

Activity and Dose

Before jumping into the discussion of detectors, it is beneficial to go over some radiation basics relevant to detection: [3]

Fig. 2: Pictured is a researcher seated in front of a scintillation counter. This device measures radioactivity incorporated into a cell culture. (Source: Wikimedia Commons)

Background Radiation

Background radiation comes from both natural and man-made sources. Some examples of background radiation include cosmic rays, terrestrial radiation, and radiation in food. Human may encounter one, or more of those in their normal activities. Passengers are subject to small doses of cosmic radiation that comes from outer space on their airplane flights. Terrestrial radiation comes from many naturally occurred radioactive elements, for example Radon, in the water and air. Food that contains isotopes such as C-14 and K-40 could lead to small radiation doses. In addition, plants and animals that uptake radioactive elements from soil or food could accumulate radioactive materials. The averaged annual natural radiation a U.S. citizen encounters is about 3.1mSv, mainly contributed from Radon gas (2mSv) in the air. It is important to note that the actual background radiation dose varies from one location to one location with at least a factor of 10. Because of that, background radiation can become very critical to one's radiation detection if one simply considers the averaged value, resulting in great artifacts or measurement errors.

Radiation Detectors

In general, there are two types of ionizing radiation detectors. One type is counting equipment that is used to determine radioactivity, and the other type is dosimeter that is used to determine radiation dose. The qualities of radiation that are of interests include radioactivity, type, energy, and dose of the radiation. For instance, a nuclear waste treatment company may want to determine how radioactive a nuclear waste is when a radiotherapist is more interested in the dose of radiation to the workers. Therefore, various detectors have been designed for different purposes although nearly all of them follow the same principle - radiation causes changes in a compound, which can be converted into measurable signals. Some examples of detecting instruments are film, thermo luminescence dosimetry, ionization tube, scintillation counters, solid-state semiconducting detectors etc.

In the U.S., RadNet has more than 100 air monitors nationwide that measure β particle level and γ radiation in the air, and it collects drinking water samples for γ composite analysis from 78 sites across the country. [4] According to NAREL's radiological methodologies report, various detectors are employed to analyze the radioactivity and dose level of the air and water samples. [5] A few of them are illustrated in the following:

Fig. 3: Setup for a γ spectroscopy experiment: germanium detector connected to a cooling dewar, scintillation detector and sample mounting. (Source: Wikimedia Commons)


Radiation detection is an important subject. This paper first briefly reviewed some important units and qualities of radiation. Subsequently, a few types of radiation detectors that are employed by RadNet were discussed. Background radiation exists almost everywhere with great variation, so detector users must be aware of that when they take and analyze their measurements.

© Hoi Ng. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] R. L. Murray, Nuclear Energy: an Introduction to the Concepts, Systems, and Applications of Nuclear Processes, 6th Ed (Butterworth-Heinemann, 2008), pp. 125-140.

[2] H. Kazem, "U.S. Residents Monitor Fukushima Radiation," Al Jazeera, 19 Jan 14.

[3] T. Henriksen and D.H. Maillie, Radiation and Health (CRC Press, 2002).

[4] "Historical Uses of RadNet Data," U. S. Environmental Protection Agency, EPA-402-R-08-007, November 2008.

[5] "Inventory of Radiological Methodologies," U. S. Environmental Protection Agency, EPA 402-R-06-007, October 2006.