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09 February 2012

Answer to Question #1044 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — General

The following question was answered by an expert in the appropriate field:

Do you know where can I find a map showing the levels of background radiation throughout the United States and a map showing NORM occurrence throughout the United States?

A nice discussion of natural background radiation can be found at the Idaho State University website, which in turn has many useful links. A color map of terrestrial gamma-ray exposure in the United States one meter above ground can be found at the U.S. Geological Survey website.

I could not readily locate an equivalent map of the cosmic radiation levels but the attached figure adapted from NCRP Report 94, Exposure of the Population in the United States and Canada from Natural Background Radiation, gives the cosmic ray dose rate as a function of elevation above sea level. One can obtain the dose rate at any point of interest by determining the elevation and looking up the dose rate in the chart.

Dose rate vs altitude

It is not clear what is meant by "NORM occurrence." Naturally occurring radioactive materials occur everywhere in just about everything.

Tom Gesell

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