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20 November 2008

Answer to Question #5680 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Soil and Fallout

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

I did a preliminary survey of background radiation levels of Vypeen Island (one of the islands situated in Kerala, India). We conducted an ambient gamma exposure survey using micro-R-survey meter UR 705. We measured the gross alpha activity of that island using the alpha counting system CS-201 manufactured by Pla Electro Appliances. From the ambient gamma exposure survey we found out that the dose rate on that island varies from 60.9 nGy/hr to 182.7 nGy/hr with a mean value 127.02 nGy/hr. We found out that the gross alpha activity on that island varies from BDL (below detectable level) to 5892.26 Bq/kg with a mean value 1083.97 Bq/kg.

Can we conclude this Vypeen Island is a low-background radiation area or a high-background radiation area?

Right now, sitting in my home in western New York state, my dose-rate meter (a Ludlum Model 19) has a reading of about 70 nGy/hr. As I go around the city, I get readings that range from about 50 to 150 nGy/hr. Rochester is not a high-background radiation area—the underlying geology is primarily limestones and sandstones that have fairly low levels of natural radionuclides. Based on that, I would venture to suggest that the readings you are getting are fairly normal.

A few years ago, when I visited the high-background radiation area in Ramsar, Iran, I had readings of about 22 microGy/hr. The soils in this area had ²²⁶Ra activity concentrations of about 6,000 pCi/gm (about 16,000 Bq/gm), with decay progeny in equilibrium—this gives a gross alpha radioactivity concentration of about 50,000 or 60,000 Bq/gm.

Based on this, I again suggest that the levels you are registering are fairly normal.

Another place to gather more information is the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reports, which are available online. The 2000 report has a very comprehensive section on radionuclide concentrations and radiation levels in high-background radiation areas and as global averages. There are other sources of information, but the 2000 UNSCEAR report is the most recent and also one of the best.

Andy Karam, CHP, PhD

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