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20 November 2009

Answer to Question #1471 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Measurements and Reporting

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

I am studying soil and groundwater contamination by thorium. Lab results for thorium concentration are expressed in ppb and norms for drinking water are in Bq/L. How can I convert ppb in Bq/L for thorium and for radionuclides in general?

An easy-to-remember conversion is the fact that for thorium 1 picocurie per gram (pCi/g) = 10 ppm. As such:

1000 pCi/L = 10 ppm
1 pCi/L = 0.01 ppm
1 pCi/L = 10 ppb (where 1 billion = 1000 million)
Given that 1 pCi = 0.037 Bq (that is, 1 Bq = 27 pCi)
1 Bq/L = 270 ppb of thorium

You can perform the same sort of calculations for natural uranium given the fact that 1 pCi/g = 3 ppm. Forgive me, but it is probably best to avoid answering the second part of your question. Performing the calculations for "radionuclides [elements?] in general" is not difficult, but it is best done by someone who has had some training and experience. A complicating issue is the fact that a given element, such as thorium, can consist of multiple nuclides (²³²Th, ²³⁰Th, etc.).

Paul Frame, CHP, PhD

Answer posted on 14 December 2001. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.