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09 February 2010

Answer to Question #144 Submitted to "Ask the Experts"

Category: Doses and Dose Calculations — Internal dose calculations

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

I understand that the average person receives approximately 360 rem of radiation per year. If you drink 2 litres of water per day that has approx 5 pCi of radium 226 and 228 per liter, for a period of 70 years, you would have a 1 in 10,000 chance of develping some form of cancer. My question to you is how much radium is 5 pCi per liter when compared to 1 rem or how many pCi would equal a rem?

When a person drinks 2 L of water containing 5 pCi of ²²⁶Ra, the internal dose received by the person will increase with time. This is a chronic intake case, with daily ingestion intake of 10 pCi ²²⁶Ra. A calculation using the CINDY internal dosimetry program gives the following results:

Accumulative dose at the end of the 1st year (or 1st year annual dose): 0.27 mrem.
Accumulative dose at the end of the 2nd year (sum of 1st and 2nd year annual doses): 0.88 mrem.
Accumulative dose at the end of the 5th year: 4.4 mrem.
Accumulative dose at the end of the 10th year: 13 mrem.
Accumulative dose at the end of the 30th year: 73 mrem.

Compared to the average annual dose of 360 mrem from natural (300 mrem, with 200 mrem from radon) and man-made background (60 mrem, medical & industrial exposures), the dose caused by drinking 2 L of water containing 5 pCi ²²⁶Ra per liter is insignificant.Chuan-Fu Wu, Ph.D., CHP

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