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Conversion of Exposure to Dose

In recent messages, some people in converting from the "old" units to SI 

units assume a one-to-one relationship between exposure in R and rem (or 

0.01 Sv).  For example, an instrument reading an exposure rate of 100 mR/h 

is stated as being the same as 100 mrem/h or  1 mSv/h - this is incorrect.



The conversion depends on the gamma energy and irradiation geometry because 

of self-shielding by the body.  For example, for gamma radiation from 

uranium-series radionuclides in the ground, the relationship is 

approximately 100 mR/h = 60 mrem/h = 0.6 mSv/h, where the mrem and 

mSv  units are effective whole body doses i.e. the doses that are usually 

cited in regulated radiation limits.



Survey meters that read in units of mrem/h or mSv/h often don't make this 

distinction.   In fact, they can't for all circumstances.  At best, they 

can give tissue equivalent dose rate (e.g. plastic detectors), but not  the 

effective whole body dose.





Leo M. Lowe, Ph.D.

Principal, Senior Health and

Environmental Physicist



SENES Consultants Limited

121 Granton Drive, Unit 12

Richmond Hill, Ontario

Canada L4B 3N4

Tel:    (905) 764-9380

Fax:    (905) 764-9386

e-mail: llowe@senes.on.ca

WWW:    www.senes.on.ca



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