Answer to Question #2779 Submitted to "Ask the Experts"

The sievert (Sv) is the System International or SI unit for dose equivalent (H). The rem is the same, but is an older conventional unit still used at an operational level here in the United States. To address your question, 1 Sv = 100 rem.

When converting units be careful of the "prefix" or "symbol" on the unit, i.e., "M" for mega, "m" for "milli," "μ" for "micro," etc. A prefix, or its symbol, connotes a certain order of magnitude with the numerical value shown. For example, milli implies one thousandth, thus, 1 mSv = 0.001 Sv, and micro one millionth, 1 μSv = 0.000001 Sv. This is a convenient way to state a smaller value of a measurement quantity without having to write out a lot of zeroes, and it can be applied to any unit, e.g., μCi for microcurie, mL for milliliter, etc.

For further reading, I would recommend the annual buyers guide supplement to the journal Physics Today. This always has the recommended values for basic physical constants and a guide to metric practice. You might also look at a Frequently Asked Question on Dose Units on our website.

David J. Allard, CHP