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Answer to Question #3142 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Personnel Monitoring (PM)

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

How do you convert a rad to a rem? I am working on putting together a comparison list for radiation exposure to pregnant women during radiology procedures and find different studies list rad results and others list results in rem. I appreciate any help on this matter.

The older quantity and unit of radiation exposure (ionization in dry air) is the "roentgen" (R), where 1 R is equal to 2.58 × 10-4. The older quantity and unit of absorbed dose is the "rad," where 1 rad = 0.01 J/kg. The material absorbing the radiation can be tissue or any other medium (for example, air, water, lead shielding, etc.). To convert absorbed dose to dose equivalent, or "rem," where we now consider the biological effects in man, one modifies with a quality factor. For practical scenarios, with low "linear energy transfer" (LET) radiation such as gamma or x rays, 1 R = 1 rad = 1 rem.

You should be aware that today we use the "System International" (SI) of quantities and units. Exposure is now referenced to "air kerma," absorbed dose to gray (Gy), and dose equivalent to the sievert (Sv). 1 Gy = 100 rad, and 1 Sv = 100 rem.

See the Radiation Basics and other Q&A; on our ATE website, and other questions and answers specific to Pregnancy & Radiation. This should be of help with the comparison of radiation doses for various diagnostic procedures.

David J. Allard, CHP

Answer posted on 11 November 2003. The information and material posted on this website 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 Website. 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.
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