[ RadSafe ] SI Purists

Philip Simpson phils at umich.edu
Mon Mar 28 19:41:04 CDT 2011

I have been reading the "traditional vs. SI units"  thread with amusement for the past couple of weeks. Having worked at a research reactor for 30+ years here's my two pence worth.

First a nit to pick:  If we're doing SI lets get it right!  When using Gy and Sv, then dose rate and exposure rates should be always be given in units Gy/s and Sv/s. Otherwise we have mixed units in the same number (hours and seconds) and, if I remember my Chemistry 113 instructor correctly, that's a no-no in SI.

Trading Rad and Rem for Gy and Sv are not like coming to terms with Ci or Bq - the last definition I saw for a Rad had it based on the metric system just like the Gy. Why trade 100 ergs for 1000 g? Just to make it fit nicely into the mks system versus the cgs system? The mks system may work fine for a car crashing into a barrier or, a little closer to home, that Pb brick you just pinched your finger with, but it stinks for radiation measurements.

Call me a troglodyte but, life sure was easy when the annual exposure limit was 5 Rem as opposed to 50mSv.  It was a simple rule-of -thumb that I could work all day, every day (8 hour days) in a 1 mR/hr gamma field and not come close to exceeding the dose limits. (My RSO, however,  would probably question my monthly exposure readings.) Likewise, I sure better stop, step back, and think about things when I pull a sample out of the pool and my ion chamber (held at arms length) passes 1 R/hr.  After all, only 5 hours exposure and I'm at the annual dose limit!

For me, nice round numbers such as 5 Rem and 1 mRem/hr are a lot easier to instantly recognize, understand and conceptualize than 0.05 Sv, 50 mSv, 10 µSv, etc. The Rad and Rem are "ergonomic".  The Gy and Sv are not.  Maybe it is just teaching and training but I'm not so sure. 

Will I work with the Gy and Sv? Yes, because I am forced to by the rest of the World.  But, I won't apologize for preferring the Rad and Rem. There are circumstances where the American way is the better way.

Phil Simpson, Assistant Mgr.(Ret.)
University of Michigan
Ford Nuclear Reactor

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