Re: Gy and Sv = J/kg

[rkathren@tricity.wsu.edu (Ron L. Kathren)]

I believe Jack Couch has the right perspective, and Danial Gollnick the
proper practical approach in using the Sv/Gy concept.  I too have used this
same concept, but always with the caveat that it is not the 'official' word.
In any case, it does not change the physical dimensions of the Sv.  Just why
those on the learned committees don't accept or allow this very practical
and logical clarification would be an interesting topic for discussion.
Perhaps there were no operational HP's on the standards body!

Ron Kathren

  G>In article  rkathren@tricity.wsu.edu (Ron L. Kathren) writes:
>>Sorry to question my old (but not elderly!) mentor Wade Patterson, but I
>>note that the dose equivalent quantities as expressed in rem and Sv are not
>>necessarily numerically equal to J/kg. The equality only holds for absorbed 
>>dose.
><snip>
>
>Louis Iselin:
>I must disagree.  Wade has expressed an idea that I have been uncomfortable 
>with ever since I was introducted to dosimetry units in Chuck Roessler's 
>Radiation Dosimetry class.
>
>In all of science, except for health physics, when a quantity is mulitplied by 
>a conversion factor that changes the units, the conversion factor has units of 
>its own that tell you how the original quantity will be modified.  Only the Gy 
>to Sv conversion is different.  Stupid might be a better description.
><snip>
>
>There are other examples, such as Circumference = 2 pi Radius. Looked 
>at dimensionally, one concludes that 6.28 m = 1 m (a mathematical 
>absurdity) for a radius of 1 m. Not unlike the way we say 20 J/kg = 1 J/kg 
>for a Q of 20 in the familiar H = QD.  
>
>In the first case, we invent the radian to be the (dimensionless) ratio 
>of circumference-to-radius for a circle, which is numerically 2 pi. By 
>analogy, the dimensionless ratio of H-to-D is the numerical value we assign 
>to Q. I don't know why we (I include myself) are uncomfortable with 
>H = QD but perfectly at ease with C = 2 pi R. Maybe its because we 
>have the word "radian" to cling to. 
>
>David Golnick* offers a nice solution to those (including my students) 
>who agonize over this point. He endows Q with the "units" Sv/Gy, which 
>is of course dimensionless (like the radian associated with 2 pi). My 
>students like multiplying 5 Gy by 20 Sv/Gy to get H = 100 Sv. This 
>of course breaks both with tradition and the formal definition of Q, 
>where Q carries no units.
>
>*Ref. Basic Radiation Protection Technology, 3rd edition (Pacific 
>Radiation Corporation, Altadena, CA, 1994).
>
>This issue was discussed at length through an exchange of letters in the 
>HP Newsletter about a decade ago. As I recall, the letters were very 
>informative. Maybe someone on the list can cite the references. 
>
>Jack Couch
>Bloomsburg University
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