Re: Gy and Sv = J/kg

[integray@ix.netcom.com]

I gave this to Charlie Meinhold in 1990 after reading the draft of ICRP 
Publication 60 (remember "effectance?"):

A DIMENSIONLESS Q OR wR VIOLATES CONSERVATION OF ENERGY

	The ICRU, ICRP, CGPM, and NIST must abandon the nonsense that Q and wR 
are dimensionless.  

	The claim by the ICRP and the ICRU that both the gray and the sievert have 
dimensions of J/kg results in 20 J/kg = 1 J/kg when alpha particles are in question, 
since 1 Gy = 20 Sv.  Merely claiming loudly and repeatedly that Q is a dimensionless 
weighting factor does not avoid the logical trap of creating energy from nothingness 
by using a committee-generated multiplying factor.

	Consider the analogous example of liters (L) of fuel and kilometers (km) of 
distance traveled by an automobile.  Suppose we have a standard, reference automobile 
that travels 10 km/L, and a new, improved model that travels 20 km/L of fuel burned.  
When we perform an experiment by putting 10 L of fuel in each car, the cars travel 
100 and 200 km, respectively.  The Relative Fuel Effectiveness, RFE, for the two cars 
is 200/100 = 2.  Clearly, the new, improved car behaves as if it were the standard 
reference car with 20 L of fuel.  But in no sense did we have 20 L of fuel in the 
new, improved car!

	Similarly, a biological system irradiated with 0.1 Gy of alpha radiation may 
behave as if it had been irradiated with 2 Gy of beta radiation, but we never had 2 
J/kg in the alpha experiment; we only had 0.1 J/kg.  We take this difference in 
biological behavior into account through the use of dose equivalent (should it be 
called dose behavior?), calling the 0.1 Gy of alpha-radiation 2 Sv.  In no physical 
sense is 2 Sv of alpha-radiation 2 J/kg.

	The ICRP and the ICRU can extricate themselves from the problem by recognizing 
dose equivalent for what it is:  a quantity that bears a special relationship to 
energy per unit mass through dimensioned weighting factors, Q (or wR), in Sv/Gy.

	How did the ICRP and the ICRU fall into this logical trap?  Quite simply, Q was 
originally taken as an average RBE for various kinds of radiations.  RBE is a ratio 
of two doses, and therefore dimensionless.  Q, however, is not a ratio, and can have 
dimensions; in fact, it must have the dimensions of Sv/Gy in order for the 
definitions of dose equivalent and effectance not to violate the well-established 
principle of conservation of energy.

	All other weighting factors are dimensionless, but Q and wR must have dimensions 
of Sv/Gy.

	Note that the inclusion of a so-called dimensionless Q in the specific effective 
energy (SEE) values in the ICRP Publications 30 and 61 methods makes the results of 
those calculations for mixed alpha-beta emitters useless when the Qs or wRs change.  
Keeping the internal dose components separated by radiation type would be a much more 
useful service to the user of the ICRP Publications.  Leave Q out of the energy terms 
weighted by absorption fractions (call them, perhaps, absorbed energies) and tabulate 
them separately by radiation type.