Re: Gy and Sv = J/kg

["Spell, Bill" <bills@deq.state.la.us>]

I wish I knew who sent this response.  It is SO logical.  Thanks for 
reminding us of the law of conservation of energy.  It's not been broken 
yet, to my knowledge.

Bill Spell
bills@deq.state.la.us

 ----------
From: radsafe
To: Multiple recipients of list
Subject: Re: Gy and Sv = J/kg
Date: Saturday, October 05, 1996 8:49PM

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.