Re: Pronunciations of SI prefixes: kilo and giga; Unit Plurals

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

Wade --

The quantities 'absorbed dose', expressed in units of gray, and 'dose
equivalent', expressed in units of Sv, are different although they may have
the same magnitude of energy absorption per unit mass (ie J/kg).  Absorbed
dose and kerma are defined in terms of energy deposition per unit mass,
while dose equivalent is defined as the product of absorbed dose and certain
dimensionless modifying factors which take into account the biological
response.  From a health physics standpoint, biological response is what
it's all about; dose equivalent is not a physical quantity although it has
physical dimensions of J/kg.

Philosophically, I agree with your point that measurement of physical
quantities is best.  In a more ideal world, we could make a physical
measurement and apply it directly to biological response. But people being
what they are, it is necessary to account for biological response.  One
alternative would be to specify what produced the dose insead of using a
made up risk based quantity.  There are, as you know, numerous problems with
the definition and use of the dose equivalent quantity.  But I don't think
replacing dose equivalent with a straight energy based measurement (ie
quantity) will benefit our health physics community in achieving protection
of people, although I would be willing to listen to any ideas you may have
in this regard.

Warmest regards,

Ron

    >Ron:
>You're correct when you say "I note that the dose equivalent quantities
>as expressed in rem and Sv are not necessarily numerically equal to
>J/kg."
>But, the fact remains that they are DEFINED as being equal to 1 j/kg.
>As is the Gy.
>I maintain that measurements should be made in physical units; flux as a
>function of energy. That way everyone would always understand what the
>numbers mean.
>We keep trying to create a dosimetric system that is proportional to
>risk. We've gone from r to rad to rem to Gy to Sv and we're still no
>closer. As you say, "dose equivalent is not a physical quantity per se."
>Until we make measurements in physical units we're just spinning our
>wheels.
>Best wishes,
>Wade
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