Re: rem vs. rad -Reply

["J. J. Rozental" <josrozen@netmedia.net.il>]

ICRP 60 uses the fundamental principles laid down in ICRP 27. However
certain coefficients have changed, especially the weighting factors for
neutrons and for certain organs.

        In a practical point of view, the average dose absorbed, averaged
for the tissue or the organ (DT for Dose Tissue or Organ) is used as an
indicator of the probability of stochastic effects which are considered as
linearly  dose dependant. Such an approximation is acceptable for a limited
dose range. It is not valid for the deterministic effects, except in the
case of a homogeneous irradiation.

        There are therefore two notions:

D: Dose absorbed useful for the determinist effects;

DT: Dose absorbed averaged for a tissue or an organ for the stochastic effects.

Note that ICRP makes no recommendations for the limits in Gy

        The probability of stochastic effects, and of numerous biological
effects, depends not only on the dose absorbed, but also on the nature and
the energy level of the radiation concerned. ICRP 60, therefore, defines a
weighting factor applied to the nature of the radiation (WR) for the average
dose to the organ. The weighted dose thus obtained is called the equivalent
dose.
Although the main object of weighting factors is to measure the stochastic
risk, the exposure limits designed to provide protection against the
determinist effects are given in terms of the equivalent dose. Such is the
case for the limits applied to the cornea, the skin and the extremeties
(hands, feet)

 J.J. Rozental <josroznen@netmedia.net.il>       

At 06:49 PM 4/2/98 -0600, you wrote:
>Otto, et al.
>
>There is a potential for confusion here.  Rem can mean the dose in rad
multiplied
>by the radiation weighting factor or it can mean rad times radiation
weighting factor
>time tissue weighting factor.  Furthermore, the unit is the same whether
you use
>the tissue weighting factors from ICRP-26 or those from ICRP-60.  The tissue
>weighting factors are based on (better, guessed-at considering) the ICRP's
>stochastic detriment.  For any other end-point, they are even more wrong.
>
>When interested in deterministic effects, clearly there is a need to
recognize that
>some radiations are more effective than others (per unit dose) but the
radiation
>weighting factors for deterministic effects certainly are different from
those for
>stochastic affects.  This was an interesting area of study when nuclear war
was of
>greater concern but it isn't popular now.
>
>Charlie Willis
>caw@nrc.gov
>
>