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Re: ANNUAL DOSE, DOSERATE and the MAXIMUM INDIVIDUAL
The term limit should only be used for a criterion that must not be
exceeded.
Many countries adopt the derived limit: A limit on a measurable quantity
set, on the basis of a model, such that compliance with the derived limit
may be assumed to ensure compliance with a primary limit.
The ICRP limit of 1mSv is the total dose which should arise from all
man-made sources of radiation exposure (excluding medical procedures).
Dose limits for skin and lens of the eye are 50 mSv and 15 mSv per year,
respectively.
If you are interested I can send by e-mail a resume in power point of the
ICRP 60, interesting to explain the System.
Jose Julio Rozental
jrozental@hotmail.com
Madrid, until 2-10-2002
>From: Quintino De Notariis <qdenotariis@novacon.it>
>Reply-To: Quintino De Notariis <qdenotariis@novacon.it>
>To: <radsafe@list.vanderbilt.edu>
>Subject: ANNUAL DOSE, DOSERATE and the MAXIMUM INDIVIDUAL
>Date: Wed, 11 Sep 2002 15:34:13 +0200
>
>If the ANNUAL dose limit for the public is an EFFECTIVE DOSE (ED) of 1
>mSv/year, why some radsafers seem to take for granted that this IMPLIES a
>DOSERATE limit of 0,114 microSv/h (1000 microSv/year x 8760 hours/year) ?
>
>So if, for example, in an X-ray facility we MEASURE 0,200 microSv/h above
>the background in correspondence of a door on an alley with a very limited
>or no time occupancy by members of the public (say, ONLY 1 hour/year),
>should we conclude that that facility is out of low, no matter that the
>total ED in a year would be ONLY 0,200 x 1 = 0,200 microSv ?
>
>Regulations give an ANNUAL dose limit NOT a DOSERATE limit.
>
>Somewere I've read that requiring the limit of 0,114 microSv/h INSTEAD of 1
>mSv/year is the consequence of the hypothesis of the "MAXIMUM INDIVIDUAL"
>(that's to say, a person who stays behind that door 24 hours a day for 365
>days = 8760 hours/year).
>Isn't this hypothesis absurd? Shouln't we consider the EXPECTED TIME
>OCCUPANCY? Or are we about to apply the LNT even to dead matter?
>
>Another related question :
>I don't think that one could MEASURE EFFECTIVE DOSE with an instrument,
>because of the definition of ED through the tissue weighting factor WT :
> ED = … WTxHT
>where HT is the equivalent dose to tissue or organ T.
>ONLY in the circumstance of UNIFORM irradiation of the body we can say that
>ED and H values coincide :
> ED = H
>where H is the equivalent dose to the body uniformly irradiated (… WT = 1).
>If PARTS of the body are striked by radiation we have
> ED < HT
>So, if we read 0,200 microSv/h Equivalent Dose above the background at the
>level of the lungs (WT=0,12), even in the hypothesis of the maximum
>individual we don't exceed 0,114 Effective Dose, because
> 0,200 x 0,12 = 0,024 microSv/h.
>In conclusion, we shouldn't take it for granted that a doserate > 0,114
>microSv/h above the background could mean that we have exceeded the annual
>limit of 1 mSv/year, because we should consider not only the EXPECTED TIME
>OCCUPANCY by the members of the public IN A YEAR but also the GEOMETRY of
>the irradiation (uniformity or non uniformity).
>
>Please, radsafers, help me to clarify and correct me if there is something
>that I miss.
>
>Quintino De Notariis
>Health Physicist
>
>
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