Re: Question RE <Working Level>

[Khalid Aleissa <kaleissa@kacst.edu.sa>]

I just want to atteract your attention that there is a difference between
measuring radon and radon progeny. Radon progeny are the major health concern
issue and the WL unit is related to it directly, however, most of the
conversion factors assume a value of an equilibrium factor of one between radon
and its progeny which is not always true (some where between 0.1- 0.8 depends
on different parameters, e.g., existance of smoke or dust in the air).

Ivor Surveyor wrote:

> Dear Radsafe,
>
> I wonder if anybody be kind enough to help me with some questions on the
> definition of <working level>.
>
> Epidemiological studies on Radon and its progeny use a unit called <working
> level>.
>
> I understand that is a historical unit, but is still very much favored by
> some epidemiologists.
>
> I am interested to know the origin of the unit.
> How did the definition 1.3 x 10E5 Mev/L of alpha energy arise?
> How did the original workers measure this quantity? Or intend it to be
> measured?
> Is it necessary to assume a form of secular equilibrium between  radon and
> its progeny in order to use the unit?
>
> I read that 1 WL corresponds to a Rn-222 concentration of approximately
> 100pCi/l or 3.7Bq/l, and/or 7.5 pCi/ or 277mBq/l of Rn-220.  Are these neat
> conversions just a coincidence?
>
> I have also read 1 WLM corresponds to an  equivalent dose  of 10 mSv, but
> the Olympic Dam mine in South Australia uses the conversion 1 WLM = 5 mSv.
> ICRP 90 (B126) page 138. Points out that the complex relationship between
> dose to target tissue and concentration in WLM. Matters such as the
> aerodynamics of particles, breathing patterns and biological characteristic
> of lungs, the lung model used etc.
> I note that ICRP gives  a conversion to the tracheobronchial region of
> between 4 to 13 mGy per WLM.
>
> This raises two further questions.
>
> In any given industrial site is the conversion of WLM to equivalent dose a
> compromise based on management, worker negotiation?
>
> Is variation in conversion from WLM to mSv a problem in comparing findings
> from different epidemiological sources?
>
> I hope these question are not considered to be too simplistic.
>
> Ivor Surveyor           [isurveyor@vianet.net.au]
> Emeritus Consultant Physician,
> Department of Nuclear Medicine
> Royal Perth Hospital.
>
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--
Khalid Aleissa, Ph.D.
224B, Institute of Atomic Energy Research
King Abdulaziz City for Science and Technology
P. O. Box 6086
Riyadh 11442
Saudi Arabia
Tel (+9661) 481-3617
Fax. (+9661) 481-3887
e-mail: kaleissa@kacst.edu.sa


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