Question RE <Working Level>

[Ivor Surveyor <isurveyor@vianet.net.au>]

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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