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Re: Fwd:RE: Question RE <Working Level>
I'm not so sure about the strange units... I think that 4 WLM equals 5
REM. It was set up this way to track the exposure of uranium miners per quater.
Mike Dempsey
At 11:24 AM 1/12/99 -0600, you wrote:
>I agree with you on the Robley Evans article; it is one of my favorite
>references on the subject of radon. The full reference is "Engineers'
Guide to
>the Elementary Behavior of Radon Daughters," Health Physics 17:229-252,
>1969. In
>Evans' article it states that "the WL unit was introduced in 1957 by the USPHS
>.." and that it is a term employed in the United States and Canada. Leave it
>to us Americans once again to develop strange non-SI units and try to inflict
>them on everyone else!
>
>ICRP 32 and ICRP 47 are also good references to have on the shelf.
>
>> I would hate to think that a WLM to dose conversion factor would be based
>on a
>negotiation, but strange things happen. <
>
>Me too, Charlie. When I started working here we used 1000 mrem/WLM & 330
>mrem/WLM for Rn-222 and Rn-220, respectively -- now it's 1250 mrem/WLM & 420
>mrem/WLM. But that's DOE; I'm not sure what others assume.
>
>Elizabeth Algutifan,
>Environmental Health Physicist
>Elizabeth_Algutifan@wssrap-host.wssrap.com
>
>
>____________________Forward Header_____________________
>Subject: RE: Question RE <Working Level>
>Author: <radsafe@romulus.ehs.uiuc.edu>
>Date: 1/12/99 10:32 AM
>
>The dosimetry of radon-222 and its progeny is one of the most complex
>problems in radiation protection. In spite of much research, it has never
>been unequivocally solved. Radon is simply a radioisotope generator. The
>short lived progeny of radon deliver the dose. How much dose and where it
>is delivered depend on many factors such as the concentrations of daughters
>inhaled, aerosol particle size distribution, free ion fraction of the
>progeny, how the progeny are inhaled (nose vs mouth breathing), etc.
>Correlation of dose with radon concentration is further complicated by the
>deposition (plate out) of progeny on surfaces - particularly
>electrostatically charged surfaces.
>The literature is full of references on this subject, but some of the more
>useful ones may be NCRP 78, FRC Report 8, and a very useful article by R. D.
>Evans with a title something like "An Engineer's Guide to the Behavior of
>Radon Daughters" in Health Physics journal in the mid 1970s.
>The Evans article gives an excellent derivation of the working level (WL).
>The key to the derivation is that the WL is defined as "ANY concentration of
>short lived radon daughters in one liter of air that can produce an emission
>of 130,000 MeV of POTENTIAL alpha energy." A quick "do it yourself" guide
>to deriving the 130,000 is as follows: (1) Calculate the number of atoms of
>Po-218, Pb-214, Bi-214, and Po-214 when each is present at 100 pCi of
>activity. (2) Calculate the total POTENTIAL alpha energy contributed by
>each of these four: (a) Multiply Po-218 atoms by the sum of Po-218 and
>Po-214 alpha energies per disintegration and (b) multiply Pb-214, Bi-214,
>and Po-214 atoms by the Po-214 alpha energy. (3) Sum the total products
>obtained in (2) and round to two significant figures.
>Short-term, real-time measurements of airborne progeny have been made by
>many techniques for counting air filters including multiple alpha counts,
>alpha spectroscopy, alpha and beta counting, and various combinations of
>these.
>This message is much longer than I intended, but this is a complex subject
>that has defied simple answers. Hope this helps.
>Bill Goldsmith
>Wagoldsmith@mindspring.com
>
>-----Original Message-----
>From: radsafe@romulus.ehs.uiuc.edu
[mailto:radsafe@romulus.ehs.uiuc.edu]
>On
>Behalf Of Ivor Surveyor
>Sent: Tuesday, January 12, 1999 2:47 AM
>To: Multiple recipients of list
>Subject: Question RE <Working Level>
>
>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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