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Re: I-125 Gas Calibration Source
Mike Bohan wrote:
>
> Reply to: RE: I-125 Gas Calibration Source
>
> Carol & RadSafe,
>
> What type of filter are you using? We used to use activated charcoal paper disks in our hood monitors. The way we calibrated them, is to stack two filters on the initial use of the hood and compare the absorption ratios between the first and second filters. This gives you the first two terms in an infinite series that you can use to calculate filter efficiency.
>
> I think you would have a hard time finding a gaseous I-125 calibration source and it probably will not be in the same chemical form as the byproducts coming off the reactions in your hood anyway. Additionally, how can you be sure that the entire amount gets to the filter. You would have to assay all prefilter components, which I would imagine could introduce a number of difficulties and uncertainties into the final result.
>
> Hope this helps,
>
> <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><
> Michael J. Bohan, RSO | e-mail: mike.bohan@yale.edu
> Yale-New Haven Hospital | Tele: (203) 688-2950
> Radiological Physics | FAX: (203) 737-4252
> 20 York St. - WWW 204 | As usual, everything I say may be plausibly
> New Haven, CT 06504 | denied at my employer's convenience ...
> ><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
>
> --------------------------------------
> Date: 05/05/1998 4:00 PM
> To: Mike Bohan
> From: radsafe@romulus.ehs.uiuc.edu
> >
> >
> > We have installed a 125-I air monitor in our iodination fume hood
> > stack.
> > We would like to calibrate this in place using 125-I gast to determine
> > the system's efficiency. Does anyone know where to obtain 0.1 uCi of
> > 125-I gas?
> >
> > Carol Lentz
> >
> carol.lentz@wl.com
Hi Carol, Mike and All,
I did this experiment attempting to validate a radioiodine air sampling
system on a hood.
With the air sampling system running, I pipetted about 5 microcurie of
I-125 solution, as NaI, in about 0.1 ml aqueous solution into a small
glass dish in the hood. I then added acid (HCl?) to the dish and heated
it with a heat gun to convert the I to I2 or HI or other volatile
species. (Using a relative survey meter reading of the activity in the
dish, only about 70% of the activity volatilized!)
I then assayed the charcoal tube and calculated the average I-125 air
concentration in the hood exhaust. As I remember, there was a reasonable
agreement with the known average concentration.
It was a bit crude, but I concluded that the air sampling system was at
least not too bad.
Regards,
Wes
--
Wesley R. Van Pelt, Ph.D., CIH, CHP KF2LG
President, Van Pelt Associates, Inc.
Consulting in radiological health and safety.
mailto:VanPeltW@IDT.net
http://shell.idt.net/~vanpeltw/index.html