[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Fwd: Re: Rn-222 in water analysis
Information from radch-l which may be of interest to some on this list ..
>X-Mailer: Microsoft Outlook Express 6.00.2600.0000
>Date: Tue, 14 May 2002 16:06:58 -0600
>Reply-To: liste de distribution pour les RADIOCHIMISTEs <RADCH-L@in2p3.fr>,
> Barry Stewart <bstewart@cemrc.org>
>Sender: liste de distribution pour les RADIOCHIMISTEs <RADCH-L@in2p3.fr>
>From: Barry Stewart <bstewart@cemrc.org>
>Subject: Re: Rn-222 in water analysis
>Comments: To: "Ewing, Judy" <jewing@SLD.STATE.NM.US>
>To: RADCH-L@in2p3.fr
>
>Hi, Judy,
>
>Allow me to offer a suggestion which served us well when I was at ASU and we
>were determining radon in water by LSC. Most would agree that there are
>instability problems associated with long-term storage of LSC standards, so
>we found a way to avoid having to do that. Briefly, what we did was sorb
>the Ra-226 onto cation resin which was contained in a known volume and
>sealed with no headspace. This releases the radon into the water, providing
>(after secular equilibrium) water standards of radon. There is no
>deteoriation of such samples. Details are given below if you are
>interested.
>
>First, place one gram of Dowex-50 cation resin (50-100 mesh) into a glass
>VOA-type vial using a teflon-lined cap instead of a septum cap. Weigh to
>obtain the tare weight of vial, plus resin, plus cap. Then fill the vial
>completely full (no headspace) with DI water, cap, dry any water on the
>outside, and weigh. The net weight corrected for density will give the free
>volume of the vial. Now carefully decant about half of the water.
>
>Next, add a weighed aliquot of NIST Ra-226 standard and mix for a few
>minutes to ensure that the radium is sorbed onto the resin. Then fill the
>vial with DI water until it overflows, and cap it. Make sure there is no
>headspace. Set the standard aside for 30 days to allow secular equilibrium
>between Ra-226 and Rn-222. Ra-226 is bound by the resin, but the radon is
>released into the water. From the volume of the vial and the amount of
>Ra-226 standard added, calculate the radon concentration (in whatever units
>you choose). When equilibrated, you will have a standard solution of radon
>in water that will exactly match your samples.
>
>After an aliquot is removed from the vial, top off again with DI water and
>set aside for 30 days to re-establish equilibrium. Prepare enough of these
>standards so that you have enough for initial calibration, plus the number
>of QC samples you would use daily. But you must keep good records so that
>you always know for each vial the exact condition with respect to secular
>equilibrium.
>
>As long as you do not lose any of the resin, the standard will be stable
>indefinitely.
>
>Barry Stewart
>Associate Scientist
>Carlsbad Environmental Monitoring and Research Center
>1400 University Drive
>Carlsbad, NM 88220
>505-234-5543
>505-887-3051 (fax)
>
>----- Original Message -----
>From: "Ewing, Judy" <jewing@SLD.STATE.NM.US>
>To: <RADCH-L@in2p3.fr>
>Sent: Tuesday, May 14, 2002 2:40 PM
>Subject: Rn-222 in water analysis
>
>
>> Hello All,
>>
>> Greetings from sunny New Mexico, USA.
>>
>> We have been analyzing drinking water for Rn-222 by LS counting, using a
>> modified version of the Hahn and Pia method. We are having problems with
>> our efficiency standards. Over the timespan of a few months, these Rn-226
>> supported standards turn yellow in the organic Optifluor-O phase, and
>count
>> at a reduced rate. The spectrum downshifts in energy, and the individual
>> peaks become less resolved. We are constantly forced to make new
>standards
>> and/or widen the analysis window, both of which are best avoided.
>>
>> We speculated that "color quench" due to cocktail deterioration
>(atmospheric
>> or acid-induced oxidation, perhaps?) might be the cause. With this in
>mind,
>> our current set of efficiency standards were made with freshly purchased
>and
>> opened Optifluor-O cocktail, a fresh DI water dilution of a new NIST
>Ra-226
>> SRM, and no added acid. These standards were put into service in October
>of
>> 2001, and our efficiency factor has steadily decreased from 6.8 CPM/pCi to
>> 6.2 CPM/pCi (1 sigma uncertainty at 0.06 CPM/pCi). There has been no
>> spectrum downshift, and no visible yellowing of the organic layer,
>however.
>> Still, the CPM/pCi ratio continues to decline.
>>
>> Has anyone else experienced this problem? Does anyone have a possible
>> explanation? Any ideas or suggestions as to what we can do about it?
>>
>> Thank you in advance.
>> JL Ewing
>> Analyst
>> Radiochem Section
>> Scientific Lab Division
>> NM State Dept. of Health
>>
>
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=
Jean-Charles ABBE
Délégation CNRS
IRCCyN
1, Rue de la Noë
BP 92101
44321 Nantes cedex 3
Tel : 02 51 12 45 16
Fax : 02 51 81 05 77
************************************************************************
You are currently subscribed to the Radsafe mailing list. To unsubscribe,
send an e-mail to Majordomo@list.vanderbilt.edu Put the text "unsubscribe
radsafe" (no quote marks) in the body of the e-mail, with no subject line.
You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/