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RE: High Dissolved Solids
Lee-
I worked for quite a while at a facility that dealt with a great deal of
uranium. We were permitted to discharge certain wastes to the nearby river,
after passing the waste stream through our own wastewater treatment facility
and receiving acceptable analysis results for numerous non-radiological
parameters and gross alpha-beta activity. We would weigh a planchette,
evaporate 5 ml of the wastewater solution onto the 2 inch planchette, fix
the material by plating then reweigh the planchette and count the sample on
a gas flow proportional counter (having a thin foil type window). We
encountered a wide range of dissolved solids, typically between 20 and 150
mg per planchette, after plating. Obviously we had media absorption
problems. Reducing the volume plated was unacceptable (MDA issues) so we
developed media absorption curves.
Essentially this is what we did. We knew the radionuclides that would be
encountered and had standard solutions of the material. We knew the general
composition of typical dissolved solids at our facility and made up
simulated wastewater solids. Thusly, we made up a series of planchettes,
each with the same activity of uranium standard solution, having variable
masses of simulated solids from 0 to 200 mg total mass. We also planchetted
a control with no uranium solution but some mass of simulated solids to
verify that the solids had no significant radioactive component.
The evaporation, plating, weighing, counting, etc. were all as per our
normal methodology. Having the counting data and material mass, we were
able to determine % absorption and thus a media absorption factor as a
function of density thickness of plated solids. We plotted the resultant
factors to density thickness and thereafter applied sample specific
absorption correction factors to adjust our counting data to account for
media absorption (separate graphs for alpha and for beta). One thing we
found somewhat surprising was how significant the beta absorption was
(primarily Tc-99, sometimes Th-234, enrichment dependent). Beta absorption
may be very significant where low energy beta emitters are present and is
sometimes overlooked. Also, where lower energy beta activity is present it
is important to carefully consider the radionuclide (s) used to determine
counting efficiency. There is too often a tendency to simply use the old
standby, Sr/Y-90 to determine beta counting efficiency and this will yield
underestimations of beta activity if low activity beta emitters are of
significance in the samples being counted (regardless of compounding factors
such as media absorption).
Hope this is helpful.
Martin J. Brennan
SNL
mbrenn@sandia.gov
-----Original Message-----
From: Lee McCoy [mailto:mccoy@tcsinternet.net]
Sent: April 12, 2000 3:26 AM
To: Multiple recipients of list
Subject: High Desolved Solids
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Does anyone know of a method for reducing the residual mass of a high =
dissolved solid sample for gross alpha beta analysis?=20
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