Detection and speciation of transuranium elements in synthetic groundwater via pulsed-laser excitation Page: 3 of 16
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Beitz and Hessler[11] have reviewed likely actinide detection limits using
LIF. The general field of the identification of oxidation states of ultra-trace
elements by radiation detection was recently reviewed by Guillaumont,
Chevallier, and Adloff[12].
Experimental apparatus and methods
The LPAS apparatus used in this work has been described previously [1]
Briefly, a pulsed dye laser (Lambda Physik FL3002 dye laser pumped by an EMG
201 MSC 308 nm XeCI excimer laser) is used as an excitation source. Its beam
impinges on a sample solution contained in a thermostated quartz sample
cuvette. A piezoelectric transducer (PZT) in acoustic contact with the sample
cell is used to measure the amplitude of the resulting acoustic wave. A 1 cm
diameter by 61 cm long quartz rod provides both acoustic contact and thermal
isolation between the sample cell and the PZT. The output of the PZT, after
preamplification and high and low pass filtering, is fed to a differential
amplifier connected to a boxcar integrator. The gate of the boxcar is centered on
one of the first maxima in the PZT response waveform and the boxcar is used to
signal average the PZT response for a few laser pulses to several thousand
laser pulses. The dye laser energy is simultaneously recorded using a second
boxcar. The outputs of both boxcars are digitized and recorded on a computer.
The PZT response is divided by the laser energy value to obtain a normalized
PZT response. The reported LPAS spectra are the result of subtracting out the
normalized response from a solution containing only 1.00 M Na2CC>3 from the
normalized PZT response from Am^+ in 1.00 M Na2C03 solutions. The dye laser
energy used (typically 3 mj/pulse) was below that at which saturation
of the normalized PZT response was observed in Am®+ solutions.
Sample solutions were prepared using analytical reagent grade inorganic
chemicals and triply distilled water [13]. The ^^Am used in this work was
radiochemically characterized so that it could be assayed using liquid
scintillation counting. All carbonate containing solutions were stored in
preconditioned polypropylene bottles. A stock solution of 1.00 M Na2C03 was
prepared and used for preparation of Am-containing solutions. An aliquot of a
stock solution of ^1Am in nitric acid was taken to dryness by gentle heating
and the required amount of sodium carbonate stock added to it to create a
solution of 1 x 10"^ M (nominal) Am^+ concentration. This Am in 1.00 M Na2CC>3
stock solution together with the 1.00 M Na2CC>3 stock solution were used to
prepare more dilute solutions.
The Am content of the resulting solutions were measured by liquid scintillation
counting both before and after filtration through an 0.2 micron Microgon
DynaGard syringe filter. Tests based on building histograms from observed LPAS
response for each laser shot identified the Microgon DynaGard filter as
superior to other syringe filters tested in minimizing interference from
suspended particulate matter. The filtrate was used to fill high quality quartz
fluorimeter cells (1x1 cm Hellma QS) equipped with quartz tubulation. The
tubulation was sealed using a molded fluorocarbon fitting (Galtek SU8MN). This
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Beitz, J. V.; Bowers, D. L.; Doxtader, M. M.; Maroni, V. A. & Reed, D. T. Detection and speciation of transuranium elements in synthetic groundwater via pulsed-laser excitation, article, January 1, 1987; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1089912/m1/3/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.