EXPRESS DETERMINATION OF SR90 IN DIFFERENT OBJECTS WITH DICYCLOHEXYL18CROWN6 DCH18C6 A. Burak1, H. F

1
EXPRESS DETERMINATION OF SR-90 IN DIFFERENT
OBJECTS WITH DICYCLOHEXYL-18-CROWN-6 (DCH18C6)
A. Burak1, H. Fischer1, O. Bilan2, E. Rudak2, O.
Yachnik21 University of Bremen , Institute of
Environmental Physics, Bremen, Germany 2
Institute of Physic of the National Academy of
Sciences of Belarus, Minsk, Belarus
Introduction
To determine strontium losses and a chemical
yield, tests were made using the radionuclide
Sr-85 as a tracer. Sr-85 was registered by gamma
spectroscopy, using a HPGe detector of 50
relative efficiency and having resolution of
2.4keV at 1.33MeV.For registration of Sr-90 a
Liquid Scintillation Analyzer (Tri-Carb 2800TR)
was used. Results of these investigations are
given below.
The present method is worked out for Sr-90
determination in objects of different origin,
especially in agricultural production, cattle
production, and food. The scientific bases of the
most exact and express method of definition of
the Sr-90 contents in the objects of environment
were developed in GEOHI of the Russian Academy of
Science (Moscow) at once after the accident on
the Chernobyl NPP. This method was later adapted
at the Institute of Physic NAS of Belarus. Now
the method is being tested and modernized in the
Institute of Environmental Physics, University of
Bremen. During this work optimum parameters for
the given method will be determined. Also the
procedure will be tested for low activities (less
than 1 Bq).
Determination of optimal desorption temperature
Eluation curves at various temperatures
Methods
The principle of the method is based on
chromatographic extraction of strontium from
nitrate solutions followed by radiometric
determination in the liquid phase of Sr-90
activity. The main element of the method is
Sr-90 extraction from the investigated sample by
dicyclohexyl-18-crown-6 in tetrachlorethane.
Dicyclohexyl-18-crown-6 belongs to synthetic
macrocyclic polyethers (so-called crown ethers)
and has the ability to bind Sr-90 with high
selectivity so that Sr-90 is extracted with 92
97 efficiency. Crown ethers are available in a
variety of sizes and are named according to the
number of atoms in the ring. For example,
18-crown-6 derives its name from the 6 oxygen
atoms in the 18-membered ring. The other 12 atoms
in the ring are carbon atoms. Dicyclohexyl-18-crow
n-6 has complexed a strontium ion in the image
below.
Chemicals consumption per chromatographic column
Multiple use of the chromatography column
Discussion
The present method provides considerable
reduction of time needed for measurement of a
sample (5-7 hours) in comparison to traditional
radiochemical method (up to 2 weeks). The method
may be applied to determine the Sr-90
contamination of objects and territories, which
were exposed to accidents at nuclear facilities,
buffer areas of NPP, and possible use of so
called dirty bombs.
A highly porous matrix of styrene-divinylbenzene
copolymer is used as a substrate to support the
extractant, dicyclohexyl-18-crown-6 (DCH18K6) in
tetrachloroethane, which is in the liquid state
deep in the pores of the matrix.
Conclusions

• Matrix of styrene-divinylbenzene copolymer (TVEX)
• Pore Diameter 50-500 x 10-9 m
• Spheres Diameter 0.2-0.5 mm

The stepwise investigation of the overall method
showed that significant strontium losses occur
only in acid leaching of the prepared samples and
in desorption from the chromatographic column.
Losses are considerably reduced by use of the
method "wet combustion". Based on the results,
re-use of the chromatographic column can be
recommended only if it is known that the measured
activities of all samples in the series are
virtually equal. Detection limits depend both on
the chemical steps and the quality of the
radiometer. The basic technical parameters of the
method are presented in the table.
Results
The main stages of the method are
The short-scheme of the method

• Sample preparation. The method of wet combustion
  of the samples by aquafortis, filtering and final
  correction of the nitric acid concentration to
  1.5 M of obtained solutions are used.
• Preparation of selective sorbent, extract
  eluation trough a column, strontium desorption.
• Radiometric measurement is performed in the
  liquid phase using liquid scintillators.

References

• M. Hiraoka. Crown Compounds. Their
  characteristics and applications. Elsevier, New
  York (1992)
• N.Yu. Kremlyakova. The Determination of
  Radiostrontium in Environmental Objects by
  Extraction Chromatography Using
  TVEX-DCH18C6.//J.Radional. Nucl Chem. Articles,
  V.170, 186-194 (1993)
• S. Zablotsky, E. Rudak, L. Stopolyanskaya, J.
  Wiley. Improvements in the method of Sr-90
  extraction from environmental samples with
  dicyclohexyl-18-crown-6. Kerntechnik, V.60,
  262-264 (1995).