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Analysis of 125I by gamma spectrometry
The procedure for 125I analysis using gamma spectrometry and a
multichannel analyser is as follows:
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FIG. 94. The photon-photon coincidence method spectrum of I25I. The 35.5 keVgamma ray of 125I is 93% converted. Intense production of tellurium X rays shown as two peaks at 27.5 and 3I.3 keV in the spectrum. Sum coincidence peaks are also shown (between 50 and 65 keV). |
(1) Filter the brine sample (1 L) by using 0.45 pm pore size filter paper.
(2) Adjust to pH6-7 by adding HCL or Na2CO3.
(3) Prepare an anion exchanger column with diameter 5 mm and 100 mm length (various resins are available commercially, e. g. Dowex 1, BioRad 1). Mesh size can be 80-100, and cross-linking x8.
(4) Percolate the solution through the column at a slow rate (a few millilitres per minute).
(5) Seal the column at both ends.
(6) Count the column in a detector set-up (preferably a well-type HPGE detector) connected to the multichannel analyser multichannel analyser by the gamma-gamma (photon-photon) coincidence method, where the sum coincidence between the X rays and between the X ray and the gamma ray are measured.
A photon spectrum from the use of the photon-photon (sum) coincidence method is shown in Fig. 94.
Appendix IV