1. After pipetting the standard solution to the mark, weigh again and calculate the exact volume of standard solution in the pipette.

  2. Transfer the standard solution into 1M HCl solution contained in the calibrating sample container. Rinse the pipette with the solution a few times, and the solution is thoroughly mixed.

  3. Perform radioactivity measurements, as described in Appendix C, at various distances from the detector.

  4. According to the procedure described in Appendix C, gamma-ray efficiency calibration curves can be obtained for each sample counted at various distances.

  5. Alternatively, a standard point source is counted at the same positions, and the ratios of activities in the point source to that in the liquid standard solution can be calculated. The geometric correction factors (relative to the point source) can be obtained for the gamma rays in various sample sizes counted at various positions.

D.4 CALIBRATION OF FILTER PAPERS

Two popular sizes of filters, 47 mm and 1-in. diameters, are generally used in radiochemical measurements. It should be noted that the actual area on the filter covered by solid samples are significantly smaller than the filter.

D.4.1 Preparation of Standard Disc Sources

  1. By using a calibrated micropipette (preferred 100 or 200 μL) carefully pipet the standard solution to the mark.

  2. On a filter paper, draw a cycle to be wetted by the standard solution. Place the paper on a sheet of plastic wrap.



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