53 TABLE 9. Spontaneous plating of various radionuctides onto silver discs. OPM of nuclide In Solution DPM of nuclide on Disc after Platina 42 hrs.* % platina SOLUTION A 28.3 Am-24] O12 0.043 35.8 Pu-242 .046 0.13 42.8 Po-208 7.41 17.3 SOLUTION B 12500 U-232 12500 Th-228 12500 Ra-224 42.8 Po-208 N.S. N.S. 100. 0.80 27.8 0.22 8.93 20.9 * Detector efficiency was 20%, From visual observations of alpha particle spectra of the samples, a further verification of the absence of these radionuclides in the plated polonium samples was provided. In the uranium spectra, however, a peak at 5.17 MeV was consistently present (see Fig. 8). This decay energy does not correspond to that of any dominant alpha emitting decay of an isotope of uranium, and it most probably results from 2394240 Pu contamination of the sample. This smal] interference occurs, even though the plutonium decontamination factor was greater than 10°, because of the Jarge activity ratio, Pu/U, in these samples. The concentra- tions of the uranium isotopes measured were subsequently calculated from only the counts measured in the high energy portion of each uranium peak; i.e. to the region corresponding to that portion of the 232 U peak which was not sig- nificantly affected by the 239+240 Pu in the sample.