Fig. 7.
Alpha-particle spectra from the isotope dilution analysis. Upper trace: typical spectrum for an unspiked natural uranium electrodeposited source, showing the peaks for 238U and 234U, along with that for the weaker 235U. Lower trace: typical spectrum for a natural uranium electrodeposited source spiked with 232U tracer (following chemical purification to remove the 228Th daughter of 232U). Both spectra were accumulated for about 1.71 d with planar ion-implanted silicon detectors. No impurities were detected.