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. Author manuscript; available in PMC: 2017 Aug 1.
Published in final edited form as: J Environ Radioact. 2014 Mar 28;134:66–74. doi: 10.1016/j.jenvrad.2014.02.010

Fig. 4.

Fig. 4

Alpha-spectra of the Th fraction obtained in the analysis of carbonate samples from Lake Bonneville. The carbonates were acid digested to allow leaching of the actinides. Electrodeposited sources were made and counted via alpha-spectroscopy for 168 h. The resulting spectrum shows natural Th (232Th, 3.9 MeV; 230Th, 4.6 MeV) and tracer (228Th, 5.4 MeV) isotopes with a resolution FWHM of 31 keV. Over the course of this time frame, 228Th decay products approached secular equilibrium due to their short half lives. The arrow shows the absence of a peak at 4.2 MeV corresponding to 238U, further demonstrating the absence of U contamination. The 230Th activity was used for age determination of the samples by isotope dilution alpha-spectroscopic principles.