Alpha particles and protons from charged particle accelerators and photons from both x-ray tubes and radioactive sources have been shown to be useful for the excitation of characteristic x-rays for multi-element energy dispersive trace analysis of environmental samples to the few ppm range. We have investigated the use of 4.5 MeV alpha particles from a thin window Po-210 source of 5 mCi effective strength to directly excite x-rays from trace elements in 1 cc water samples evaporated on 1.75 mg/cm2 thick mylar backings in a helium atmosphere in a lucite enclosure. Minimum detectable amounts (MDA's) were established for 19 elements (22 ≤ Z ≤ 82) using K-, L- and M- radiation and 50 minute counting times. The smallest MDA determined was 0.11 μg for vanadium. Other representative MDA's, in μg, are Fe-0.54, Mo-0.31 and Pb-0.43. MDA's lower by an average factor of about 10 over an eight month source life would result from the use of 1 Ci of Po-210 for 50 minutes per sample. Thinner sample backings and improved source encapsulation will reduce background radiation and further improve sensitivity. Comparison of our MDA's (5 mCi-Po-210) with those of Blasius et al., who used radiophoton sources and 40,000 sec. counting times to determine trace metal pollutants in water samples, shows radioalpha excitation to have comparable sensitivity in the worst case, arsenic and better, by more than two orders of magnitude, sensitivity in the best case, vanadium.
Radioalpha induced x-ray trace element analysis offers the same advantages of portability, ease of operation, low maintenance and cost, and "in house" availability as radiophoton induced analysis. Because of the availability of more intense sources (up to 10 Ci), the fact that the detected radiation (x-rays) differs from the excitation radiation (a-particles) and that K, L, and M x-ray emission cross-sections depend essentially only on the emitted x-ray energy, lower MDA's are obtainable for many elements in thin samples for comparable counting times, as well.