Samples of ash from the 18 May 1980 eruption of Mount St. Helens were collected from several locations in eastern Washington and Montana. The ash was subjected to a variety of analyses to determine its chemical, physical, mineralogical, and biological characteristics. Chemically, the ash samples were of dacitic composition. Particle size data showed bimodal distributions and differed considerably with location. However, all samples contained comparable amounts of particles less than 3.5 micrometers in diameter (respirable fraction). Mineralogically, the samples ranged from almost totally glassy to almost totally crystalline. Crystalline samples were dominated by plagioclase feldspar (andesine) and orthopyroxene (hypersthene), with smaller amounts of titanomagnetite and hornblende. All but one of the samples contained from less than 1 percent to 3 percent free crystalline silica (quartz, trydimite, or cristobalite) in both the bulk samples and 1 to 2 percent in the fractions smaller than 3.5 micrometers. The long-lived natural radionuclide content of the ash was comparable to that of crustal material; however, relatively large concentrations of short-lived radon daughters were present and polonium-210 content was inversely correlated with particle size. In vitro biological tests showed the ash to be nontoxic to alveolar macrophages, which are an important part of the lungs' natural clearance mechanism. On the basis of a substantial body of data that has shown a correlation between macrophage cytotoxicity and fibrogenicity of minerals, the ash is not predicted to be highly fibrogenic.

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Two unreported gamma rays of energy 0.44 and 0.49 Mev are assigned to Np 239 by reason of chemical properties and decay constant. The intensities of these gamma rays relative to a previously reported Np 239 gamma at 0.334 Mev have been determined to be 71 (0.33 Mev): T 2 (0.44 Mev): 73(0.49 Mev) = 100:0.40:0.50. Measured yields (gamma rays per decay) for the 0.44-and 0.49-Mev gammas are 1.6X10 -4 and 1.9X10 -4 gamma rays per decay. It seems probable that both of these gamma rays originate from a single Pu 239 level at 0.49 Mev.S EVERAL high-activity samples of Np 239 were obtained by ion exchange separations from neutronirradiated uranium. The neptunium was purified by repeated anion exchange on Dowex A-l resin 1 and by TTA 2 extraction. Reduction to the Np(IV) valence state necessary for the separations was made with ferrous sulfamate.Each sample, when observed with a gamma-ray scintillation spectrometer, was found to emit gamma rays of energy 0.44 and 0.49 Mev. These gammas were of very low intensity compared to the lower-energy Np 239 radiation, so lead absorbers were used to eliminate pileup of pulses from low-energy gamma rays while maintaining a reasonable counting rate at the higher energies. Figure 1 shows a spectrum obtained with a lj-inch diameter by 1 inch thick Nal(Tl) crystal through a 8.12-g/cm 2 lead absorber.The decay of these gamma rays relative to a known -Np 239 on I'/fe-X I-in. Nal 8.12 gm/cm 2 Lead Abs. Source at 1.5cm 40 60 80 PULSE HEIGHT FIG. 1. Gamma-ray spectrum of Np 239 from a Nal(Tl) scintillation spectrometer. 1 Dow Chemical Company, Midland, Michigan. 2 Thenoyl trifluoro acetone as a 0.5 molar solution in xylene.Np 239 gamma at 0.334 Mev 3 was followed intermittently for twelve half-lives by comparing peak counting rates. The relative half-lives of the Np 239 gamma ray and the new gamma rays were found to differ by no more than 0.3%. The decay data and chemical separations justify assignment of these gamma rays to the Np 239 decay.By correcting for the variation with energy of counter efficiency and lead transmission, it was possible to determine the intensities of the 0.44-and 0.49-Mev gamma rays relative to the intensity of the 0.33-Mev gamma ray. These values are included in Table I. The gamma-ray yields (gamma rays per decay) were determined from measured counting efficiency and source activity. The counter efficiency was determined at 0.411 Mev by counting a calibrated Au 198 source in the same geometry as the Np 239 sample. By correcting the measured efficiency to 0.44 and 0.49 Mev, the total emission rate of the 0.44-and 0.49-Mev gamma rays was determined. The total neptunium source activity Ey (Mev 0.334 0.440 0.490 TABLE I. Relative intensity and absolute yield of two high energy Np 239 gamma rays. Relative intensity Yield (gammas per decay) 100 0.40±0.05 (1.6±0.5)X10-4 0.50±0.05 (1.9±0.5)X10-4 was obtained from a 47r beta count of an aliquot of the Np 239 sample. The gamma-ray yields of the 0.44-and 0.49-Mev gamma rays are included in Table I. The gamma-ray yields are some...

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