Description: The purpose of this study is to "establish a data base and methodology for classifying...the streams of the Roanoke Basin into a hierarchy of ecological systems" and to "establish evaluative criteria and methodology for classifying and ranking streams within the ecological systems relative to their state of environmental quality" (p. R1).

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Description: This article discusses K-shell ionization of elements ₁₅P to ₂₈Ni for 0.4 to 3.8 MeV/amu ₅¹⁰B-ion bombardment. Abstract: K-shell x-ray production cross sections, Kβ/Kα x-ray intensity ratios and Kα and Kβ x-ray energy shifts have been determined for thin solid targets of ₁₅P, ₁₉K, ₂₀Ca, ₂₁Sc, ₂₂Ti, ₂₃V, ₂₅Mn, ₂₆Fe, ₂₇Co, and ₂₈Ni for 4-38-MeV ₅¹⁰B ion bombardment. Comparisons of the cross sections were made to direct Coulomb ionization and electron-capture theories by means of fluorescence yields corrected for multiple-ionization effects. The dominant contribution to K-vacancy production for these projectile-target combinations is believed to be direct ionization. Electron capture is expected to be important only for the lighter target elements and then primarily at the higher velocities. The direct-ionization theories employed were the binary-encounter approximation and the plane-wave Born approximation (PWBA) both of which overestimated the experimental data especially at the lower incident ion velocities. The PWBA was modified for increased target-electron binding, Coulomb deflection of the incident ion, polarization of the target-electron wave functions due to the passage of the incident ion, and relativistic target-electron velocities. The experimental data were found to agree quite well with the sum of the theoretical predictions of the modified PWBA and electron capture.

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Description: This article discusses K-shell x-rays of selected elements from Nb through Gd for incident protons and alpha particles from 0.6 to 2.4 MeV. Abstract: K-shell x-ray production cross sections and Kβ/Kα ratios are presented for 0.6- to 2.4-MeV protons and alpha particles incident on thin targets of selected elements from Nb to Gd. The Kβ/Kα ratios are compared to the theoretical predictions of Scofield and agree within 10%. The experimental cross sections are compared to the theoretical predictions of the plane-wave Born approximation (PWBA) and the PWBA modified to include binding energy, Coulomb deflection, and relativistic effects. It is seen that the PWBA modified for binding energy and Coulomb deflection effects agrees with the experimental data for Nb to within uncertainties, but its predictions are lower than the data by larger amounts as the target Z increases. Inclusion of an ad hoc semiclassical relativistic correction to the theoretical cross section, as suggested by Hansen, improves the agreement with the data, but overestimates the data for the highest-Z elements.