1. The Heliospheric Heii30.4 nm Solar Flux During Cycle 23
2. Axford, W. I. 1972, in The Solar Wind, eds. J. M. W. C. P. Sonnet, & P. J. Coleman, NASA Spec. Publ., 308, 609
3. Barnett, C. F., Hunter, H. T., Kirkpatrick, M. I., et al. 1990, Atomic data for fusion. Collisions of H, H2, He and Li atoms and ions with atoms and molecules, ORNL-6086/V1 (Oak Ridge, Tenn.: Oak Ridge National Laboratories)
4. Electron-impact ionization cross sections for elements Z=1 to Z=54