1. F.B. McDonald, Voyager CRS collaboration, private communication.
2. G.A. Lentz et al., in: Proceedings of the 13th International Cosmic Ray Conference, vol. 2, Denver, 1973, p. 743.
3. B.J. Teegarden et al., in: Proceedings 13th International Cosmic Ray Conference, vol. 2, Denver, 1973, p. 749.
4. J.A. Van Allen, in: Proceedings 13th International Cosmic Ray Conference, vol. 2, Denver, 1973, p. 750.
5. Observations of the eleven-year cosmic-ray modulation cycle