S. N. Vernov, A. Ye. Chudakov, P. V. Vakulov, Ye. V. Gorchakov, Yu. I. Logachev, G. P. Lyubimov, A. G. Nikolayev, 1964, Investigation of Radiation with the Flights of the "Mars 1" and "Luna 4" Interplanetary Automatic Stations, Cosmic Research, vol. 2, no. 4, translated from the Russian, https://apps.dtic.mil/dtic/tr/fulltext/u2/605513.pdf