Radiation shielding in General Atomic's 10 and 20 meter Orion designs
From GA 5009 Volume 3
"Most missions for the 10-m configuration require less than 3,000 pulses,
so a bottom shielding requirement of 1Z0 g/cm^2 of hydrogenous material
was used for most conceptual designs.
Shielding of Z5 g/cm^2 or more was thus provided on all sides of
the powered flight station. According to recent studies of planetary
exploration requirements, this shielding is sufficient to attenuate the
probable solar-flare radiation to dose values similar to the 50 rein
allowed for propulsion. the total mission dose from both sources
was expected to be about 100 rem".