welp.
Reading up on the topic, a team of Chinese and German scientists discovered that
the radiation exposure on the Moon totaled out to 1,369 microsieverts per day; for reference, the article compares this to a flight from New York to Frankfurt, being five to ten times greater. Searching even deeper,
information is beautiful reports that
exposure to 1,369 microsieverts is not even as extreme as exposure to a spinal X-ray. In fact, a CT scan exposes the body to
10,000 microsieverts, and exposure only reaches dangerous levels at
1,000,000 microsieverts
after several hours. The amount of radiation Goku might have been exposed to on Moon for a
very brief period of time is practically nothing. This is not Resistance to Radiation.