[Ozark Tom]

Seem to recall Van Allen’s belts trap much of the particle radiation? ISS avoids much exposure through location.

Thin metal stops initial particles and produces secondary particles plus X-ray. Thin layers of foil alternating with speciality plastic sheeting performs better as shielding.

New sunblock and internal medication, which combines melanin with selenium, offers another approach to avoiding radiation damage.

[A Navy Vet]

I forgot about the Van Allen belts. Can't recall all my basic science at 70 years. However, those belts and Earths own protective magnetic bubble only reach so far. A manned mission to Mars would not benefit from the above and be bombarded by not only Solar Energy Particles (SEPs - Solar Flares) which are difficult to predict, but Galactic cosmic radiation, while weaker, tends to be more penetrating and is always there.

Here is a good link and different safety protocols that NASA is working on : https://www.nasa.gov/feature/goddard/2019/how-nasa-protects-astronauts-from-space-radiation-at-moon-mars-solar-cosmic-rays