Radiation sickness

Acute radiation sickness in Mars settlements may result from prolonged exposure to solar radiation or accidental exposure to radioactive materials.

Sources of radiation

Solar radiation

Settlers on the surface of Mars, with no protection (only a light weight space suit protecting them from the tenuous and cold Mars atmosphere) may receive leathal doses of solar radiation during solar storms.
Astronauts in Mars orbit will also be unprotected (unlike Earth orbit, where low orbits are protected by the Earth's magnetic field), so some spacewalk tasks should be carried out by robots whenever possible and sufficient protection must be provided when a solar storm is imminent.

Galactic cosmic rays

Galactic cosmic rays (GCR) are a form of damaging radiation that require shielding for protection against long term exposure. GCRs are mostly protons (hydrogen with no electron) or other atomic nuclei. They move at very high velocities and the fastest ones have much more kinetic energy than even the highest energy photons. They therefore do proportionally more damage than other types of radiation and are difficult to protect against. On Earth, the depth and density of the atmosphere protects life from radiation damage from galactic cosmic rays. But on Mars the atmosphere is not dense enough and additional protection is required.

Accidental exposure to radioactive material

Should nuclear power be required by an expanding settlement, accidental exposure to radioactive material may result in injury or death. Long-term health problems (such as cancer) may result from being in close proximity to such materials.