The combination of a magnetic field and atmosphere protect the Earth's surface from high levels of radiation. The atmosphere does most of the work.

An equivalent mass of anything will do the same job, more or less. Build a habitat dome with 4 meters of glass, and you are protected. This can be multiple panes for practical manufacturing and safety. Or an equivalent amount of dirt piled on the dome with sunlight piped in through side windows.

If you pump up the atmospheric pressure to Earth levels, it will be more than enough. Mars' lower gravity means you need more atmosphere thickness to generate the same pressure.