Radon is the breakdown or decay of radioactive elements, thorium and uraniam in the soil. The inside of a home has a naturally occuring slight negative pressure as opposed to the exterior / outside.

Radon gas then migrates to the lower pressure INSIDE the home. Through cracks in basement flooring and walls, through openings for sewer, potable water, cassions, anywhere a gas can penetrate, even through the concrete itself, it is porous.

Correction can be as simple as PAINTING and or SEALING those openings and the concrete or as elaborate and creating a negitive pressure under the concrete by way of a Mitigation system.

I would suggest a simple test, you can purchase a Home Test at most local Hardware stores. Follow the directions carefully, then when you get the results back it will be a good guide as to what you should do, further testing and or mitigation.