We are exposed to ionising radiation every minute of every day, much of it in the form of background radiation including cosmic rays, rocks in the ground, radon gas, water and food.

Bananas, for example, contain naturally occurring potassium-40, a radioactive isotope of potassium. Incredibly, there is even something known as the ‘banana-equivalent dose’, an attempt to contextualise artificial radiation exposures for the general public.
An X-ray screening at a US airport is roughly two and a half times a banana-equivalent dose.
From Simon Flynn, The Science Magpie (2012)