They are not detected by human senses (cannot be seen, heard, felt, etc.).
They travel in straight lines at the speed of light.
Their paths cannot be changed by electrical or magnetic fields.
They can be diffracted, refracted to a small degree at interfaces between two
different materials, and in some cases be reflected.
They pass through matter until they have a chance to encounter with an atomic
particle.
Their degree of penetration depends on their energy and the matter they are
traveling through.
They have enough energy to ionize matter and can damage or destroy living cells.