In recent years artificial sources of radiation have increased dramatically. In the workplace and at home new technologies expose us more and more to various kinds of radiation.
Most radiation is unseen and unfelt.
But we do sense some radiation. We see by the visible rays from the sun and feel the warmth of its infra-red rays. We are aware of ultraviolet rays by the way they tan our skin. Our radiation exposures are broadly classed as either ionising or non-ionising according to how they effect body tissues. X-rays and the rays emitted by radioactive materials are ionising.