Electromagnetic radiation with wavelengths between approximately .01 nanometers to 200 nanometers. These energy beams are powerful enough to penetrate most substances except heavy metals (such as gold and lead). X-rays are used to examine body parts; the x-rays are absorbed by tissues containing lots of calcium (bones, teeth, etc.) and thus x-ray films are useful for detecting fractures, misalignments, abnormal cavities, etc.