- Better known as X-rays. electromagnetic radiation whose wavelengths range between approximately 10-8 and 10-11 meter, which corresponds to frequencies of 1016 to 1019 Hz respectively, although the defined interval varies. Such rays are located between ultraviolet and gamma radiation. roentgen rays consist of high-energy photons, and penetrate living tissue and other matter to varying degrees, with less penetrating rays called soft X-rays, and more penetrating rays, whose energy and frequency are higher, known as hard X-rays. X-rays are produced, for instance, when matter is bombarded by electrons with sufficient energy, as occurs in an X-ray tube. X-rays are used as a medical diagnostic technique, for therapy, and in the study of the structure and quantitative analysis of materials.