wavelengths carrying more energy
than longer ones. The main
categories of electromagnetic
radiation, going from shortest
wavelength to longest, are: 
 gamma rays: High-energy, with the
shortest known wavelength, gamma
rays are produced by extremely
energetic reactions. 
 x-rays: Because these short
wavelengths possess high energy and
can pass through soft tissues, doctors
have long used them to make
diagnostic images of human bodies.
X-rays, generated only by  very
high-energy phenomena, are