ultraviolet, X and gamma rays

• Ultraviolet:

•  wavelengths shorter than visible, down to about 10 nanometres. UV is more useful in chemistry, because each photon has energy comparable with that of a chemical reaction.

•  It is dangerous for the same reason: a UV photon has enough energy to damage DNA molecules in your cells (so remember to wear sunscreen and a hat). If objects are hotter than the sun (eg some massive young stars), they radiate in the UV.

•  Bees can see in the near UV and so flowers have UV colours to attract them. (Bees can also see the polarisation of light, which they use to navigate, but that's another story.)

•  When the energy of photon is high enough, it is often expressed in electron volts: an ultraviolet photon with 10 eV or more has enough energy to ionise an atom if its outer electron is held at an electric potential of 10 Volts. This is typical of the binding energies of atoms, which is why UV is chemically potent.

• X rays: 

• wavelengths from several nm to 10 pm (a picometre is 10^-12 m). Xrays with wavelengths comparable to atom dimensions are used to determine the structure of crystals, in a technique developed by the Australian physicists, William and Lawrence Bragg, for which they received the Nobel prize in 1915.

•  X rays are divided informally into 'soft' X rays with long wavelengths and 'hard' X rays with shorter wavelengths and higher energies.

•  Their energies are enough to ionise atoms and to destroy chemical bonds. They are produced naturally by some radioactive sources, or by very hot objects like neutron stars. They are also produced by smashing high energy electrons into metal targets: X rays thus produced are used to treat cancers including breast cancer. Soft X rays are stopped by (enough) air. Hard X rays can penetrate deeply into tissue.

• Gamma rays:

•  wavelengths less than about 10 pm. They have very high energy, and often come from deep space, sometimes in bursts from cataclysmic cosmic events, such as the collapse or collision of stars. A 10 GeV cosmic ray has the same energy as an electron would have it were accelerated through 10 billion volts.

•  This is enough energy to cause a chain reaction of ionisation events in the Earth's atmosphere, leading to a shower of charged particles.

http://www.animations.physics.unsw.edu.au/jw/EMspectrum.html