Gamma rays have the smallest wavelengths in the electromagnetic spectrum. They have the most energy of any wave. The waves are generated by radioactive processes such as in nuclear explosions. Like other areas of the electromagnetic spectrum, they can be used to kill living cells, such as cancer, but can provoke DNA alteration by interfering with the genetic material of the cell.
Image acknowledgement: A nuclear test conducted by the United States in 1953 in the Nevada Desert. Public domain.