Backscatter machines use X-rays, while millimeter wave machines use radio waves.

CNN: TSA removing 'virtual strip search' body scanners

In the U.S., the TSA uses both types of scanners: 250 X-ray scanners and 264 millimeter wave scanners.

FORBES: Europe Bans Airport Body Scanners For "Health and Safety" Concerns

Instead of X-ray scanners, European airports will use millimeter-wave scanners that utilize low-energy radio waves.

FORBES: Europe Bans Airport Body Scanners For "Health and Safety" Concerns

In addition to the backscatter machines, the TSA has also deployed about 260 millimeter-wave machines which use radio waves and do not emit X-rays.

CNN: SHARE THIS

The series -- about a group of space explorers given various superpowers after being hit by cosmic rays -- began a new era for Marvel Comics, signaling the start of their wave of Silver Age characters, including Spider-Man, the X-Men, the Hulk, Iron Man and many more.

CNN: 2011 is bringing a death to the 'Fantastic Four' family

If an aggressor launches a nuclear device of whatever size and detonates it above the atmosphere and in the line of site of its target country, the x-rays and gamma rays emitted by the blast will cause an electromagnetic pulse, or wave a million times stronger than the strongest radio wave.

CENTERFORSECURITYPOLICY: An urgent memo to the next government