In comparison to other members of the electromagnetic spectrum (such as visible light, infrared, ultraviolet rays, etc.), gamma rays have the longest frequency and hence the smallest wavelength. Gamma rays have frequencies in excess of `10^19` Hz. Since the frequency and wavelength are interrelated (through velocity of light, c), these high frequencies mean that gamma rays have a very low wavelength (less than 10 pm or pico meters). These are roughly the dimensions of diameter of an atom and hence the wavelength of gamma rays could be as long as the diameter of an atom (or even smaller than that). Since, wavelength and energy are also interrelated, these extremely small wavelength mean that gamma rays are the most energetic among all the electromagnetic spectrum components. It is due to these properties that gamma rays are extremely harmful to us and can cause cell mutations.
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