In simple words,
Gamma rays are like
x-rays, but the waves are smaller in wavelength. Both gamma rays and
x-rays are photons with very high energies, and gamma have even more energy. They are also a type of ionizing radiation. Gamma rays can travel through thicker materials than x-rays can.
-Gamma rays are high energy (high frequency) electromagnetic radiation. They have high ionising power and hence they can pose a health hazard when absorbed by living tissue. They are produced by decay of high energy states in natural processes and man-made mechanisms. Gamma rays produce free radicals when they strike anything which contains electron. Free radicals easily damage DNA, and ionizing radiation may also directly damage DNA by ionizing or breaking DNA molecules.