What are Gamma Rays used for? Why? Are they Bad?

-Gamma Rays can be used to Sterilise Medical Instruments, as they can kill Bacteria -This makes it better than Boiling the Instruments - they may Deform -Food also can be Sterilised, making it more Safe to Eat -GR can also be used to kill Cancer, however the Cells may be Damaged so this needs Precaution