Which of the following method is used for cold sterilization?

X-rays, gamma rays and cosmic rays are highly lethal to DNA and other vital constituents. They have very high penetrative power. Since there is no appreciable increase in temperature in this method, it is referred to as cold sterilization. Commercial plants use gamma radiation for sterilizing items like plastics, syringes, swabs, and catheters. Ref: Textbook of Microbiology By Ananthanarayan, 6th edition, Page 28.