• Tags: UV, X-ray, gamma, high-energy
• Difficulty: Foundation

Ultraviolet (10 nm - 400 nm) is produced by very hot objects (T > 10,000 K) and gas discharge tubes. UV-A (315-400 nm) causes tanning; UV-B (280-315 nm) causes sunburn and vitamin D synthesis; UV-C (100-280 nm) is germicidal but absorbed by ozone. The ozone layer (O3 in stratosphere) is critical for blocking harmful UV. X-rays (0.01-10 nm) are produced when fast electrons decelerate upon hitting a metal target (Bremsstrahlung) or through inner-shell electronic transitions (characteristic X-rays). Used in medical imaging (bones absorb more than soft tissue), crystallography (Bragg diffraction: 2dsin(theta) = nlambda), and security scanning. Gamma rays (lambda < 0.01 nm) originate from nuclear transitions and matter-antimatter annihilation. Most energetic EM radiation. Used in cancer radiotherapy, food sterilization, and gamma-ray spectroscopy. Penetrating power: gamma >> X-ray >> UV.