Sources Of Radiation

Each region of the electromagnetic spectrum is associated with characteristic sources and a definite frequency range. Gamma rays occupy the highest-frequency, shortest-wavelength end of the spectrum and are produced in nuclear processes such as radioactive decay and transitions between nuclear energy levels. Their extremely high frequency, above roughly 10^{19}\ \text{Hz}, corresponds to very high photon energy. Microwaves are far lower in frequency and are generated by electronic devices like klystrons and magnetrons, not nuclei. Infrared radiation arises mainly from thermal motion of molecules in warm bodies and sits below the visible range. Radio waves have the lowest frequencies of the four and originate from oscillating currents in antennas. Linking each band to its typical source is a standard expectation of the NCERT and JEE syllabus on Electromagnetic Waves. As a consistency check, nuclear transitions involve energies of millions of electron-volts, far larger than atomic or molecular transitions, which is exactly why they emit the highest-frequency gamma radiation rather than any of the lower-energy bands listed.