Answer: Gamma rays (from positron-electron annihilation).
- A Gamma rays (from positron-electron annihilation)
- B X-rays generated by an external X-ray tube source
- C Radio waves emitted by excited atomic nuclei
- D Microwaves absorbed selectively by body tissue
Correct answer: A. Gamma rays (from positron-electron annihilation)
Explanation: In PET, radioactive tracers emit positrons. When a positron meets an electron, they annihilate producing two gamma-ray photons in opposite directions. Detectors locate the annihilation events to create 3D images.
In an electromagnetic wave, the oscillating electric field (E) and magnetic field (B) are perpendicular to each other and to the direction the wave travels - a purely transverse wave that needs no medium, unlike sound.
Concept context
Maxwell's equations, EM spectrum, properties, and applications of each band.