A device that senses and records the passage or properties of particles or radiation.A detector is any device that senses and records the passage or properties of particles or radiation. In physics, detectors are the essential bridge between theoretical predictions and observable reality: without them, phenomena like cosmic rays, neutrinos, or gravitational waves would remain invisible. Detectors range from the human eye (a photon detector) to enormous instruments like the Large Hadron Collider's ATLAS, which tracks billions of particle collisions.
Most detectors rely on converting the energy deposited by a passing particle or photon into a measurable signal. For example, a scintillator absorbs radiation and re-emits it as visible light, which a photomultiplier tube then amplifies into an electrical pulse. Other designs, like semiconductor detectors, directly generate electron-hole pairs that produce a current. The key is that the signal is proportional to the energy or intensity of the incoming radiation, allowing physicists to infer its properties.
Detectors are used in medical imaging (X-ray detectors, PET scanners), radiation safety monitors, and particle physics experiments worldwide.
The simplest detector—a photographic plate—was what Henri Becquerel used in 1896 to accidentally discover radioactivity.
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