
The ability of a detector to distinguish between particles of slightly different energies.Energy resolution is a measure of a detector's ability to distinguish between particles or photons that have slightly different energies. It is typically expressed as the full width at half maximum (FWHM) of the energy peak divided by the peak energy, often given as a percentage — for example, a resolution of 1% means the detector can separate two peaks that differ by about 1% of their energy. High energy resolution is crucial in nuclear and particle physics, astrophysics, and medical imaging, where identifying the exact energy of a particle can reveal its identity or the process that produced it.
The concept of energy resolution became central in the mid-20th century with the development of scintillation counters and semiconductor detectors. The theoretical limits were worked out in the 1960s, and modern high-purity germanium detectors achieve resolutions of about 0.1% for gamma rays.
When a particle deposits energy in a detector, it creates a signal (such as a number of electron-hole pairs or photons) that is proportional to the energy. Statistical fluctuations in this signal — due to the random nature of energy deposition and charge collection — set a fundamental limit on resolution. Better detectors minimize these fluctuations by using materials with low Fano factors (like silicon or germanium) and by reducing electronic noise. Advanced techniques, such as cryogenic operation or pulse-shape analysis, can push resolution to parts per million, as seen in some gamma-ray spectrometers.
It is essential in gamma-ray spectroscopy for identifying radioactive isotopes, in particle physics for distinguishing particle types, and in medical imaging (e.g., PET scans) to improve image quality.
The best energy resolution ever achieved for gamma rays is about 0.0001% (1 part per million), using cryogenic microcalorimeters that measure the tiny temperature rise caused by a single photon.






