4.135668e-9
eV
4.135668e-12
keV
4.135667697e-15
MeV
6.626070150e-28
J
1,000,000
Hz
1.000000e-12
EHz
299.792458
m
299,792,458,000,000
pm
2.997925e+17
fm
4.135668e-9
eV
4.135668e-12
keV
4.135667697e-15
MeV
6.626070150e-28
J
1,000,000
Hz
1.000000e-12
EHz
299.792458
m
299,792,458,000,000
pm
2.997925e+17
fm
Gamma rays are the highest-energy form of electromagnetic radiation, with photon energies typically ranging from 100 keV to over 10 MeV. They are produced by nuclear transitions, particle annihilation, and high-energy astrophysical processes. As photons, gamma rays follow the fundamental relation E = hf = hc/λ, where h is Planck's constant, f is frequency, and λ is wavelength.
The distinction between gamma rays and X-rays is based on origin rather than energy: gamma rays originate from nuclear transitions or particle physics processes, while X-rays originate from electron transitions or deceleration (bremsstrahlung). A 100 keV photon is an X-ray if produced by an electron striking a target, but a gamma ray if emitted by a nucleus transitioning to a lower energy state.
Common gamma ray energies provide useful reference points: the positron-electron annihilation gamma is always 511 keV; Cs-137 emits 662 keV gammas (the most common radioactive source); Co-60 emits a pair at 1.17 MeV and 1.33 MeV; and nuclear resonance reactions can produce gammas up to ~15 MeV.
Gamma ray energies are measured using gamma spectroscopy — typically with NaI(Tl) scintillation detectors for field use or High-Purity Germanium (HPGe) detectors for high-resolution laboratory measurements. HPGe detectors can resolve gamma energies to within a few tenths of a keV, allowing identification of specific radioactive isotopes from their characteristic gamma signatures.
In medical physics, gamma ray energies are carefully chosen for different applications: Tc-99m (140 keV) is ideal for SPECT imaging because it is energetic enough to escape tissue but low enough for efficient detection; therapeutic cobalt-60 units use the 1.25 MeV average gamma for external beam radiation therapy.
In astrophysics, gamma ray astronomy (using satellites like Fermi and INTEGRAL) observes the universe at energies from 100 keV to over 300 GeV, revealing neutron star mergers, black hole jets, and dark matter annihilation signatures — phenomena impossible to observe at any other wavelength.
Select whether you are providing a frequency (Hz), wavelength (m), or energy (eV). Enter the corresponding value. The calculator converts between all representations using E = hf = hc/λ with CODATA 2018 values for Planck's constant h = 6.62607015 × 10⁻³⁴ J·s and speed of light c = 2.99792458 × 10⁸ m/s.
Gamma rays typically have energies from 100 keV to several MeV, corresponding to wavelengths of 0.001 to 0.01 nm (1-10 pm). Higher energy gamma rays are more penetrating, requiring thicker shielding. Even low-energy gammas from nuclear transitions are far more penetrating than alpha or beta radiation.
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Cs-137 emits a 661.7 keV gamma from Ba-137m nuclear de-excitation. This is the most-used calibration energy in gamma spectroscopy.
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511 keV is the rest energy of an electron/positron (m_e c^2 = 0.511 MeV). Positron annihilation always produces two back-to-back 511 keV gammas — the basis of PET imaging.
Gamma rays are generally defined as photons with energies above about 100 keV (0.1 MeV), with no strict upper limit. Astrophysical gamma rays have been detected up to 100 TeV. The boundary with X-rays at ~100 keV is not sharp and is based on origin (nuclear vs. electronic) rather than energy alone.
Gamma rays are attenuated by dense materials via three processes: photoelectric absorption (dominant below ~0.5 MeV), Compton scattering (dominant 0.5-5 MeV), and pair production (dominant above 1.022 MeV). Lead (ρ=11.3 g/cm³) is the standard shielding material. The half-value layer for 1 MeV gammas in lead is about 8 mm.
511 keV is the rest mass energy of an electron (or positron): m_e c² = 0.511 MeV. When a positron from β⁺ decay or pair production annihilates with an electron, conservation of energy and momentum produces exactly two 511 keV photons emitted in opposite directions (180° apart). This is the physical basis of PET imaging.
In gamma spectroscopy, the Compton edge is the maximum energy deposited in the detector by Compton scattering, when the gamma is back-scattered at 180°. For a 661.7 keV gamma, the Compton edge is at 478 keV. The full-energy peak (photoelectric peak) sits at 661.7 keV. The separation between these features fingerprints the isotope.
When a gamma photon with energy greater than 1.022 MeV (2 × 0.511 MeV) passes near a nucleus, it can convert into an electron-positron pair. The excess energy above 1.022 MeV becomes kinetic energy of the pair. The positron then annihilates with another electron, creating two 511 keV escape peaks in the gamma spectrum.
Each radioactive isotope emits gamma rays at specific discrete energies characteristic of its nuclear energy level transitions — a unique 'fingerprint.' By measuring the gamma spectrum and comparing peak energies to databases (NNDC, IAEA), specific isotopes can be identified and quantified even in complex mixtures, with no sample preparation required.
A gamma camera (Anger camera) is the primary imaging device in nuclear medicine. A large NaI(Tl) crystal detects gamma rays from a patient injected with a radiopharmaceutical. Collimators define the direction of detected gammas. The spatial distribution of detected gammas creates a 2D image of the isotope distribution in the body (SPECT imaging).
Gamma rays in reactors come from: prompt fission gammas (emitted in microseconds), capture gammas (neutrons captured by structural materials emitting gammas), and decay gammas from fission products. Prompt fission gammas have energies up to ~7 MeV. Reactor shielding must account for all these sources, which is why reactor biological shields are meters of concrete or water.
A nuclear isomer is a metastable excited nuclear state with a measurable lifetime before emitting a gamma ray (internal transition, IT). The most common example is Tc-99m (m = metastable), which emits a 140 keV gamma with 6-hour half-life. Nuclear isomers are exploited in nuclear medicine because they emit useful imaging gammas without the tissue dose from beta or alpha particles.
The highest-energy photons ever detected were by the LHAASO observatory, which recorded photons up to approximately 1.4 PeV (1.4 × 10^15 eV) from the Crab Nebula in 2021. These ultra-high-energy gamma rays are produced by inverse Compton scattering of relativistic electrons off cosmic microwave background photons.
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