Gamma Radiation
Gamma radiation consists of high-energy electromagnetic photons emitted by an excited atomic nucleus as it transitions from a higher energy state to a lower one, typically following alpha or beta decay. Unlike alpha and beta radiation, gamma rays carry no charge and no mass, so gamma emission does not change the atomic number or mass number of the nucleus. Due to their extremely high energy (typically 10 keV to 10 MeV) and penetrating power, gamma rays are used in cancer radiotherapy, sterilisation of medical equipment, and industrial non-destructive testing.
Key Formula
E_γ = h × f = (h × c) / λ
LaTeX: E_{\gamma} = h f = \frac{hc}{\lambda}
| Symbol | Meaning | Unit |
|---|---|---|
| E_γ | Energy of gamma photon | J (or eV) |
| h | Planck's constant (6.626 × 10⁻³⁴ J·s) | J·s |
| f | Frequency of gamma radiation | Hz |
| c | Speed of light (3 × 10⁸ m/s) | m/s |
| λ | Wavelength of gamma radiation | m |
Worked Example
Problem
A gamma ray has a frequency of 3.0 × 10²⁰ Hz. Calculate its energy in joules and in MeV.
Solution
Step 1: Apply E = hf. h = 6.626 × 10⁻³⁴ J·s. Step 2: E = 6.626 × 10⁻³⁴ × 3.0 × 10²⁰ = 1.988 × 10⁻¹³ J. Step 3: Convert to MeV: 1 eV = 1.602 × 10⁻¹⁹ J, so 1 MeV = 1.602 × 10⁻¹³ J. Step 4: E = 1.988 × 10⁻¹³ / 1.602 × 10⁻¹³ ≈ 1.24 MeV.
Answer
E ≈ 1.99 × 10⁻¹³ J ≈ 1.24 MeV
Electromagnetic Spectrum — Position of Gamma Rays
| Radiation Type | Wavelength (m) | Frequency (Hz) | Energy (eV) | Source |
|---|---|---|---|---|
| Radio waves | 10³ to 10⁻¹ | 10⁵ to 10⁹ | < 10⁻⁶ | Antennas, stars |
| Visible light | 7×10⁻⁷ to 4×10⁻⁷ | 4×10¹⁴ to 7×10¹⁴ | 1.8 to 3.1 | Sun, LEDs |
| X-rays | 10⁻⁸ to 10⁻¹² | 10¹⁶ to 10²⁰ | 10² to 10⁵ | X-ray tubes |
| Gamma rays | < 10⁻¹¹ | > 10¹⁹ | > 10⁵ (> 100 keV) | Radioactive nuclei |
Interactive Tools
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Related Terms
Beta Decay
Beta decay is a type of radioactive decay mediated by the weak nuclear force, in which a neutron converts to a proton (beta-minus decay, emitting an electron and an antineutrino) or a proton converts to a neutron (beta-plus decay, emitting a positron and a neutrino). Unlike alpha decay, the mass number of the nucleus remains unchanged, but the atomic number increases or decreases by one. Beta decay is responsible for the natural transmutation of elements and is exploited in positron emission tomography (PET scanning) and food irradiation.
Radioactive Decay
Radioactive decay is the spontaneous transformation of an unstable atomic nucleus into a more stable configuration by emitting radiation in the form of particles or electromagnetic waves. This process occurs because the nucleus has too many protons, too many neutrons, or excess energy, making it thermodynamically unstable. It is the foundation of nuclear medicine, radiometric dating, and nuclear power generation.
Nuclear Binding Energy
Nuclear binding energy is the energy required to completely separate a nucleus into its individual protons and neutrons, or equivalently, the energy released when these nucleons combine to form the nucleus. It arises from the strong nuclear force overcoming electromagnetic repulsion between protons, and is directly related to the mass defect — the difference between the mass of the nucleus and the sum of masses of its constituent nucleons via Einstein's E = mc². The binding energy per nucleon peaks around iron-56, explaining why both fusion of light nuclei and fission of heavy nuclei can release energy.
Named "gamma" by Ernest Rutherford in 1900, using the third letter of the Greek alphabet (γ) to indicate it was the third type of nuclear radiation discovered, distinguished by its even greater penetrating power than alpha or beta radiation.