How Does Gamma Decay Occur? Key Concepts & Examples
The radioactive decay of atomic nuclei produces electromagnetic radiation, of which gamma-ray decay (gamma radiation) is penetrating form. As it has the shortest wavelength electromagnetic waves, it imparts the highest photon energy. Gamma radiation was discovered in 1900 by Paul Villard, a French chemist and physicist while studying radium radiation. Also, Earnst Rutherford, in the same year, named another two types of decay radiation of less penetration which he called alpha and beta rays. He, in 1993, named gamma rays based on their ability of intense penetration of matter.
The energy range of gamma rays is a few keV (kilo electron volts) to around eight megaelectronvolts. The decaying radionuclides can be identified by using the energy spectrum of gamma rays. Some sources, such as Cygnus X-3 microquasar, can produce very-high-energy gamma rays of around 100-1000 teraelectronvolt (TeV). The natural source of gamma rays is radioactive decay and secondary radiation from atmospheric interactions with cosmic ray particles. Other natural sources are from terrestrial gamma-ray flashes. Fission in nuclear reactors, physics experiments such as neutron pion decay, and nuclear fusion are artificial ways to produce gamma rays.
Discovery of Gamma Decay
Gamma decay, a radioactive process, resulted in the discovery of the first gamma-ray. In its excited state, a nucleus emits the gamma-ray almost immediately when it is formed. The alpha particles, beta particles, and gamma rays are increasingly powerful as far as emission energy is concerned. The radiation process results in alpha decay, beta decay, and gamma decay only in the energy formation.
Gamma rays were initially thought of as fast beta particles, but the absence of magnetism proved that it is not so. However, it was confirmed that they are electromagnetic radiation when, in 1914, it was found that they get reflected from crystal surfaces. Gamma rays were found to be similar with X-rays when Rutherford and Edward Andrade measured its wavelength from radium (but with short wavelength and hence higher frequency)
Sources of Gamma Rays
The natural sources of gamma rays are radioisotopes such as Potassium-40 and secondary radiation from cosmic rays. Several astronomical processes produce very high-energy electrons resulting in gamma rays.
Gamma Radioactive Decay
Though all alpha, beta, and gamma particles are part of the radiation, their resultants differ considerably as alpha has a positive charge. The beta has a negative charge, and gamma rays are neutral. Thus gamma decay definition can be stated when a radioactive nucleus emits alpha and beta particles. The nucleus left in excited state decay to a lower energy state, releasing gamma rays.
The emission of gamma rays in the excited state is a very rapid process, and it takes on 10-12 seconds to emit gamma rays. The gamma decay process can also result in neutron capture, nuclear fission, or nuclear fusion. The formation of fluorescent gamma rays is also a subtype of radioactive gamma decay.
Any excited state emits gamma rays that may transfer energy mainly to the electrons in the K shell, resulting in the ejection of that electron from the atom, which is called the photoelectric effect. Most of the time, high-energy gamma rays scatter from the atomic electrons and transfer some of the energy to the scattered particles is called the Compton effect.
Application of Gamma Rays
Because of their properties, gamma rays are used in many fields with different applications. E.g., the medical applications of gamma rays are widely used in imaging techniques. Remember, gamma rays are more similar to X-rays. Applications such as positron emission tomography (PET) and very effective radiation therapies are used in detecting cancerous tumours. Positron emitting radioactive pharmaceuticals contributes to a particular physiological process like brain function. This is the reason why a short-lived positron is injected into the body.
They quickly combine with electrons and result in two 511-keV gamma rays that travel in opposite directions. This helps to form an image of the biological process under examination and highlights the location.
The radioactive traces of uranium and thorium can be searched with gamma-rays present on the Earth’s surface. They can trace the minerals containing these radioactive elements. Gamma rays can help other applications such as mineral exploration, geology, and environmental contamination identification. Orbiting satellites, telescopes, or high-altitude balloons can observe the Earth's strongly absorbing atmosphere for gamma rays.
Another established field of research is gamma-ray astronomy. There are many undiscovered gamma-ray sources, including powerful pulsars, quasars, and supernova remnants. Also, the gamma-ray burst has remained the most amazing unexplained astronomical phenomena to date (brief but intense emissions isotropically distributed in the sky).
Gamma Decay Definition in Particle Physics
Gamma rays are products of neutral systems which decay through electromagnetic interactions. In an electron-positron pairing, two gamma-ray photons are produced. Radioactivity is a neutral part of nature. Earth is said to have many stable elements with lower mass, like hydrogen, to highest like Pb or Bi. All elements with higher Z than Bi are radioactive. Some isotopes are long-lived. They can decay by more than one method.
FAQs on Gamma Decay: Meaning, Process, and Applications
1. What is gamma decay, and why does it typically occur in an atomic nucleus?
Gamma decay is a type of radioactive decay where an unstable atomic nucleus dissipates excess energy by emitting a high-energy photon, known as a gamma ray (γ). It occurs because a nucleus is often left in an excited, high-energy state after a preceding alpha or beta decay event. To transition to a more stable, lower-energy state, the nucleus releases this surplus energy in the form of a gamma photon, without changing its number of protons or neutrons.
2. How is gamma decay fundamentally different from alpha and beta decay?
Gamma decay differs from alpha and beta decay in its nature and its effect on the nucleus. Here’s a comparison:
- Nature of Emission: Gamma decay emits a massless, chargeless photon (electromagnetic energy), whereas alpha decay emits a helium nucleus (2 protons, 2 neutrons) and beta decay emits an electron or a positron.
- Effect on Nucleus: In gamma decay, the atomic number (Z) and mass number (A) remain unchanged. In contrast, alpha decay decreases Z by 2 and A by 4, while beta decay changes Z by +1 or -1 with A remaining constant.
- Reason for Decay: Gamma decay is a process of energy release to de-excite a nucleus, while alpha and beta decays are processes that change the nucleus's composition to achieve a more stable proton-to-neutron ratio.
3. What is the general equation that represents the process of gamma decay?
The general equation for gamma decay shows a nucleus in an excited state transitioning to a lower energy state. It is written as:
AZX* → AZX + γ
In this equation:
- AZX* represents the parent nucleus in an excited (metastable) state, indicated by the asterisk (*).
- AZX represents the same nucleus in its lower-energy (ground) state.
- γ represents the emitted high-energy gamma ray photon.
4. Can you provide a specific example of a gamma decay process?
A common example is the decay of Cobalt-60 to Nickel-60. First, Cobalt-60 undergoes beta decay to form an excited Nickel-60 nucleus:
6027Co → 6028Ni* + e- + ν̅
The resulting Nickel-60 nucleus (6028Ni*) is still in a high-energy, unstable state. It immediately releases this excess energy by emitting one or more gamma rays to reach a stable state:
6028Ni* → 6028Ni + γ
This two-step process is a classic illustration of how gamma decay follows other radioactive decay types.
5. Since gamma decay releases energy, does it affect the mass or atomic number of the nucleus?
No, gamma decay does not change the atomic number (Z) or the mass number (A) of the nucleus. The emission involves a gamma ray, which is a packet of electromagnetic energy (a photon) and has no mass or charge. Therefore, the nucleus does not lose any protons or neutrons. It only transitions from a higher energy level to a lower one, becoming more stable in the process.
6. What are the key properties of gamma rays emitted during gamma decay?
Gamma rays have several distinct properties that are important in physics and its applications:
- They are high-energy electromagnetic radiation, similar to X-rays but typically with higher energy.
- They have no mass and no electric charge.
- They travel at the speed of light (c) in a vacuum.
- They possess very high penetrating power, capable of passing through thick materials like concrete and lead that would stop alpha and beta particles.
- They have significant ionising ability, meaning they can knock electrons out of atoms, which is why they are useful in some applications but also hazardous to living tissue.
7. What are some important real-world applications of gamma decay?
The high energy and penetrating nature of gamma rays make them useful in various fields:
- Medicine: In a technique called radiotherapy (e.g., Gamma Knife surgery), focused beams of gamma rays are used to destroy cancerous tumours. They are also used in diagnostic imaging, such as in PET (Positron Emission Tomography) scans.
- Industry: Gamma rays are used to sterilise medical equipment and to kill bacteria and other pathogens in food, a process known as food irradiation. They are also used for industrial radiography to inspect welds and structural integrity.
- Scientific Research: Gamma-ray astronomy helps scientists study high-energy phenomena in the universe, such as supernovae and black holes.
8. Why are gamma rays considered particularly dangerous to living organisms?
Gamma rays are dangerous primarily due to their high energy and extreme penetrating power. Unlike alpha or beta particles that are stopped by skin or thin materials, gamma rays can pass deep into the body. As they travel through tissue, they cause ionisation by stripping electrons from atoms and molecules. This process can damage or destroy vital biological molecules, including DNA. Significant DNA damage can lead to cell death, harmful mutations, or the development of cancer, making controlled exposure and shielding essential for safety.
