Radioactivity gamma decay: Sources & Applications

Radioactivity is a process in which a heavy nucleus disintegrates into small nuclei to achieve stability. This process was first discovered by A.H Becquerel purely by accident. Subsequent studies found that radioactivity is a nuclear phenomenon and involves the decaying of nuclei. Today, there are 40 elements in the periodic table that are radioactive in nature. There are mainly three types of radioactive decay which are alpha decay, beta decay, and gamma decay. Alpha and beta decays are independent but gamma decay accompanies alpha and beta decay. The unstable nucleus can even decay multiple times until it comes to a stable state. This is called the decay chain. In this article, we will have a look at radioactivity gamma decay, its sources, and applications.

Key takeaways: Radioactivity, alpha-decay, beta decay, gamma decay, radioactive particles, sources of gamma rays, applications of gamma rays, pair production, nucleus, radiation

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What is Radioactivity?

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Radioactivity is a phenomenon where a highly unstable nucleus disintegrates into a stable nucleus by the emission of some particles. Several elements in the periodic table are radioactive in nature. According to quantum theory, it is impossible to predict when an atom will undergo radioactive decay. There are mainly three types of radioactive decay which are alpha decay (α-decay), beta decay (β-decay), gamma decay (γ-decay). In all these decay processes more than one particle is emitted. As the gamma decay is accompanied by alpha and beta decay, let us learn about the first two decays.

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Alpha decay

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The alpha particle is actually the nucleus of the helium-4 atom. It carries a double positive charge. When a nucleus becomes stable after rejecting an alpha particle, it undergoes alpha decay. The mass number of the parent atom is reduced by four and the atomic number is reduced by two. Alpha decay mainly occurs in heavy nuclides. The general equation of alpha decay is given below:

\(^{A}_{Z}X \rightarrow ^{A-4}_{Z-2}Y +^{4}_{2}He\)

\(Q=(m_{_{x}}-m_{y}-m_{He}) c^{2}\)

Here, X is the parent nucleus 

A is the total number of nucleons 

Z is the total number of protons 

Y is the daughter nucleus formed after alpha decay

Q here is the disintegration energy that is released and its value is the difference between initial mass-energy and final mass-energy of the decayed particles. 

Do you know - The Chernobyl nuclear plant disaster was one of the most disastrous events in human history. Today, 27 years after the disaster, still people do countermeasures to mitigate its impact of it.

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Beta-decay

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Beta-decay involved the emission of beta particles from a nucleus, transforming the original nuclide to its isobar. In beta decay, a nucleus emits an electron( (β − decay) or a positron (β+ decay). Beta-decay of a neutron transforms it into a proton by the emission of an electron and an antineutrino or a proton is converted into a neutron by the emission of a positron and a neutrino. Neither the beta particles nor the neutrino exists in the nucleus before the decay process. They are formed during decay. 

An example of beta decay is the decay of Carbon-11 to Boron-11 by the emission of positron and neutrino.

\(^{11}_{6}C \rightarrow ^{11}_{5}B + e^{+} + v^{{Q_{\beta +}= 0.97 MeV}}_{{t_{\frac{1}{2}}=20.4 min}}\)

The basic nuclear process under β − decay is –

\(n\rightarrow p+e^{-} + \bar{v}\)

The basic nuclear process under β+ decay is –

\(p\rightarrow n+e^{+} + v\)

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Gamma decay

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Gamma decay is the emission of electromagnetic radiation of high frequency releasing enough energy to stabilize the nucleus. It exhibits two internal processes also, that is internal conversion and pair production. In internal conversion, the excess energy of a nucleus is transferred to its outer shell orbiting electron leading to its emission. In pair production, the excess energy of the nucleus is directly converted into a pair of electrons and a positron which are emitted together. Gamma decay doesn’t normally occur on its own but the unstable nucleus that undergoes gamma decay must be a product of alpha or beta decay or any other radioactive processes. The gamma rays are of very high frequency comparable to that of X-rays. The gamma rays are found to be more penetrating than X-rays.

The gamma decay of Barium-137 

\(^{137}_{56}Ba \rightarrow ^{137}_{56}Ba + ^{0}_{0}\gamma \)

Gamma Decay

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Natural Sources of gamma rays

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In nature, gamma rays are mostly found as a result of gamma decay or due to the intervention of cosmic rays in the earth’s atmosphere. Mostly heavenly bodies from outer space are the major sources of gamma rays. 

• For example, the pulsars, quasars, black holes, distant galaxies, etc emit radiations of gamma rays. 
• On Earth, they are generated by a lightning strike, nuclear explosions, etc.

Gamma rays are highly penetrable and can cause damage at the cellular level and serious diseases to the human body.

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Applications of gamma rays

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The applications of gamma rays are:

• It is used in chemotherapy. Gamma rays are used to treat cancer, tumors and also sterilize medical equipment. 
• Earlier, an x-ray or gamma-ray was used to see the morphological structure of internal organs. 
• Gamma rays are used as an external beam in particle accelerators.
• Gamma signals from space are used to locate different galaxies and stars by astronomers.
• Gamma rays are used in the nuclear industry for research and development purposes.

Therapeutic Application of Gamma Rays

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Things to remember

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1. Radioactivity is a process in which a heavy nucleus disintegrates into small nuclei to achieve stability.
2. Radioactivity is a nuclear phenomenon and involves the decaying of nuclei.
3. There are mainly three types of radioactive decay which are alpha decay, beta decay, and gamma decay.
4. Alpha and beta decays are independent but gamma decay accompanies alpha and beta decay.
5. Gamma decay is the emission of electromagnetic radiation of high frequency releasing enough energy to stabilize the nucleus. 
6. The gamma-rays are of very high frequency comparable to that of X-rays.
7. In nature, gamma rays are mostly found as a result of gamma decay or due to the intervention of cosmic rays in the earth’s atmosphere.
8. Gamma rays are used as an external beam in particle accelerators.