Beta Decay, Types, Examples, Fermi’s Theory and uses

Beta decay is a type of radioactive decay that involves the transformation of an unstable atomic nucleus into a more stable one by the emission of either a beta-minus (β-) particle (an electron) or a beta-plus (β+) particle (a positron). This process allows for a change in the atomic number (Z) while conserving the mass number (A). 

What is Beta Decay?

Beta decay is a type of radioactive decay that involves the transformation of an unstable atomic nucleus into a more stable one by the emission of either a beta-minus (β-) particle (an electron) or a beta-plus (β+) particle (a positron). This process allows for a change in the atomic number (Z) while conserving the mass number (A).  The beta particle is a high speed electron when it is a beta-minus (β-) and a positron when it is a beta-plus (β+) decay.

Beta Decay,
Beta Decay/image credit/

Types of Beta Decay:

There are two primary types of beta decay:

1. Beta-Minus (β-) Decay:

 In beta-minus decay, a neutron in the nucleus is converted into a proton, an electron (beta-minus particle), and an antineutrino (a nearly massless, electrically neutral particle).

 Example of Beta-Minus Decay:

Carbon-14 (C-14) undergoes beta-minus decay, where a neutron is transformed into a proton, emitting an electron (beta-minus particle) and an antineutrino. This results in the conversion of C-14 into stable nitrogen-14 (N-14).

C-14 ⟶ N-14 + β- + antineutrino

2. Beta-Plus (β+) Decay:

 In beta-plus decay, a proton in the nucleus is converted into a neutron, a positron (beta-plus particle), and a neutrino (an electrically neutral, nearly massless particle).

Example of Beta-Plus Decay:

Sodium-22 (Na-22) undergoes beta-plus decay, where a proton is transformed into a neutron, emitting a positron (beta-plus particle) and a neutrino. This results in the conversion of Na-22 into stable neon-22 (Ne-22).

Na-22 ⟶ Ne-22 + β+ + neutrino

Uses/Applications of Beta Decay:

Beta decay and beta particles have several important applications in various fields:

1. Radiation Therapy:  Beta-emitting radioactive isotopes are used in medical radiation therapy to treat cancer. Beta particles have a relatively short range in tissue, making them suitable for targeting cancer cells while minimizing damage to surrounding healthy tissue.

2. Radiometric Dating: The use of beta-emitting isotopes, such as carbon-14 (C-14), is crucial in radiocarbon dating. By measuring the ratio of C-14 to stable carbon-12 (C-12) in organic materials, scientists can estimate the age of archaeological artifacts and fossils.

3. Positron Emission Tomography (PET): Positron-emitting isotopes, such as fluorine-18 (F-18), are used in PET scans for medical imaging. When the positron emitted in beta-plus decay encounters an electron, they annihilate each other, producing two gamma-ray photons that can be detected to create detailed images of the body’s internal structures.

4. Neutrino Research: The detection of neutrinos produced in beta decay is essential for neutrino research. Neutrinos are elusive particles that carry valuable information about astrophysical processes, nuclear reactions, and particle physics.

5. Nuclear Physics Research: Beta decay is fundamental to the study of nuclear structure and the behavior of atomic nuclei. It provides insights into the weak nuclear force and the interactions between quarks and leptons.

6. Energy Production: Beta decay is involved in certain types of nuclear reactions used in experimental fusion reactors and may have future applications in controlled nuclear fusion for energy production.

Fermi’s Theory of Beta Decay:

Fermi’s theory of beta decay, developed by Italian physicist Enrico Fermi in 1934, was a groundbreaking contribution to the understanding of beta decay processes. This theory laid the foundation for our modern understanding of the weak nuclear force, which is responsible for processes like beta decay.

  • Fermi’s theory specifically addresses beta-minus (β-) decay, where a neutron is transformed into a proton, an electron, and an antineutrino.
  • Fermi proposed a four-point interaction term in the Lagrangian of the system to describe beta decay. This interaction is now known as the “Four-Fermi interaction” and is one of the fundamental interactions in particle physics, associated with the weak nuclear force.
  • Fermi’s theory provided an amplitude (probability) for the beta decay process by considering the interaction between a neutron and a proton through the exchange of a virtual W-boson (now known as the W-boson in the Standard Model of particle physics). This amplitude described the probability of a neutron turning into a proton while emitting an electron and an antineutrino.
  • The theory introduced the Fermi constant (G_F), which quantifies the strength of the weak interaction. It is a fundamental constant in particle physics and has a value of approximately 1.166 x 10-5 GeV -2
  • Fermi’s theory provided a matrix element that describes the transition from initial to final nuclear states during beta decay. This matrix element incorporates information about the quantum states of the particles involved.
  • Fermi’s theory also allowed for the calculation of the rate at which beta decay events occur. This rate is essential for understanding the half-life of a radioactive substance undergoing beta decay.

Nonetheless, Fermi’s theory remains a crucial historical milestone in the development of particle physics, and it laid the groundwork for subsequent advances in our understanding of the fundamental forces of nature.


These applications demonstrate the significance of beta decay in fields ranging from medicine and archaeology to fundamental particle physics and energy research. The characteristics of beta particles, such as their ability to penetrate matter to varying depths, make them valuable tools in these applications.

FAQs of Beta Decay:

Q1. What is beta decay?

A. It It is a nuclear process in which an unstable atomic nucleus transforms into a more stable nucleus by emitting either a beta-minus (β-) or beta-plus (β+) particle.

Q2. What is a beta particle?

A. This particle can be an electron (β-) or a positron (β+). In beta-minus decay, an electron is emitted, while in beta-plus decay, a positron is emitted.

Q3. What causes beta decay?

A. It is caused due to the weak nuclear force, one of the fundamental forces in nature. It is responsible for the transformation of a neutron into a proton (beta-minus decay) or vice versa (beta-plus decay).

Q4. What is the significance of beta decay?

A. This is essential for maintaining the balance of protons and neutrons in atomic nuclei, which, in turn, stabilizes the nucleus.

Q5. What are the types of beta decay?

A. There are two main types of beta decay: beta-minus (β-) decay and beta-plus (β+) decay. In beta-minus decay, a neutron is transformed into a proton, while in beta-plus decay, a proton is transformed into a neutron.

Q6. What are the properties of beta particles?

A. Beta particles are high-energy, high-speed electrons (β-) or positrons (β+). They can be emitted with various energies, and their behavior can be affected by external fields.

Q7. How is beta decay used in science and technology?

A. Such a phenomena is utilized in various scientific fields, including particle physics and nuclear physics. It is also used in applications like radiometric dating and nuclear medicine.

Q8. Can beta decay be harmful?

A. In certain situations, exposure to beta radiation can be harmful to living organisms. However, it is also used in medical treatments and diagnostics, such as positron emission tomography (PET) scans.

Q9. How can beta decay be detected?

A. Beta particles emitted during decay can be detected using various instruments, including Geiger-Muller counters and scintillation detectors.

Q10. What are the key equations or laws related to beta decay?

A. The Fermi-Kurie plot, the decay rate equation, and the Fermi theory of beta decay are some of the mathematical and theoretical frameworks used to describe this phenomena.

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