Weak Nuclear Force

The weak nuclear force works only at the sub-atomic level, i.e., inside the nucleons, with a concise range, approximately 10^-18 m. It is weaker than the strong nuclear force and the electromagnetic force but more potent than gravity.

It is responsible for powering stars and creating new elements. Much of the radiations present in the universe can be explained through weak interaction. The weak force occurs when there is beta decay, especially during a neutron’s transformation into a proton and vice versa. During this process, a down quark disappears, and an up quark is produced. The weak force is responsible for the fusion of neutrons and protons to form a deuteron. It is significant in nucleosynthesis and stellar interiors.

The theory describing its behavior of weak interaction and effects is often called quantum flavourdynamics (QFD). Particles interact through this weak interaction by exchanging force carriers, known as W⁺, W^–, and Z bosons. They are known as intermediate vector bosons.

Here are some facts and characteristics of the weak nuclear force.

• Exchange force – neither attractive nor repulsive
• Short-range (~10^-18 m)
• Non-central and non-conservative
• Does not follow product law and the inverse-square law
• A million times weaker than the strong nuclear force

1. Beta Decay

An example of a weak nuclear force is converting a neutron into a proton and vice versa, resulting in beta (minus) decay. During this process, a neutron is replaced by a proton, an electron, and an antineutrino. This equation is represented by,

₀n¹ → ₁p¹ + _-1β⁰ + ν_e (antineutrino)

Similarly, a proton decays into a neutron, a positron, and a neutrino in the following way,

₁p¹ → ₀n¹ + ₊₁β⁰ + ν_e (neutrino)

2. Electron Capture

Electron capture, or K-capture, is the process through which protons transform into neutrons. This reaction occurs when there is an excess number of protons relative to neutrons. An electron from the inner shell falls into the nucleus. The products are the daughter nucleus, with one less atomic number and a neutrino.

An example of electron capture is the decay of krypton-81 into bromine-81.

⁸¹Kr₃₆ + e^– → ⁸¹Br₃₅ + ν_e

3. Nuclear Fusion

In a nuclear fusion, two protons are smashed together with enough energy to overcome the electrostatic repulsion, which results in an unstable ²He. One of the protons undergoes beta decay mediated by the weak force.  A series of reactions follows, involving the formation and fusion of the intermediate ³He into a stable ⁴He nucleus. The overall reaction is,

4 ₁p¹+ 2 e^– → ⁴He + 2 ν_e