Beta Decay

Beta decay is a type of radioactive nuclear decay. In it a beta particle (fast-energetic electron or positron) is released from an atomic nucleus, converting the initial nuclide into an isobar of that nuclide. For example, a neutrons beta decay converts itself into a proton by emitting an electron following the anti-neutrino. Or a proton which converts into a neutron by the emission of a neutron-positron in so-called positron emission. Neither beta particle nor it’s related (anti-)neutrino occurs inside the nucleus before beta decay but produced in the decay process. As a result, unstable atoms obtain a more stable ratio of protons to neutrons.

The occurrence of nuclide decay due to beta decay and other decay forms determines its nuclear energy binding. The binding energies of all known nuclides are called the nuclear band or the stabilization valley. For the electron or positron emission to be energetically feasible, the energy release must be positive.

History of Beta Decay

In 1934, Frédéric and Irène Joliot-Curie bombarded aluminium with alpha particles to effect a nuclear reaction and found that the result was an isotope. It emits a positron similar to those present in the cosmic rays (discovered by Carl David Anderson in 1932). It was the first example of beta decay, so they named it as “artificial radioactivity” because it has a short life span (short-lived nuclide), and does not occur naturally. In recognition of their discovery, the duo was awarded the Nobel Prize in Chemistry in 1935.

Types of Beta Decay

There are two kinds of beta decay

1) Beta Minus \(\beta-\) and,

2) Beta Plus \(\beta+\)

Beta Minus Decay (\beta-)

• In beta minus, the neutron converts into a proton that causes an increase in the atomic number of the molecule. The proton is positive, but the neutron is still neutral.
• In order to preserve charge stability, the nucleus in the process also releases an electron and an anti-neutrino.
• Anti-neutrino is an antimatter equivalent of neutrino. Both are neutral particles of a minimal mass. They interfere very weakly with matter, and they can also travel through the earth without being disrupted.
• In the case of beta minus decay, the transition in the atomic configuration is;

\({_{Z}^{A}\textrm{X}}\rightarrow {_{Z{+1}}^{A}\textrm{Y}}+e^{-}+\bar{v}\)

\(N = p+e^{-}+v^{-}\)

• And the best example of the beta minus decay is \(^{14}C into ^{14}N\)

Beta Plus Decay (\beta+)

• In beta plus decay, the proton disintegrates to create a neutron that causes a reduction in the atomic number of the radioactive sample. The nucleus experiences a loss of a proton, but it gains a neutron.
• Again, it is necessary to conserve the charge. In order to comply with the conservation law, beta plus decay also produces positron and neutrino.
• A positron is the antimatter counterpart to an electron; they are same in all aspects except that a positron has a positive charge.
• The nature of a neutrino is the same as that of an anti-neutrino. Expressed in the equation:

\({_{Z}^{A}\textrm{X}}\rightarrow {_{Z{-1}}^{A}\textrm{Y}}+e^{+}+v\)

\(P = n+e^{+}+v\)

• Beta plus decay will only occur if the daughter nucleus is more stable than the mother nucleus. This disparity goes into conversion of a proton into a neutron, a positron, and a neutrino. There is no change in mass number, as the protons and neutrons have the same mass.

Electron Capture

Electron capture is concurrent to beta plus decay. Instead of converting a proton into a neutron with a beta particle that emitted with a neutrino, the proton absorbs an electron from the K shell:

\(P = n+e^{+}+v\)

The energy of the released beta decay particles is significantly 3 MeV, while the speed of the emitted beta particles is equal to the speed of light.

Beta particles can penetrate into the matter. In collisions with the atoms, they lose energy. In fact, there are two mechanisms involved:

1. A beta particle passes a small fraction of its energy to the collided atom.
2. Every collision deflects a beta particle from its original path. Because of the change in velocity, it contributes to the emission of electromagnetic radiation, as the energy is lost in the form of low-energy x-rays.

Application and Importance of Beta Decay

Elements that have beta decay can have beneficial medical applications. Radionuclide therapy (RNT) or radiotherapy is a treatment for cancer that involves beta decay. In this process, lutetium-177 or yttrium-90 is bound to a molecule and sent inside the human body. When it is inside the bloodstream, the beta molecules get to the cancer cells. Radioactive atoms then undergo a decay process, emitting beta particles and destroying cancer cells.

FAQs about Beta Decay

Q1. List some of the applications of beta decay particles.

Answer. The uses of beta decay particles include:

• Treatment of cancer
• As thickness detectors to monitor the consistency of thin materials such as paper.
• In phosphorescent lighting for emergency lighting since it needs no electricity.

Q2. List a few sources of beta decay particles.

Answer. Many beta decay emitters actually exist in radioisotopes present in the naturally occurring radioactive decay chains of uranium, thorium and actinium. Few examples are lead-210, bismuth-214 and thallium-206.