Beta Decay

There are two types of beta decay: beta-minus and beta-plus.

Beta-Minus Decay

In beta-minus decay, a neutron in an unstable nucleus transforms into a proton. This transformation causes the original, or “parent”, nucleus to emit a beta-minus particle (electron) and an antineutrino, forming a new, or “daughter”, nucleus. The emitted electron has a tiny mass – 1/1836 of a proton’s mass or 1/1838 of a neutron’s mass – and carries a charge of -1. An antineutrino is a tiny, nearly massless particle with no electric charge. It is the antimatter counterpart of a neutrino. As a result of beta-minus decay, the atomic number of the nucleus increases by one, effectively changing the element.

The nuclear equation representing a beta-minus decay is:

\[ ^{A}_{Z}X \rightarrow \text{ }^{A}_{Z+1}Y + e^{-} + \bar{\nu} \]

Where:

– A is the mass number

– Z is the atomic number

– \(^{A}_{Z}X\) is the parent nucleus

– \(^{A}_{Z+1}Y\)  is the daughter nucleus

– \(e^{-}\) is the emitted electron

– \( \bar{\nu} \) is a antineutrino

Examples

1. Carbon-14 to Nitrogen-14

The atomic number increases from 6 to 7, changing the element from carbon to nitrogen.

2. Tritium (Hydrogen-3) to Helium-3

The atomic number increases from 1 to 2, transforming from an isotope of hydrogen to an isotope of helium.

3. Potassium-40 to Calcium-40

Beta-Plus Decay or Positron Emission

In beta-plus decay, a proton in the unstable nucleus is converted into a neutron. The parent nucleus emits a beta-plus particle (positron) and a neutrino to form the daughter nucleus. A positron is the antimatter counterpart of an electron, having the same mass but a positive charge (+1). A neutrino is a tiny, nearly massless particle and has no charge. Beta-plus decay decreases the atomic number by one, resulting in the formation of a different element.

The nuclear equation representing a beta-plus decay is:

Where:

– \(^{A}_{Z}X\) is the parent nucleus

– \(^{A}_{Z-1}Y\)  is the daughter nucleus

– \(e^{+}\) is the emitted positron

– \( \nu \) is a neutrino

Examples

1. Fluorine-18 to Oxygen-18

The atomic number decreases from 9 to 8, indicating that fluorine transforms into oxygen.

2. Magnesium-23 to Sodium-23

3. Nitrogen-13 to Carbon-13

The energy released during beta decay is shared between the beta particle and the neutrino. This results in a continuous energy spectrum, as the energy is not fixed but varies depending on the distribution between the two emitted particles.

The nature of neutrinos has already been briefly introduced in previous sections. They are almost massless particles that carry no charge and play an essential role in the beta decay process. They balance the process by conserving the energy, linear and angular (spin) momentum, and lepton number.  

Neutrinos interact weakly with matter, and their detection becomes challenging in spite of their presence in beta decay. However, they are fundamental to our understanding of nuclear reactions.

1. Nature and Charge: Beta particles are either negatively charged electrons (β-) or positively charged positrons (β+) with a value of ±1. This charge gives them the ability to be influenced by electric and magnetic fields, leading to observable deflections in their paths.

2. Mass and Speed: Beta particles have a mass that is approximately 9.11 x 10^-31 kg, which is the same as the mass of an electron. Their small mass enables them to move at high speeds, often close to the speed of light (3 x 10⁸ m/s), depending on the energy released during decay.

3. Penetration Ability: Due to their small size and high speed, beta particles have moderate penetration power. They can pass through several millimeters of human tissue or thin metal foils, like aluminum. However, materials like plastic or glass a few millimeters thick can effectively block beta particles, making these materials useful for shielding in applications involving beta radiation.

4. Ionizing Power: Beta particles have moderate ionizing power and can ionize atoms and molecules along their paths. This ionization occurs as beta particles collide with electrons in atoms, knocking them out of their orbitals. This interaction is significant in applications like medical imaging and cancer treatment.

Due to their penetration ability, beta particles can be a health hazard to the human body. When beta particles interact with biological tissue, they can cause cellular and molecular damage. Beta radiation exposure can harm the skin or internal organs if the radiation source is inside the body. Proper handling and shielding of beta-emitting materials are necessary to protect against these risks.

• Medical Imaging and Treatment: Beta decay is the basis for positron emission tomography (PET) scans, a crucial tool in medical diagnostics for detecting cancers and monitoring brain activity.
• Carbon Dating: Beta decay of carbon-14 is used in radiocarbon dating to determine the age of archaeological and geological samples, such as fossils and artifacts.
• Nuclear Energy: Beta decay plays a role in the decay of fission products in nuclear reactors, contributing to the management of nuclear waste.
• Environmental Monitoring: Beta-emitting isotopes are used to track pollution and study the movement of contaminants in the environment.
• Material Testing: Beta particles are used in thickness gauges to measure the thickness of materials like paper, metal, and plastic in industrial processes.