Nuclear Decay (or radioactive decay) is the process by which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This process transforms the original nucleus (the parent) into a new nucleus (the daughter).

The instability is caused by an imbalance in the forces within the nucleus, particularly the ratio of neutrons to protons.

The rate of nuclear decay is a random, probabilistic process, but for a large number of atoms, it is characterized by a constant known as half-life.

There are three primary types of radioactive decay, each distinguished by the type of radiation emitted:

1. Alpha (α) Decay: The nucleus emits an alpha particle, which consists of two protons and two neutrons (identical to a helium nucleus, ⁴He). This reduces the mass number by 4 and the atomic number by 2, changing the element.

2. Beta (β) Decay: This occurs when a neutron in the nucleus is converted into a proton, and an electron (a beta particle) is ejected to conserve charge. This increases the atomic number by 1 but leaves the mass number unchanged.

3. Gamma (γ) Decay: The nucleus emits a gamma ray, which is a high-energy photon. This often occurs after an alpha or beta decay, as the nucleus transitions from a high-energy (excited) state to a lower-energy (ground) state. It does not change the atomic or mass number.

Nuclear decay processes are represented by balanced nuclear equations. In a balanced equation, the sum of the mass numbers (superscripts) and the sum of the atomic numbers (subscripts) must be the same on both sides of the reaction.

Alpha Decay of Uranium-238: ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He

(Mass numbers: 238 = 234 + 4. Atomic numbers: 92 = 90 + 2)

Beta Decay of Carbon-14: ¹⁴₆C → ¹⁴₇N + ⁰₋₁e

(Mass numbers: 14 = 14 + 0. Atomic numbers: 6 = 7 - 1)

Nuclear decay, while potentially dangerous, is harnessed for many beneficial applications.

Smoke Detectors: Many common household smoke detectors contain a tiny amount of Americium-241, an alpha emitter. The alpha particles ionize the air in a small chamber, creating a steady electric current. When smoke particles enter the chamber, they disrupt this current, triggering the alarm.

Medical Imaging (PET Scans): Positron Emission Tomography uses isotopes that undergo a type of beta decay (positron emission). These isotopes are attached to a tracer molecule (like glucose) and injected into the body. The emitted positrons are detected, allowing doctors to create detailed 3D images of metabolic activity, which is crucial for cancer diagnosis.

Nuclear Power: The heat generated by the controlled radioactive decay of elements like uranium is used in nuclear power plants to boil water, create steam, and turn turbines to generate electricity.