Physics - Nuclear physics (Radioactivity and half-life)

Radioactivity is the spontaneous emission of radiation from an unstable nucleus. It is a random process, meaning we cannot predict which individual nucleus will decay at any given time.

The structure of an atom is represented as $^A_Z X$, where $A$ is the nucleon (mass) number and $Z$ is the proton (atomic) number.

Alpha particles ($\alpha$) consist of 2 protons and 2 neutrons, represented as $^4_2 ext{He}$. They are highly ionizing but have low penetration power (stopped by paper).

Beta particles ($\beta$) are high-speed electrons emitted from the nucleus when a neutron turns into a proton, represented as $^0_{-1} ext{e}$. They have moderate ionizing and penetration power (stopped by aluminum).

Gamma rays ($\gamma$) are high-energy electromagnetic waves. They have low ionizing power but high penetration power (reduced by thick lead or concrete).

The Half-life ($t_{1/2}$) of a radioactive isotope is the time taken for half of the nuclei in a sample to decay, or the time taken for the activity (measured in Becquerels, $Bq$) to fall to half of its initial value.

Background radiation is the low-level ionizing radiation that is constantly present in the environment from natural sources (radon gas, cosmic rays, rocks) and man-made sources (medical X-rays, nuclear fallout).