Physics - Nuclear Physics

The atom consists of a nucleus containing protons and neutrons (nucleons), surrounded by electrons. The notation for a nuclide is $^A_Z X$, where $A$ is the nucleon (mass) number and $Z$ is the proton (atomic) number.

Isotopes are atoms of the same element with the same number of protons ($Z$) but different numbers of neutrons (different $A$).

Radioactive decay is a random process in which unstable nuclei emit radiation to become more stable. The three main types are alpha ($\alpha$), beta ($\beta$), and gamma ($\gamma$).

Alpha ($\alpha$) particles are Helium nuclei ($^4_2\text{He}$). They have high ionizing power, low penetration (stopped by paper), and are deflected by electric/magnetic fields.

Beta ($\beta$) particles are high-speed electrons ($^0_{-1}\text{e}$) emitted when a neutron turns into a proton. They have moderate ionizing power and penetration (stopped by few mm of aluminum).

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

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

Nuclear fission is the splitting of a large nucleus into two smaller daughter nuclei, releasing energy. Nuclear fusion is the joining of two light nuclei to form a heavier nucleus, occurring in stars at very high temperatures.

Background radiation is the low-level radiation present from natural sources (radon gas, cosmic rays, rocks) and artificial sources (medical X-rays, fallout).