Nuclear Physics - Radioactivity

Radioactivity is the spontaneous and random emission of radiation from the unstable nucleus of an atom. It is unaffected by chemical or physical conditions such as temperature or pressure.

The structure of the nucleus is represented by the notation $^A_Z X$, where $A$ is the nucleon (mass) number and $Z$ is the proton (atomic) number.

Alpha ($\alpha$) decay: The emission of a helium nucleus $^4_2\text{He}$. The mass number decreases by $4$ and the atomic number decreases by $2$. Equation: $^A_Z X \rightarrow ^{A-4}_{Z-2} Y + ^4_2\text{He}$.

Beta-minus ($\beta^-$) decay: A neutron in the nucleus decays into a proton and an electron. The electron $^0_{-1}e$ and an antineutrino $\bar{ u}_e$ are emitted. The atomic number increases by $1$. Equation: $^A_Z X \rightarrow ^A_{Z+1} Y + ^0_{-1}e + \bar{ u}_e$.

Gamma ($\gamma$) radiation: High-energy electromagnetic waves emitted to allow the nucleus to reach a lower energy state. There is no change to $A$ or $Z$.

Activity ($A$) is the rate at which a source decays, measured in Becquerels ($1\text{ Bq} = 1\text{ decay per second}$).

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

Nuclear Fission: The splitting of a heavy nucleus (e.g., $^{235}_{92}\text{U}$) into two smaller daughter nuclei and neutrons, releasing a large amount of energy.

Nuclear Fusion: The process where two light nuclei (e.g., isotopes of Hydrogen like $^2_1\text{H}$ and $^3_1\text{H}$) combine to form a heavier nucleus, releasing energy.