Unit 10: Comprehensive Summary

Radioactivity is the spontaneous emission of radiation from an unstable atomic nucleus. This process, called radioactive decay, occurs to allow the nucleus to become more stable.

There are three main types of radiation:

• Alpha (α) particles ($^4_2He$): Consist of 2 protons and 2 neutrons. They have a +2 charge, high ionising power, and low penetrating power (stopped by paper).
• Beta (β) particles ($^0_{-1}e$): High-energy electrons formed when a neutron becomes a proton. They have a -1 charge, medium ionising power, and medium penetrating power (stopped by aluminium).
• Gamma (γ) rays ($^0_0\gamma$): High-energy electromagnetic waves. They have no mass or charge, low ionising power, and high penetrating power (reduced by thick lead).

Nuclear equations must be balanced such that the sum of mass numbers and the sum of atomic numbers are equal on both sides.

The rate of radioactive decay is unpredictable for a single atom but predictable for a large sample. It is measured by half-life ($t_{1/2}$), which is the time taken for half of the radioactive nuclei in a sample to decay. A shorter half-life indicates a more unstable nucleus.

Radiation is dangerous because its ionising power can damage or kill living cells by altering DNA, potentially causing mutations or cancer.

• Internal Hazard: Alpha particles are most dangerous if ingested/inhaled.
• External Hazard: Gamma rays are most dangerous from an external source.

Radiation is detected using a Geiger-Müller tube.

• Nuclear Fission: The splitting of a large nucleus (like Uranium-235) into smaller nuclei by neutron bombardment. This releases a huge amount of energy and more neutrons, which can lead to a chain reaction. This is used in nuclear reactors (controlled) and atomic bombs (uncontrolled).
• Nuclear Fusion: The joining of two light nuclei (like hydrogen isotopes) to form a heavier nucleus. This releases even more energy than fission and requires extremely high temperatures and pressures. It powers the Sun and is the principle behind hydrogen bombs.

Radioactive isotopes have many beneficial uses:

• Carbon-Dating: The decay of Carbon-14 (half-life ~5,730 years) is used to determine the age of organic remains.
• Radioactive Tracers: Isotopes with short half-lives are used in medicine (e.g., Iodine-131 for thyroid function), industry (detecting leaks), and agriculture (monitoring fertiliser uptake).
• Radiotherapy: Focused beams of gamma radiation (e.g., from Cobalt-60) or internally administered radioisotopes are used to kill cancer cells.