Structure of the Atom and Radioactivity Overview

Proton

Charge: +1; Found in: nucleus of atom

Neutron

Charge: 0 (neutral); Found in: nucleus of atom; Mass: similar to proton

Electron

Charge: -1; Found in: shells/orbitals surrounding nucleus

Atomic number

Number of protons

Mass number

Protons + neutrons

Neutral atom

In a neutral atom, electrons = protons

Isotopes

Atoms of the same element with different numbers of neutrons

Radioisotopes

Unstable isotopes that decay and emit radiation

Radioactivity

Process of emitting radiation from unstable nuclei; Measured in: Becquerels (Bq)

Alpha radiation

Helium nucleus: 2 protons, 2 neutrons (⁴₂He); Very ionising, weakly penetrating; Range in air: 5-8 cm; Stopped by: paper

Beta radiation

High-speed electron (⁰₋₁e); Medium ionising, moderate penetration; Range in air: 5-10 m; Stopped by: aluminium

Gamma radiation

Electromagnetic wave; Low ionising, highly penetrating; Range in air: infinite; Stopped by: thick lead

Ionising radiation

Knocks electrons out of atoms; Leaves atoms positively charged

Alpha decay example

²¹¹₈₄Po → ²⁰⁷₈₂Pb + ⁴₂He

Beta decay example

⁹⁰₃₈Sr → ⁹⁰₃₉Y + ⁰₋₁e

Geiger-Müller Tube

Detects ionising radiation; Ionises gas inside tube → allows current to flow; Clicks/count rate indicate radiation levels

Natural sources of background radiation

Rocks and soil; Radon gas; Cosmic rays (from space)

Man-made sources of background radiation

Nuclear weapons; Nuclear power stations; X-rays; Smoke detectors

Contamination

Object has radioactive material on/in it

Irradiation

Object exposed to radiation (does not become radioactive)

Dangers of ionising radiation

Cell damage → can kill or mutate cells; DNA mutation → increases cancer risk; Burns and radiation sickness (high exposure); Long-term exposure → cancer

Nuclear waste disposal issues

Long half-lives → remains radioactive for a long time; Risk of leaks → can contaminate soil/water