Radioactivity and Nuclear Physics
Radioactivity happens when unstable atoms break down and release particles or rays. Think of it like an overpacked suitcase that keeps spilling out its contents! There are three main types you need to know about.
Alpha radiation consists of helium nuclei (2 protons + 2 neutrons) with a +2 charge. It's the most ionising but weakest - even a sheet of paper can stop it. Beta radiation is high-energy electrons with a -1 charge, stopped by aluminium foil. Gamma radiation is electromagnetic waves with no charge and the least ionising power, requiring thick lead to block it.
Scientists discovered atoms through brilliant detective work. Rutherford's gold foil experiment proved atoms have a tiny, dense nucleus with electrons orbiting around it - imagine a football stadium with a marble in the centre! Later, Bohr found energy shells and Chadwick discovered neutrons.
Quick Tip: Remember the stopping materials: Paper stops alpha, Aluminium stops beta, Lead stops gamma - PAL!
Half-life tells us how long it takes for half the radioactive atoms to decay. Activity measures how many atoms decay per second - 1 decay per second equals 1 Becquerel. Marie Curie pioneered this research and discovered new radioactive elements, proving that determination can literally change the world.