Atomic structure

Atom

nucleus (protons + neutrons) and electrons.

Isotope

atoms with same protons, different neutrons

Radiation types

alpha (α), beta (β), gamma (γ).

Half-life

time for activity to halve.

Compare alpha, beta, and gamma in terms of penetration and ionising power.

• Alpha (α): Low penetration (stopped by paper), high ionising

• Beta (β): Medium penetration (stopped by aluminium), medium ionising

• Gamma (γ): High penetration (stopped by thick lead), low ionising

✅ Must mention penetration and ionisation for each.

A sample has a half-life of 3 hours. After 9 hours, how much remains?

• After 1 half-life (3 hrs): ½ remains

• After 2 half-lives (6 hrs): ¼ remains

• After 3 half-lives (9 hrs): ⅛ remains

✅ Final answer: 12.5% remains