Alpha, Beta and Gamma Radiation

Radioactive decay is the spontaneous emission of radiation from an unstable nucleus. The three main types are alpha ($\alpha$), beta ($\beta$) and gamma ($\gamma$).

Properties comparison

Property	Alpha ($\alpha$)	Beta ($\beta$)	Gamma ($\gamma$)
Nature	2 protons + 2 neutrons (helium nucleus)	High-speed electron	Electromagnetic wave
Charge	+2	-1	0
Mass	4 (heaviest)	1/1836 (very light)	0
Penetrating power	Stopped by paper or a few cm of air	Stopped by a few mm of aluminium	Reduced (never fully stopped) by several cm of lead or thick concrete
Ionising power	Strongest	Moderate	Weakest
Deflection by fields	Deflected by electric and magnetic fields	Deflected (opposite direction, more curved)	Not deflected

Nuclear equations

Alpha decay: the nucleus loses 2 protons and 2 neutrons.

${}^A_Z X \rightarrow {}^{A-4}_{Z-2} Y + {}^4_2 \alpha$

Example: ${}^{226}_{88}\text{Ra} \rightarrow {}^{222}_{86}\text{Rn} + {}^4_2\alpha$

Beta decay: a neutron converts to a proton, emitting an electron.

${}^A_Z X \rightarrow {}^A_{Z+1} Y + {}^0_{-1} \beta$

Example: ${}^{14}_6\text{C} \rightarrow {}^{14}_7\text{N} + {}^0_{-1}\beta$

Gamma emission: the nucleus releases energy as a gamma ray. No change in proton or nucleon number.

Common errors and how to correct them

Saying alpha is an electron. Alpha is a helium nucleus (2 protons, 2 neutrons). Beta is the electron.

Getting the nucleon and proton number changes wrong in equations. In alpha decay, $A$ decreases by 4 and $Z$ by 2. In beta decay, $A$ stays the same and $Z$ increases by 1. Check both numbers balance.

How to apply this in an exam

Write balanced nuclear equations with correct nucleon and proton numbers. Both sides must balance: total $A$ on the left = total $A$ on the right; same for $Z$. State the nature, charge and penetrating power of each type.